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Modern and Refrigeratior nrnS Air Cbnditio by 8.S.,(M.E'),M.A. ANDREWD. ALTHOUSE, Consultant Education Technical-Vocational LifeMember,AmericanSocietyof Engineers andAir-Conditioning Heating,Refrigerating, B.S./(M.E.),M.A. CARI H, TURNQUIST, Consultant Education Technical-Vocational ot society American Member, Associate tngineers Air-Condilioning and RefriSerdting, Healine, Associdlron andTechnicians TnBineers ^aembernefrigeririnB ALFREDF. BMCCIANO, 8.S.,M.Ed.,Ed.SP' Consultant Education Technical-Vocational Society SewiceEnBineers Member,RefriSeration Member,AmericanSocietyof Associate Engineers andAir-Conditioning Heating,Refrigerating, America of Contractors Aii Conditioning Mem-ber, Member,Aisociationfor CareerandTechnicalEducation

Publisher

INC' COMPANY THECOODHEART-WIttcox TinleYPark,lllinois

Copyrghl2004 by

TheGoodheart.Willcox Company, lnc. Previous editonscopylghl2000,1996,j 992,i 9BB,j 982,1979,I 97S,1968 Ar ghrsreserved. Noparlofthisworkmayb€reproduc€d, sloredjor transmitted tn anyiormor by anyetectronic or n€chanicaimeans nctLdingnformaUon storageand rorevarsyslems, wtlhoLt thepriofwrien permiss onoi The coodhean-Wi tcoxCompany, tic. I4anulactLrod 'r theUniled States of Ameca. Librafy of Congfess Catatog CardNumber 2003052840 tsBN-13: 978-1-59070 280,2 ISBN10:I -59070-280-8 678910-04-0807 The lechnologica changesin the reiiigeralion andair condition ng industryin aecent yearsfiavebeenveryextensve. Theaccuracy, reliabiljty, carty, and feadingevelofth s bookhavebeenachieved throughthe asssianceof the fottowing individuats: AssociateAuthors DanielC. Bracclano,B.S.M.E.t SeniorHVACEngineer, ceneratUoiors Corporation,Warren, fulichigant Associatet\,4ember, American Socielyof Healing,Reirigerating and Air,Condiion ng Engineersi [,,lember, Refrigerat]on ServiceEngineers Sociely, GloriaM, Bracciano,8.A.,lL4.A., Ed.Sp.iPrincipat, LakeOrionSchoos, Lake Oron, lvlichigani Assoca1e l\,lember, AmericanSocietyof Healing,Fefrgeratingand Air-Condilion ng Engineersil\,{embef, Feffigelailon andServiceEngineers Sociely. Consultants Albe Buller,AutomotiveService,ceneral lloiors Retailer,Lapeer, l\,4lchigan RobenH.Edgeon,B.S.M.E., M.S.lV.E., Ph.D.Engineering Robe Ottolinl,B.M.E.,M.S.M.E.; Engineefing lllanager, c6neralMotors Corpofalion, gan Flint,I\,{ich JesseR. Riojas,8.S.,Assoc.CllmateControlTech.i Instructor, Oaktand Communiiy Co lege,OaklandTechnical Cenier,IVichigan Connie Habermehl,AdministratveAssistanl,Assocaled T6chnical Alrthors, PortHurcn,l,,lichigan The authorsandp!blishergratetully acknowl€dg€ th6lollowingcompanies lor useoi maierialsfor the cover:TlFlnsirumenls, Inc.iCa(ier Corpo€tion,ResdeniialProductsi Clmatelvlasler, Inc. Libraryof Congr6ssCataroglng in AJbricationData Allhouse, And.ewDan€. Modernrelrigeral on andair condilonng/ by AndrewO.Aihouse,Car H.Turnqusl, AllredF.

tsBN1 59070,280-8 L R€trig€ration and€liigelatngmachnery. 2 .A r c o n d i l o n i n Lg .T u r n q u sC l ,a r l H a r o d , 1 9 l 0 l l . B r a c c i a nAof,r e dF . l l . T t l e . TP492.A432003 621.5'6.-dc21 2003052840

IN T ROD U C T I O N

Modem Refrigeration and Air Conditioning provides a thorouth and authontahve course on the basic and advanc€d pdnciples of refrigeration and air conditioning. As the technolo8y in the field has advanced, so has the leading text in the educational 6e1d, Modern Refrigeration and Air Conditioning. lt contains all the most recent information and advances that arc nec€ssaryto prepare the teclmician Ior today's world. lt incoryorates the lat€si technical chanSesand EPA mlinSs, cove$ the newer refrigerants, and prcvides current inJomration on ihe rccovery reclaiming, and reryclint of refrigerants. It contains basic information on numercus cedfication exams. Mod€m Reftigeration and Air Conditionint presents all these pdnciples in a very easily rnderstood format. To make this book more "user 6iend1y," the t'?e face has been enlarg€d, and the readability imprcved. Sentencesand paraSraphs have all been reviewed so that comPrehension is maximized. Thrs edition retains the sequenceof topics that has proven successful.Some oI ihe lrlaterial has been corelated into modules to h+ you obtain a better underctanding oI the subjeci. A[ dmwinSs have been coded to a standard color scheme to aid in recognition of items. The safety seciions are highlighted in red, as in the past; ihe ser\,1cefeaturcs arc identified with blue. Cu:rrent cylinder color coding is given for each reftgerant. An expanded table of contents is one of many features designed to enhance the leamint process.Each chapter has an idendJication of key words you will encounter in that chapter Learning objectives also are provided for each chapter. Test Your Knowledge questions aPPear at the end of each chapter. Modem Retngeratron alrd Air Conditioning is writt€n using both U.S. Conventional and SI Metric uniis. The metric equivalent appears alongside the conventional unit throughout the texibook. This allo}r's you to use the system with which you are most familiar. Modem Refrigeration and Air Conditioning is intended for use in rcfrigeration and air conditioning classesin hith schools, technical schools, and community colleges. lt may also be used in aduli educatron classesand apprenticeship pro$ams. It Prcvides the foundafion on which a solid, thorough knowledge of refrigeration and air condiiioning may be based. It also Provides an excellent basis of inJormation for you in the areas of sefficing and troubleshoofing Beginnerc and apprentices will find in Modem Refrigeration and Air Conditioning an eYcell€nt aid lor starting and pu$uing a pleasant and prcfitable career. ExPerienced se ice technicians will find it a valuable guide and reference. Congratulations on selechng the best seilin& most popular book on refrigeration and air conditioning! Modern Refrigeration and Au Conditioning will Suide you to a successfii carcer and provide you with a valuable reference in ihe Profession.

HOW TO USETHECOTORKEY Colors are used tlEoughout Modem Refrigeration and Air Conditionine to help show dif_ rerentstdtesand condition!_ofgdsesand Uquid!. OLhercolor. indicaLeele(tric;]. mechanicdl, and spe(rarcomponenis. the touowing tey shows whdt each color represents.

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CONTENTS

Chapter1 25 FUNDAMENTATS OF REFRIGERATION OF REFRICERAIION HISTORY AND FUNDAMENTALS MODULE 25 1.1 Development of Refrigeration25 RefriSerator 1.2 How a Mechanical Operates 26 1.3 ColorCodingSystemin ThisText 26 1.4 Heat 27 1.5 Cold 28 PRESSURE, AND MEASUREMENTS TEMPEMTURE, MODULE 28 andTemperaturc Measu€ment28 1,6 Ternperatufe Arithmetic30 1.7 Basic Conversion32 1.8 Temperature Difference Calculations33 1.9 Temperature 1.10 Dimensions 33 37 1.11 Pressure States39 1.12 TheThreePhysical 1.13 Density41 1.14 Force 41 1.15 Work 42 1.16 Energy42 1.17 Powet 42 1.18 Unitof Heat 43 1.19 Effectof Pressure on Evaporating Temperatures 46 Tempetature on Freezing 1.20 Effectof Pressure of Water 47 Effectol lce 47 L21 Refrigeraiing 1.22 AmbientTemperature49 1.23 Heatof Compression49 1.24 Energy Units 50 AND TERMS SYSTEMS RETRIGERATION MODULE 50 50 1.25 Refrigerant 1.26 HeatTransfer50 Water 51 1.27 BrineandSweet 1.28 Drylce 51 Temperature 52 1.29 Cfitical

'1.30 1.31 ] 32 1.33 1.34 1.35 1.36 1.37 1.38 1.39 '1.40

CriticalPressure52 Enthalpy 52 Cryogenics 52 PerfectCas Equation 53 Dalton'sLaw 54 Evaporator 54 Vapor Cas 54 Humidity-RelativeHumidity54 ElementaryRefrigerator 54 System 56 MechanicalRefrigerating Reviewof Abbreviationsand Symbols 57

1.41 Reviewof Safety 57 1.42 TestYour Knowledge 58

Chapter2 REFRIGERATION TOOTSAND MATERIATS 61 TUBINCAND FITTINCS MODUTT 6,I 2.1 Tubing 61 2.2 Cuuingand BendjngTools 64 2.3 Connecting Tubing 66 solde^-do- Brd,,pd-tJbrlg Fi I rgs bq 4.1 ruoeLoupIng5 /5 2.6 Swaging CopperTubing 75 2.7 TubeConstficror76 2.8 PipeFittlngs and Sizes 76 REFRIGERATION TOOTSMODULE 77 2.9 HandTools 77 INSTRUMENTS AND CAUCESMODULE 88 2.10 Instruments and Cauges 88 2.11 Measuring Tools 92 SUPPTIES AND USEMODULE 94 2.i 2 Fastening Devices 9,1 2.13 Refrigeration Supplies 96 2.14 ServiceValves 98 2.15 Purging 99 2-l6 EvacuatinS99 2.17 Reviewoi Salety 99 2.18 TestYourKnowledge 100

Chapter3 BASICREFRIGERATION SYSTEMS103 3.1 3.2 3.3 3.1

lce RefrigerationI03 EvaporativeRefrig€ration(DesertBag) 104 (SnowMaking) 104 Evaporative Refrigeration CompressionSysternUsing Low Side Float ReirigerantControl 105 (Open)Refrigefating 3.5 External-Drive System 106 3.6 Compression SystemUslngHigh-Side Floar RefrigeraniContro 107 3.7 Compression SynemUsingAutomatjcExpansion Valve {AEV)RefrigeraniControl I 08 3.8 Compression SystemUsingThermonatically ControlledExpansion Vave (TEV) 108 3.9 Compression SystemUsingCapillaryTube RelrigerantControl 109 3.10 MultipleEvaporator System 110 3.ll CompoundRefrigerating Systems 111

3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 1.22 3.21 3.24

Cascade Refrigerating Synems 113 ModulatingRefrigeration Cyce I1.1 l c eM a k e r 1 1 5 DrinkingWaterCooler 116 Expendable Refrigerant Refrigeration System I1 7 Thernroelectric RefriSeration 118 Dry lce Refrigeration118 Intermittent Absorpiion System 120 Coniinuous CycleAbsorption Systern I22 SolidAbsorbent Reffigeralion124 Sophisiicated Commercial Systenrs125 Hot-CasDefrost 125 ElectricDelrost 128

1.25 TestYourKnowledge 129

Chapter4 131 COMPRESSION SYSTEMS AND COMPRESSORS .I31 SYSIEMSMODUTE COMPRESSION 4.1 Lawsof Refrigeration131 4.2 Compression Cycle 131 4.3 Evaporator134 4.4 Accumulator 134 4.5 SuctionLine 134 4.6 Compressor135 4-7 Oil Separator136 4.8 Condenser137 4.9 LiquidReceiver 139 4 . 1 0 L i q u i dL i n e I 3 9 4..I 'ypFsoJ RefriBeraql Flo\^Conlrol I40 Motor Control 145 4.'12 MODULE 146 COMPRESSORS 146 4.13 Extefnal-DriveCompressors 4.14 HermeticCompressors147 4.15 Typesof Compressorc 147 4.16 Motors 168 4.17 Seryice Valves 168 4.18 Mufflers 169 4.19 Compressor Cooling 169 4.20 Lubrication170 Volumetric Efficiency170 4.21 Compressor Ratio 172 4.22 Compression 4.23 CheckValves 172 4.24 Urloader 172 4.26 O Rings 172 4.27 CrankcaseHeater I73 4.28 Reviewof Satety 173 4.29 TestYour Knowledge 174

Chapter5

.I77 REFRIGERANTCONTROTS 5.'l 5.2 5.3 5.4

CompfessionSystemRefrigerantConirols 177 Controls 202 ComparingRefrigerant CheckValve 202 Valves 202 SuctionPressure

5.5 5.6

Reviewof Safety 203 TestYour Knowledge 204

Chapter6 EI.ECTRICAT-MAGNETIC FUNDAMENTAI.S 207 ELECTRICAL FUNDAMENIATS MODULE 207 6.1 CeneratinS Elecrricity207 6.2 Typesof Electricity208 6.3 CircuitFundamentals 210 6.4 Electrical Materials222 6.5 Magnetism224

APPTIED ELECTRONICS AND EIECIRICITY MODULE 234 6.6 Eiectronics214 6.7 Electrical Power 242 6.8 Electrical Codes 250 6.9 CircuitProtection250 6.10 Reviewof Safety 253 6.11 TestYourKnowledge 254

Chapter7 ELECTRIC MOTORS 257 ETECTRIC MOTORSMODULE 257 7.1 ElectricMotorApplications257 7.2 The MotorStructure257 7.3 Typesof ElectricMotors 258 7.4 Motor Speeds 261 7.5 Sta{ingand RunningWindings 262 7.6 StartingCurrent 263 /./ MOtOrConnecton\ 164 7.8 HermeticSystemMotors 265 7-9 DirectCurent and Universal Motors 272 7.10 Motof Horsepowerand Motor Lnatactefl9irc5 l/J 7.11 ElectricMotorCrounding 273 7.12 MoIor Prctectior 274 7.13 MotorTemperaiure277

7-14 7.15 7.16 7.17

Standard Motor Data 278 FanMotors 278 Shaded-Pole Moio|s 279 Electronic VariableSpeedMotors 280

ELECTRIC SERVICINC MOTORSMODULT 282 7.18 Seryjcing ElectricMotors 282 7.19 Pulleys 287 7.20 Belts 288 7.21 Motor T€siingStand 290 7.22 Servicing and Repairing HermeticMotors 290 7.23 Revie\r,oiSaiery 292 7.24 TesiYour Know edge 292

Chapter8 ELECTRIC CIRCUITA S N D C O N T R O L S2 9 5 ELECTRIC CONTROLCIRCUITS MODULT 295 8.1 ElecticalCifcuits-CompleteWiring Diagram 295 8.2 Eiectical Circuits-Laddet Diag]am 297 8.3 ControlSystems-Fundamentals 297

ETECTRIC CONTROTS MODULE 309 Refrigerator 8.4 and FreezerContros 309 8.5 lce MakerControls 310 8.6 ComlortCooiingAir Conditioning Controls 314 8.7 CentralAir Conditioning Conlrols 315 8-8 WaterCoolerControls 316

I

8.9 8.10 8.11 8.12 8.13 8 l4 8.15 8.16 8.17 8.1B 8.19

RemoteTemperature SensingElenrents 316 Pressure MotorContfos 317 Motor SafetyContfols 317 Motor SradingRelays 319 AutomaticDefrostControls 324 Sen;aLrorrri(Det.onControls l2t Hot-CasDefrostControls 327 lce BankControls 328 De-lceControls 329 Hum;dityContfols 330 Timers 330 Defrosting

8.20 Reviewol S.rfety 131 8.21 TestYourKnowledge 131

Chapter9 REFRICERANTS 335 9.1 9.2

R e f r i g e r a n tasn d t h e O z o n e L a y e r 3 3 5 Requirementsior Refrigerants 337

9.3 9.,1 9.5 9.6 9.7 9.8 9.9 9.10 9.1I

Curves 337 Use of Pressure-Temperatur€ Cfouping and classificationof Refriseranis 338 CroupA Retrigerants 338 Croup B Reffigerants351 Refrigerants 352 Combustible ExpendableRefrigerants352 Wateras a Refrigerant 354 FoodFreezanis354 Fluids 354 Cryogenic

9.12 9.13 9.14 9.15 9.16 9.17 9.1I 9.19 9.20

Refrigerant Cylinders 355 Tables 357 Use of Pfessure-Temperaiure (HighSide) 357 HeadPressures 357 RetrigeratorTemperatures Refrigerant Applications358 358 Changing/ldentifyingRefrigerants in a System 158 Amountof Refrigerant Requjred Refriseration Oil 36'l Moisturein Refrigerant361

9.21 Revi-.wof Safety 362 9.22 TestYour Knowledge 363

Chapter10 365 RECOVERY/RECYCLING/RECLAIMING REFRIGERANT (CFCs), 10.1 Chlorofuorocarbons (HCFCs), Hydrochlorof luorocarbons and the OzoneLayer 365 Recycling, Reclaiming 10.2 Recovery, Refrigerants 367 of Recovery Equipment367 10.3 Refrigerant R^,\r lirS EqLipme'rl {-/ 10.4 Relrigprdnr '10.5 Procedure375 Refrigerant Reclaiming 10.6 Retrofit 377 10.7 MobileAir Conditioning378 10.8 Revie$r of Saiety l/9 10.9 TestYourKnowledge 379

Chapter11 AND FREEZERS381 R EFRIGERATORS DOMESTIC Foodsby RefriSefation 11.1 PreseNing and Freezing 381 and FreezerInsulation 382 11.2 Refrigerator ManualDefrost 382 11.3 RefrigeratorSingle-Door, Mdrudl Defrosl J84 ll.4 Re-flSer"loFFreeze AutomaticDefrost387 11.5 Refrig€rator-Freezer 394 11.5 Refrigerator-Freezer-Frost-Free 11.7 RefrigeratoFFreezer-Frost-Free, Side-by-Side 395 lce Maker 401 11.8 Solid-State Freezers 401 11.9 Chest-Type

1l .l0 UprightFreezers407 or Freezef 409 11.11 Care of Refri8erator in CabinetInsulation410 11.12 lceAccumulation 11.13 ButterConditioner410 11.14 CabinetHardware 411 11.15 CabinetCaskets 412 1 1 . 1 6R e p a i r i nFgi n i s h e s4 1 3 11.17 CabinerThermometers413 11.18 Revicwof Safety 414 11.19TestYourKnowledge 414

Chapter12 SERVICINGAND INSTALIINC SMALL HERMETICSYSTEMS 417 12.1 Instruments, Tools,and Supplies 4j7 12.2 InstallingRefrigemtors and Freezers 419 1 2 . 3 TroubJeshooting the Hermetic RefrjgeratoFFreezer 421 12.4 HermeticServicing 427 ExternalSeruicingOperations 427 12.6 InternalServiceOperations 433 12.7 Cauge(Servjce)Manilold Types and Construction 434 12.4 HermeticServiceValvesand Adaptors 438

12.9 LocatingRefrigerantLeaks 444 12.10 Repairing Leaks 448 12.11 RefrigerantRecoveryand Evacuaiion 449 12.'12Diagnosing Componenr Problems 452 12.13 ReplacinS System Components459 12.14 Evacuating a Synemwith a VacuumPump 463 12.15 Overhauling a HermeticSystem 470 12.16 Reviewof Satety 470 I2.17 TestYourKnowledge 471

Chapter13 COMMERCIAI. SYSTEMS473 COMMERCIAL SYSTEMS MODULE 473 13.1 Construction of Refrigeration Components473 13.2 Refrigeration Components473 13.3 Packaged Commercial Systern Components4 7 5 13.4 Commercial Evaporators496 COMMTRCIAI.SYSTEMS--{ONTROtSMODULE 513 '13.5 Refrigerant Controls 513 13.6 MotorControls 513 13.7 lce MakerControls 519

3.8 VendingMachineControls 519 3.9 DeirostTimers 520 3.10 Pressure Regulating Valves 524 3.ll CompressorProtectionDevices 529 3.12 ManualValves 536 3.13 Relrigerant Lines 539 3.14 Engine-Driven Systems543 3.15 Reviewof Safety 544 3.16 TestYourKnowledge 544

sutlpat a2kknd uDanmt Ltudrh

10

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Chapter14 547 COMMERCIAL SYSTEMS_APPLICATIONS l4.l

C o m m e f c i a lC a b i n e tC o n s t r u c t i o n 5 , 1 7

548 14.2 Supermarkets I4.1 CroceryCablnet(Reachln Cabinet) 5,18 I4.4 Wa k-lnCablnet 550 14.5 DisplayCas€s 553 Cabinet 556 14.6 FrozenFoodStorage 1.1.7 Fast-Freezing Case 558 14.8 lce CreamCabinet 558 1,1.9 SodaFountain 559 Freezers559 14.10 Dlspensing Synems 562 14.11 ModularRefrigeration

1,1.12WaterCooler 562 14.13 Automaticlce Maker 563 14.14VendjngMachines 564 1 4 . 1 5M i l k C o o l e r 5 6 5 1 4 . 1 6B a k e r i e s5 6 5 Heat RecoverySyslern 566 l4.l 7 Refrigerant-to-Water Incubators 566 14.18 LaboratoryRefrigerated 14.19 IndustriaApplications567 l.:1.20Reviewoi Sai.'tv 5{r8 1.1.21TestYourKnowledge 569

'l5 Chapter SYSTEMS521 COMMERCIAL AND INSTALLING SERVICINC MODULE 571 COMMERCIAT SYSTEMS INSTALLING I5-l Typesof CommerciaInstalatlons 571 Unils 572 15.2 Installing Condensing 15.3 Instaling Evaporators574 Refrig€ranl Piping 575 15.4 Installing 581 E ectrical Connections I5.5 15.6 TeningCodelnstallaiions582 Synem 586 15.7 Evacuallng I 8 L l-e.(r rg \).lar" bpfoe Slnrlr'lt 58t) '15.9 Comnrercial Sysiems586 Charging 15.10 Starting a System 588 SERVICINCCOMMERCIALSYSIEMSMODULE 590 Unlts 590 15.11 S€rviclng Commercial

1 5 . 1 2S e r v i cEe q u i p m e n t5 9 1 15.13 CeneralServiceInstructlons591 Units 596 Condensing 15.14 Servicing 15.15 ServiceNotes 625 15.16 Sunrmary of RefrgeratorMechanism Servicing625 I5.1/ PeriodicInspections625 Trolrbes 625 I5.18 Locating Service Contracting628 15.19 Reiigefation and Recyclng 628 Recovering 15.20 Refrigerant oi 5.rer,v 629 li.2l R-.\,iew l;.22 TestYourKnowledge 610

11

Chapter16 COMMERCIAL SYSTEMS_HEAT LOADSAND PIPING 633 HEATLOADSMODULE 633 16.1 HeatLoad 634 16.2 Thermodynamics of the Relrigeration Cycle 645 I6.3 Evaporator and Condensing Unit Capacrtres650 I6.4 Evaporator Instalations 65i 16.5 WatercoolingLoads 659 16.6 lce CreamFreezing and Storage Load 660 16.7 System Capacity 661 16.8 Compressor Capacities 662 16.9 Cascade System 664 16.10 Two StageCompressor664

16.11 Bypass Cycle 66,1 16.12 MotorSizes 666 16.13 Condenser Capacities 666 16.14 Servicing: RefrigerationTroubleshooting 669 LINESAND PIPINcMODULI 670 I6.15 Refrigefani Ljnesand Piping 670 16.16 Seasonal EnergyEfficiency Ratjo{SEER)6gl 16.17 Reviewoi Safety 681 16.18 TestYour Knowedge 683

Chapter17 ABSORPTION SYSTEMS-PRINCIPTES AND APPTICATIONS 685 ABSORPTION SYSTEM PRINCIPLES MODULE 6S5 17.1 TheAbsorptionSystem 685 17.2 Typesoi AbsorptionSystems 685 17.3 Principle of the SolidAbsorption System 686 17.4 EfficiencyofAbsorptionSystems 686 17.5 Princjple of the Intermitient Absorption System 686 I 7.6 Principle of the ContnuoLrs Absorption System 687 I7.7 Installing an Absorption Refrigerator692 17.8 Poriabe AbsorptlonRefrigerators 695 17.9 AbsorptionRefrigeraiors for Mobile Homes 696

RESIDENTIAL AND COMMERCIALABSORPTION SYSTEMS MODULE 696 17.10 Residentia Absorptlon Air Conditioners696 17.11 Commercial Absorption Sysiem 702 17.12 Absorption Unit for Air Conditioning and Heatlng 702 17.13 Servicing Absorption Refrigerators704 17.14 Reviewof Saiety 706 '17.15 TestYourKnowledge 706

Chaptert 8 SPECIAL REFRIGERATION SYSTEMS AND APPTICATIONS709 18.1 I8.2 I8.3 18.4 '18.5

TransportationReffigeraiion 709 Portable Air Conditioning/Spot Cooling 715 ThermoelectricRefrigeration 715 VortexTube 7l 7 JetCoolingSynems 718 I8.6 MultistageSystems Cascade and Compound 719 18.7 SnowMakinS 721 1'.'

18.8 HeatPipe 721 18.9 lmmersion(FastFteeze) 722 18.10 Cryogenic Refrigetation723 18.11 Ozonizedlce andWatet 724 18.12 Sterling Cycle 724 l8-l3 Reviewoi Safely 725 18.1,1TestYourKnowledge 725

Chapter19 OF AIRCONDITIONING 727 FUNDAMENTATS MODUIE AIR MOVIMTNT AND MEASUREMENT 19.1 DefinitionofAir ConditioninS727 19.2 Air-Atmosphere 728 Properties ol Air 728 19.3 Physical 19.4 VaporBarriers 736 19.5 Air Movement 736 19.5 Climate 740 '19.7 HeatInsulation 742

727

ArR QUAUTY MODUTE 744 '19.8 Air QuaLity 744 Air Quality and Residential 19.9 Conrmercial Systems 750 19.10 ComfortConditions 753 1 9 . 1 1N o i s e 7 5 4 I9.12 Reviewof Safety 758 19.13TestYourKnowledge 759

Chapter20

BASICHEATINGAND AIR CONDITIONINC SYSTEMS761 Crd\iq HeatingSy>'en 76 | ,10.I Cas-Fired 20.2 Cas-FiredForced-AirHeating 762 HydronicHeating 763 20.3 Cas-Fired Heating 765 20.4 Oil-FiredForced-Air 20.5 Oil-FiredHydronicHeating 766 Heating 767 20.6 EleciricalResistance 20.7 RadiantHeating 768 20.8 Air-to-AirHeatPumps 768 -71 Hcal PumpSyrens 20.9 Ccorhermal 20.10 RoomHumidifiers 773 20..l1 RoomDehumidifiers773 20.12 RoomAir Conditione$ 773

20.13 CentralAir Conditionerc 775 20.14 AbsorptionCycle Systems 776 Condensers779 20.15 Evaporative 780 Towers 20.16 Cooling 20.17 SteamJetCooling 781 20.18 VortexTubeCooling 782 Cooling 784 20-19 Evaporative 20.20 AutomobileAir Conditioning785 20.21 Reviewof Sarety 786 20.22 TestYour Knowledge 787

l3

Chapter21 HEATING AND HUMIDIFICATION SYSTEMS789 CAS HEATINGSYSTEMS MODULE 789 21.1 Typesof Systems789 21.2 Combustion 789 2l.3 FuelCases 791 21.4 BasicForcedAir Components292 21.5 Cas Burners 794 21.6 Furnace Typesand ConstrLrction 795 21.7 Cas FurnaceEfficiency296 21-8 Two-stage Furnace 799 21.9 Unit Heaters 799 21.10 Ventingof Furnaces and Chimneyor Exhalrn Cas-.s 799 21.11 lgnitionSystems80,1 21.12 Pipingand Cas Pressure805 2'1.13StartUp CheckSheet 806 21.14 Maintenance807 21.15 Serviceand Instrument CheckList 807 HYDRONICMDIANT HEATINGMODUTE 8.I1 21.16 HydfonicHeatingSystem 811 21.17 lnstalling HydronicSyst€ms817 21.18 Troubleshootjng HydronicSystems8lg 2l.19 SteamHeatingSystems819 21.20 SteamHeatingInstallation820 21.21 Servicing a SteamHeatingSystem 820 OIL FURNACES MODULE 820 2 l . 2 2 F u eO i l s 8 2 0 2l.23 Oll Fumaces 821 2l.24 Cun-Type Oil Burne6 822

21.25 Cun-Type Oil BurnerPumps 825 (TransforneFElectrode) 21.26 Electrical lgnition 826 21.27 PtimatyContol 829 21.28 Oil TankInstallation829 2l.29 Oil Burnerlnstallation83i 21.30 Servicing a FuelOil Burner 833 ETECTRIC HEATINCMODULE 834 21.31 EjectricHeat 834 2l.32 Principles of ElectricHeating 834 2'1.33Appiications of ElectricHeating 8j4 2 | 14 P-inLolesol I re(t i' R..i.rrn(e Hed-ng 836 21.35 ElectricRadiantHeat 839 21.36 Installing HeatingCo;ls 840 21.37 Servicing HeatingCoils 840 ALTERNAIIVEHTATINCMTTHODSMODUTE 441 21.38 HeatPumps 84'l 21.39 CoalandWood Heating 841 21.40 SolarHeating 842 21.41 Cogeneration842 HUMIDIFICATIONMODULE A42 21.42 Humidifiers 842 21.43 Typesof Humidifiers 844 21.44 Servicing and Installing HLrmidiiiers846 2l.45 Reviewof Saiery 847 21.46 TestYour Knowledge 848

Chapter22 C O O L I N CA N D D E H U M I D I F Y I N S CY S T E M S8 5 3 22.1 22.2 22.3 22.4

Principies of Atmosphere Cooling 853 ComfortCoolingSystems 855 Self-Contained ComfortCoolers 855 RernoteComfortSysiems 869

22.5 Dehumidjfying Equipment869 22.6 Reviewot Safety 870 22.7 TestYourKnowledge 871

Chapter23 AIRDISTRIBUTION, MEASUREMENI AND CTEANING873 AIRDISTRIBUTION MODULT 873 23.'l Air Properties andBehavior873 23.2 Air Circulation875 23.3 BasicVentilation Requirements 875 23.4 A,i Duc\s 877 23.5 Special DuctProblems andDuct Maintenance 892 2 3 . 6 D u c tS i z i n g8 9 3 14

AIR MEASUREMENT AND CTTANINCMODULE 9OO 23.7 Air Measurement900 23.8 Air Cleaning 903 2:1.9 Revie\^, ol Salety 911 23.10 TestYourKnowled8e 912

Chapter24 C E N T R AA L I R C O N D I T I O N I N GA N D H E A TP U M P S 9 1 5 HEAI PUMPSMODUTE 915 24.1 HeatPumpTheory 915 24.2 Typesof HeatPumps 915 24.3 HeatPumpOperation 916 24.4 Heat PumpSystems 920 24.5 HeatPumpsand SolarHeatingSystems929 24.6 Heat Plmp Water Heaters 932 24.7 HeatPumpInstallation933 Heat Pumps 934 24.8 TroubleshootinS HeatPurnps 914 24.9 Seruicing CINTRAI-AIR CONDITIONINC SYSTEMS MODUtt 936 24-10 Typesof CentralAir ConditioningSystems 936 centralAir Condiiioning Residential 24.ii Installing Sysiems 942 CentralAir Condidoning Residential 24.12 lnspecting Systems 945

Residential CentralAir Conditioning 24.13 Servicing Sysiems 946 Humidity and Relative Systems 24.14 Air Circulation 947 Controj LARCESYSTIMSMODULE 949 24.15 ChilledWaterSystems949 24.16 Typesof Chillers 949 24.17 ChillerCompressors952 24.18 ComfortCoolingSystems 955 24.19 RooftopUnits 956 Systems962 Air ConditioninS 24.20 Complete 962 lce-Based Systems 24.21 24.22 Total EnergySystems 963 24.23 District Heatingand Cooling Systems 965 24.24 Reviewof Safeiy 966 24.25 TestYour Knowledge 966

Chapter25 ENERCY959 SOTAR 25.1 25.2 25.3 25.4

of SolarEne€Y 969 TheNature Systems971 SolarEnergy Storage Systems973 SolarEnergy Heat 976 Supplementary

25.5 SolarEnergyCoolingSystems 978 25.6 ConvertingSolarEnergyto Electricity 979 25.7 Revicwof Saiely 981 25.8 TestYouf KnowledSe 981

15

Chapter26 A I R C O N D I T I O N I N GA N D HEATINCCONTROLSYSTEMS983 CONIROTMECHANISMS MODUTE 9S3 26.1 Conirols 983 26.2 Thermostats984 26.3 Thermostai Operation 985 26.4 HeatingThermosiats989 26.5 CoolingThermostats994 26.6 Combination Thermostats994 26.7 Electronic Thermostats995 26.8 TimerThermostats 998 26.9 Multistage Thermostats998 26.10Hydronic Thermostats 999 26.11 Porrable Themostats999 26.12Thermostat LocationandServicing 999

CONTROLSYSTEMCOMPONENTSMODUI.E ,IOOO 26.13 Controllers1000 26.14 PrimaryControls 1002 26.15 Sequential Operating Controls j004 26.16 LimitControis 1004 26.17 FanControls 1005 26.18 ControlCircuits 1006 26.19 AirflowControls 1017 26.20 Distribution Controls 1018 ENERCYMANACEMENTMODULE TO22 26.21 Total Ene€y ManagementSystems 1022 26.22 Enegy ManagementSystemTypes and Functions 1026 26.23 Control SystemDiagnosticsand Repair 1029 26.24 Reviewof Safety 1030 26.25 TestYoufKnowledge 1030

Chapter27 AIR CONDITIONINGSYSTEMS_HEATING AND COOTINC TOADS 1033 27.1 27.2 27.3 27.4 2-.5

HeatLoads 1033 Design Temperatures 1047 Insulation andVaporBarriers1050 Energy Conservation 1051 Con{rLctior Tvpes dnoDesiSr. '052

27.5 Reviewof Safety 1054 27.5 TestYour Knowledge 1054

Chapter28 AUTOMOTIVE AIRCONDITIONINC1057 28.1 Automotive Air Conditioning and HeatingSystems 1057 28.2 Air Conditioner Operation 1058 28.3 Operating Conditions 1059 28.4 E ectricalSystems1071 28.5 Air Distribution 1071 28.6 Insulation 1073 28.7 Typesof Control Systems 1073 28.8 Truckand BusAir Conditioning 1078 28.9 Servicing AutomobileAir Conditioners1078 28.10 Reviewof Safery 1083 28.11 TestYourKnowledge 1083

16

Chapter29

SIMPLIFIED 1085 AND TROUBIESHOOTING SERVICING 29.1 29.2 29.3 29.4

1085 Seruicing andTroubleshooting 1086 TroubleshootingProcedure Troubleshooting Charts1087 Relations1088 Customer

29.5 Reviewof Safety 1102 29.6 TegtYour Knowledge 1102

Chapter30 EXAMS 1105 CERTIFICATION TECHNICIAN PASSING FOR EXAMSMODULE 1105 PREPARINC and Associations1105 Certification Technician 30.1 TYPes 1107 30.2 Certification Procedures1107 30.3 Recovery 30.4 LeakRepairs 1108 30.5 ExamPreparation1108 30.6 TestFormat 1109 30.7 Takingthe Test 1109 '1109 30.8 Areasfor Reseatch Air Excellence 30.9 NorthAmericanTechnician 1110 HVAC Exam Excellence ConditioninS and Industry 10.10 SeryiceOrganizations Associations1110 TYPTCAL QUISTIONSMODULE 1lI1 30.11 Typesof Questions 1111

17

Chapter 31 TECHNICAT C HARACTERISTICS 11I3 31.1 31.2 31.3 31.4 31.5 31.6 31.7

KataThermometer1113 Infrared Thermomerertit4 Weightsand SpecificHeaisof Substances. t4 Ene€y 1114 (U.S.Conventionat)1115 EnergyEquivalents (StMetric) |j5 EnergyEquivalents LinearMeasurement Equivalents (U.S.Conventional-Sl Metric) 1115 31.8 Fractional (Decimals Inch Equivalents ano M i l l i m e t e r s1) 1 1 5 3 1 . 9 A r e aE q u i v a l e n i1s 1 1 5 31.'10VolumeEquivalents|16 3l.11 Pressure Equivalents1116 3 1 . 1 2V e l o c i tEy q u i v a l e n t|s1 7 3l .13 LiquidMeasureEquivalent5j j t 7 31.14 WeightEquivalents1117 3 1 . 1 5F l o wE q u i v a l e n i1s 1 1 7 31.16 HeatEquivaients 17 3 1 . 1 7P L r m p i nRga t i o 1 t 1 7 31.18 Compression Ratio 1118 31.19 Temperaiure Conversion Table 1118 31.20 Seasonal EnergyEfficiency Rating(SEER)1119 31.21 Standard Temperature1119 3'1.22Standard Pressure1120 31.23 Standard Temperature and pressure Sample 1120 31.24 Standard Air 1120 31.25 HeatingValueof Fuels 1120 3l.26 Single-Source Energy 1120 3l.27 Therrnodynamic Laws 1120 31.28 HeatConductivjty1121 3 1 . 2 9E n t r o p y1 1 2 1 31.30 Theoryof Matter '112'l 31.3'l Electron Theory 1121 3 i . 3 2 T h eA t o m 1 1 2 2 31.33 The Electron 1122 31.34 Electrical Unitsand Symbols 1123 31.35 Motor SizeCalculation 1124 31.36 LoweringVoltageSav€sPower l l25

3 1 . 3 7Resistances of Conductors,Serniconductors, ano Nonconductors1125

3 1 . 3 8ColorCodefor Resistors1125 3 1 . 3 9Resistance in Series and Parallel Circuits 1.126 3 1 . 4 0Electrical Codes 1126 3 t .41 RootMeanSquare(rms)Values 1j26 31.42CalvanicActionSeqLrence1127 31.43 Electrolysis1127 31.44Moisture-Holding Properties of Air 27 3 1 . 4 5Evaporation Sources 1129 31.46Desiccants1129 3 1. 4 7 Psychrometric ChartFormula 1129 31.48 Boyle'sLaw 1129 31.49Charles's Law 1130 3 t . 5 0Cas Law 1130 3 1 . 5 1Adiabat;cExpansion and Contraction ofaCas ll31 3l-52 lsothermai Expansion and Contractjon of a Cas 1131 3 1 . 5 3C a sa n dV a p o r 1 1 3 1 31.54 RefriSerant Propenies1t 31 3l.55 CharacterGtics of Little-Used Refrigeranrs lt31 31.56 MetricPressure-Heat Diagrams tj33 3'1.57Moisturein LiquidRefrigerants1133 31.58 Dryness of Refrigeranrs 1133 3l .59 Refrigerant Oils 1133 (Phase-Change) 31.60 Eutectic Materials 1133 31.61 Cryogenic Temperatures 1136 31.62 BrineFreezing Temperatures 1136 3 1 . 6 3T w i s D t r i l lS i z e s 1 1 3 7 3l.64 PjpingColorCodes 1138 31.65 Solders and BrazingMetals 1'138 31.65 FlareNlt Wench Sizes 1138 31.67 Solvents and Cleaning 1138 31.68 CleanRooms 1139 31.69 Reviewof Safety I I39

DICTIONARY OF TECHNICAT TERMS 1140 ACKNOWLEDGMENTS 1166 INDEX1170

IB

OPPORTUNITIES CAREER

IN HE A T I N GVE , N T IL A T IN G, AIRCONDITIONING, AND REFRIGERATION In ihe past fifty yeais, the heatinS, ventilating and air conditioning (HVAC) {ield has expedenced massive technological change. It has gone from the era oI the iceman to thai of the educated and highly tained technician. SeeFigurcs A and B. The most rapid advances have occurred in the last ten years. Today's iechnician needs more than a small box of tools and a cylinder of r€ftigerant You must now have a broad background in working with comPuterized, automated electronic lryAC equiPment. Many of the recent changes in the fryAC {ield are due io rapid chdntes in lechnologyand a Srowint concern Ior the environment. Scientists have wamed ihat

F i q u r eA . O n l } a h a l f L e n t u r va q a t h c \ F m d o a a 5 a ,anit'ar heL're 'n no* neiBhbothood,. dPlitetiag blo.ks of ice to keep food cold. (Edward Hulyk Studio)

continued rclease of rcfiigeranis to the atmosPhere will desiroy the earih's ozone layer This layer, located appro\imaiel) l5 miles dbovP Lhe Sround prolP.Ls raysof lhe sun tie earthfrom the damagingLrlfraviolet affect humans, laver would Desiruchon of the ozone life. and sea animal, Elants, To prevent continuing damage to the ozone layer, laws have been passed governing the t,?es of refriterants manuJactured and how thev can be used. New equipment has been developed that requires skill alld training for pnPer operation. A t€chnician todav must be familiar with the com_ ple)' eleclroni. device- u.ed in reln8eraiion "yslem) lt i, common lo ree fully dutomatedhealrng dnd coolin8 systems in homes, These systems can be sei lor varying t;mDeratures and humiditv ievels Ior each individual roo;. CommercralbuiJdmg.as usin8 comPuterized systems that are even more soPhisiicated.

Figure B. Today's HVAC technician must be able to work with conputercontrolled electronic systemsand use sophisticated diagnostic and chaqing equipment (Ridge Tool Company)

19

Importance of Refrigeration andAir Conditioning There are few phases of modern living untouched by refrigerdfion and dir conditioning. Bucinessoperahon), manufacturrng procerie5.stordge. and shipping are almo-r aluays c;;ied out todd) inder controlledtemperature conditions. Skilled specialists are required to design, install, and maintain conirotted environmenrsrn encloseddrea5tndr rdnge from homesto rpace satellite-Tl-e u5e ot .ompuierL/edequipmentna- increased the need Ior facilities ihat are totally energyconirolled. The refrigeration and air conditioning industry helps make possible this sysiem of livin8. Air conditioning has improved business and industrial efficienry, while adding to human comJort- More and morc ractodes and heavy indusides are being air conditioned.The plesent scale of farming is made possible, to a great extent, by the use oI air-conditioned hactot cabs and refrigerated harvesting equipment. Many fruits and vegetables are re{rigeraied immediately upon being harvested. The quality of such products is much better for this reason. Cooling and fteezing of meat and meai products makes possible iheir handling in a much more sanitary way than would be possible without mechanical refrigeration. Beverages,desserts, and even staple foods are all at least partially processed by refrigeration equlPment. Designin& manuJacturing, se11in8,installing, and maintainint this equipment provides for man, many jobs that did not exist Iess than a generation ago. Opportunities for employment in writint specifications for refrigeration and air conditioning equipmeni and sellint this equipment have natwally grown wiih the indushy. Since refrigemtion is used in so many enterprises, it follows that anyone who has to wotk in these industies must be lamiliar with the basic air conditioning and reftigeration processes. All the cafeers in this field are available to anyone interested, r€gardless of mce, creed,

kets, domestic central air conditioning, water coolers, beverage coolers, marine refrigeration and air conditioning, automotive air conditioning, and tmck retrigeralion and air condilioningcy.tem'.See Figurese, and D, fhe industrial fieH in(ludes large proce,sint dnd air Londitjoning svstem5.pa(king plinti. cold +orage. and ice dnls. These systems require the attention of a relrigemtion operaiing engineer. See Figure E,

CareerOpportunities Someof the oppofunities for employmentin retiigeration and air conditioning includel

lobs at variouslevels: . Seniorskilied. . Skilled. . Technicians.

. SupeNisors. . Prc{essionalpersonnel.

(partiallist): Variousspecialties . . . . . . . . . .

gngineers. Technicians. Test technicians. Salesengineers, Application enSineers. Installers. TesteIS. Maintenance technicians. Se ice persons. Repair specialists. Assistants,

Salesengineers. q,lacn6.c^."

Counterpersons, Partspersons, qhihnind

in;

recervrngPer. Operatingengineels. R p Frioari ti^-

.

Industrial. Sheetmetal experts.

TheAir Conditioning and RefrigerationIndustry The air conditioning and refrigeration industry is usualy divided into three areas: . . .

Domestic. Com]nercial. Industrial.

The domestic field coyets home rcfrigeFtors, fteezers, and window air conditioners. The commercial field includes all small automatic systems.Such systemsare used for stores,supermar-

'ro

Figute C. Two service technicians repairing a rooltop air conditioning unit. (Superior Contract Servtces,tnc.l

EiglJie D, Installation and servicing of home air conditianersis one ot' the many careetsopen to a person knowledgeand handson trainingin refrigeratianand air conclitioning.(Lennoxlnternational,lnc.)

A salesen4ineerwas requiredto selectand specifythe proper Fif]rtreE. An air mavement systembeing installecl. eiuionent. and skilleclworkeis*ere n.idecl to installit. A servicetechnicianwill be neededto periodicallv service and maintainthe system.(KnaufFiberClassCmbH)

21

HVACand Refrigeration lob Descriptions As y.ou might expeci, the responsibilities of per_ 5onr working in the herting, vendlafing.dnd air co;dirroningindu-fry wiu v.r) greaLly. So;iI ihe kind or work that is done. Con-ider dir condrironinS. hearinp. and rernter_ dlion reLhnicians.for e^ampte.Wor[ng Lmder'the .uper!tsron- o! enguFerc the) help design. manuacture. >ett. and >ervice equipment. Often, a tecl^ni_ cian wiil specialize in one area, such as research and developmeni. Those working in manufacturing may design and ie:t or supe^jse produlhon of Fquipment.They ma\ arso *orr a5 nanuldcfurer'srepre. A unit of measurewhich hasbeen used for reading high vacuums (prcssurecloseto an absolutevacuum) is the fol/, One torr equals a pressure of 1 mm of mercury (mrn Hg,0'C). It is named after the man who invented the mercury barometer,The unit torr may be expressed in fractionsof an atmosphere.One torr = 1/760 of an atmosphere.A pressure of one iorr is almost a perfect In soh'ing most pressure and volume problems, it is recessaryto use absolutepressures(psia).Absolute p F-"urei- tduge D'

1 1 0 230 - -99 -21 88 190 66 1 43 32 27 21 16 10 1

11 90 80 7a 60 50 3 4

rroezrns Point-r' ! 0

5 AbsolulePressuren KiloPascals

pressure, waterbailsat 212"F(l,CC). At pointA, curvefor water.At atmospheric rigure1-23. Temperature-pressure raises boiling pressure aboveatmospheric wi'thvacuunof 2i HEea kpa),waterbailsat 142"F(62'C).lncreasing (133'C) is 271"F af 15 psia(311kPa),boilin! temperature At B, whichis at a pressure temperature.

on Freezing 1.20 Effectof Pressure of Water Temperature The temperatureat which water freezesis affected by the pressureon the su ace of the water. Incleasing the pressurelowers the freezing iemperature Decreasing the pressureraisesthe fteezing temPeratureFigure 1-25shows this relaiionshiP. Thls relaiionship Soesthe oPpositeway from the g e n e r ",l! l e B r \ e ni ' ( F c t r o nl l 8 4 T h r s i . b e . r J ' e h d ' :"r erpand, hhen jl freF.,e,.Mo5r -ub-Idn(ese\paid when they me1t,and obey the rule in Section1 18 4. For them, the higher the pressure,the higher the melting

Effectof lce 1.2'l Refrigerating Ice is stillimportant to ihe refriteration industry.As siated before, ice changesto water at 32"F (0"C) and aimosphericPressure.Heai absorytion to produce this chanseis 144Bhr/lb. (335kl/kg) ihe specific heat equaiion for changing ice to water is: Heat = wt. of ice x sP hi. caPacit]'ol ice x tempenture change. Heat will be in Btu The weight (Wt.) will be in pounds. Specificheat (SP.ht.) will be given in Btu/Ib. (The sPecificheat of water is 1 Btu/lb.

in "C al: Evaoo.alino TsmDerature 200kPa 89 R-12

100 -?9 -38

122

is shown on evaporating of p,ressure Figure1-24. E_ffect aI thtee suDsance'. temperatures The speciJicheat oI ice is 0.50Btu/lb ) The latent heai of tusion of ice is 144Btu/lb. Formula: Sensibleheat (Btu) = Mass x sP ht. x AT Latent heat (Btu) : Mass of ice x Latent heat of fusion heal - ldtenl hea folil .han8e= Se15'ble Example: Aow many Btu will be absorbedin changing25 lb. of ice at 5'F to water at 40'F? Solution (in steps): 1. Raisethe temperatureof ice from 5'F io 32'F: Btu : 1\,t oI ice x sp. ht. capaciiy ol ice X temperaturechange

Btu= 25x 0.50x (32 5) B t : J: 2 5 / A 5 A t 2 7 Biu = 337.5Btu

48

Modern Refrigeratioiand Air Conditioning

kPa b./sq.n. 13981 2Q28

aims 140

12161

1764

120

10134

1470

100

8107

1176

6081

2027 0

'c

-1 -4.9 -0.8 -0,7 -0.6 -0.5 -{.4 -0.3 -0.2 -01 0 0.1 4 . 2 3018 30.36 30.54 30.72 30.90 31.08 31.28 31.46 31.64 31.82 32 32.1A 32.36

"c

Temperatu.€

Figure1-25. Chartshowseffectof pressureon freezingtemperatureol water. 2.

To melt the ice ai 32"F: Btu = wt. of ice x latent h€at of fusion of ice

Btu=25x144 Btu = 3500Btu 3.

To warm the water from 32'F to 40"F: Btu = wt. of waterX sp.ht. capacityoI waterX Biu=25x1x(40-32) Btu=25X1x8 Biu = 200Btu

4.

Total heat required to change25 lb. of ice at 5"F to waterat 40'I: Btu : 337.5+ 3500+ 200= 4137.5Btu

Sl Metric Units Tn SI met c, .he specificheat capac;$ o ce 2.11kJlkg K. Its heatabsorptionabi1irywhen changing from a temperature below0t to 0'C, is 2.11kJlkg per degrce change.The latent heat of tusion (melting) of ice = 335 kjlkg. Tle specific heat ot water: 4.19kllkg K. Example: How many kJ will be absorbedin changing93 kg oI ice at -20"C to waterat 4t? Solution(in three steps)l 1. Tofind heatneededto bringicefrom 20"Cto 0'C: kl = massof ice x sp. ht. capacityoI ice x tempemturechange kI=93x2.11x24 kJ = 3924.5kJ

2. To find heatneededto melt ice at 0"C: kJ = massof ice x latent heat of fusion of ice kJ=93x335 kI = 31 155.0kJ 3. Tofind heatneeded to raisewatertemperature from 0'C io 4"C: kJ = massof waterx sp.ht. capacityoI waterx temperature chante kJ=93x4.19x(4 0) kt = 93 x 4.19x 4 = 1558.7kJ 4. Totalheatrequiredto change93kg of ice ai -20'C to waterat ,l"C kl = 3924.6kl + 31 15s.0kJ + 1558.7 kJ kl : 36 638.3kI Equivalents 1 kJlkt. K = 0.239Btu/lb.'F 1 Btu/lb.'F= 4.187kjlk8.K 1.21,1 lce and Salt Mixtures Refrigeratint by ice alone will not provide temperaiuresbelow 32"F (0"C). Therefore,to tet the lower iemperaiues rcquired in someinsiances,ice and salt mixfures are used.Thesemixfures,ice and sali (sodium chiorideor NaCl),and ice and calciumchloride (CaC12), lower the meltinStemperaiureof ice.An ice and sait mixiure may be made which will melt ai 0"F ( 18.c). A solution of water and salt freezesat a lower temperaturebecausemore energy must be removed from the solution beforeice will start to folm. This phenomenonis called "freezingpoint depression."

Effect 1,21.2 Tonof Refrigeration The coolmg capaciiy of older rcftigerahon rmits is often jndicated ln "tons ol rctuilenti,on" Aton of rcfriqe/aflon represenis the heat energy absorbed when a ton (2000lb.) of ice melts during one 24-hour day. The ice is assumedtobe a solid at32'F (0"C)initial)' andbecomes water at 32"F (0'C). The energy absorbedby the ice is the latent heat of ice times the total weight. Todat refrigeration uruis are often rated in Btu/hr. instead of tons. The Btu equivalent of one ton of refrigeration is easy to calculate. Multipl)' the weight of one ton of ice (2000tb.) by the latent h€at of tusion (melting) of ice (14"1Btu/lb.). Ther! divide by 24 hours to obtain Btu/hI. One ton of refriteration effect= 2000x 144/24 One ion of refrigerationeffect= 288,000Btu/24 hours One ton of reftigeration effect = 12,000Btu/lrA 12,000Btu/hr. cooling caPacity is equivalent to one ton of refrigeration. A refrigerating or air conditioninS mechanism capable of absorbing heat can be rated in tons per 24 hours by its heat-absorbing ability (HA) in Btu divided by 288,000. T = tons of refrigelation effect HA = heat-absorbinSability

HA = tons of refri8eration ef{ect 288,000 = 12,000 Btu/hr' 1 ion of refrigeration Example: The heat-absorbingability oI a reftigerator unit is 1,440,000 Btu per 24hou|s l lhat is its ton miing? Solution: 1,440,000 1140.000 -

'=r4"1r!oo=,88poo

T = 5 tons of refrigeration effect

Example:

What wi[ be the "ton" rating of a refti$rating mechanism capable of absorbing 1,728,000Btu in 2,l hours?

Solution: -' = 1,728,000 ,8g,ooo T = 6 tonsof refrigerationeffect Example: What is the Btu heat absorbing caPacity of a 1/2-ton refrigerating system?

Solution: = 144,000 Btu Perday,or 5000Btu 1/2 x 288,000 per hour Most room air conditionersare rated on theil heaiabsorbingability in Btu Per hour. A l-ton machineis 288,000= 12,000 Btuper hour 24

sl Metric Unils

The SI metric system has no unit which caJl be compared with dre "ton of refrigeration." 1 ton = approximately 907 kg latent heat = 335kl/kg energy absorbed = Iaient heat x weiSht energyabsorbed= 335k] /kgx 947kB enerty absorbed= 303845kJ The meliint of this ice in one day has a cooling or refrigeration capacity o{ 303 845 kJ. To convert th€ Gting to kilowatts: 1kW = 1 kJlsec. I ton relrigerationcdpa(ity - l0l845 (24t 1600sec) I ton retriSerddoncapdcin = J0384q 85 400 sec 1 ton refrigeratroncaPacity= 3 52 kT/sec 1 ton refigeration capacity = 3.52 kW A refrigerator which Produces an equivalent cooling rate of ihis ice melting will be rated as a 1+on unit-

Equivalents 1 kW = 3415Btu/hr. 1 Btu/hr = 0.29W Btu/hr. 1 "ton" = 12,000

1.22 AmbientTemperature Afl1biefit tefipetutute i5 the temperatuie of the air surrounding a motor, a control mechanism, or any oiher der.ice.For ixample, a motor oPeratedat full Power may be guaranteednot to 8et hotter than 72"F (40"C)above the ambient temperature. Then, if the room temPerature (ambient temper;turc) is 86"F (30"C), the temPerature of *le motor co;ld get as hrgh as 158'F (70"C)when working' at fu]l power. Ambient temperature is not usually constant. It may change day by day and hour by hour, dependlng on usage of the sPace, sunshine, and many other

1.23 Heatof ComPression rites See itr iemPerafure As a gai's con'pressed. h {erer8) ) added to lhe Fisure1-1.This ic due to l\e orl is ofien added The energy gui Uy tlte comprcssor. " termed "heat of compression oI ihe vaPodzed (gas) refrigerant The tempemture _the compressor from the evaPorator will returninq to probablv-be at, o..lighlly below l'1eroomtemPerabure ihlr rrrn" uupot. leaving the conpre'.or and eI]terhg the condenset will be at a much higher temperature _efrigeranl in a lhe conpression of \dPorized tobe a nearlyadireciqeralor,ompre..orii considered doati'cprocess.AdiabaHc,ompression ls a Processir which i gas is comPressed without losing heai to the surroundings. The refriSerant Passes through th€

50

ModernRelrigeratlon andAir Conditioning

compressorvery quickly.Therefore,it only losesa small amount of its heat of compressiontherc. The corpres,ed vapor in ihe condenseris no( much warmer ihan ihe temperatu-reof the surrounding air Heat of compressionwill be rapidly transferred ihrough the condenserwal1sto the surounding ai or condenser coolint water.(SeeSeconal Law of Thermod)'namics,Chapter31.)

1.24 EnergyUnits In rcfrigeration work, three conrmon, related forms of energy must b€ considercd: mechanical, electrical, and heat energy. The siudy o{ refrigeGtion deals mainly with heat energy. However, a refrigerator must make use of electdcal and mechanicalenergy to move heat energy Fr^m

nnp nl,.a

t.

:hn+hcr

In a compression refriteratint unit, electrical energy flows into an electric motor There this electdcal energy is iumed into mechanical energy. The mechanical energy is used to tum a compressor. The compressor, in tum, compressesthe vapor to a high pressure and hith tempemture. This process transforms mechanical energy mio heat energy. Various uniis are used for measudng mechanical, heat, and electrical energy. Energy conve$ion units arc expressedas follows: Mechanical to heat

t hp:2545 Biu/hr 778Jr.-Ib.:1Btu Mechanical to elect cal t hp = 745 watts (W) Electdcal to m€chanicat 746watts = t hp Electdcal to heat 1 watt (1 joule/sec.)= 3.412

Btu/hr 1 kilowatt(kW): 3412 Btu/hr Heat to mechanical Heat to electdcal

1 Bt!/hr : 0.000393hp 1 Btu/hr = 0.293watts

These conversion units are used in calculating loads and determining the capacity of equipment required for specificrefrigerationapplications. Sl Metric Units In SI metric, the unii lor measu ng energy in all three of these forms is the joule. The kjlowatt hour is widely used, however, as a measure of electric en-

e$v Equivalents Ll = a.n76rt.-Ib. 1 It.lb. : 1.3558 J 1W = 0.7376ft.-Ib./sec. 1It.lb./sec.= 1.3558 W 1 kW = 1.34hp : 3412Btu/h t hp : 0.746kW

REFRICERATION SYSTEMS AND TERMS MODUI-E 1.25 Refrigerant ln refrigerating systems, fluids which absorb heat inside the cabinet and releaseit outside are called /el gIn the evaporator,under a reduced pressure,the fluid changes ftom a liquid to a vapor, thus absorbint heat. In vapor form, lhe fluid is taken into the compressor. There tlle temperature and prcssure are increased. This allows the heat that was absorbedin the evaporaior to be released (squeezed out) in the condenser. Ihe rcft*erani is ihen returned to a liquid fom for another cycle. The refrigerants most commonly used and their -echnicalchdra.Leristics are e\plained in Chapter q.

1,26 Heat Transfer Heat may be transfered or moved from one body to anotherby one of three methods:Iadiation, conduction, or convection, Some systems of heat hansfer use a combination of these three methods.

1.26.1 Radiation Radiation is ihe transfer of heat by heat rays. The earth receives heat from the sun by radiation. Litht rays ftom the sun tuIn into heat as they st le opaque or translucent matedals. These materials will absorb some or all oI the rays. (Opaque means light cannot shine through. Translucent means light can go through but one cannot see through. See Chapter Air is heated very little as light rays pass throuSh it. Likewise, a glass pane absorbs littie heat as rays pass through it. Sunlight geneiates more heat when striking darkcolorcd objects than when striking litht-colored or polishedsurfaces.This is becauselight-coloredand polished objecis reflect the rays. Rellected rays are not absorbed and changed inio heat. Routh, dark-colored sudaces will get hoiter than lighi-colored or polished surfaces, so they wiil radiate more heat. Any heaied su ace losesheat io cooler sunounding spaceor surfacesthrough radiation. Lik€wise, a cold surface will abso$ radiated heat. Some space heating systems us€ ndiant heating sources Iocated in the ceilings, walls, or floors.

'1.26.2

Conduction

Cotldltctiolr is the llow oI heat between pats oI a substanceby molecular vibrations. The flow can also be

Chapter1

of RefriSeratlo. Fundamentals

from one substanceto another substancein direct con-

1,27 Brineand SweetWater

A piece of iron with one end in a fire will soon become warm from end to end. This is an example of ihe transfer of heat by conduction. The heat travels through the iron, using the metal as the conducting medium. Substancesdiffer in their ability io conduct heat. In general, substanceswhich are good conductors of electricity are also good conductors of heat (Wiedmannhank Law). which conductheatpooily are calledin_ Substances sulato$. Suchsubstancesare used to insulaterefrigerators and homes.Any structure that is to be maintained at a temperature diJference from its surroundings may use insulatom.

Some refrigeration and air conditioning apPiications reqrdre thai water be kept from freezing ai tempeFtures considerably below the normal freezing temperature oI 32"F (0'C). Other aPPlications require that water at atmospheric Pressure be kept ftom boiling at tempelatures above 212"F (100'c). Sait, sodium chto de NaCI), or calcium chlodde (CaClr),added to water, raisesthe temPeratureat which the waier will boil. It also lowels ihe iemPeraiure at which it will freeze. See Chapter 31 for tables of brine solutions with a freezing point and specific gavity for

'1.26.3 Convection Cor?re.fio, is the movement of heat from one place to another bv way of fluid or air. For examPle,heated afu moves ftom a furnace into the rooms of a house lt releases its heat to the rooms. Then cooled air returns ihrough cold air ducts to receive another supply of The samemethod may be used to cool a sPace.Unwanted heai is collected and discharged outside the sPace.

1.25.4 Controlof HeatFlow The t'lo$' of heat by radiation,conductioD and convection can be controlled.The transler of heat by each can be incieasedor cut back accordingto need. Use of matedalsthat are good radiatorsof heai improves tnnsfer of heat by radiation. A colo! known to Le a good radiator can also be used. Radiationmay also oe improved by the tlpe of recei\irg surfacesused.Materidl; or .olor' thdi are Eood absorbersrPoor refle(ior-) o{ radiated heat should be used. Radiation may be reduced by revercingthis aPplicaiion Dark mate als or colorsabsorband radiaie readily Light-coloredor shiny maierialshave the oPPositeProPerties. Conduciion may be imProved by Providing large conductingsurfaces.Good conductingmaierials,suchas copper, aluminum, and iron also imProve conduction. Cork, foam plastics,mineral wool, and many oiher similar matedalsare poor conductorsof heat. Poor conductors of heat arc commor.ly rcfened to as heat insulatorc (insulaiion). Convection may be improved by increasing the flow of the conveying medium. Forced-air circulation arean e'.ampleA blower'peedsup airhedting>ystems ( conr ection' an be slowed by rerarding onr ersely, flon. ihe circulation of air. Heat iransfer is also contrclled (affected) by the remperaturedifferencerT D ) The Sreaterlhe temperaturtdiJference,the greaiertle heat llow

Some reftigerating and air conditioninS insiallationsuse tap water without adding any salt or oiher sub siance lhir js reterredlo a-,'.seet water.

1.28 Dry lce Solid carbon dioxide (COr) is sometimesused for refriseration. Solid CO, is a wlite crystalline (like crystab);ubsiance. It is fomed when Iiquid carbondioide is atlowedto escapeinto a snow chamber(heat-insulated The heat for vapodzing the liquid is dral'n from ihe interior of the chamber A very low temperaiure (-108'F, -78"C) is Iormed. As a result, quantitiesof the ca$on dioxide solidify This solid is pressedinto various shaPesand sizes and sold for reftigeration purPoses li is given such names as dry ice, zero ice, and so forth, lt remains at a temperahrreof 108"F( 78'C) while in a solid stat€at atmosphe c pressure. Diry ice does not melt into a tiquid lt goes directlv from the solid to the vapor state This is calte'd "subiimation." Dry ice has some desinble characieristics.It does not wet the surfacesthai ii touches. '5 a pre5endlive The -oh Ihe vdDor ql!en o-f Lerrperaiure majilained peimiF handlinS frozen loods withoui using a heavily insulaied container The latent heat of sublimation is 248 Bt!/\b (577 b) the vaPorin p.s8in8hor kl ^s,. The heatdbsorbed r O8-'l-| 78'Cr io lz'f ,0'C, is appro\imately 27 Bfu /lb (ol kj, kp,'.Thi(, addeo io the latenl heatof rublimatio l makes i total heat-absorbingcap.cri) of 275 Bru/lb

(640kllle).

cdPabilitylhdn Dry iie hasa greaterhea!dbsorbinS exPensive than mole It is generaly water ice. does

Equivalents 1 kI /kg = 0 4299Bt.u/lb. i Btu/lb. = 2.326kl./kg

Modern RetrigeEtionand Air Conditlonlng

Neverplacedry ice in a sealedcontainer!At ordinarytemperatures, the dry ice will sublime(turn into a vapor).The resultintpressuremay causethe container to explode. Avoidtouchingdry ice. tt will instantlyfreezethe skin.

'1.29 Critical Temperature The ffitical tenperat re of a substance is the highest tempemture at which the substancemay be liquefied, regafdless of the pressure applied upon it. Chapter 31 lir|5 c-rical lemperdturc) for common reingeranrs, The condensing temperature for a refrigerant must be kept below iis critical temp€rature. Oiherwlse, rne rc ftigerator vrill not operaie. Carbon dioxide (R-744)has a c tical temperatureof 87.8'F (31'C). This refrigemnt is not used in air-cooledcompressionsysiems.This is because the condensing temperature would usually be ,h^wc

rLi< rpmnorrr

ra

1.30 CriticalPressure The citical pressure oI a substanceis the minimum pressure necessary to liquetr a 8as that is at iis critical tempemture. Less prcssurc wil not liquefy it.

1.31 Enthalpy Eflthalpyis the measurcof the heai contentof a substance. The amountof enthalpyis determinedby both the temperature and ihe pressure of the subEnthalpy is ali the heatin one pound of a substance calculaiedfrcm an acceptedreferencetemperature,32'F This referencetemperafurecan be used for water and water vapor calculations. For rcfuigerantcalculations, the acceptedreferencetemperatureis 40"F.SeeFigure 1-21A.. Formula: H=Mxsp.ht.xAT (Enthalpy= Massof substance x Specificheatof substancex Changein tempemture) Example: \ /hat is th€ enthalpy of 1 Ib. of water ai 212'F,assuming0 enthalpyat 32"F? Solulion: Thespecificheai of wateris sp.ht. = 1 Btu/lb./'F Heatto raisetempeEtureoI 1 lb. of waterfrom 32'F to 212'F:212- 32 = 180'F H=MXsP.ht.XAT H=1x1x180 H = 180Btu (totalenthalpyat 212"F)

5l Metric Units In SI, the zeroenthalpiesfor water,refrigerants,and air are also takenat a convenienttemperaturc(reference tempemtureor T,) and pressure: . Forwater,0 enthalpyis at 0"Cand 100kPa. . For refrigerants, 40"Cand 100kPa. . For air,25'Cand 100kPa. The enihalpy is measuredin joules 0) or kilojoules (kJ)' Formula: H=Mxsp.ht.XAT Example: Whatis the fotalenthalpyof 5 kg of waterai 80'C? Solutionl Enthalpy at 0"C = 0 Specificheatof water (sp.ht.) = 4.19kJ,/kg K Heatneededto raisetemperature of 1 kg oI water from 0'C to 80"C:80- 0 : 80'C H=MXsp.ht.xAT H : 5 x 4 . 1 9x ( 8 0 0 ) H:5x4.19x80 H = 1676kJ (totalenthalpyat 80'C) Figure 1-218showsthe rclationship of enthalpy io temperature.

1.31.1 Specific Enthalpy Specificeflthalpy is enthalpy per urlit mass. It is measuredin Btu per pound o/kg). Tablesof the enthalpy of subsiancesand pressure-enihalpydiagrams, such as Figure 1-21,use speciJicenthalpy Formula: h:H/M (Specific enthalpy= Enthalpyabso$ed/Mass) Example: If 100lb.of a substance absorbs2000Btu oI energy when heaiedfrom the rcferencestateof 0 Btu/Ib., what is the specificenthalpy? Solution: Specificenthalpy = enthalpy absorbed- mass

2oooB*: h: E = zos,,.,ltlr. M

100lbs-

1.32 Cryogenics Cryogefli.s rcfers to creatin8 and using temperatures in ihe ranSeof 115K down to 0 K (-251'F dora'n to 460'F,or -157"C down to -273'C). The term cryogenics has increased in common usage. This is due to frequent use of liquid helium, nitrogen, and liquid hydfogen in refrigeration. The term is also applied to the low-temperature liquefaction of gases and their handling and storage. It includes insulation of containers. instrumentation, and techniques used in such work.

ChapterI

Figure 1-25 shows boiling (evaporadng) temperafures at aimospheric pr€ssure of some common cryogenic fluids. [t also indicaies the cryogenic ftnge of temperatures. These temperatures are in Kelvin (K). atAhosphericPr€ssure BollingT€mperaiu€

Celsius "C S€le)

FLUID 212 22 109 EthyLene ol ihe Beginning

-250 258

Oxygen -320 423 452 460

672 438 419

100 30

351

-75

195

325

-93

t80

210 202 163

-157

116

183 192 -196 -246 253 270 -273

90 81

140 49 37 I 0

373 243 230

27 20 0

ot some cammon Figure1-26. Boiling temperatures ptn7etanlgand -ome alhet fluidsdt almotphe'i( prcssure.Note differencebetweenbailing pojnts al some commanly useclrefri4erantsand boiling points oi fluids tn the cryoqentcranqe.

1.33 PerfectGasEquation If a quantity of gas is enclosed in a tiSht container, the relationship between pressure, temPerature, and volume may be expressed by the formula: PV : MRT = = : =

Pressure in pounds per square foot absolute Volume in cubic feet Mass of gas in pounds Gas constant (R will differ for different gases).(Figure 1-27gives the value of R for some common substances) T : Absolute temperature in "R

P V M R

Mate al

Oxygen

(R) GasConslant J/ks.K _l!l!!-

SpeclflcHeal kJ/t(g.K

2A8.68 53.34 666.98 123,24

1 00 2.13

0_71 1,46

210.10 125.08 262.76 224,87 450.45

0.92 2.01 0.92 1.S8 2.03

0.71 1.84 067 1,67 1.55

38.82 23,11 44.55 41.55 83.23

fot some Figwe 1-27, Tablelistsgasvalues(constants) usedin reiigeration watk substances

Fundameniakof Refrigelation

Example: what will be the volume of 2 ]b. of carbondioxide at 240"Fwhen the piessureis 185Psi? Solutionl PV = MRT P = (185+ 15)= 200psia: 200x 144= 28.800Ib. per sq. ft. absoluie M =21b. R = 38.82ft.-Ib./lb.'R* T = (240+ 460): 700'R MRT ,. P 2 _. : x38.82X700

"

,8foo

-28,800 V : 1.89cr. ft. '

*Thernit "ft.lb." is usedinsteado{ Btu Btu ls not dnd'R iu)l ascdldrenol wil'1feet,pounds. compatible with N m : Joule,kg, and'K compatible

1.33.1 Sl MetricUnits The equation in SI may be exPressed:PV = MRT. P : Pressure in pascals (Pa) V = Container volume in cubic meters (m3) M = \4acrbe r.ed or ihe.e \dl\p.. 'l i. be5r to use.o(let, (ith ball oearinggr,Dper>. Therei. l*. ,.hanceoi loiing tools w\e worling in dif i(ult po5rtions. Figure 2-58illustratesa set of ihesespeciatrools. Al-o included,rre)oclerctor pacling gldncjti.tirg,. Torque Wrenches All materials are elastic (witt stretch, compress, and tr^'isi).Even cast iron and hardened sreelsuaed in the \or.tructiol of con pres.or5are plil.ti. up ro n porn.. Wl^enhthtFningbol,.. ruis. and orhe.an.chment-on compressorpa s and assemblies,it is important to E sd-uretl'F ."nol I ot hShfne:..Or re-qi"e *drpjgc or otherpdn dcmagend) o.cur To n-ea.urerl.edmounL of tightness,a torque wrench is used, Figure 2-59. Torque wrenches are usually wrenci handles only _. They are made to be used with socketsof different size;. The handle is equipped wirh a dial or pointer which measuresthe foot pounds or inch-poundsof torque. T h e l o r q u ei - , o u r d b \ r n d r i p ' ) i n S r h F t L n B , 6 o f f h e . h.rndle{in 'eet)b) LhepJl ,rn pound"rapptieJ .o the handlertool-pL'und.,I t long wre,r.h hancl.epu ed by a spring scale reading 50 pounds will produce a

Fi8ure2-56, Refri7erationservicevalve wrench. Fixed end it fot "cracking' valves.Ratchetenctis tor rapn valve stemaperatian.Leftend has 1/4,,squared ve for use with valve stemand packin! gland nut sockets. Other openjngsare 3/16', th", and 5/16,,square.Ihe 6-point socket fits 3/8" nuts. (Durolndestro, Duro Metal

Figure2-58. Specialservicevalve socketset. A PackingEland socketsand valve stem sockets. B Varietyof 6-point and 12-pointsacke]d.C-Handles and extenders.D Ratchetwrench. E-Adaptarc. Figurc2-57. Reversibleratchetwrench.Square apeningswith 1/4" and 3/16" at one end, and 3/8,,ancl 5/16" at the other end. (Uniweld Products,lnc.l T-oqueScale

ServiceValve Wrench Adaptors Many manuJacturersuse valve stems other than the 1/4" squarc. Some valve stems are made so that the milled end is inside the valve body.This requiresa tood socketwrench to turn it. To accommodatethese valves, adaptors are availablein various sizes.The male or drive paft oI the socket is usually I /4" square.Therearea few which use a larger drive 19132"). The socketwhich fits the valve siem comes

Figure2-59. Torquewrenchusedto measure the amauntof tightness of nutsandscrews.Thiswrcnchis (Reed madeto be usedwithstandard sockets. ManufacturinE Ca.)

83

ToolsandMaterlals Chapter2 Refriseration torque of 50 foot-pounds. (Technically, foolpounds is the wrong ierm. The corect term should be Pounds-feet The foot-pound is a unit of work. However, PoPular usage has made the telm fooFpound acceptabie for the measurement ol torque.) To calculate inch-pounds, multiply the length oI the handle (in inches) by the pull on ihe handle (in pounds). The manufactureEof equipment (automobiles,airplane..refrige'arir8equipmeni.eic.)are able ro determine lhe proper torque thdt shouldbe aPpliedto the fasteners on their various mechanisms,The rccommended torque Ior the many pats of refrigeGhng mechanisms are specified in manufacture$' service To use a torque wrench, the oPerator fits lhe Proper size of socket onto ihe wfench The socket is then aPplied to the nut, and the handie of the wrench is Pulled until the indicator shows that the required torque has been applied. At that torque, the nut is at the tightness rccomm€nded bY the manufactwer

2.9,2 Hammers A hammer is a necessiiy in the refriSeration shoP The 12- or 16-ounceball p€en hammer is a usetul tool SeeFigure 2-44,No. 47.A carPenter'sclaw hammermay also be needed for mounting piPe suPPorts and fastening sheet metal to wood. Ii is imPodant that the hammir head be firmly fastened to the handle The handle musi also be in good condition Gftsp the handle about two-thirds of the way back ftom fhe head. For light, accurate blows, hold the hammer with the index finter on the toP of the handle and use wdst action. For heavy blows, hold the ham_ mer with fingers arormd the handle and use elbow

2.9.3 Mallets In seffice work, a mallet is often needed to ddve parls into place or to separdtethem w:thout injury lo it eir surfaies.For 'uch ;orl,, I l/2-lb ro2-lb mallet is desirable,made of rawhide, mbber, wood, Plastic,or Iead. A mallet is shown in Figure 2-44, No. 48.

2.9.4 Pliers Pliers are universal tools. Pliers are made of alloy steel. usually with manganese, although some are chrome-vanadium steel. Top quality pliers are usually drop forged. Many different q?es are available Use only pliers with insulated handles when working on electricalpats. .

Gas prierc are slip joini combination ptiels, which are handy Ior geneml use. However, th€y should not be used on nuts, bolis, or fittings. They could slip and injure the surface.SeeFigure 2-44 No. 20. . Cutting pliers are mostly used when working on refrigerator wiring. One type, called ihe lineman's Pli ers, is a powertul cuiting and SriPpint tool. Another it?e, called the diagonal Pliers, is used to cut in closequa ers. Refer to Figure 2-44,No. 9. . Nut pliers are used to good advantage on some iobs. The jaws always stay Paraliel.Some have an adjustablecam action that locks the jaws on the nut or bolt. In geneml, it is not good Pmctice to use nui p1ie6 on bolts or nuts However, on a job such as holding a boli head while turning the nut with a wrench, the us€ of nut pliers is permissible. . Slim-nose Dliers, needle-nose pliers, and duckbill pliers are Aequently used in hird-to-reach places SeeFigure 2-44 No. 10. . Round-nose plierc are used to shaPewire into looPs and to bend sheetmetal €dges.

2,9.5 Screwdrivers A complete ecrt by the tap. Sin.ed tap i. ,ron_ adju-.able.d?..an u-ud ! be adiu-rFdto perm.,\dre_ 'ul mal.hing of the thread..Tap-ano diec ma) dl.o be u

. - 4 E e - - . - . -

Explain howa system usinganexpendable-type of re frigerant works. Discuss andcompare domestic andcommercial re frigeration systems.

i N

Explainthe operationof thermoelectricrefrigeration. Comparethe differencesbetweenhot-gasand electric defroslsyslems.

: 4 ilti

t;:-:,4217

s:5 ll:'" , i i::t ' X - -l.cr

ii:

;18.

i l.'{r( :' : ir r i| .4l i '

:

I, ir-

et,.

Figure3-l. BasicdesEnandoperationof an ice

103

104

Modern Refrigerarion and A r Condirioning

ftom the ice compartment. It cools the food on the shelves below The air becomes warmer and dses ftom lre borton of rhe.abineLtred stripeddrroh.r. Il trdvelj up the:ide. and back of the cabinei.Rowing over rhe ice, ii cools and again flo\^/s down over the sielves. Tcerelrigeration has the adrdntage ot mdintaining , the inrerrorof the cabinetat d farrly high rrrrridity tmoi,: fure level). Jood sfored in lhic rlpe oif relrigeratordoec not dry out mpidltr Until the development oI rhe mechanical r€frigera_ ror.narur"l ice refriSprationwas quite h idely used.iince then. arflfi.ial lce ha: been manuJ.cruredior rerrigera_ tion. Temperaturesinside an ice refrigerator are controlled byairlow Theair flows overtheiceand through -lemperdfLres rl-F_cabinet. *ril u,ually range berwein 40'F and 50'F 14.4'Cand t()'C). When it is necessaryto use ice for cooling tempemtures belorv 32'F (0'C), ice and salt mixtures may be used..Temperaturesdown ro 0'F (-18.C) may be obtained with ice and salt mixtures.SeeChapter 31 for a table of ice and salt mixtures.

3,2 Evaporative Refrigeration (DesertBag) When a fluid evapomtes,hear is absorbed.Evaporation of water is an eaample.This is why humans and animals perspire. Evaporation of moisture from the skin su ace helps to keep a pe$on cool. {nother e\dmpleof the e\ dporaLj\ e principlers Lhe tleseft bog used {o leep drjnkng water cool. i hi, bag. Figure 3-2, made of a tightly woven fabdc, is 61ted with drinking water Since ihe bag is not watetproof, some 'ater seepsihrough. Thus,the outsidesu aceof the bag rcmains moist. Desert conditions are usMlty both hoi and dry Moisture on ihe surface of ihe bag evapomt€s rapidly.

r Plug

: Figure3-2, Thedesertba! is an exampleof coaling by evapo rative refrigeratian. Much of the heai which causesthis evaporation comes from the bag and its !^.aier This hear removat cools the d nking water inside the canvas.The water temperature is now several degrees below rhe rempera ture of ihe sunounding air.

3,3 Evaporative Refrigeration (SnowMaking) Another colnnlon application of water evapomtion refrigeration is the meihod of making artificial snow for ski slopes. A snow machine, Figure 3,3, consisrs of a water nozzle inio which a high-pressurejet of air

1 5 0p s i

% T l4!i)

100psi

W

tigure 3-3. A waterkompressed ai nozzle is usedfor makingartificial snow.

ChapterI

BasicRelfigefaton Systenrs

105

is inseried. Water (dark green) flor.s irom the nozzle. The air (green stripe) under high pressure causesthe water to brcak up into tinv droplets. The droplets are similar to a fog. The surrounding air ternperatutemust be near freezint or belo\a.freezingfor sno\a'to form. The .lroplets of water will tend to evaporateand rapidlv cool. At this point, tinv drops of ice are fomed. Using this meihod, artificial sno\a can be made r,hen the iemperaiure of the surounding air temperaiure is 32'F (0"C) or lorver. In lorv trurni"dity,art#ictal snow can be made ufien the temperatureis as high as 3,1'F(1'C).This is possiblebecauseof rhe rapid evaporation and cvaporativecoolingcausedby the lor",.humidity. AroLa e Jrnpe.levrnord \e,ooli.q.,rnFVaporative cor'rdenserEvapoiative concler.rsers are olten used in connectlo with air condltioners.SeeChaprer 13. The evapofationoi waier helps cool ih€ condenser.

3.4 Compression SystemUsing Low-Side FIoatRefrigerant Control T11eloru-sidefloat rcfrigerc t co trol systen was oiten used in early refrigeraiint mechanisns.Ii is also known as a /oo,led syste',r. Figure 3-4 is a schematicdiagam oi this svsiem. 'I'e l i q L r i or e f r i c e - d n rl ^ \ ' l r . r r L l r el i q u i d r e c L i \ e r through the liquid line. It continuesto florv up to the 1o$.side float needle.Thc evnporaiorin this svsterncon - r - t -o l . i r ' _ F dl . ' r r , e \a p . " do r ' | 1 e i d r l , o n . d i r .n " float and needlccontrcl. Thes€maintain a constantl€vel of liquid reirigerani under a lo\a'side pressure. This refrigerant,sinceit is a liquid on the low side, is at a lo$' temperature.The cold liquid rcftigerant {'i11 absorbmuch heat in both thc on and the off cvcles. \"pol|,,rd refrite-drl 'no\e. lhrouBl. \e -u,rion (\'apor) line to the compressor.Thereit i! compressedto a high pressureand dischargedinto the condenserIt is coole.l b], ihe condenser,reiurns to a hquid and flolvs inio the liquid receiver.The operationcontinuesuntil ihe ctesiredlo .temperature is reached. The pressureon the lorv side in a flooded system such as this will vary 'ith the temperature.The higher the t€mperature,th€ higher the lovr'side pressure. The sysie shown in Figure 3-4useea pressuremotor.onirol. A springloaded pressure-sersiiivedevice is locatedon the suction line or on the evaporaior.Ii activaies a motor coltrd slvitch. As ihe moior drives the compressor,the pressureand ienperaiur€ in the evaporator will be reduced.At a given pressuresetting, the notor compressor'!vi11stop. When the pressurein the evaporatorrisesto a level correspondingto a presei retuigeraniiemperaiure,ihe cvclc will repeat.The motor compressoi1\dll then start again. The cabriet ternperaturc may be controlled bv the ternperature control swiich. ln ihis cas€, the element ma]' be ,rlamped to the temperature-sensitive fins on the evaporaior.

Motoru

Lqud

Compressor

Re.erver

rigure 3-4. Co,rpreirton stsl€nl usinEla$,-sidefloat

This refrigerating cycle is useful \'!l'Lena consiant temperature is dcsired. lt is often used otl drinking fountains ard other installations requiring a constant

106

M o . l € r nR e r g r e r a t i o n n dA r C o n d i t i o n i n g

The pressuresdo notbalanceon the offcycle.There_ fore, it is nec€ssarvto use a motor r4rich will start r'ln d c r I l o . , d .q r c h - n . e n r e . . irr e . r r d t l . L r r - S e rei|gerc I ! .drge.Thl, . opcru.e.he-er. liquid -errig erant.in both.fie lictuid receiverand in the evaporatoi AIl flooded svstemsare quite efficient.Coli, liquid r r. r r q en n t \ \ a l - t h r L \ d p o r d t o.rJ r .e- Fr,.\rJinge\_ ., llert lre.rlIr,] 51p. he,< -\-tpm- "rre ea.r lo -er\.\e. The floai needle and searnust be kepi in gooo cond1, iion to avoid possibleflooding of the jo . srcie.

3.5 External-Drive(Open) Refrigerating System Ii thpr\ t, m al-rlrire sUs!c,r.rl-, .orpre.- * i. L:r _ allv belt-driven from an electricmoior. The speedoI ihe compressoris usualv considerably1essthari the speed oi the motor. A small pr ley is used on the motor +aft. A larger pulley (flywheel) is used on the compressor s h " r . v h r . e a r l \ r e l i g c r a .. g . r . t e r n . w e r r t i i e ! t r ajr opcn system. SureJ-5lllustratcs

Cabfet S!ction

figure 3-5. Compreriionrystemu5hg exter].il-drivelapen).om/essor. A erankshaftsealis requireLlat he place \\here crankshaftextendsthtuuEh.nnkcase of the can)pressor.

Chapter3 BJsicRetriger.ton Systems

'107

The liquid refrigerant (dark red), und€r high pres s re, flor{,sthrough the ih€rmostaticexpansionvalve. It thenentersthe evaporatorh'hereii is under lo\ . pressrre. It boils, vapodzes,and absorbsheat in ihe evaporaior. lvhen the comprcssoris running, the vapodzed ieftigerant (lighi blue) is drawn ihrough the suctioi line and hto the compressorThe refrigerantis compresseLl io a high pressure(1ight red) before beinB discharged (vaporized refrigerano ]n the condenser,the "d/or gives up its latcni heat of vapoiization. It ls cooled,and r€tums to a liquid (dark red). Fron here,the cvcleis re |edrcd. A ihermostatic bulb moior contfol is sho\,{n.Thc startingmechanismon €xtemal-drive(open)svstemmo tors is usuallv buili into the motor. An external-drivesvsien requiresa crankshaftscal on the conpressor.The motor anclthe compressordrive are at atmosphericpressure.Thc pressure inside the crankcasewill vary depending on the reirigerant used and iha temperaiure.Sometimesit may bc considerably aboveahnosphedcpressure,at other tines, ii may be bel \'. Refrigerantvapor cannotbe allolved io Ilow ort or air to ilor{'into the crankcase.Eitherr,,.ouldquicklv ruir1 the operahon.

3.6 Compression SystemUsing High-Side tloat Refrigerant Control

Lne

,-____-__.:::::::::-

The hiEihside float systemis a flooded system.The eyaporatoris always fi11ed .ith liquid refrigerant. Figure 3-6 is a schematicdiagrarn of a hiSh side float refrigerantcontrol sysiem.As the compressorruns, refrigerantfrom the cond€nserflo$,s into the high side When enough liquid refrigera t has eniered the hiSh si.le float mechanism,it raisesthe float ball- The refrigerant will then begin to flow through the conirol io the e!,aporator The evaporatoris under lorv pressure. Therefore,the iubing connectingthe high side float and the e\.aporatorshould be insulaied.A capillary tubc refriterant line is ftequentl"vused. lf a different size line is used, it should have a weight valve at the evaporator.This preventsthe reftigerantftom €vaporatingin the connectintline. Figure 3-6 shorvsa weight valve n the connecihg line. Refrigerantent€ring the e\.aporatoris under low pressure(dark blue). It h'ill rapidllr evaPorate(boil) al1d absorbheai frcm the evaporator. The vapor (light blue) then florvs thiough the suciion 1lne to the compressor.There it is conpressed (squeezed)to the high side pressure(1ightred). In the condcnser,the heat absorbedin the evaporator is re noved. The retuigcranijs reiurned b the liquid siate (dark red). It llo('s into ihe hiEih-sidemechanism .here ihe cycle is repeated.

systentusing hi{h .i.1efloat tigure 3-6. C'oDrpresrion

Either a temperaiure or a pressuremotor control maybe used on this refrigerationc),cle.Figur€ 3-6 shoh's a temperaturemotor control located h the refrigerated This systcn is most useclnr commercialapplica tionswherehigh opeiathg efficienq' is desired.Itis easy to service.Ho('evet thc anount of reftigerant charge.t inio ihe systemmust be very accuraiel)rmeasured.

108

Mocrefn R e i r i S € roanr a n dA i r C o n d i to n n g

3,7 Compression SystemUsing AutomaticExpansion Valve(AEV) Refrigerant Control h . u p F r ,. . . r u f d n , u t . n . , r . c r . f d r . i . l ^ \ d t \ e _ A r v r e l g e r , . . t. o r t r J l r c l : g p r n r g L r . . . n , , r T . ! -,f.h.r in fiture 3-7. Ine.o,nlre..,mor.- dro /or_ r e . . F _/ \ . r L r e n '.l p r r i t j a r , . . 1t l , Fb n - , o . h e . . b i n e t . Liquid refriterant (dark red) flows from the tiquid re ceiver ihrough the liquid ]ine. It flol\'s through the fitrer to the auiomatic e\pansion vahe. Relfigerant can flol{i througtr an AFV onty if the e\'aporatorpressureis reduced by the compressorrun_ r' q \- llre . q u, , r J t . r g ( . d r n. t. i . ll e ,uo e \ J r . - i ^ .\ d l \r . t r r - - p - . r . a r. 'n . o "l r-'opu\q. o h . f . , i o r L"). rr ^l i .b 1 . . , ,H e c. du. tJ od pre*u-" the refrigerant boils iapidty and absorbsheat.-Thisva_ porized refrigerant (light blue) moves back rc !11ecom pressorihrough the suciion line. _ In the compressor,the refrigerantis compressedto th€ high-sidepressureas vapor (tighi red). Wtrite florn, ng through the condenser,it is cooled.The refrigerant gives up th€ heai ihat it absorbedin the evdporarorano returns to a liquid (dark red). It then flo{,s into ihe liq_ uici receiverreadv to repeai the cycle. The nlotor control ihermal elemeni is ctamped ro the end of the elaporator. This is tocatedat the begin ning oI the suction line. Aft€r the evapotatoris coolecl to jts proper ternperature,the control bulb pressure causesthe ,notor control to tlrn off ihe current to the drivhg motor. The compressoris stopped. The operating characterisiicsoa ihis svstem are qnite satisfactor.,:The r€frigerantoil is circulaied ,ithout troubl€. Th. tenperature control hniis can atso be kept qriite clos€. This i,vpe of refrigeration cvcle is used r,{jdety in - r ' d l l, o n - * e c a l . . p f ' . . 1 ii,. - r n . eL . r p - F - ,r r F -J . -^ b.,l r.eon \eoff,\. (.rl.r rro^ ..mpre.\,, n-u\l slart h hile underload. A fault)' needleor seai in the etpansion vah,e (,'itl allorv refrig€rantto leak in the off cycle.Liquid refrigerant mav flow inio ihe suction line. lvhen the compres sor ihe suction ' starts,this rLill be indicatedby irosthg-of r".5 rc .' p-oblFrr . , , i d e r r i l F ' .t e r tering the compressorthrough ihe suctior line. This mav cansethe compressorto knock severel)..

3.8 Compression SystemUsing Thermostatically Controlled (TEV) Expansion Valve A schematic.liagranl oi a thernrostaticallycon irolled expansion valve ITEV) retiigeraiion cycle is shown in Figure 3-8. This systemis used on large commercial refrigeratorsas .ell as on nan\, air condition ing applications.

Motor

Receiver

Figurc3-7. Camprcssionsystemusingautomatic expansianvalve (AEV)reiigetant cantrcl. The liquid refrigerant(dark red) florvs from the liq uid receiverthrough the liquid line. It llows to the iilter drier and to the themostatic expansionlahe.

C h a p t € ' l B a s i cR e i r i g e r o an l Systems

109

must be hither than the evapotator refdgerant tem, perature before the valve w'ill open. The amount of opening will be governed by the temperature of the evaporatoxIf the evaporaioris quite r{arn'\,ihe neeclle will open quite rvide. This a11ows a rapid flort of liquid (dark blue) into the evaporaior.In this mannet cooling is speededup. As the temperature of ihe evaporaior drops, the TEV needlevalve r'ill decreasethe reftiger, l.u!Dre\!ure r\rpor/cdr refrigerdnt'lig i btue lronl ihe evaporatormoves back into the conpressor. There ii is compressedback to the high-side pressure (light red). As it f-iowsthrough the condenser,ihe refrigerani givesup the heat absorbedin the evaporaior.Now cooled, the reftigerani is condensedto a liquid (dark -Fd) To$ - b".l ro re ..ourdnre vF'. I re rernEer ating cycleis then repeated. When the evaporatorreachesthe desirecltemperattue, the rnoior contrcI ,illturn off current to ihe motor and stop ihe compressor.When this happens,the TEV needle vah/e !vi1l close.No more refrigerant !{i11flo$. through it until the compressoragain lo$.ers the pressure in the evaporator Pressuresdo not balanceon the off cycle.Therefor€, it is necessaryto provide a motor compressor\'!'hich\,vill start undef load. The TEV conirol remains closeduniess the evaporaior is under redricedpressureand the temperatureis abo\-enonnal. A leaking valve will usuall)' be indicated by a frosted or slveatingsuction line.

SystemUsing 3.9 Compression CapillaryTubeRefrigerant Control

Compressor

F e . ev e r

Figure3-8. Conpress;orsysienrusing thenlostatically con olled expansianvalve ITEV). The operation of the thermostaiicelpansion valve is controlleclblr ha'o condifions.Theseare the temperature oi the TEV control bulb and the piessure in the e1'aporator.The temperaturc of the TEV control bulb

The capillary t be sltste-, shorvn in Figure 3-9, is sysiems.This one of the most popular compression-t)'pe si/stem is commonly used in household refrigerators, fteezers,air conditioners,dehumidifiers,and small commercial applications. Liquid refrigerant (dark red) florvs from rhe .ondenserup throuSh the liquid line. lt ihen flows ihrough ihe filter (b'hich mav also be a drier). From ihe filier, iefrigerant flows through ihe capillar), tube rcftiger' ,rt .o-rro ro thF e\.por.to-. Tl-e lr.IuiC reargerant, entering ihe capillary tube at the filter end, is . r n I ' i 8 h p r e - . u r el d I ' d . r l i - i - r l ' \ . d h pressure side. The pressure in the evaporator is The capillary tube is ctesignedso that it rnaintains a pressuredilferencervhile the compressoris operating. The compressormaintains a los' pressurein the el'aporaior The refrigerantboils, rapid\' absorbinilheat. The vapodzed refrigerant (light blue) moves ihrough the suction line back to ihe conpressor Here it is com pressedto a high pressureand dischargedrnb the condenser(light red). The i'apoiized refrigerantis cooled in the condenserand returns to a liquid (dark red). It again flora.sirto the liquid line.

'| l0

M o d e f r R e r g e r a t i o n n dA . C o i d i t i o n i i s

motor ..ntrol mechanism.It tums off power to the nro_ to-. I te rei gerrr:nnc\.le -tuD..lt \,ril . r .r -!opper LJ'rillhe,l-errul Jf. Tl , rle. rdt b, tpressure\,!'r11 ctosethe motor control contactsto again operdia_ 5c . o-1orP-.^r. Thi. r pe or , v. r .- .tlrii. -)h, arron lur mo.t re - !( rdr,rg .ppli.a..un,. I n t h eo l l . v c l e .t h e c n p i l l " r I L r o e. ^ h \ l h r p r - . sures tLrbalanc€behr.eenthe high and lo1r,sides.It is not usualty n€cessart rhen, to uae a moioNith a high starting torque.

3.10 MultipleEvaporator System _Somecommerciatrefrigerating svsteDrshave one conclensnt unit connectedto h{o or rnore evaporarors, Figur€ 3-10.Muliiple (ha'oor more) evaporarorretuigeration systemsare commonly used in commerclatre trrgemiion applications. Liquid refrlgerant(dark red) flo$.srhfough the ther, mostatic erpansion valves to the evaporators. The evaporatorcmay have identical or differeni el,aporator lf ihe €vaporator temperaturesare identical, the systen usesonlv a lo$',siL]efloat or the TEV to control the refrigerant. If h{o or more €\,aporating iemperaiures are desired (a frozen foods temperature and a h . , t e Lr ' o o g [ o ' e . , m p e , . n d e ' r (j.r u . l o e u - e d t o \ . e p . , n eo t t h e e \ d p o r . , u r - ; r i oh.. " lor.side pressure. Look at the lchematrc slown rn Figure 3-10. A t('o-temperature vah,e in rne suctron line (upper-left)keepsthe lolt. side pressureieftigerani liquid (dark blu€) ancl vapor (light btue) in evaporator B at a higher pressure ihan at evaporabr A. The evaporaioriemperatureis govemed bv the evaporaiing pressure.The lor{'er the pressure,the lower ihe temA checkvalve is locatedin ihe suction line coning from the colder evaporator,A. It pre!,entsthe $.arme; h r g L e rp e . - u r e' o h ' - i d e\ . p o | l i g . r L b u e r c r r "r,err g t h - , o l d e re . n p u -r l o r q . d u n n g t h e . f f , \ . r . The \.prn,,ed retrigeJi,r lrtht btLe, r- qh -ned to the motor con'\pressor.It becomesa high-pressure and high-temperaturevapor (light red). This vapor is cooled in the condenser becoming a high-pressure liquid (dark red) to be stored in the receiver until

Figure3-9. C.,/rpfessionsystemusingcapillarytube

This operationcontinuesuntil the thermal elenent has been cooledb a presetlow tenperaiure. When that teDrperature is reached,the themal elementoperatesthe

Note the filter drier on the liquid lnre. li keepsthe refrigerantcleanand dr!'. A s8i,fglass (liquid indicaior) is often inctuded in the liquic:tline. The techniciannlay use it to seeif there is enough refrigerani in the svstern.Bubblest'!'ill inllj, catea refrigerantshortage.This svstem,as shorrn, r]ses a pressuremotorcontrol. The operatingpressurers taken lionl the low side of the svsiem. A line from ihe hith pressureside also enicrs ihe moior control. This operatesa safetydevi.e rvhich stops the motor if the condensingpressure(hjgh side)goestoo high.

ChapterI

Basc ReirigefalionSystems

111

Thermosl.tic Valve E)pansion

E operates'1t25"F( 4'C) A operatesatA'F ( 18"C) Evaporatar Fisure3-10. A muhipleevapot,ttots)'stentEvaporator

Systems Refrigerating 3.11 Compound In cornpound refrigeraiing svstems,two ol rnore compressorsare connectedin series,Figure 3-11.In this illustraiion, compressorNo. I clischargesinto the intake side of compressorNo. 2. CompressorNo. 2 ihen dis' chargesinio the condenser(light red) Here the vaPor

condenses.The licluid iefrigerant (dark red) floh's into the liquid receiver ReftigerantvaPor is not condensed between compressors.An intercoolerlowers the vaPor lemperrnr-e. hr- LVpcol.rt 'lla "n u'uall' r, qu're' al' oil separaiorfor each compressor' Froir the liquid receiverthe liquid reftigerant(dark red) flo\,'sup to the thermostaiicexPansionvalve lt then

112

M o d e r nR e f f i g e r o an t a n dA i r C o n d i t i o n g

w

I T T

Figure3"11. Compoun.J refri]eratin7systen.

Chapte,I

entersihe evaporator.In the eYaporator(dark blue) the rcfrigcrant boils and absorbsheat (light bl!e). From rhc cvapolator,the vaPorizedrefrigerantflo\^,sbackio com pressorNo. 1. From here thc cvcleis repeated. A contpoulrd sysrem increases capacity when pulling dorvn to exh.cmelvl.r\a.pressurcs(lo$, tempcratures).A singtecompressor('ould havc diffic!lty rcaching thescpressures/temperaturcs. A sif gle-iempelatulc motor control opcr.res all tnoiors.A ihermostaticexpansionvalve controisthe liquid reffigerantflo!\. into thc c\ aporaior The prcssurcs Llo not balance on thc off cvcle. Therefore,motors capablc of starting under load are Compound installations uslLallv opcraie under rather heavv service requirements. Conclensersand reliigerant nrust be kept c1ean.Compressorvahcs musi be kept in good condition.

uis c lt-"irigerilon Systenrs

'113

3.12 Cascade Refrigerating Systems In a cascadcrcfrigeratingsvstern,t$,o or more refuigcrating svstemsareconnected as shownin Figure 3-12. Cascndcsvstemsare often used in industdal processes.hereobjcctsmusibe cooledto tenperaturcs lrelos, 50'F ( 46"C). Both systemsoperateat the sarnetime. SystemA (on the right) has its eYapofator,A, (heat absorbingpari) arr.nged to cool the condenserB for ihe systemB. The cYaporabr for systern B slrpplies the coolhg effect desired.EachsvsteDrhasa thermostaticexpansio. vah.e (IFV) for refrigerantconirol. The lorv-pressureliquid (dark blue) of s),stcm A coolsthe hjgh-pressurevapor (light red) of svstemB. On€ motorcorltrol is uscd forboih moiors.Itis connectedto a tcmperature-scnsjng bulb on e|aporator B.

Bulb

T

n tr T

Figure3-12. ans.ade relr8crnrnrgsy5lenl

114

M o d c r nR e i .s e r a t i o na n dA r C o n d i t i o n i r g

Motors used_onaascadeslrstemsmust be capable . oi starting under load. Wiih the use of therlLosraacex_ panslon valves/the pressuresdo not balanceon the off

cvcle.

T \ " c u n o e - - . r F \ a p o r ' t o. - u r u a .f J r t h e . 1 c 1 , and-tubefloodedevaporatori\,pe. -rrr^ it.F-..\-.;r. oo., ie .erv tor.ren-por r u r e c . r n Lr e l r d e r r n tI n u n b , \ F "r r\ d n . A . r y r n o i . tr r e ., ou d rondr''-e dr tlrFnecdiF-ent of .re_lE\ nno -top the refrigerant _ilo\{rSystemB must haYespecjalre6.ig: erant oll ($'ax-free,moisture-free,and the abilitv to flo; al extra 10 r temPeratures). Oil separators shouid be instaled in the compressor-ioconclenserlines on both of thesecondensnlt units. This r\,ill help keep the oit h itre corrpressors.

3..13 Modulating Refrigeration Cycle Mosl refrigerarioninsralarions have enouth cool mg or rehrgerahngcapacityto naintain the desiredrem_ perature un.ler the heaviestload. This temperatureis

maintainedbv the motor conirol.It startsihe moiorcom pressorwhen cooling (heatremoval)is reqr.tired.It shurs rff n, -n,,n r. ihe de.ireJ rFn-peraturp r: iearteo Ho\"!er. iI r]-ehe,ttlo.L1 ) irqhr ,l.t- L.1di, .v* tem may be overcapacltyfor fie job. The operafing ex_ penseis.greaterihan if the machinecapacitvlnore easily matchedthe neected1oacl.The sysierntenos !o coor roo tast and tuin on and off too quickly. A n ' u d u ' d f i | |\ 8d r \ i n g . n p . i i . - v - e I l h a . b e e n d F \ a ^ t e ot o . r i L r h F r r r . h i r; ;dc, , i m o L c r o . q , ) . oc neededheat load. This is sometine; done by using two or more compressoFconnectedin parallel. Each com_ pressor1soperaieciby a motor controi. the heatload increasesand the tenperatlue starts .If io nse/ one compressorwitl still nur. However, if the temperaiure keeps rising, the seconc{compressorr{jlt .tnrt Lu "uer".e. Ad.lr ron .,,mpr,-,or- 1.,) r Jl ... u-_ hl enoL,ghcapircii) is obrarred. Figure 3-13illustratesa typicat cyclecl,d8ramror a modulated installation.Thts inita ation has ihree con, pressors,A pressure control connectedto uLe sucflon lines operatesthe motors.The control coniainsa special

Thermosral c Expansion va ve

Press!reMolorContro

Figure3-13. Madulatingrcfrieeratiancr,clen-ochanism, which usesthreenotar .onpressors.ptessuretnotor contrcl ts arranqedto aperateone ar tnore compress()rs as needed_

ChapterI

shitching de\.ice.This rotatesthe serviceof the various conpressors.Each compressorwill be used aboui the sarnearnolrni of time. The nodulaiing cvcle maintains unifoin ternperaturesand operateseconomicallv Any conventionalreirigerant control can be used, H u w e \ F rt h e . r e m o . t . i i . e \ p n n n . n \ l r p , . r o , L . o n mon tvpe. The same condenserand liquid receiver may be used by all the compressors,or each mav have its own condenserand receiver.The same evaporator is corl nectedto all the compressors. A modulating systen may use a nultiple cylinder cornpressor. Eachcvlinder is equipped$'ith an unloader device.Vadablespeednotors are also used to provide a modulateclrefrigefationcapacity.

3.14 lceMaker Ice makers rise various i)rpes of refrigerating s)'s iems. Note in the snnple ice making unit, Figure 3-14, the motor compressorand condenserare usually locaied in the bottom of the cabinet.Liquid refrigerant(darkred)

Ba! c ReiriBer:rtion Synems

115

flor{s from the bottom of the condenserup through a filier drier. It entersthe evaporatorthrouth a capillarv tube. The evaporabr sunounds the inverted (upside, dor,{n)ice cube molds. From ihe evaporator,the refrigerant vapor (light blue) flows into an accumulator. This container has a coil from the liquid refrigerant line in ii or around it. Such an a angement serves as a heat exchanger The refrigerant vapor (light blrie) is drawn trom ihe accumulator back to the compressor.Here it is compressedup to the high-side pressllle (lighi rcd). It is forced inio ihe condenser-From here the cvcle is The mechanismwhich makes and handles the ice is also shown. Cold rvater is sprayed into the in1'erted ice cube molds. The iemperature of the molcls is very lor'. Water striking the molds freezesto the nrold surface.lt gaduallv builds up urliil conplete ice cubesare formed. Next, an electricheatint unit heatsthe ice cube molds until ihe cubesfall out. They slide do\.n a chute into the ice cube bin. Then the reftiterating cvcle is stopped.Mosi sudacesin coniacir,l'ithwater and ice are staiiless steelfor cleanliness.

lnvertedce Cubel,lold

\l/ilil B.

Motor

condenser

Figure3-14. ln at1ice maker,watetis sptayedintoice cubemoldsto produceclearice cubes

116

N,1o.lern Rerrlgeration and A r Conditioning

3.15 DrinkingWaterCooler ivaier cooler is a specialuse of a retuigerating .The mechanism.It is used to cool r,ater ,,ontap,, at ; drink i-t founlair. l l^eJ:Lrrll?pmrcir airtrsl.r;.on-pres-o. relfrge-.rttng:L-lem i. L,eC T\e rpfrigpranr (ontr^l . d capillary tub€ A schematicof a drinkiing warer system is sho 'n in Figure 3-15. Liquid reftigeraniflor\.sfrom the bottom of the con d€nserlhrough the liquid line. It flor\,srhrorgh a filter drier (dark red) and inio the capilafy tube. As it flol\,s mto ihe evaporator,it vaporizesand absorbsheat from the evaporator surface (iight blue). The evaporator is next to or surrounds the ctrinkint water cot or (.ater

From ihe evaporatot the relrigerantl,apor goesinio an accumulatoi in the suciion line. The accumulator stops anv liquid refrigerant from rlor{nlg into the suclior line and or into the orotorcon pre.5or From the accumulatot the vapor is dra ,n nto the motor compressorh'here it is pumped into ihe con, denser(light red). Here the heat picked up in the evapo rator is released.Mean!!'hi]e,the refrigerrnt returns to a liquicl and collectsnl ihe bottom of ttrl contlenser.From here,the cvcle is repeated. S - . e r h eo e n e - o . r d r i n ^ l n go u r t d i r i - \ c r i r " regr Jr r. nJ-i hare ,ore holo-oie c.pd.ih. )tiu i Le mL-t nol over oo \dte.. The n..e...n cao..t$ , provided b)' usint eiiher an insulated srorageran( or large cooling surfacesin the €\,apomtor

:

Capiary

tr E

r

I T I Figure3-15. A drinkinBiauntaincaoleclbv a contpression system reiip,entin]mechanism.

C h a p t eI

To increase ihe mechanism's efficiency, ihe waste (rater flows down a tube alongsideor att;ched to the frcsh water inlet. In ihis way, the warmer fr€sh water (water-in) is cooled by the cooler waste water leavint the fountain. A water pressure regulator adjusts the water flow The condensing unit is aii-cooled. This ensures that the fountain can deliver enoughcold water under heavy demand. A condenserfan is used to increasethe condenser capaciiy. The fan is connected into the electdcal circuit. It rurc wheae\er the . orden,rnguru. ic runIinS. A thermostat with a control bulb is attached to the water-dispensing iube. It maintains the desired d rking water temperaiurc in the forntain. Water leaving ihe founiain should be at approximately50oF(10t).

3.16 Expendable Refrigerant KeTngerauon 5ystem This simple system, sometimes called chemical refriSeratioll or opeft-cy.le refrigeration, is becorri\g ncreasinglypopular. Ii is used on trucks and other vehicles in the transpoiiaiion industry and in the storage

E a s c R € f, g ea t o n S y n e m s

117

of refrigerated or {rozen {oods. Basically, an expendable refiigerant reftigerating system is a heavily insulated space. It may be cooled by bein8 sur:rounded by tubes canying evaporatingliquid niaogen.Another meihod of cooling consists of spraying liquid nitrogen directly into the space to be cooled. In a\y eyent, an eryeflilable

t+igennt svstemis onein which the systemdiscards the refrigeiant after it has evaporated. Figure 3'15 illustratesthe spmy sysiem.The liquid nitrogen (dark rcd), supplied from a cyiinder inside the refrigerated space,is kept under pressure (200psi). Dark blue indicates low-pressure liquid refrigerant. The pressurized cylinder is insulated. However, an automatic pressure relief vah'e will open as a safety measure,if necessarlrIt would allow the niirogen vapor to escapeshould pressure exceed the relief valve seiiint. Heat sunounding the cylinder may cause the vapor pressure to rise above the automatic pressure releasesetting. Cold nitrogen vapor is then released by the automatic pressue release valve. It is discharged into the rcfrigerated space or into the refrigeratinS tubes, depending on the system being A temperature-sensint element, control box, and liquid control valve, control the flow of liquid nitrogen

Lquid

reftigeration system Figure3-16. Expendable rcfrigerant

118

Mod€fn Retrgerationand A r Condirioning

ftom the nozzles.They maintain the desired temperatures inside the refrigeratedspace. Liquid dtrogen (dark rcd) vaporizes 6oi1s and turns rnto a gas) at a temperatureof 320"F( 196.C) at atmospheric pressure (Figure 1-26). This type of sysiem is excelient for shipping lrczen Ioods. Tem_ peratrres may be kept as low as desired-usually about Simple conshrction such as rhis demandslitrle attFntion.O.. j.io rall\. it ma\ be necesa fi\ed onrt oI lhe \l-df . Tl'e roro. rengrhmJ,t be a.( irJrp ,u .0005"(.0127mm). Usually the slois for the bladesare on a mdius to the center of the shaft. To lower the starting load..one desigrpuh .he\rot. rt dn anglF.Thi. pre\ent: lhebl.de, from rou.hint LhFL) tinder;Hr ihFLomprey sor nearsits operaiingspeed. In the stationary blade compressor,the rotor (some ti-ne, cnllFdthe inpellert nccurdtel\f,ls lhe pc(eItric. The eccentrrcrs a Iired part ot rhe shaft. Figure 4-54illustratesa popular iype of rotor con_ struction used on €xtemal-drive commerciatcompres_ sors. Figure_4s8 ilustrates a srationary-bladerorary con pre\sor.Ihr. i. a hermefic.ompres.oru.po bot\ in retri8erafionand air condirjonmgurts

Blade(Vane)Construction .nore Rordrng b "de compre-.or- uce r!\o or blrde,. Figure4-5s.l.r. B. :how. a rotor w LhF gt-l L,f them. Thesebladesmay be made of cast iror! steel atu, minum, or carbon. T].c compre.-o ettic:encydeDend-g'e,ity on ihe , ondihor of the blndeedgetr hereir rLb5on ,he c\ liI der. The blade must be very accriratetyground. It must be ground to fit the slots, the €nds of the cylinder, and other contact surfaces wiih the cylinder

4.15.3 ScrollCompressors Tne scloll colnpressol is commonly used in rcsidenria air,ondilion ng and hea.punp rdtion. Ben"pp efitc of rhF scroll :n,ludp feuer morirg pan>. tesintemal frictlo0 smooth comptession cycle with low torqre, low noise levels, and low \,ibration levels. A scroll compressor generates a sedes of crescentshap€d gas pockets between tvlo scrolls,Figur€ +S9. One scro11-the fixed scroll-remains srahonary The

Sige Blad€

Anachng Cap Soew -_

-1/,,

si

"& Q

.g

g

tigure4-57. Hermetic, singlestationary-blade rotary (Iecumseh compressaL Products Company)

Figure4-58. A hermeticstationaty-blade ratary

162

Modern Refrigeration and Air Condiioning

ffinton eresswevaoor Figure4-59. Compressianin the scrcll is causetlby the interactionof an otbiting scroll mated within a statianary scroll. l-Cas is drawn into an outer openingas one ot the scrcllsorbits.2 As the orbiting mc)tioncontinues, the apen passaBeis sealecloff and the Eas is forced to the centerof the scroll.3 Thepocket becames proetessivelysmallin valume. This createsincreasingly higher Baspressures.4-Discharge pressure is reached at the centet of the pocket. Cas is releasedfron the port af the stationaryscroll member.5 In actualaperation, are in variousstagesof comprcssionat sixBaspassaEes all times.Thiscteatesnea y continuoussuctionand discharge.(LennoxIndustries,1nc.) other scroll-the orbiting scroll rotates through the use of the swing link. As ihe motion occurs,the pocketsbetween the two foms are slowly pushed to the center of ihe two scrolls.This reducesthe gas volume. When ihe pocket reachesthe center of the scrcll, the gas is at a high

Sl.tonary

A

usedin light Figure4-61, scrollcompressor , onmFrcial tn.tdlldtioa".Notp thc I omprc.-ion drca (CopeIand Corporation) pressure-It is dischargedout of the centerPoft. During this compression process, several pockets are being formed at the same time. The suction process from the outer portion of the scroll and the discha€e Ircm the inner ponion are continuous. This continuous Process gives the compressor very smooth action, Scrotl compr€ssor design is shown in Figur€ 4-60. A scrcIl compressor used on domestic room afu conditione$ is shown in FiSur€ 4-61. A scloll compressor designed for commercial installahons is shown in Figure 4-62. It has a low sound level. Note the compressor comes equipped with service valves on ihe inlet and outlet sides.

Olbting Sfio!l

design.A Two scrallsare usedta praduceavapor compression.The uppet scroll isFieure4-60. Scroll compressor ]s s;tianaN and the lowet scroll dtiren. Note intakeand discharSeports. B Note how the rctation of the motar shaft causesthe obiting scroll to otbit-not rctate abaut the shaft center lThe TraneCo )

Chapter4

Compre* on SysteN and Conrpre$o6

163

Figure 4-63illustratesa crosssectionoIa screwcornpres sor.The two roton are not the sameshape.One is male, ihe other female.TIe male rotor A, is driven bv ttre mot u - . . 1h ; - f o r - r ' , , b e .l.l . e f p n . i e r o . o r B , n e . l e . u i t h and is driven by the male rotox lt has six nrtertobe spaces-The cylinder,C, enclosesboth toto$. In Jpe.dlion.lhF -e - Bef. r. \dp^r i- or.,\ r rn \ .',\r n in Figure4-64.Tl^, int )Le '1,,h'p.e*u-p v-p.r, enters ai one end of the compressorand is discharged (compressedvapor) at the oppositeend. The male rotor revolves more raDidlv than the female rotox (There are four lobes onihe mate roror and six on the fenale rotor.) The roiors are helixes. They provide a continrous punping action rather than pulsatjng as with a reciprocaiinilcompressor.With this Figure4-62. Hentetically sealedscr.)llcompressor. Nole ihe /ocaiin oi the setvi(e valvesfot easeof access.(CapelandCorporation)

The scroll compressorhas fewer mo\.ing parts and less torclue variation ihan reciprocating compressors. This resulis in very smooth and quiet operation.

4.15.4 ScrewCompressors Scre$'compressorsare often used in large capacitlr systemsranging from 20 to 300 tons. Thev are oflered as open, e\ternallv driven cornpressors,or hermetic, iernally-ddven compressors. Open screh'conpressors afe most often used 'ith ammonia svstems.Herrneiic scre$, compressorsare us€d with halocarbonrefrigerThe screw compressoruses a pair of special helical rotors. These trap and cornpress ak as they revolve in ar1accuraielyrnachinedcomprcssorcylinder

Figur€4-63. Crcsssectionaf screv/compressar. A Male rctot. B-Fenale rctor.C CylindeL Vaparized reiigerant entersat ane end and exhaustsat ather end. (ABB StalRetriEeratian Caryoratian)

Dscharge

Oulet

yapor A Canprcssotinterlabe Figure4-6,1. Basicoperationof screw conprcssor.Revolvingrator conrpresses spacesbeing iilled. B Beginninqof canptessior. C-Ful/ coDrpression oi tapped vapaLD Beginningaf discllarge oi.anprcssed vapaLE Conpressedvapor fully clischareed frcn interlabespaces.(Dunhan-Bush,lnc.)

164

and Air Conditjoning Modern Refrigeration

ShaflSea

Capaciy Motor,Driven Conirc [4ateFoior

lnc ) whichuaesa matchedsetof helicalrotors.(Dunham-Bush, Figure4-65, Sctewcomptessor

pumping action, there is very litile vibration during oP€ration. Figure 4-65 illushates a cutaway view of an extemal-drive sclew compressor. It is Powercd by an extemal-electdc motor, which drives the drive shaft. As prcviously mentioned, the motor ddves the maie rotor. Two matched helical roto$ Inale and femaleturn together This action traps and compresses the reftiseiant. Th€ male rotor in the illushaiion is an exieision of the drive shafi. The other rotor is made io tum bv the action of the male rotor. A conhol device mouni;d outside the housing regulat€s the capacity oI the unit. A hermetic screw compressor is shown in Figure 4-66. lts inlet pot is located at right an81esto the rotors. Tle outlei port is throuSh the motor housing. Its capacity control d€vice is mounted inside the housing. This Lapacitycontrol slide in lhe housing wall is used to vary the capa.ity of the screw compre$or. thi! provides a unique reatureof t}\e screw.its abiliLy to control capacii) ihrough inlinitel) variable unloadinS.Such d design allows for smooth, accurate conirol of temperatrre in the conditioned space.The pumping aciion ol the comPres9or is continuous, creating very little vibmtion durinS oPeratron. Figue 4-67 illustates a 3600-rym, single screw compressor. It utiljzes one main rotor that meshes with two diametrically opposed star-shaped Sate rotols. The main rctor contains six gtooves. It has sEaight roller bearings at the shaft ends. Two capacity control slide valves, one on each side, helP io determine the capacity control. FiSure 4-68 is a comPlete single screw compiessor unit using a micrcprocessol control

Figure4-66. HermeticscrewcompressotNotevapor injection usedto incrcasecapacitywithout comparable Inc ) incteasein power. (HartfotdCompressors

Many scrcwcompresso$operatewith oil injechon This sealsthe clearancebetweenthe rotors and between the rotors and the cylinder It also h+s cool the comprcssor.The efficiency of these comprcssoisis quite high.

Chapter,l Compression Systemsand CompressoE

FiSlre 4'67- sinElescrew camptessor.Note the locationof the nain rotor in retationto the two gate rotors.(viltel ManutactuI ing Corporati on)

Figure:l-68. A commercialsinglescrew comptessol system. (Vilter Manufacturinq Corporation) Figure 4'59 illustlatesa pair of screwlype rotors in operatint position. Sincescrew compressorsoperateat Iairly high speed,adequatebearingsare neededfor good rotor bearing life.

4.15.5 CentrifugalCompressors Centifagalcothlrcssors aredesigned for usewith large-capacitysystemsranging in size ftom 50 to 5,000 tons. In this type of compressor.vapor moves outward

as it is moved npidly in a circular path. This action is called centrifugal lorce. (However, the corect term is "centdpetalforce.") The vapor is fed into a housing near the center of the compressor A disk rfith mdial blades (impellers) spins iapidly in this housing.This forcesvapor against the outer diameter, The pressure gained is small, so several of these compressor wl€els or impellerc are put in se es. This creates greater pressurc difference and pumps a sufficient volum€ of vapor. A centrifugal comprcssor looks like a steam turbine or axial flow air compressorfor a gas iuibine engine. The cenirifugal compressorhas the advantage of simplicity. There are no valves or pistons and cylinders. The only wearint pa s are the main bearints. Pumping efficiency increases r .ith speed, so ihe compressors are designedto operateat high speeds. Figure 4-70 is a cross sectionthrough a iwo-stage cenhifugal compressor.The driving motor is mounted betweenstages.The inlet is at the left on the illustration. The dischargeis in ihe back ai the right end of the ilus' tration and is not shown. Figure 4-71 pictures a centritugal compressor mounted in a rcfriterating system. A cutaway view showing the refrigeEnt as it passes through the system is illustrated in Figure 4-718. The compressorcontinuously dmws rcftigerant vapor ftom the cooler As the

166

Modern Relrigerailonrnd Air Conditionng

Figure4-69. Sctewcampressotwith natchecl setof helicalrotors.Designedto operatewith anmonia, R-l34a, someother typesof rcfriqetants.(ABB Stal Refrigeration Carporation)

vatiableinlet guide vane 2 Fist-sk]e impeller' Figure4-70. Iwo-stagecenttiiu]al camprcssot.1 Second-stage impeller.!-Watercoaled motaL 5 Base,ail tank,and lubricatingoil punp assenbly 6-Fiststage 3 Secon(l+taqe guide vanesand capacityconttol. 7 Labyrinthseal.I Crassover cannectian 9 Cuide vaneactuatar'10 Volute casing.11-PressurelubricatedsleevebeatinS.Note that dischargeopening is not shown.

[/]icoF o.essor Conlro

Condenssr )5"F CEndenser

lAlater

120psigl98"F

ComDressor Refiigerant

tlFC-134a 39.0psigl44"F

,rar5 System -'-..' -J7 r chiiled water

Figure4-71. H(\netic cen ifLtg.lli.tLtidrhiller. singlert;Be .on)!r.iidr l/r.Jtr,scs R I J',1, A Note rhe rse oi .r ,t)ti.tr.\L\sat rontrol.ts Rettiqe"'l]t llow tlia,r';]n) rharing syslc/,) opc,"lior. lcarri.-r Coeontiotl. Subtidt,jt \, ol I Ic.htloloEi(s Caryat.ltnn) L.ni1..! .Lrmpressofsu.tion ..dures the pressllreln ih. coder, th€ remainnrgreirigcr,nntboils ofi. Energ\'requircd fof bojling is obtrincll fflnn the 1\.rterflol\'nrg throu:lh the cool€r lub€s. \\Jiih the heat enefg\' rcmor cd, ihe rv.tel b..Lrrnescolclenorgh for rtsein an air ronditioning cir.'rit. Aft€r rerlto\.inghe.1tfrorn thc r{ iicrt the rcirieefant rapor is tlrlnplcsscd. ii is th€n dischargeclironr the

compressorinto th€ condens€r. Cooledwatcr fl(njng i.io the co.densef tuLr€irem.r|es heat tiorr thc rcfrigeLailt.ll1e vapor corlctenses to a liquid. Thf liquxt re irigernnt passes through the oriflccs inkr the flash sr.lllc.rolcrchanbcr. Piirt of th. li.luid flashesto r apoa . o o l r f. l - n ' .',. r '. ,r l-.l.-. l densed or1 thc iubc\, rlhi.h nrc .dned b\. entefxrg

r6B

M o d e r nR e f r i S e r a t laofnd A i r C o n d i to n n 8

Fi9ute1-72. Hernetic centrifuEalcompressot.The impeller is sha$,nat left above.Major conpanentsai the impeller.D Hetmetic mator.E E\haust. compressorare:A lntake.B Firststageimpeller.C Second-stage (CarrietCopa?tian, Subsidiaryai United Technologies Caryaration) condenser r{'ater. The liquid drains into a float valve chambefby the flash chamberand cooler.The float vah.e prevents any of the flash chambervapor from ente ng the cooler.Refrjgemniis now ai a temperaLureand pres sure at which the cyclebegan.The clrcleis completed. Figure 4-72,right view shows a sectionthrorgh a hermeticcentrifu8alcompressor.Thesecomprcssorsoperateai a high speed.Thev are$ually ddven by an electric motor or steamturbine. Stator and Rotor Construction l,L Ja or ^r cd\irt of d cenrntugalLompresor . usually made of cast iron. It has a changing radius inside. The radius adapts itself to the vapor pickup by the impellers. The casing(cylinder)also holds the main bea ngs, oil pressrirepump/ and the vapor iniake and exhaust ports. When an extemal motor is used,the cylinder also holds the shaft seal where the shaft extendsoui for the power drive. Boih the first stageand secondstagehave adjustable inlet vanes to conircI the caPaciiy of the pumP The roro'or "npellerir a ccn rtugalcnmp'e\-^r \ keyed to the compressorshaft.lt is made of cast iron or steel.It is speciallydesignedto move the vapoE wiih out going above gas \.elociiy limits. It is desigied so there will be no \.apor-trappingpockets.A typicai rotor is shown in Figure 4-72,left vie$'.

Figure4-73. Motar usedan externaldive compressor. A Motor shaft. B-Motor rotor. C-M()tot statar D-Starting mechanism.E-Motar bearing.F Motor

4.16 Motors

SeeChapter 7 Ior infofmation concernin8motors. Chapter 8 has more informaiion about starting devices and motor controls.

Two differeni types of motors are used for d vinS retuigerationcompressors.Exiemal'drive compressors use conventionalmotors.The compressoris driven with one or more V belis or by direct drive. Figure 4-73shoa's a sectional f.iew of a tyPical motor used on small externaldrive comPressorsin her etic compressois/the motor is mounied under the samedome as the comPressol.Thesemotors are iubricated by the oil ca ied in the refrigerant. Hermeiic motors do not use brushes or oPen Points ilside the dome. Afcing would causepollution in both

the oil and the reftigerani. This would lead to an electricalbumout. A specialelectricalstafiing device is located ouiside the dome. Figure 4-74 sho{.s the three mah parts of a notor used in a hermeiic reftigeration

4.17 ServiceValves Servicevalves are shown Figures 4'10 and 4-11. Many small hermeticsysternsdo not have seNicevalves of any iype. To atiach gaugesand sen ice manifolds, re frigerant lines must be tapped. SpecialtapPins valves are available-These are clamped to a tube so that ihe valves pierce ihe trbe. Ai the same time, the necessary gauge anctserviceconnectionsare provided.

Chapter4 Compretsionsysremsand Compresou

'169

4.18 Mufflers Most heimetic units and many extemal_drivesys_ tems use mufflers to redr.rcenoise that may be caused by gasprrlsation. The muffler allows the gas to expand in the -Ilow. mufiler chambers, smoothing out irs It ;€duces rhe sharp gasping sound on the iniake stroke and the even sharper puff oI tlle exhaust. MuftleE may be located on both the intake and the exhaust openings of the compresror. Iigure 4-75shoh- a Lrnitequ pped with both.r di.hf rgemutflerdndd.u(tion.o' intale,nulnej. Mllfflels are constructed of brazed cvlinders with baffleplatesmountedinside.Figure 4-76illistrat€s a muf fler attachedto both the suctionand exhaustopenings. Filure 4-74. Hermetic mator statot and rotor. Rotor is mounteddirectly on campressorctankhaft. Nate counterweight,which balancesweight ol crank, connectingrod, and piston.

4,19 CompressorCooling The temperature of the compressoris greatly fechd by the heat of compression. As vapor

MolorSlackng

Top[4ain

Suclon Mufler

Figure4-75. A ttilo cylinder hermeticconpressorsuitablefor useeither in a commercialapplicationor as part of a rcsidence air conditioning system. Note suction and discharge nufflers. (Tecunseh Products Company)

170

Modern Reirigeration and Air Condltioniig

up to the boitom of d1emain bearingsor to the middle of the .rankshaftmain bearings.At eachcrankshaftrevolution, the crankthrow, or the eccentric, dips into the oil. It splashes the oil around the inside of the compressor. Oil is thrown onto cylinder walls and piston pin bushings. It is also ihrown into small openingswherc ii can drain into the main bearinss.Thisis an excellentsystem for normal use in small compressors, Some compressorconnectingrods have little dips or scoopsattachedto the lower ends. Thesescoop up small amounts oI oil and sling it around to other palts. Cleanncesbetweenthe moving parts must be less in this type system.Noisy bearingswill occur at smaller clearancesthan in the pressuresystem.This is because there is no oil under pressure to cushion the bearint sur-

Figure4-76. Hernetic conpressorcylinderhead. \4ut'{tcrs arp ara(hed to .Lr tion and p\hau.t oppnines.

"squeezed" and forced into the condenser.the vapor iemperature is laised. Friction (rubbind between moving paris alsoadds to compressortempenture. This heai must be removed to prevent loss of efficiency of the pump. This heat must also be removed in oder to maintain the lubricating qualitiesof the oil. The oil that circulatesin the compressorremoves much ofthe heatftommotor and compressorAs itflows over the heaiedsurfaces,it picks up this heat. Ii caries the heat to cooler suifaces. Many compressorsand many domes have metal fins on their outer su aces.Thesefins help carry the heat away. Some units even use a motor-ddven fan to force coolirlg air over the comprcssor. With a water-cooled condenser, the water is often used to cool the comprcssoror dome. Moto$ are often cooled by passingthe suction vapors and retum oil over the windings. Some units circulate ihe crankcaseoil through an air-cooledcoil. The cooledoil then helpsio cool the motorcompressorSome larger hermetic units are water cooled.

4.20 Lubrication Lubricatint oils have been developedespeciallyfor reciprocatint and rctary refriSerationcompressoE.Usually, these are mineral oi1s,which are completely dehyThey hd\e d vielhey bolh operate!ro"n -. A. changing pressures B. temperature C. a capillary iube D. All of the above. 2. Thermostahcmoior control bulbs are chargedwith A. R-12 B. volatile liquid C. R-134a D. nitro8en 3. \^hat controls the temperature difference between the cut-out and cut-in seidngs in a temperature conA. Differeniial adjushrent control. B. Range adjustment. C. Thermosiaticadjustment. D. None of the above. In a temperature control mechanism, what provides arl increaseor a decreasein the desired temperature? A. Differentialadjustmeniconirol. B. Range adjushnent control. C. Temperaturecontloi. D. None of ihe above. !\4ut is a common color used for ground wire? A. Red. B. Black. C. Green. D. Any of ihe above. 5. \\&at is the purpose of a ladder diagram? A. To identify actuallocahonof specificdiagams. B. To help iroubleshoota system. C. To provide a siandard elecbjcal circuii diagram. D. AII of the above. 7. How doe, a bire al >F-ip,F.pondto d.r ir.rea:e in temperaturerange? A. It expands. B. It contracts. C. It remainsthe same. D. It bends. I44rich of the following is a type of mechanism used in motor control thermostats? A. Sensingbulb. B. Bimetal strip. C. Solid-state(with thermistor). D. A11of the above.

9. What is the common size wire used in a domeshc refrigerator? A. No. 12. B. No. 14. C. No. 16. D. No. 1810. \ 41ai is the common size wire used for heavy duty air conditioners? A. No. 12. B. No. 14. C. No. 16. D. No. 18. CONTROLSMODULE ELECTRIC I A molor may oe operatedbv A. low-side pressure B. high-sidepressure C. Both A and B. D. None of the above. 12. Hermetic moior controls have startint relays to disconnectthe siarting winding.This occurswhen the motor reaches of its rated speed. A. 1/3 B. 1/2

c.2/3 D.3/4 13. Identify the stading relay used on hemetic compressorsystems. A. Curreni or potential (magnetic). B. Thermal. C. Solid-stateelectronic. D. A11oI ihe above. 74. What devicesare built mto motor controls io protect ihe motor from using too much cullent? A. Bimetal strips. P

Ilacicr'n.o

h6,rind

rrn+

Thermistorc with positive temperature coefficient (PTC). D. All of the above. lhe current flow when a motor is starting is when th€ moior is ruruing. A. greater than B. less than C. the same as D. Either B or C. 16. I44ich of the folowing is a common starting relay? A. Curlent. B. Potential. C. Solid-stateelectronic. D. All of the above. 17. When a system is rurfling, in what position are the potential rc1ay contact points? A. Mldway. B. Open. C. Closed. D. Any of the above, depending on the unft C.

ChaprerI

1 8 . Fl'ghhead conder.mg p?*u-e 'rd\ (du+ al1increasein the temperature of the vapor an increasein the temperature of ihe oil an increase in the formation of carbon, acids, and sludge D. Any of the above, depending on the un1t. 19. If a rclay is not operating,which of the follorving is nol the proper ;7?ilial procedure? A. Replacingihe relay. B. Checking the moior. C. Checkingthe capaciiorand overloadcui-out. D. Checkingihe thermostat. A. B. C.

E ectric CircuitsAnd Contros

333

20. The term "central air conditionint" indicatesthat a slrstemcanprovlde -. A. heatingand cooling B. humidification and dehumidificatil'n C. electrostaticair cleaning D. All of the above.

cantrol usedon heatpumps Thissalid statelogic module Microprocessor cantrclsthe quantityand sourceof back up heat and reducesthe nLtmberot defrcstcycle:sandshutdownson operationsin the eventaf a pawer lossar when prissuresor refrip,eanttempeftturesateabnanlal lYotk lnternatianal Carp., Unitary ProductsCrouP)

Modern Refrigeration and Air Conditioning

Cammon refri7erant cylinders. Refrigerantsand prcper storage of them are covercd in Chapter 9. (NationalRefri7erants, |nc.)

REFRIGERANTS

and the OzoneLayer 9.1 Refrigerants

KeyWordsl azeotropic chlorofluorocarbons laFacJ enthalpy ilammability hydrochlorofluorocatbons (HCFCS)

hydrofluorocarbons (HFCS) ozone retrofittinS toxrcrty zeotropic

Learning Obiectives: {fter 'rLd}ing lhis.hapter.uou ''rill be ableto: a Understandthe differencesbetween CFCS,HCFCS, by a Correctlyidentifyand classifycommonrefrigerants thetTnLrmoeTs. a Listthe necessarypropertiesof refrigerants i) Reada pressure-temperature curve and identify the propef refrigerant. a Demonstrate ability to read pressute-enthalpy diagrams. a Discusspropeties of different refrigerantsand their applicationsin a systern. l) Demonstratehandling of refrigerantcylinders and identifycolor codes. a Follow approvedsaletyprocedures. a ldentify the safety proceduresfor using refrigerant cylinders.

The word "ozone" has become a part of our everydav terminology.A very thin layer of the earlht upper ins ozone l he o/one layer actsas a filatmosphere. o-nta -un s L traviolet rays Thi' Prolects human ter foi the plant, and sea Me ftom the damaging effects of these '

Scientists have lound that releasint chlorofluorocarbons (CFCS)Ircm some refriSerants can harm the ozone layer. The CFCs de'lroy thjs Protective layer of lhe eirth ' atmo.phere.This.oncern has de\eloPedinio what we rcfer to as the EPA (Environmental Pmtection Aqency, reslrlafions. These reguiations identiS the tries of retiigerant' ihal cdn be Prcduced. They also rizut"t" tlo' ihe refrigerant' will be uted For more infoimation, seeChapter 10 Most refri8€rants commonly used today are classi_ fied inio foul areas: . . . .

Chlorofluorocarbons (CFCs) Hvdrochlorofluorocarbons (HCFCS). Hydrofluorocarbons (HFCs). R;frigeiant blends (azeohoPic and zeohopic)

by Number 9.'1.1 ldentifyingRefrigerants and Color Code Reftiqerants are identified by number. The number Iollows th; letter & which means refiiterant. T}lls identifying sysLemhas been standardled by the Amedcan gocretyof Heating, RefriSerdtingand Air{ondjtionint Eneinee$ (ASHRAE). Refer io ChaPter 31 for a summary of the ASHRAE numberint system You should becom; Iamiliar with refrigemnt numberc, as weli as with Reftigerant cvlinde$ are often color coded to Per' mit easy identificition of the rcfiigerants they contain This prictice helps io prevent accjdentaLmi\int of rer,serants within'a sysiem Alrra)' read the label dnd ide"nrifurhe renieerantbeforeusing a q iinder' The color code sirolvn is not a requirement for all manuJacturers' PoDular rcfriqemnts, with their R-numbers and cylind€r col'or codes, ire shown in Figure 9-1. Cylinde$ for rc cooeredrcfrigerat]l(s arc gtay with yellow ends.

and Air Conditon ng Modern Re{riSeraiion

336

Chemical

Cyllnder Oran9e

w tr F - 1 2

TrichlorctLuoromelhane luorornelhane cFc Dichlorodif

Lghl blLe

E

ChoroirllLuorcmelhans

cFc

Coral

w R-1381

Bromollluoromethan€

cFc

a-22 R,23

Chorodfluoromelhane

HCFC HFC

F-113

Trichlorolrill!oroelhans luoroethane Dichlorotetraf D chLorotr fluoro€lhan€ !oroelhane Chlororeiral

cFc cFc

Lighlgray

Lghl gray

Lighl(sky)blu€

N ! I t

a T I !

n

tr tr I I

w

Orange Lighrgray-greon I B ght green

E

tr brown T Chocolate tr !

I @ I LshtPurpr€ I Teal

lsiu",

R-13

R-123

ons chllersior largeappllcal Used n centrifugal androlary_lvpe VersatiLe, wdely usedin reciprocaiing applcaljons. d andinduslrial equipmenthouseho in ow stageof feirlgerant used Lowienrperature wilhon€or applcalions [,ledun- to Low-iemperalure on. bxostagesot comprcss applcallons andinduslrial commercial, R€sideniial, relrigeranl lo b€ usedas €placem€nl Lowlemp€ralurs in ow $age of cascadesyslem Lowcapacty certrilga chilers. P ncipallyusedwilhchllerslor hlghercapacilies chil6rs. seryesas a repacementior R_11 in c€nlrilugal refrgeranilorchilerapplicatons Mediurn-pres$re Usedin marne applcalions. reJrgeralion lor usein lowtemp€ralure substitute

HCFC HCFC

F-125

HFC

R-134a

HFC

a - 2 2 + 4 . 1 5 2 a + B - 1 2 4 zeotrcpic(HCFo) R-4olB a 2 2 + A - 1 5 2 a + F ' 1 2 4 R - 4 0 1 C B - 2 2 + R - 1 5 2 a + R - 1 2 4 zeolropc (HoFC) R - 2 2 + F I - 1 2 5 + R - 2 9 0 zeolropc (HCFo) (HCFC) F-4028 B - 2 2 + R - 1 2 5 + R - 2 9 0 Zeotropic (HCFC) zeolrcpic R-125+R-143a+R-134a R - 2 2 + R 1 4 2 b + F - € 0 0 azeotloplc(HCFC) (HFC) F I - 3 2 + R ' 1 2 5 + R - 1 3 4 aZ€oiropLc F-4078 R - 3 2 + R - 1 2 5 + R - 1 3 4 azeotrcpic(HFc) (HFC) F-407C R - 3 2 + F - 1 2 5 + R - 1 3 4 aZgotropic + R-125 R-32 F-500 22/115 Refrgeranls 23113 Relrigeranrs 125/143a B€rriserants

B 502 R-503

N !

I

= CFC Chloroiuorocarbors

= HFCs Hydrolluoroc.lbons

'e aLtorob ' lv€oiJm-enpe'aLre elioe'ar Jsedin syslemsin resdenna, induslryand r€irigeralion andindustialapplcalons commercial. ev$€ms usein mostmediurnl€mperalure Subsiiiuteior anddomeslic €quipment usedin lranspoftreirigeraion relrigsralors. and comrnercial a r.ondillonng ret gerartin mobiL€ Fleplac€menr loodservice,vendng,suPermarket ce machines, Supemalkel,tlanspodloodseruice. Mediumandlowlemp€ratu€appications Usedfor R-502relrott Usedlor F-502relrofil. F e p l d c e - € 1r e1l 4 e t a . li . ' e s d e 1 r . a i c o n dt i o r i r q r induslraand Usedwilh recProcalifgcompressors applications. commercia cases Supgmarkellfeezersand refrgeraied sysierns usedin lowsiageoi cascadetyp€ ior lowtemperature rclrigeranl Beplacemenl ons. applrcat rsirigeration commercial and conpresso|s Us€dn larg€recprocaling sbso'polrvp€ >ylLers Hydochlorcl uorocabons= HcFCs

with their colar codesand typical applications Fisure9-1. fhe nrostcommontyused refrigetants,

9.1.2 CFCRefrigerants Ihe first halogen-based refrigerants (fluorinated hy&oca$ons) were develoPed over sixiy years a8o These refrigerants are comPosed of chlodne, fluorine, and carbon, and are called chlorotl orocatborrs (CFCs). .loncorrGive, fhese _efriger.nt-are lo\^ rn to\i.ity l\ rth ol\er mdle':al. T\e\ are nol fdmdnd con_p"fiblF mauleoi erplosre. bul si.'dbleqlrintitie neverdn) visible frost accumulation in this ilPe of ftost control. Cabinets Cabinet construction foi automatic defrosting refrigemtor-freezers is differcnt than manual defrcsi mod;h. The condensation,which collectson the evaPorator, must be melted ftom iime to time. DiJferent methods are used for disposing of this condensaiion.The cabineimust have iubing to conductthis moishrreto the iop of the motor compressor. UsuaIIy, it is collecied on a plaie or surfacejust over the motor comPrcssorThis suriace,or plate, is heatedby the motor compressorand by

heat ftom the condenser The moisture then evaPorates and soes back into the room. Some refrigerators use eleciric defrost. Piovisions musi be made ii the cabinet fol housing elechic heate$ and thef cont|ols. Figure 11-11 shows a refrigerator-freezer It Provides other temperatures besides that of the freezer and the reftigemtor compatments. The air circulation Provides lower tempemtures to areas reached fkst. It Provides higher temperatures to those areas reached last The evaporator is beneath ihe fast-freezinS sheu at the boitom of the fieezin8 compartment All of the refrigerahng effect comes from this evaporaior The air circulation svstem, consists of a fan, ducts, and a damper. These areiocat€d at the back of the cabinei. It provides the necessary airflow to give the iemThe condensinS peraturedesjredin eachcomPartmen.. umt t localed in the bo'.om of the cabinei. Refriqeration Mechanical components Some mecharical comPonents provide morc than iwo temperatures in the reftigeraior with a lreezer .ompartme*. A typical system is shown in FiSure 11-12.

SideViewol Air FlowDiagram

FronlV ewot Air FlowD agram

Length

SeisingTubeif Air DuctBehind

7(

Eleclical

Energy Saving 32" Top-Mounl RefrigeralorAir Flow Fieurel1-lt. ,i^p"n."ntr.

Evapontorlan forcescirculationof cooled air throuqhvarious Ai ciculatrcn in ret getator-freezer. (AmanaRefriBeration. Inc ) openings and thus, control cabinettemperatures. ai duct Damperscontrol

'11 Domestc ReirgeratoEand Freezers Chapter

389

Exchanger

Outlet

AirOlt

DeiroslTimer

EnergySaving32" Top-MounlRefrigeraior

in therctrigerctor electricdefrostrefrigerator freezerthatprovidesmultipletemperatures Figure1t-12, Automatic at testpaints, Tt, T), and 73. compartmenLCorrectoperationmay be checkedby detemining temperatures temperatures are:Tt= 1soFta 13"F(-26'Cto 25'C),Tz=-15'Fto 14'F( 26'C), Recommende.l operatin! T:='a'Fto103"F(27Cto39"C).TemperatureT3ishighbecausethecapillarytubeisincontactwithsuctionl inlet (Amana at thecompressor heatta thesuctionline, Thisincreases thesuperheat transfer excess condenser

Evaporator The evaporatoris locatedai the back of the shel{.It separatesthe freezercompartment{rom the refrigerator compartment.The rcftiterant used is R-12 or R-134a. Reftigerant evaporation in the evapoiator provides the heat absorption (coolind required in the cabinet.Usua1lt a motor-driven fan forcesair over the evaporator surface.Air is forced through the vaiious ducts. This provides all the necessary rcfrigerator temperatures for ihe compartments. Motor Compressor The suctionline frcm the evaporatorextendsdown the wall of ihe cabinet.lt exiendsto ihe inlet side of the hermetic motor compressorln the cabinetbase. Condenser The condenseris a \ .ire-and-tubetype. Forcedair circulationis provided by a motor and fan. They are located at the back of the compartment containing the compressorand the condenser,

Capillary Tube The relrigeiant is condensed in the condenser. It flows through a high-side filter-drier into a capillary tube. The capi11arytube is aiiached to a seciion of the suction 1ine. This provides a heai exchange beiween the capillary tube and the suction line. The refrigerantfrom the capillary tube then flo 's into ihe evaporator The cooling cycle is .ompleted. Features Only the refrigerator compartment has a light. It is operated by a switch, which is activated by the door movement. The butter condiiioner temperature is slithtly above the cabinet temperatur€. There arc control dampers for the refrigerator and the Ireezer compartments. These dampers regulate flow of cold air ftom the evaporator.

Heaters Sevemiheating devicesare used as drie$. heateris locatedat ihe top of the eiectdcalresistance

390

and Air Conditioning Modern Refrig€ration

cabinet,inside the outer case.This keePsthe outside of the cabinet wann so ihat it will not coileci condensation durine damp davs. i second dier wile is placed inside the center mullion to keep its surface dqa A third heating device is around thi {reezer flange ({reezer door oPening) A fourth heateris placedin the ddP Pan.It evaPoratesthe condensation which flows into the drip pan after automatic defrost. A "powet-saver" switch is located inside the cabiner. ll provideca meansol diicorne(tirg thesehealerv\ne.1iemperdrureand humidiq condiuon' allow it Normatly, ihe heaters are in continuous oPenhon Automatic Defrcst The evaPomtor is automatically defrosted by an electric resist;nce heater Tlds occurs every six hou$ oI comDressorrunning hme The heater is located in the fin area on the underside of the evaporaior A timer activates the switch, which tums on the defroster A thermostai attached to the evaporator opens the deftost heater circuii. This ends delrostint when the evaPorator temperarurereacheecondshelf rron rne boLtom Three settings are provided {ff, Normal, and Cold The deftost tiner is in the compressorcompartment/ Figure 11-52.

Chapterll

DomesticReirgeratorsand Freezer!

409

Fiture'f1-52. The dei()st timet is locatedin thc compressorcompartnentat the battan ai the frcezet.

'fl-51. Larlclerwiing cliagranfor an upright Figure freezer.Nate that all paftsarc Braundedthtouqhthe and threeprang extensionphtE and cord. Compressor ian circuits areapen duting defrastcycle. Note the deiost heaterand the tetminationswitch. lFrigidaireConpany)

11.10.2 Cabinet,MechanicalComponents, and ElectricalCircuits-Whirlpool to the singleThe upright freezercabinetis siniiar -o.1 . do.,r retrite-,'or l hp d.ur oller h.. . Th€ evaporaior of the manual defrost unit is usu alli, a part of the cabinetshelves.No-frost systemsuse an evaporatorlocated behind a baffle. A ian cuculates ihe all th(ough the evaporator and then throrigh the food seciion.A filter drier is also used, FiSure 11-53.A -rgral liglrr i. u:ed .o Ird:(.rlenl'en oow< i' on. "f elight may warn \\'hen cabinet some models, a signal On temperaiureis above nomal. The freezer mechanicalcomponentsare similar to thoseoi a siandardreftigeraiing sysiem.They in.lude a motor compressordesigned for lorv evaporator pres' condenseris used t'ith both sures.A forced-conwection suppllr and reiurn Fill€s. These grilles are lo.ated .t the loh'er ftont of the cabinei. The r{'iring lor this type of fteezeris also sinilar to thai of the refrigeratoi system.Figwe 11-54shows the

Figure11-53. A domesti. uptight trcezerLtnttwtth a fiher-drier(whirlpoal Corparation)

a'iring of a manual defrost system. Noie ihe cabinet light, swiich, and signal litht, Nhich indicaie that the system has electdcal poaer. A 23.6 VA stile heater is used. Figure 11-55sho 's a system ihat has a Polarize.:l circuit (ground 1vire, etc.). The cabinet and all otller metal paris are grounded.

or Freezer 11.11 Careof Refrigerator The refrigerator or fueezerdoor should not be al_ lowed io remain open for long Periods of time when the unit is operatinS.There is a Sreatdifferencen1 iem peraturebetween the inner cabinei and roo iemP€ra ture. Tiis djfferencew'ill set uP convection.rtrrenis as soon as the door is oPened.A Sreatdeal of heat $'ill be

410

Modern Refrigeralioiand Air Condltioning

in Cabinet 1l.12 Ice Accumulation lnsulation

D o o rS w t c h

uaurErLrsn

fisure 1'f-54. Laddet$'irin! diagramfor a nanual difrost upright ieezer. Note the stile heater ancl the signalli+ht, which indicatespower is an

carried into the cabinet quickly Articles should be removed from or placed in the cabinetquickly The cabinet musi be kept clean on the outside as r\'ellas on the inside,The condenserand motorcompressor should be wiped clean at least every six months. A vacuum cleanermay be used for cleaningthe lini fuom the condenser. The door tasket should be checked for tightnesspedodicallY

Ice accumulation is one of the main prcblems encountered with imProperly or carelessly assembled units. A rcfiigerator or freezermay have an air leak in the outer casing (shetl). This auows moisture from the in ihe in'ui.tion t hi' ro en.erdrd conden5F .rtmosphere p-oblem' in d lreezet conditinnwill cau.econ'rderable dbililv of he.dbiintulahnS lc" buildupa.soredu.es .he conditjor more lf the to run lhe unil npf. rhLl.adusinB run continuously may unit the condensing is severe, Ice accumulation in a freezer may be indicated b)' on lhe out"ide -urfd.e lo a ,olo )por or condensation etimndl; $e ulwanted ice,-hul o'l lhe freeTP'dndallow ii to warm uP for a fer{' days The unwanted ice will melt and drain. If coid spots or condensationaPPear,remove the breaker stripa. Insert lightly Packed, fine fiber8lass insulation to fill air Pockeis Some freezers provide an oPening in the inner lining. Any moisture in ihe insulation is alowed to escaJe into the freezer compartment Therc it con denies on the cold suface of the evapomtorand keePs the insulation drY.

11.13 ButterConditioner 'i

Various devices are used to soften butter storcd rhe reargera.or..brnet The

Grounded Componenis

v 6 0Cycle

,+

r/7

DoorSwltch

Cabn€l Light

pa\\'et cord is grcundedby a wirc Fisure 1'f-55. Lad.ierwiring dialram for an uprightfreezet Middle conductorof n6[,uorkto a]l metal partsaf the cabinet,hardwarc,and rcfrigeratingsystem

Chaprer ll

will hold a recess h the refrigerator door which -he rece.. i- 'eoa.l.rrr.e-oound (or murel oi bul e_. 'a)or nrJ:l Io--os. f i g u ; e l 2 - 8 5 d i " g r r. ' . . n e b . - i ' { F P ' o r l h e u . e u f l h i unit. After steps1, 2, and 3, the Pressrireieading deteraciion.lf pressureis 0 PSi,Proceedwith minesvour next 8. a. drd 0 ll \F prF-'urei- rorrr P'i slep.4. c n r . i l o w - t " p - + q , : c , o A , 7 A ,d n d 8 A F o ' d d J i l i o r d:ln formaiion on ihe operationof recovery/recvclinguniis, seeChapter 10.

Cdiipi;;;i r r2xi.2'Rdiliiiii'; }t€rniliic' Follow fhjs procedure to remov€ a motor comPres1. 2.

Disconnect the electrical circuit. lnstall the gauge manifold. Use a piercing valve if

3. 4.

Recoverthe refiigerant. Disconnectthe lines. Wear goggles! A. Cleanboth ihe suctionand dischargetubing on siraight sectionsnear ihe compressor Use a tube cutier. Pltl8 llie li,lesdf orlre

rccoverysyste bein! used Fiqure12-84. A ret'riP,ercnt (Recvclins lnternational) Specialists o; a damesticunit. Cl€an the tubing or littings at the comPressor' Put braznrg fh1x on the comrection Heai the joint andPull ihe.tubingol1tofthe fitthgs ?ft/8 'penlngsLntnealatetr:l 5. Removethe notor conpressor' 6. If ihe motor comPressorhas oil cooler lines, the)' rr.r-l bF p:nc\ed.thencrr' \\:ih a Lrl_irt utler'Tl'e c.r'rpre-aorrubir.qoPFrire- 'l'oulo bp -ealPd The unit is nor\' ready to have a iePlacementmotor comprcssorinstalled. B.

A sfrong pungent refaiSerantodor may be Present rhen d pier.ing \al\e i5 oPened'tiShil\"fhi5 i. a cerrainindiiafionor a o'rnout. \4u.h .tud) ha' beendone on why motor comPressorsbum out MoisiLue, dirt, and air in the systemare PossiblecausesAnothel causemav be too much curent flo\^'frcm inaccuratesafet,vdevices in the electricalcircr.dt.Additional rcasonsmav be a stiff compressor,lo1\' voltate, or a lack of refri8erant (Poor High he;d pressureis one of the most ftequent reasonsfor moior burnout. This pressure.reatesvery high temperaturesas ihe vaPol passesthe compressororschaigevalves.The high temPeraiureincreaseschemical aciion. This adds to oi createsnew corroding elements in the system.Oil bteaks down and forms carbon and sludge.lf ihe tempelature at the dischargeline io ihe reaches350"F(177"C),oil breakdown is iakcond"enser -

lr :. \er\ irrportdnt r\dl ll-e condFr-Prbe l.r8e enorgh. lr n:-. be cr"rn dnd r\e drr sholrldfos .vFr it

460

Modern Reirgerationand Air Condltionng

Ve lyA/C SeflicsBequesl

ussGaugesonl/C System Pressurc io Check

Chalq€r/C Enoughto

P€riormLeakTesiwiih a LeakDeieclorand Check Openllon ol l,/C System

Recha€etheAC System withCleanB€lrigeranl by Weightor GaugeSei Relalionship Tempeature

a rcfrigetant for usinF, Figure12-85. Procedurcs rcadinBat Step3 determines recoverysysten.Pressure

efficiently. (Fans, fan motors, .lucts, air-in, and air-out must a1lbe in good condition.) The head pressureof each unit should be checked. All the necessarythin8s must be done tobint this pressure down. Purge the system through the hith-side line to the manifold gauge. ComPletely clean the condenser rvith high-pressuregas (ait carbon dioxide, nitrogen). SeeSection12.9.1.wear goggles!Biush the condenserio remove dust and dirt. Use lont bristle brushes and a vacuum cleaner.Check the air in and air-out passages. The,vmust be in good conclition.

r' ' Motarlairndut ctiiniiparrLr

lvhen a motor begins io burn out, it overheats. This overheating will cause lhe rcfrigerani to break down. IJ moisture is presmt, overheafing can causethe formahon of hydrochloric and hydrofluoric acids. Oil in this con dition is said to be "a.idic." The acid will causeinsula iion on moior windints to deteriorateand increasethe the motof windings wili motor temperature.E\.entuall,v, and burn out. short circuii If a svstemhas a motor comPressorburnout, refrigefani controls should be repairedor replaced.(This inciudesAEV solenoidvalves,ieversingvah'es,etc ) Flush wjth nitrogen or the same refrigelant used the s_vstem in the system.

motor comDo not touchthe oil from a burned-out wear Caution: pressor. lt will causea severeacid burn! ind rubber8lo\e\' gogsles lIoilcooler linesmu5lbe r ul, be e\en Inore(arelul Do not allow oil to run on the floor' Trap it in glassconlatners. The bumout can be mild or se\'ere.If severe,the oil will be black a]rd acidic .ifi a Pungent, very unPleasant odor.Ifmild, oil ivill be clearbui ihere will be a Pungent odor and a mild acidic condition Many acid iest futs are available for deiermining the amount of contamination. SeeChapter 15 for further inJonnation lf oil is clean and odor-free,there is no bumout The trouble After reDlacinqa motor compressor,install two filter driers. Se; Figu're 4'9. One should be in the suction line beiil'een the evaporator and ihe compressor. The other should be behdeenthe condenserand the liquid retuiserantline. (If acapitlary tube isused, the filter-dder should be just before the capillary tube ) The system may be flushed using a recovery unit ihat inco+orates the use of filte$ Normally the Process i, pe4o meo mo e lhdn oice lo en(ureEood flusl'ire \iirog.n o l-e refriee-drt .n l_e)\ 'tem m.\ be Lo "urrounding.ubctance,. it can cool the remaining liquid to the lower temperahre. The vapor formed during this operation is called

flashsas.

The effeciivelatent heat is the total heat at E in Figure 16-19minus ihe heatof the liquid at F The effective laient heaiis anaveragevaluebecauselow sidepres-

648

andAir Conditjoning ModernRefrigeratlon

'| Vapor 6.2.6 Superheated

t

E E

13,59

Heai Bt!/lb. + 39.56

i01.89

113.0

diagnm-Rl31a. At A, Figure16-19. Pressure-heat Iiquid is boiling in evaporatorand pressureis canstantas heat is bein! addecl to refrigerant. At B, the compressor raisespressure ta condensing pressure;heat ol compression is added, and temperature rises.At C, the candensercaols hot vapor to saturatedvapor line, then candensesvapar into a liquid. Pressureis constantand heatis rcmoved.At D, the refrigerantcontrol quickly rcdu p. prc.-urc rc e\apotdtin?at lot\-s;dporc.

; .g E E 9 2

o B

2 '

It-

E E !

I

6

!

s!

!

E E

E E

E

3o

9.

t6 s z ! o

I b 9 i Fg P 9

.!

e d 6

E

s

+2 4 .P

:. I I I I

6 6_9

n62

93S

d

n

6 =

I 6 9 .9

ChapterI7

(Cooler ammonia vapor is flowing throuSh the inner hrbe in the oppositedirection.) From ih€ iiquid suction heat exchanger the liquid ammonia enterc the second rcshictor. Thete, pressure and tempemture arc furiher rcduced. The low-pressure, Iow-temperature liquid refrig€rant then flows through the cliller coil (evaporator).Here,a glycol anclwater solution cascadesdown across the evaporator. It gives up heat and vaporizes liquid r€fiigerani. The refriterant vapor ieaves the chiller. It then passesthrough the inner hrbe oI the liquid suction heat exchanger. In passing, it picks up heat from the liquid refigerant flowing through the outei iube in the opposite direction. Finaly, ihe vapor enters ihe abso$er header This completes the re{rigeration circuit. Hot. sfront.olution :s ell behinda' anmonia vapor is driven out of ihe weak solution in the genefator. This solution then passesup throu8h a coil in fte generator The solution then leavesthe generatorand enters the inner coil of the rectifier. Here, ihe strong soluiion comesinto thermal contactwith the weak sollrtion.(The weak solution is flowing in the opposite direction through the orter coil.)As ihe strong solution leavesihe rectifier. it passesdlrough the sironS solution rcstrictor. This restricior reduces the solution from high-side to low-side pressure. As the strong solution leaves the rcstrictor, it enters the absorber header. This is a tube-within-a-tube. The inner tube contains the strong soluiion. The outer tube containsammonia vapor which is being returned from the chiller (evaporator).The strong-solutiontube contained within the absorber header has two small holes. Theseholes allow stront solution to llow out into direct

AbsorptionSysiems-Principlesand Applicatlons

699

contaci with the surrounding ammonia vapor At this point, the strong solution and ammonia vapor begin to form a weak solution.

Strongsolutionandammoniavaporthenleavethe absorber header They leave by way of the two hrbes and begin to flow into the absorber Throughout ihe absorber, the strong soluhon completely absorbs the vapor, forming a weak solution. As ihe weak solution leaves the absorber, it is picked up by the solution pump. This will move the so lution back io the high-pressurc side o{ the unit. As the weak solution leaves the solution pump, lt passes fhrough the rectifier. Heat is picked up from sfrong solurion vapor lohing in the oppositedireclion. Preheating the weak solution as ii flows through the rectfier rcduces the heat input rcquired. The ovemii efficiency of the cycle is increased.The weak solution leaves th€ rectifier and dips back into the 8en€rator analyzer assemblyto start anothercycie.

Absorption Air 17.10.1 Residential Installation Conditioner and Construction A typical gas and water single unit zone application is shown in Figure 17-24. The unit is instaled on a concreieslab.The installationis similar io that of a standard aii conditioning unit. As in the standard unit, the supply and return connections are covered with flexible hose.The hose is securedwith stainlesssteel clamps to prevent sound iransmission. The coll for this aPPlication is locaied on ihe typical air conditioning-tl?e gas turnace. The coil may need to be located in the hoi air

Figure17-24, Singleltnit, single-zoneapplicationof absorptioncoolinB systemcombinedwith a basic aii-conditioningtype gasfurnace.Note the variousinsulatedlinesfrom the caoling systemta the furnace' lRobur Coryoration)

700

M o d e r nR e t r i g e f a t l o a n dA i r C o n d i t i o l j n S

strearnof the furnace.In this event,plasticpiping should not be attacheddirectly to the coil. Copper pipifg extensionsshorild be used in this area. The cond€nsate drain lines must also be insulated-All piping should compjy to local codes. Acontrol iraNformer appliesihe powerfor the control circuit. The circuit includes gas valve, direct spark ig tor and tirne delay switch Ior both heating and cooling. An electromagneticignition sysiem provides a direct sparkignition of the main bumei.lthas a ten second flame detections)rsiem.The svsternhasa solid-stae time dela)r.This prevents coniinuous circulation of both reftigeration solution and chilled r{'ater. Circulation is delayed for three minuies and fiJteen secondsafter the ihernostat has been satisfied.The basicsystem has numerous safety controls.Theseirclude flame det€ctors, chjll€d water swiiches,and heating-sjdeoperating con trols. Theseare ill addiiio]r to basicsafeiy controlsi. The capacitvof air'cooled chillers varreswrth ambient air ienperaflrre and leavingchilled h'ater tenLperature. Capacity characteristicsof the units are sho,rn in Figure 17-25. h the sellcontained nnit, Figure 17-26,the insulated evaporaiorcools a glycol and lvater solution. The solution then circulatesthrouth a heai exchante coil in ihe hlmace bonrlet.It ma)' also be used in a separateair circulation systemwithin the building. The absorytions)'siemis sholvn in Figure 17-27.Controlsare shown in Figure U-28. The absorpiionsysiemcanalsobe utilized as l,art of a multiple unit load system.Typical applicationsrre in large office briildnlgs, strip malls, and efficiencv,rparinent complexes.An iniernal iemperature-sensing.Le\-ice monitors the return h'ater temperature.Temperatures higher than normal indicateincreasedneed for coolingAnother unit is ignited to brinS the chiued $.atel i€m perature down to proper le\-el.The chiled water is directed by means of valves to the proper fan coi.. The proper zonecontrolis therebyaccomplished The lol{' pressureand iempemiure of ihe chilled water svsten alioh'sthe useofPVC. Cas units are singlephaseporver,l 15V or 230V Individual units rangefrom 3 tons to 25 ions.

Thesesystems are madeoi steelandaluminum.Use of copperor copperalloysis verydangerous. An explosionmayresult.

tiflJre lT-26, Exteriorview of Eas-fueledabsarption systemusedfor residentialair concllioning. (Robu Corparation)

Filwe 17-27. Absorptionsystetnair conditionerwith hausingremaved.( Robur Catpoztian)

("F) condenser AirTemp€ralure Eniedng

50"F

1C= 46'F

ltt

42"F

_9L 9 5 1 0 0 60.,16 58.50 36.76 36.28 35.10 33.64. 49.01 48.37 47.37 44.45 3672 3614 34.92 32.61 48.96 48.24 47.13 43 53 6i 20 60_30 58.20 60.06 57.50 36.65 36.04 34.50 31.3i 48.A6 4A.O4 46.57 41.76 47.?6 45_41 39.45 99!S 36.57 60.60 36.36 35.53 32.30 27.40 48.,13 47.37 €60 36.00 35.03 30.60 23.40 48.00 46.70 41.30 31.20 60oo-58.38 51.00

qrc

105 56.07 54.42 52-20

39.00

Figure17-25. Capacitiesoi ait coaled chillersin thousandsoi Btu/h. Note that capacitiesvaty with ambientair teinperature and the tempetaturcof chilled waterexitinBthe Ltnit.lRabu Caryarattan)

701

ChapterI Z AbsorptlonSystemr-Prlnciplesand Appllcatons

LiqlidSuctionHsatExchang€r

S€rvice

rJI

Seruicg ValveO

Chll€d

'"1

Dran Plug

Eigwe 17-2A, Cantrolsaf absorptionair conditionerare easyto reachfot servicewhen housingis renoved. (Robu Corporation)

Absorption Air 17.10.2 Residential Conditioner Service Mosi residentialabsorptionsvstemsare se iceable. They are equipped with servicevalves. How-evet you should be trained by the manufachrrerbefore attempting to servicethesesystems. Ammoniais toxic and flammablewhen mixedat certain ratios with air. Wear a {ace shieldor safetygoggles. Ammonia reactswith somemetals.Useonly steelor aluminurn tubing, gauges,fittings, and manifolds. Figule 17-29 shows a system equipped with four seNice valves.ValvesA and D are on the low-pressure side.ValvesC and E are on the high pressureside of the sysiem.ValveC is not shown. ValvesD and E are gauge mounts Ior checking pressureson the system. Ilefei back to Figure 17-23.It also shows the location of the service The systemis chargedwitll a solution of ammonia, distilled 'aier (pH 6.0 -), and a co osion inhibitor A solution cylinder is used to chargethe systemwiih the solution. This cylinder usually has about a 45 1b. capacity.The solution chargeis about 35 ]b. of distilled water. It contains inhibitor and 15 lb. of anhydrous (fueeof water) ammonia. The solution cylinder is filled with distiled \r'ater and inlibitor (yellow in coloi). It is put in through the fi]] plug. If a white precipitateforms in the soluhon,discard it and make a new batch. The soluiion cylinder is then charged wiih anhydrcus ammonia. Anhydrous ammonia is available in 25 1b. cylinders.The cylinder has both a vapor and a liquid valve.Figure 17-30showsthe chargingatangement. Noie that the charging line is connectedto the liquid

Eigwe 17-29. Absotptionsystemtar air conditioning. service valveA is mountedon solution-cooledabsorber. Servicevalve D is mauntedon pump inlet tank.Service valve E is mountedan pump dischar1etank.Service valve C is not shown.

Solulion Oylinder

Figure17-30. Cylinderssetup for rcchaginq an absarptionsystem.A Salutioncylinder hasliquid valve, vapor valve, and center pluq. ]t is bein1 charEedwith Iiquid amnonia fram cylinderat right (1 lb. anmonia for each 2 Ib. distilled water). B-Ammonia cylinder. C-Pail halds waterand a purge line connectedto Bas valve of cylinder A. Purging decreasespressure tn A to allow ilow fron B. lRobu Carparation)

valve of the anhydrous ammonia cylinder. The pail is partly lilled 'ith ra'ater. It is coniected to the vapor valve oI the solution cylinder.VaPor is purSed from the solution cylinder if necessaryto lower the pressure (This will enable anhydrous ammonia to {io1\ into the

702

Modem Reirlgerationand Air Condit onlng

solution cylinder.)The water in the pail ra.illabsorbthe small amouni of ammonia purged. The systemmust have ihe corect pressuresand the correct amount of anhydrous ammonia, It musi also have the co ect amount of distilled waier and inhibitor. To check pressures,install a 100% steel constructed taute manifold, steellines,and steel6ttings. Do not us€ copper or brass.A steel gauge manifold is shoft'n in Figure 17-31.Noie the steel manifold. It is consiructed of standard steel fiitings and steel valves. The manifold oPerates exactly like the manifolds described in Chap'12 ters and 15. The four service valves on the system are used for a number of serviceoperations. Valve A: . . . . .

Checksabsorberpressure(low-side pressurc). Purgesamrnoniavapor Adds ammonia liquid or vapor. Adds solution. RFdu(e,.)nem pre-\ureto dtmocpheri.pfes:Lre.

Valve C: . . . . .

Checkshigh-sidepressure. Checkssolution level. Removesexcesssolution. Adds solution after repairs. Redu.e-j-!em pressrrero almu5oheric.

Valve D (not shown): '

Purgesair.

. .

Adds solution. Rernovessolution.

Valve E: . .

Removeslarge amounts of solution. Determines if discharSe chamber has l,roper amount of noncondensables.

Figure17-31. All-steelgaugenanifold E connected ta valve C (hiEh-pressureside) and valve A (lowprcssureside). ValveE is far remavaland checkingof

Absorption 17.11 Commeycial System Absorption systems are used successfullyfor air conditioning comfoft cooling installations.Suchsystems may also be used for heating. Some units use the ammonia-water hydiogen continuous cycle. Others use water as ihe rcfriSerant, and various chemicals as the A sysiem using water as the rcfrigerant and liihium bromrde.r-thedb-orberrsshownin I igur€ l7-32.Sleanheat applied to the teneraior percolates water vapor (red dois) and weak soluiion up to the separator The liqrid lithium bromide (shown in black) then flows by gravity through the heat exchanger It flows to the absorber where it absorbs the evaporated water. The strong solution (black dois) settles to ihe bottom of the absorber. It rctums to the generator after passing through the heat exchanger The pressure difference is mainiained by the pressure head of the lithium bromide liquid. The water vapor (red dots) in ihe separatornses io the condenser.There,it is condensedand becomeswater. The water flows by gravity through an orifice inio the evaporaior,The water evaporatesat a low temperatllre due to a near-perfectvacuum in the system.The water vapor is absorbedby ihe lithium bromide (black). Note that the absorberand condenserare both cooled by water coils. The condenserwater is then taken to a coolingiower.Itis cooledthereand used over atain. The condensingpressureis aboui 50 mm to 60mm Hg (about 1 psia or 6.9 kPa).The evapoFting pressureis 8 mrn io 10 mm Hg (about 0.17psia or 1.2 kPa). Lithium chromate is often used as a corosion inhibitox A typical cooling tower is shown in Figure u-33. More deiail is sho .n in Chapter 13.

17,12 AbsorptionUnit for Air and Heating Conditioning The applicationof absorptionrefrigeraiingsystems in comfort cooling air conditioning and heatinS is increasing. Absorption units have advantages in solar energy systems. Solar energy, as a source of heat, can cool buildingswhen usedin absorytionsystems.Installaiions using steamheat can use it as a heat sourcefor absorption cooling in the summer. Thesesystemsare also used to prcduce chiiled water. The chilled water, in ium, may be used for various purposes. Ii may be used as quenching baihs and ddnking water It may also seNe as a specialcoolant to lower ihe working temperature of welding tips. An absorption system for chilling water and heating is shown in Figure 17-34.The cooling cycle is shown in Figure 17-35A. The iefrigerant which is dispelsed in ihe evaporator extracts the heat ftom the chilled water. It is then vaporized. The chilled water then passesihrough the system.

andApplications SysiemsPrinciple5 Chaptef17 Absorpiion

703

Evaporalor Wat$(B€lrig€rant) Changos to WaterVapor

6t ji:

RemovesHeal From Absober and Condenssr

tfi:.i;;!,:,:;i;:;:!ii!ll;;ip H€atExchang& wam soiuiiontromc€neEtorts flomAbsober Cooledby Solulion

Fig)re 17-32, Absorptionrefrigetationcycle which useswateras refriSerantand lithium bromideas absotber.

Eliminalorc (copper) Sp€y Nozzl€s (Copper)

Figure17-33. Coolin1towerusedto cool condensel and absorbercooling water.Towerevaporatesabout 15y. of condenserwatet.ln doing so, it coolsrestof waterdown to wet bulb temperatuteof air. Thetower consistsof watersprays,packing sheex,overtbw tubes, make-upwaterfloat valve,and waterpump. Eliminator plateskeepwaterlrom beingdrawn into fan. Air ente6 at bottomand leavesat top.

Bl€edOff

(coppet (copp€4

(Brass)

The heatint cyde is shown in Figure 17-358.During the heating cyde, the evaporator functions as a condenser. Hot water ir the evaporatot fubes absorbs the heat given off dudng condensaiion of the refuigerant. The heated water is circulated throughout the system. Absorption system heat can be supplied by exhaust gas from another industrial or residential system. This results in large efficiency gains.

704

Modern Reifigeralionand Air Condltionn8

Figure17-34. A larBecapacity,double effectabsorptionchillet and heater.Systenproducesboth coating and heatinl.

KeTrrgerarors The following paragraphs discuss some oI the more .ommon proceduresand problemsthai the refrigeration technicianmay encounterwhen seFicing an absorytion sysiem. The basic electrical,conirol, and maintenance sen'ice can be achieved by most technicians.How ei'er, prcblems r,l'iihin the absorption svsiem should be handled by a iechnician with trainint by the When servicing tas-fired absorption refrigerators, be sure the 8as suppl)' is at the correctpressure.Check the gas pressure using a $'ater-fil1edmanometer, as shorvnin Figure 17-36.The safetlrvalve body has a manometerconnection.The amount of €iasfed to the reftigerator malr be checkedby the t'lamesizeThe flue must be kept cleanto allo ' good transfer heat. of Bmshes should be used to clean the flue. Fins on the ammonia condensermust be cleaned pe odical,v This $.ill ensure good heat removal {ron1 these If a servicecall indicatesthat the refritemtor is too cold, check the tenperature control dial. It may be set too cold. The evaporatorunit temperaturemay be lower ihan that indicatedby the i€mperaturecontrol dial set tjng. A time-temperahlregraph of the evaporatortem peratureshould be iaken. Perhapsthe most commor seivicecall r,l'illbe "little or no reftigeration." Possiblecausesinclude an overloadedcabhet, nnproper condensingtemperatures,little orno heaiing of the generatingunit a restdchonor shut oif of the gas suppl,v, and a residcted or dirty gas flue. !d- ired Ind kero-e e fircd refi:gefalor-dreequip ped rvith flues. They direct the hot gasesaround and

away frcm the generatinSunits. Occasionally, a flue may be residctedbecauseihe reftigerator is too closeto the wall. A flue also may be obstructedbv objectsblocking the opening or failint into it. Flues musi be kept clean to ensureproper funciioling of the retuigerator. After a period of operaiion,the generatorflre Li11 normally becomecoatedwith sooty deposits.\ rhen this occurs,mpid iransfer of heat from the gas flame to the generatoris impossible.This soot deposit must be removed periodically. (Usualll' once everv one h) two months is sufficlent-)Frequentcleaningalso reducesgas consumptionof the unit. When scrapingthe generatorflue or removing soot frorn anv surfaceoF the generatot take careto prevent darnageto the surface.Always put papers or cloih un der the refrigeratorr.hen cleaningflues. lf either the condenseror absorberis diriv or linicovered.poor refrigeration $,ill result. This is due to poor airflow around thesecomponents.Wipe, brush, or \.acuum away theseaccumulations. A tempora lv un{sed absorption unit mav not fteeze.Make sure the burner is lit. AiI may have fi11ed the gas line; it may take severaltdes to light the burner If the bumer is lit, the problem is likel)' due to blockage within the unit. Manufaciurersrecommendtilth8 to remove theblockage.After l0 minuies of operation,tilt the reftigeratorto the right for about 30 seconds.Then tili it io ihe left for 30 seconds-Do this thfee to four fimes, then put the unit back in the uprighi, level position.If it still does not cool, replacethe cooling unit. If the slrstemis overheated,the pipe going to ihe condensemiu overheat.The percolationpump r'ill siop $.orking.If the paint on the pipe to the condenseris blis tered,overheahnghas taken place.To rcmedy this problem, shut oIf ihe heat and alloh' the svstemto cool.Then iurn the unit upside doad several times to put the

ChapterI7

AbsorptionSystems Princples and Appl cation,

/tt5

LosT€mperalure Generalor High-Terilperat!re Generaior

Ouiler

A t

(water ii Ammon,a)I

I

HoatExchars€r _ | H€alExchanser

rwateirnammonrar fllllll Ferrs€ranr cooiis water

I r,i,Ta

chilodWal€r Hotwarer

I I

Low-Temperalure Generalor

Exhaust GasOunel High-TemperaiLre G€neralor

High-Pr€ssure VVTI/7777V7) Ammoniavapor @ Medium-Strong Ammo.iasotutionu

Oulet

I

I

X Valvec: Open

B-Heatin| cycleaf A-Cooling cycleol chiller,heater. FiSure17"35, Schematic diagrcms oi an absorption system.

706

Modern Reirlserationand A r Condit on ng

Evacuationof the systemis necessartafter the system is opened,for two reasonsl . .

To be able io reach40'F (4'C). To rcmove noncondensables.

Evacuationis needediJ the s)'siemprcssureisl"Hg. (25,400microns)or more.The pressureis determinedby a manom€tefconnectedby meansofa servicevalve.

17.14 Reviewof Safety Figure17-36. waterfilled manometernleasu,esgas prcssureto bLtrner.(CeneralElectricCo.) fluids in their proper places.Restart the 1,.ii wiih a lower heat irlput to the boiler (generator). If there is a leak, a yellow deposit .il1collectat the point ofleak. If the leak occursat the evaporator/an ammonia odor \!i11be noiiceable.A burnlng sultull candle will produce lvhite smoke at an ammonia leak.

I 7.1r'1 seillcldgI'ri$),i't'\Eio'iilSe\y$iNs Li!hiun bro,nideis a nonlotc, nonflammable,non-

exDlosive,and chemicallvstablesubstance.In a lithium br;mid€ absorptionsystem,water is used as the rcfrigerant.Lithiumbromide,a typeoI salt,is mixedwiih the r,"ateras an absorbingsolution. lt is used as a liquid. It can be handled in open containersbut becomescorrosive h'hen exposedto air. It may initate skin, eyes,and mucous membranes.Oct,vlalcohol is soneiimes added to reduce surfacetension of liihium bromide. (lt acts as a rverrlnSa8en..l Sixty-five percent lithium bromide b1' weight will stafi io crystallizeai 110'F(,13'C).Solution musi ]rot be allowed to reach high concentrationsor 1ow iemperatures lvhich a11owcrystallization. The typical chargeis a: . . . .

Lithium bromide solution 120gal. Inhibiior 1 pt. Refiigerant(water) 35 gal. ociyl alcohol (2-ethylhexanol) 1 gal.

The solution becomes thicker as the amount oi lithium bro ide increases.This will causea greateriemperature difference between reftigerator iemPeraiure and chilled water temperature.If solution conceniraiion gets too high, the refriSerant lvill lunl solid and must be dissolved.II ihe absorberbecomestoo cold (below 85'F or 29'C), sohlificaiiol can also occur Nate: ln lilhiton bromidel/slens, "stto118"koncell "Wenk"ldi hlabilitVto absorh. tnted) sal tion leansstrc1ry lltc) mednsweaki11its dbililVta nbsoth The svstemis chargedwith R-13vapor (not soluble ill water) to test for leaks.An electronicleak detectoris used. Then the systemis evacuatedcomPletelyHelium may also be used for leak iesting. However, ii requires the use of a specialdetectoror soap bubbles.

The refrigerantmost commonlyusedin the smallabsorption refri8eratingunits is ammonia.lts odor is pungent Gharp or irritating and tends to r€strict br€athing. It is toxicand iniuriousto thc skinand eyes.Avoidpuncturing the systemor cr€atingtoo hi8h a presqurein the system.A leak may result, refritCaution:Nevercut or drill into an absorption ammonia solutions Th€high-pressure eratingmechanism. are dangerous.Ih€y may causeblindn€ssif the fllid gets into the eyes. Many of the absorptionunits are heatedwith LPgas or naturalgas.The gas piping systemmL'stbe l€akproof. Al$,aysuse soapsudsto check for leaks. Never use an open flame, such as a match. An €xplosionmay occur. or a poor Theburnerfluesshouldbe cleanedperiodically flame may result. The flame safety device should be checked.To do this, smotherth€ flame and checkto determineif the safetyvalve closes. The condenser duct system and the condenser should be cleanedat least every six months. Otherwisc excessivecondenserpressuresmay result. Some absorption syst€msuse electrical current as w€ll as iuel gas.The usualprecautionsshouldbe usedin handlingthesecircuits. A circuit may becomeSround€dto the cabinetframe Thiscould resultin a shock. or part of the mechanism. To eliminatethis danger,it is a Sood;deato Sroundthese refrigerators.

17.15 TestYour Knowledge Pleasedo not write in this text. Placeyour ansr\'erson a separatesheetof PaPer. MODULT PRINCIPLES SYSTEM ABSORPTION provides heat energy in a continuous ab1. sorption system. A. Kerosene B. Propanegas C. ElectriciiY D. Any of the above

ChapterI7

2. What type of heat sourcemay be used on an absorPtionsystem? A. Elechic heat or kerosen€. B. Natural gas or LP gas. C. Steamor solar energy. D. Alt of the above. J. discoveredthe adsorptjonpdnciple. A. Tohr Dalton B. Michael Faraday C. ThomasEdison D. JacobPerkins .1. In a continuousabsorptioncycle refrigerator,what happens first as ihe temperature is lowered in the A. The flame increases. B. The flame decreases. C. The ammonia vapor decreasesD. None oI the abo\.e. 5 . why must the absorytion unit be level? A. t ril depend.on grav;$ flor\ tor FfFciel,). B. Heat generated in the absorber must be C.

Heat rcmoved by the condensermust De catr ed .h.r) .o $e ,urroundirs drmo5plere. D. ALLof the above. 6 . l4rat is provided on an absorption system to re leasethe refrigerantin caseoI high tempefatures? A. Three-wavservicevah'e. B. Fusep1ug. C. Pressuresafetyvalve. D. None of the above. 7. In a continuousabsorptioncycle,what occurswhen the name is nlcreased? A. The gas consumptionincreases. B. The systemproducesmore cooling. C. The systemefficiencyis reduced. D. The systemtemperafutedecreases. 8. Upon what does the liquefaction oI the refrigerant depend? A

nrasi dtso be desiFned io with5tdndlhe srre..and \ibrdLionsihdt w'll ocArr.Dependint upon the system type and size, the rruck unii may also utilize back-up units.

'18.1.1 Truck Refrigeration Truck refrigeration requires special trailer bodies and refri8eration units. Such bodies are 9, to 18, (3 m to 6 m) long. They use a 1 1/2 hp io 2 hp (1120W to 1490W) re{rigerating system. Bodies should be light and well-insulared. Constant vibration and rough handling might deshoy the insulating r/alue o{ the y/alls iJ ihe body is not constucted Figure 18-l illustrates a rcfiigeration system used on a trailer system. The main components are the compressor, air-cooled condenser,expansion valve, and direct expansionevaporaiorThesesyst€mscommonlyuseR-134a as a refrigerant. Figures 18'2 and 18-3 iilustraie th€ cooling and heat-defrost cycl€s of a dieset-powered unit. Vadous insulating matedals are used. Most traileE have all-metal bodies with various insulation thickress, depending on the application. Ioamed-in-place insulation is most often used. Figure 18-4 shows this insulation being installed in the side of a trailer bod]'. There arc numerous applicaiions for trailer rcftigeraljon.tach appliLdhonmu.t be.tudied beforea re;peiature may be recommended. A truck using dry ice Ior rcfrigeration must be insulated for 109"I (-78t). An ice cream truck must be insulated for - 15'F ( 26'C). Fresh foods require insulation for only 32"F to 35'F (0"C to 2"C) temperatues. Fresh ploduce, flowers, and fiuits need accumte confol of temperature, humidity, and

709

7to

Modern RefriSerat on and Air Cond tioning

ventilation. These matedals have a tendency to lose fluids to the surrounding air Thereare Iour main truck refrigerationsysiemsi .

.

Mechanical: A. Blower system B. Hold-over eutecticplate f\pendablp rerrgeranr,liqurdnirroSenand tiquid carDonoroloel

. Dry ice Mechanical refrigeration is similar, in most cases,to typical reftigeratint uniis. The major difference is the compressor drive. Two common ddves are: . .

Figure18-1. Refrigerated trailer.Refrigeration system maybe eitherelecttic,Easoline, or diesel-powered. (CarrierfransicolclDivision, CaffierCarp.)

Engine-ddvenelectricgeneratorand motor Separategasolineor diesel engines.

Electric generatorsand motors use standard voltages, cycles,and phases.These pemit the unit to be plugged into a waII outlet in the garage,and are usetul if the trailer must be kept cold while ofI the road. Units driven by gasolineenginesare automaticallycontrclled to start and stop as ihe sysiem requires.

High-P€ssure Liqud I @@ High-PrcssueVapol

E

j-1

I

DschargeLine

Low-Pressure Liquid Low-Pressur€ Vapor

|

I (sv1), No

Figure18-2, Diagramof a coalingsystemusinga diesel-powered ias en\ine,showingthecoolingcycle. Division,CarrierCarp.) CarrietTransicold

Chapterl8

SpecialRefrjgerarion Systemsand Appticariors

I

High-Pr€ssure Liqud

@

High Prcssutevapol

I @

Low-Pressure Liquid Low-pressub Vapor

'asorber

I

Figure'f8-3. Diagmm of the heay'defrost cycle af a coolin| systemthat usesa cliesel_powered gasengine (Carriet Transicold Djvisjon, Carrier CorD.)

Figure'f8-4. Iruck boclyis being irculatedwith plastic foam insulatian.Excesswill be trimmedaway.

711

(sv1), No

Somevans and short trucks use a cube-style, or thinlire. wall mounlede\dporalor.Aroot-D.ounFd orbod) mouniedconden-erand eng:re-dnvFrcompre,sorare used. There is also a remote Cab Command control module. SeeFigure 18-5. The remote in-cab module includes solid state temperature controller, tempelature selectot and manual deftost operations. Figure 18-6shows ihe inside of the standby motord ven compressorcompartment. In addition, a comPrecsormounledabo\e /dnd drivenbv) tle erginemay be used. See Figure 18-7.Most of these systemsuse a hot gasdefrosi.Somelarger commerialunits utilize diesel fuel. In some systems a generator provides power for the evapomtorfans.Figure 18-8illustratesa iypical finished instalatior mounied over the truck cab. Eutecticplates ope:fatewithout the use of mechanical assistance during normal operating.SeeFigur€ 18-9. A small electrical condensing unit is normally connecied at night. This freezes the eutectic solution stodng enough energy for positive cooling throughout the day. The plates act basically like a battery with stored energy. The euiectic plates are constructed of smali diameter tubing for circulating refrigerant. Fins are aitached to the

'71'

M o d e h R e f r i E e r a t iaonnd A l r C o n d i r i o n i n E

Baltery

FigwelS-7.

This refriBeratian compressot is driven by (Carrier lransicold Division, Carrier

Carp.)

Figure18-5. Shorttruckrciilerationcaolingsystem designed for low cabclearances. Caolingcapacityfor freshand lrozenproductsis in the rangeof 0"F to 55"F ( 18'Cto 13"C).(CanierTransicald Division,Carrier Corp.)

Figure18-8. Canpleted overthe-cab installatianaf a condensing unit of refrigeratecltruck. (Carriet lransicold Division,CarrierCorp.)

Figur€18-6. Truckrefrigerationunit. Note e/ecfflc !cadbJ

Carp.)

notat.

t

"triet

lrcn-i, alcl Di\i-ion

I dtie.

tubing and corlduct heat from the refrigerant inio the eutectic solution. The assemblyis inserted beiween iwo wiih euieciic steelpans.The condenseris vacuum-fi11ed solution that freezesat a specificiemperaiure-Various sizesare available. Ice and dry ice are seldorn used today. Ice is not used becauseoI iis weight and load requirements.Dry ice is lighi and requiresno drainage.Howevet it is seldom used becauseof diffict ry in controlling and main taining specifictemperatures. Another form oftruck refrigerationinvolves ihe use

Figure'f8-9. Twa KOLD-HOLD plateevaporatars installed in a reftigerated truck bady. (Tranter,lnc. cauftesyof HackneyBrathercBody, Wilson,N.C.) of liquid nitrogen and liquid carbondioxide. In this system, $'hich provides excellent low temperature iefrigunit is not needed. emtion, a cor'rdensing

Chapterl8

SpecialRefrigerarion Systemsand App, car ons

713

18.1.2 RailcarRefrieeration Refrigeratedrailcars,long used to transpori perish __ abie goods, often have mechanical re{rigeiation. Car construction and insulation is similar to that of the fruck r-diler 1*o gcreraltvpe, of coolingr-e u,ed on trarnLrreght -plr.gerd,,on and oa.>enge. car : r condi. Like truck refrigeration, there are foul methods of freight refrigeration: . .

Mechanical(used exctusivelyon passengercars). Chemical(expendablereftieierant).

.

Dry ice.

Compressorsin mechanicalinstallationsare usually driven from the car axle while railcarsare in motion. A; electdcmotor is used while cars are stopped or held in the rail yard. Sometrain refrigention systemsuse the absorption sysiem.Othe6 use the steamjer sysiem.

18.1.3 MarineRefrigeration \4drinerefrigeration equipmenfl. ba(icdllythe,arre _ a. ldrd ba,edrefrighouldbe lepl Lo d minimum. lf Lhetelo'ity can.roi be d"..eas"d, noise may be rcduced by other means. An acoustical dischafge chamber may be used' The ducts may be lin€d or wraPped with sounctabsorbing matedal such as felt

19.'11.1NoiseMeasurement Sound waves are rapid changes of air pressure The amplitude or stren$h of the sound pressure waves may

756

Modern Refrigerarion and Air Conditioning

be measured. Sound strength and sound piesswe l€vel (SPL) are rated in decibels (dB). Two woras are useo m connectionwiih the definition of soundl Souftdstftngth. This is the total amount of sound, in decibels,coming from a unit. Sound,prpssurc.lhj. i. rhe strengrh.rn de, iber -({ "+ ("N'4

Fiqure2l-71. E^ptode(ltiew of lun'type oil burner' 1 Air tube combination.2-lBnition transformet3 Drive -'ota,. +-Blo"ei uneel s-Fte\ible rcuplng 6-Burner housingassemblv,with inlet bell T Pedestalsuppott |-lJnit flange,at squareplate. g-Nazzle line escutcheonplate l1-Hole plu! wiing box 11 Bulkairband' 12-End aiishutter.13-Fuel unit. 14-Pump outlet fifting. ls,Connector tube assembly.16 Extendedpedestal. I7-Adjustable mounting flange.(R.W.BeckeftCoQoration)

Chapter2'l

Heatingaid Hum diJicaton Systems

825

is fastl) The excessair also allows for airflo$. deffease in the pedod between fumace inspectionand cleaning. (Fanbladespick up lint, causingairflow to decrease.) Excessair will slow down evaporationof oil droplets. Adjusting an oilburner to obtain a p6per flame can be misleading.A flame may look like ii needsmore air when it does not. This may be due to a dirty nozzle or impingement (striking the choke vanes).It may also be due ro oil ledla8eduflng Lhe'off" pdrt ol lhe rycle. The only gootlway to checkan oil bwnet is z|itl1i11' stru le ls. Usea CO2allalyzer,orVgetlnfialV2er, slnokelesl, 5afell de\i(es dre in'ldlled lo droid \prdring unburned oil into a furnace (a dangeroussituation).Safety devicesalso prevent continuousoil pump operation in caseof ignition failure or if the oil flame goes out. The stackcontrolis on€ method.SeeChapter26for oil burner controis and wiring circuits.

21.25 Gun-Type Oil BurnerPumps Sevelaltypes of fuel oil pumps are used in gun oil burners.Theseinclude th€ geartype and ihe rctarytype. The rotary oi1pump is morc common,but the SeartyPe is more easily selviced.

FuelOil Pump 21.25.1 Rotary-Type Figure Rotarypumpscomein eithersingle-stage, of 21-73,or iwo siagemodels.Theiniemalconstruciion rotaryfuel oil pump is shownin Figure a single-siage 21-74. The oil supply systemcarriestuel oil ftom the tank through a filter in the line. lt is caried through the inlet

FiEurc21-73. Single-staBe 4un typeoil burnerluel pump. Notearrowon nameplate showinEshaftrctation lnc.) lndustries, direction.(Suntec

Ei9ure21-74, Single'staierotaryiuel punp for gun-typeoil burners.A-Shali. B Shaft seal.C Punp rotor.D Pumphousing.suntec lndustties,lnc.)

screen to the pump. From there ii goes into the pressure rcgulaior and relief valve. The Pump rotates counterclockwiseand oil Ilow is from toP to bottom in FiSure 21-73.Note ihe shaft dircctionarow on the pump nameplate. The oil leavesihe lower central axis of the pressure regulator and passesto the gun nozzle. This is shown in Figure 21-75. Anothef design for a single-stagerotary fuel oil pump is shown in Figure 21-76.The inlei is ai ihe bottom 1eft.The return/bypass is at the bottom ri8ht. The outlet is at the top leIt. Many systemsare equipped rviih a iwo-siage tuel oil pump when the two-pipe systemis used. Part of the oil is rctumed to the tuel tank. The pdnciple of operafion is shown in Figute 21-77. SelectionoI a single-stageor tno-stage PumP is determined by the limitations of the oil itself.Most singlestagepumps are sold for inlet vacuumsof 7" Hg (78kPa) single-pipe.(For iwo-pipe, inlet vacuums would be 10' Hg t68 kPal.) When fuel oil is subjeciedto a vacuum . t li Hg l 0 H B . r i s r a r l , l o . o m ea P d r tA (51 kPa), it is a mixture of foam and clean oil. A twostagepump is shown in Figure 21-78.It is Ported so thai, at 15"Hg, the second(pressurestage)inlet is submerged in clean oil. The intake from the tank is at the toP. Oil pa,,e. throughLnefir-l.tdge of the pump inlo lhe -eguldrof. from lhere it p.5.F- bdcl io thr Lanl. The sF.ord stage removesonly oil from ihe strainer chamber'The oil is pumped into the nozzle. Excessoil is returned to the strainerchamberin somepumPs.It is returnedback to the tank in oihers. Details of the relieI valve are shown in Figure 21-79. Oil prcssurecreatesa force againstihe Piston.When ihis force equals the compression spring force, ihe Piston moves down. This permits oil to flow back into the pump rnlet.

426

Modern Reirlgefationand Air CondiiioninS

Diaphragm Valve

ToSea Clramber

Caulion:Thisvalvemust or an aulhodzed setoice Fleturn

Retumpon

Figute21-75, Diagran af ail flow thtougha sin9|e-stage oil pump. The iour colorsrepresentthe dihirent pressure levels.Creen-Suctian or inlet pressure.Red-Cear prersure.yellow-Nazzle pressure.Blue Returnptessure. (Sunteclndustries.lnc.)

Figurc21-76. Cutawayal sinqle4tagerotary tuel ail punp for oil burnerc.(Sunteclndustries,lnc.)

of the gea$. In B, the oil then goesftom the lower suc tion side to the upper pressureside of the gears.It nows into the valve. At a pfedeterminedpressure,the valve piston moves. The oii flows out the nozzle port. ln C, the surplus oil reiuins to the ftont chamberthrough the surplus returll passage.Oil lubricating the internal shaft and seal rctums io the front chamberthrouSh the seal drairl. Nozzles are generally of two types. The 60' type gives a hollow cone spray pattem. Thesehave a capacity of 0.75 gph to 1.75gph (gallonsper hour). The 60' hollow-cone9pe has a capacityof 1.75gph to 12 gph. A nozzleline Ileater(Figure21-82)maybeused on some oil bumers- It maintains oil temperatureand viscosity du ng off cycle in ambient situations. The oil is heaied to 120'F to 130'F (48'C to 54'C) at the oil nozzle. This improves the ignition and ol,erall combusLion. The gun-type oil burner is an efficient heating unit. However, ii must be properly maintained io give peak performance. AIr experienced technician should check, clean,and adjust the sysiem eachyear Someof the important items to checkare shown in FiSure 21-83.

FuelOil Pump 21.25.2 Cear-Type

(Transformer21.26 Electrical lgnition Electrode)

The gear-typeoil pump is avaiiablein both singlesiage and tr,l'osiate models. FiSur€ 21-80 shows the externalappearanceof a sinSlestasegearpump. Singlestage pump operation is shown in Figure 21-81.In A, the tuel oil entersthe single-stageunit and fills the ftont chamber.The rotating blades tiiter the oil. This occurs as it passesfrom the froni charnberto the suction sides

Gun-type oil burners generally use electricalignition. Ignition controls are describedin Chapier 26. The system includes a transformer and two electrodes The transformef is mounied on the oil burner Ii transfoims l20 V ac to about 10,000V ac. The igniiion sys tem must raise the oil temperaturekr 700'F (370'C)for

Chaple2 rl

H e i t n g a n d H u m L d r f , co. rnt 5 v s t e m s

827

Chamber

Dlscharge

To Nozzte

Serond^Slag€

BalancedBeliefValve pump fctroil burners,LEe(lwith twa-pipe systemfrcm storagetank Note the flow of some Filute 21-77. Two-stage ail back to the storaeetank.

EigrJIe21-79. Cutawayview of relief valvefor a luel oil punp. (Sunteclndustties,lnc.) ti9urc 21-7a. Two stale fuel oil punp used with tl/vopipe systemfrcm storagetank. lsunteclndustries,Inc.) buming to occur The electrodes,made of stainlesssteel are mounted in ceramicinsulators.No part o{ an electrcde should be closer than 1/{'(6 mm) to any metal part. The electrode ends are Positioned in front and above the nozzle. The aiomized oii swirls out of the

nozzle and mixes wiih the turbulent air. At the same time, a spark jumps betweenthe electrodeends and igniies the mixture. The ignition may be continuouswhile the oil bumer is in operation, or the ignition may oPer' ate only until the fuel i8nites. The etecirode gap should be between 1/8" and 3,/16"(3 mm and 5 mm). The electrodeends should be approximately1/2" to 5/8" (13mm to 16 mm) abovethe nozzle, and 5/16" to 1/2" (8 mm to 13 mm) in front of the nozzie. For over-45' nozzles, this last dimension should be apprcxi ately 1/2" (13 nm). For 30'nozzles.

828

Moderi Refrgeratlonand Air CondltioninS

Figure21-80. Sin'le stagegearpump for Eun-typeoil burners.lsuntec Industries,Inc.)

B

Figurc 21-82. Nazzle |ine heaterattachedta combustionhead. (CarlinCombustionTechnolagy,lnc.)

C

(Webster Heating) gearpumpunit operation. Figure21-81, Single-stage the electrodeends should be 5/16" (8 mm) in ftoni of the nozzle. Refer to the manufacturer'sseryicemanual for exactsetiiig specifications.The porcelaininsulators must be kepi clean or the hiSh voltage will short. The spark should jump a 1" (25mm) taP with the blower off. Aflame inspectionmiror, Figure 21-84 canbe used to observe ignition and spray action. This is done to checkif operationis normal. Delayed igniiion and a pu{t-backmay be due to any oI the following: . . .

Weak ignition. Wrong Position of the electrodes Poor insulation,

Figure 21-85showsan ignition transformercase.An ignition transformerand iine voltage tesiing instrumeni is shown in Figure 21-86 A p flack is the ignition of a large amount o{ va' podzed oi1 in the firepot. Sometimes,it will blow soot into the furnace room and into the living quarters This makes a major cleaning job necessary.In no case should the elechodeends be touching ihe oil sPray.If they do, the electrodes r4.ill become carbon-coated Moisture in the oil will retard combustionand may even cause a "flameout-" When a flameout occurs, combustion stops but fuel continues to feed into dre combustionchamber.If rnoisture is causinSPoor combustion, colltinuous i8niiion is usuallv lecomme ded'

Chfper ?l

H e r t n Ba n d H u m d r i L d to n S v s r e m s

829

.:t:j::::':l -,:1.;

Figure21-83. Six nain itens to be checke.Jat saft of each heatingseason.l-Sllutofi valveand line fiheL Replace 3 Clean strainerusin! filtet cartridle. 2-Check and cleannozzle assenbly.Fallow nDnufacturer'srecommenclations. cleaniuel ail or kerosene. +-Check connectionsfor tiljhtness.5 lnseftpressurcSaugetntopressureport. Stanbunrcr anclacljLstpressureseftin1tonanuiacturer'sspecifications,usuallyabout IOApsig 1115psiaar 79A kPa).6 Pressure gaugercaclinSfar correctpressurcsettinS.6untec lntlustties,lnc.)

21.27 PrimaryControl The primary control unit has two main tunciions. First, it provides the meansfor operaiing the unit. lt re ceivesthe low-voltagesignal frcm the room thermostat. This carisesihe burner notor and ignition transformer io operate.lts second tunction is that of safet)r If the burner does not ignite, or the l'lameis extinguished,it rvill tdp the primary rc1aysafety switch. The primary reiay must be reset manually.

Oil burners must be installed with great care. A completeinstallationincludesa 200gal. to 1000gal. storage tank, hand shutoff valve, filter and trap comb;nation, and copper tubing oil line. Figure 21-87shows an installaiion for a one-pipe sysiem. The storagetank is locateditl ihe room with the fumace. Rememberthat th€ storag€tank should be al least 7' (2 m) away from th€ furnace. In this installaiion, oil feeds by gravity to the oil bumer. The storagetank should be elevatedlessthan 25' (7 m) above the burner. This $.ill keep the feed line pressurebelovr 10 psig (25 psia or 170kPa). Othen'ise, a pressure-reducingvalve must be used. In someinstallations,ihe ftlel tank is placed outside the building, eiiher aboveground or underground.Some

loca1codesallow only 3 psig to 5 psig (18 psia to 20 psia or 120kPa to 140kPa) on the pump inlet. The two most common installationsare: . .

Placing the tank above the oil buner, as in a resa dencewith a basemeni.SeeFigure 21-88. Plac g the tank below the oil bumer level, as in a home without a basement.SeeFiSure 21-89.

These installations should have the iank located within a reasonabledistanceof the oil br.rrnerOn runs of50'to 100'(15m to 30m),3/8" (10mm) tubingshor d be used. For runs of 200'io 300' (60 m to 90 m), 1/2" (13 mn1) tubil1g should be used. The nanuJacturer's specilicationsshould be checkedif the oil must be raised The oil iank should be installedwith a slighi slope away ftom the oil line connection.This provides 2 low spot in the tank for diri and lvater to collect.The vent pipe is very importanti . . .

Ii provides atmosphericpressure inside the tank and permits volatiles to escape. Ii must be designed .ith a 180"bend (to keep out di and min). It must have an opening that is above the hiShesi possibiesnowfall or other blockage.

The oil fill cap shoulll all{'avs be in place, except when filling the iank. The cap helps keep the tuel oil cleanand reducesthe chancesof fite ot exPlosion.

Figure21-84, tnspectianni ot usedto checknazzle condhion.electo.Jecanditian,and flame. 4

TFtp.t opin7 tdndtp

B

HrtLP

I

UP dt nr,.t

VoLlnnB pl"t Figure2f-85. l1n tJn ttdr'iotnF] \ o t 4 e ( r , o 4 ' . I - H i E h ' \ o t" g P B - L o r \ o t t a g ep n " t j , secondaty bushing. D-Hi8h volta4e teminals (Dongan

Figure21-86. Ignitionttansfarmetand line voltage terter.A-Cannection an{l testinstuctions. B-Hign-oltage rtnpcr ' annc tion' C t'nPAnd hilh-\alt"8e rnact. D loq tolaBe lead' to [an'[otmP' (DonganElectricMfg. Co.)

Eigwe 21-87. Typical gun type oil bunet hnattation Note fill pipe, vent pipe, and ail line installation (Webstef HeatinE)

ElecuichlfB.Co.) As stated earlier, the fue1tank is olten located outside of the building, either above Sround or urlderqround. It is important to rememberthat oil and ivater ;o.oi mix and measuresshould be taken to ensurethat no water is allowed io seep into outdoor tanks Boih above grourd and undeiglound tanks require a suitable e.c(et drounJ tl'e prug to prP\enlwiler seepageThe ir.rg ana gr.Ler m,-t be t 8r-t dnd kFPlrn good cordrrion: lhF ierr pipe mu'' hd\e a 'fuerded.aP dnd be located above the "snow line" and away from gutter do$rnsDoutsand roof edges. Uirderground tanks-require piPe fittings to be tight ened and all threads be sealed with a temperature

resiliert .orpound \e\er u'e leflon idpP l^o'e or p o o r l y 5 e d l e di o L l l ' h i l l d r o s g r o u n d r d t e f l o i n J i l t r a L e

ihe siorage tant. During installaiion, keep ihe tubing ends sealedwith tape to keep dirt and moisture out. Remove the tape when connecting ihe iubing. The 3/8" or 1/2" (10mm or 13 mm) OD coPperiublng is aitached to the fittings with standard SAE 15' flares. Flaring techare discussedin Chapter2 nioues ' With both underground and above ground tanks, it is sood practice to check the iank with water finding oaJte before each fill-up or at least annually. The paste ihanees color when waler is Present Any accumulation shoul'd be pumped out. A leaking tank must be rePlaced in accordancewith local and other codes.

C h a p t el,l

oi

shuroli

figure 21-88. CLlnIype oil burner installationwith storagetankinstalledunderBround,but above oil burner. Note two ail lines.(WebsterHeating)

H € a t j n 8a . d H u r nd i f c a to n 5 ! n e m s

831

The oil bltmet ifistallatiofl tfi1.tstbe fiLde in accotdance with lacal codesand the man lact rer's instructions. The bumer must be the correct height above the bottom of the combustion chamber Burners are mounted either on adjustablelegs or on a flangebolted to the fumace. The buner air tube and nozzle must be inserted into the combustion chamber an exact distance. The distance must be exactly as the manulacturerrecommends.The openint inio the furnacemust be cafefully sealedto prevent air leaks.(Somehave flange adaptors-) The nozzle must be the correctsize,and it musi be in good condition. The nozzle o fice (hole)size and the amount of oil pressuredeterminesthe rate at which fueI oil bums. Therefore,this also deiermines the rate at which heat js produced.The size of the nozzle selecied must match the heating requiremenis of the heaied space.IJ the nozzle is too small,the bumer may not heat ihe space adequately.If the nozzle is too large, the bumer lnay tum on and off quite frcquently. Nozzles are usually supplied with a line Iilter at iheir in1et.The filter is designedto eliminate ihe possibility of dirt entedng and pluSSing the nozzle. Be carefulnot to twist the tube or move the nozzle tube oui of line. A tool for safelyremoving the nozzle is shown in Figure 21-90.

Figur€2'l-89. Cln type oil burner installatianwith stange k nk undergro uncl, below the level of oil burner.

Tankslocatedoutdoorsand aboveground may genente $'aier through condensation.Use ihe following service techniqriesto alleviatethis problem. .

. .

Paint the tank silver io reflectthe sun's rays and reduce thermal expansion. Locate ihe tank ll1 a shadedarca iJ possible. Insiall the tank so the fill pipe end is pitched facint

Figure21-90. Toolfor removingand installingnozzles. A Nozzle tube socketwrench and handle. B-Nozzle socketwrench and handle.(MonarchNozzle ConpanJ,)

Keep ihe tank filled during warm weatherto reduce air spaceat ihe top and minimize condensatlon.

The oil Iines in the tanks should be mounted so the tubing opening js 3" to 4" (7.5 cm to 10 cm) above ihe boitom o{ the tank. The return oil line, if ihe systemhas one, doesnot need io go near the botiom of ihe iank for light oils (Number 1 or Number 2).lt should go to wifiin 4" to 5" (10 cm to 13 cm) of the iank bottom for hea\T tue1oil.This will keep the oil more fluid. Neverusecompression fittingswith fuel oil systems.

Before starting the oil burner, air should be rcmoved ftom the lines and the pump. A vent plug (air bleeder fittint) is mornted in the pump housing. Usually, this vent plug sealsthe Port used for pressureSaugeinstallf €noughoil and air collectsin the combustron chamberand ignit€s,anythingmal happen Theremay

432

and Air Condilioning Modern Refri8eration

be a puff of flame or an explosion,The explosionmay be forcetul enoughto wreck th€ building,and maim or kill. Inspectthe firepot. lf oil is presenl,shut otfoilvalves and v€nt the combustionchamber.Removethe oil by means of a suction pump, rags,etc. Continue removal until all dangerof oil fumesis gone.Usean explosion-proofflashlight. Air in an oil line will lorm bubbles, which could result in: . . .

Oil not being pumped. Blowbacks. Flame failures.

The line must be completely Pu€ed of aii A twopipe >yslemredlrce: lhe ' hdnceof air remainjnt in t]1e iy'tem. Ho-ever, air can stili be rrdPPedjn hiEh sPo,. in the lin€. A leak in the oil line will alnost always cause air-in-line houbles. Always check the fuel oil nozzle to be sure ii is the correct size. Also be sure ihat it is in ihe center of the gun air duct. The electrodes musi be kePt clean and in aolleci relation to the nozzle Figure 21-91 shows a tlPi(ai orl burnernozrle. Ihecenorzle' comein \driousLdpacrties.AI'are basedon Sdllonsper hour igPh\ al range from |00 psrg { ll5 psraor 7q0 lPar. CaPacities gph. la-rge enough lo gph nozzle5 dre 28 Some to 0.40 feedibO gph. A I gph nozzte delivers 140000 Btu hJ Thus, iJ the overall efficiency is 60%, the usetul heat woutd be 84,000 Btu/hr. Poor oil deiivery may be the rcsuli of clogging. The main filter, the Pump filter, or the nozzle filter may be partialy clogged. Check all three filtering devices when seruicing the unit. Fdme {ailuie may be caused by one or more of the following: . . . . . . . . .

Oil tank out of oil. Oil tank not vented. Clogged filter in oil line. Ice in tuel line. Loose oil line conneciion (air in line) Dirt in supply line. Water in supply line. Loosewiling or connections Motor not running (check reset button).

. . . . . . .

Defective pump. Pump iosinc prime Changing pressure or low Pressure at Pump (sliPping coupling). Clogged nozzle. Damaged nozzle. Improperly installed bypass plug. No spark at electrodes: . Loosewiring. . Bad transformer, . Low voltage. . Crack in electrode porcelain. . Elechodesca$oned. . Electrode spacing too far or too close. . High-voltage widng loose.

Pfoper flame appearance is luminous (mainly yelIow). If there is insuflicient air, the flame turns dull orange or rcd. Th€rc may also be smoky tiPs io the flame. Figure 21-92iltusiratesa Properly adjustedflame. The draft in the firepot is measured by th€ air prcssure drop (in the firepot). It should be aboui 0.02"to 0.05" (0.5 rffn- to 1.3 mm) WC. (Use an inclined water tube manomet€r.) See Figure 1-16. This check will also helP determine if the automatic draft is working Foperly Some oii burner moto$ are reversible FiSure 21_93 shows the method oI rcvelsing one ilPe of oil burner motor Controls for oii burne$ are described in Chapter 26. Testing instruments are described in ChaPter 23.

Elfl.re21-92. Gun-typeoil buner flame (Catlin CombustionTechnoloqy,lnc.)

Threads Fieure21-9I. Stainlesssteelnozzle used with qun-tvpe oi buners. Notefine filterat nozzle inlet. (Monarch Nozzle Campany)

Fiqure21-93. Methodof reversin!dircctionof rotation by oian oil burnermotor.Thisis accomplished |ines dashed by wircs, as shown two reconnectini

C h a p t e2r l

lnspect the electrodewires. If they are cracked or brittle, replace the wires. lnspect the elecirodetubular ceramicinsulators,If the ceramictubes are cracked,replace them. Soot deposiis in a combustion chamber typically collectr'hen the unii first starts.The more often the unit siarts,the greaterthe soot deposit.A .onectly sized oil burner that operateslessfrequentlywill depositlesssooi in ihe furnaceand stack. If an oil line is dnitr or clogged,b]o .it orlt L'ith nitrogen gas.Always use a pressureregulator and relief vah'e. Neverus€compressedair or oxygen!A violent explosionmay result.

Oil bunef pfoblems, synpioms, and possible causes are glven in the following troubleshooting outL Burner motor does not start, starts and locks out (CAD cell shuts off the control sh'ltch),or cycles. A. Does not start. 1. Relaydoesnot close(will not closeor contacts difiv). 2. Saiet,vlockout siays open. 3. Bad relay coil. 4. Lo$, voliage. 5. Open high limit control. 6. Broken lvires or loose connectior.". 7. Rela)rtransformeropen. 8. Thernrosiai open (dni on coniacis,loose or dirty connections). 9. Siack s\aritchoperl. 10. Heat sensingcor'\tacts out of place or open. 11. Motor overload open (bul.rled out, or has dirty contacts). B. Starts,bui locks out. 1. No fuel oil oui of nozzle. . Clogged. . Pressuretoo 1(r\r . Punp noi working. . Loosemotor couPl g. . Air leaks in fuel line. . Fuel oil line hand vahe closed. . StraineF or screensclogged (fi1ier,PUMP screen,or nozzle strainer). . The pressureregulator h the p mp is stuck open. . Vent on fuel oil tank closed. . EmPty fuel oil tank. 2. Fuel oil coming out of nozzle but no lgnition. . Electrodesnoi positionedco ectly. . lnsulators cracked. . Ignition wires worn, loose, or with dirtv . Transformernot operating. . Pdmary wires rvorn, 1oose,or with dirty . Low line voltage.

H e a t i n ga n d H ! m i d r i . a t i o nS y s t e m s

833

3. Fuel oil to nozzle,igniiion OK, but no flame. ' Clogged nozzle ' Cloggednozzle strainer . Nozzle loose. . Pressuretoo low . Fuel oil too heavy (wrong oil or too.old). . Excessiveair or too nuch draft. . Electrodesin h'rong position. 4. Flameburns only a few seculds. . Flame sensornot in conect position. . Stacks(.jtch not operatirg correcily. . Excessii'eair or air too cold. . Flameis too lean. C. Cycles,but not on lockout. L Thermostatdiflerential too close. 2. Anticipator set too close. 3. Limit s 'itch sei ioo lo\,'. 1. Overfired (reacheshigh iimit temperahlretoo quickly). II. Burner does not operatecorrectly. A. Smoke,soot, odors, and/or pulsaiing sound. 1. Wrong oil pressure. 2. Flame touchescombustionchamber. 3. Not enough drafi. . Diri)r chimney. . Draft control is out of adjustment or it is stuck open. . Dirty flue. . Either the combustionchamberor ihe heat exchangerleaks. 4. Poor mixht of ai and oil. . \ , z , . l e r -* ' " r . r u - . d i r l ! . o d r p . . . Oil pressuretoo lo!\.or hith. . Poor air !'elocity and turbulence. . Not enough air (shutter closed too nuch, fan bindhg, or iighi beari]lgs). B. Puffs back. 1. Water in oil. 2. Delayedignition. . Electrodesnoi positionedcorrectlyorl.rose. . tnsl ators carbonized. . Nozzle i{orn, loose,diriy, or drips. . Voltagedrop $,hen bumer starts. . Oil pressureioo low or too high. . Transfomer leads looseor difty. . Transformernot operating collectly . Excessiveair or high draft. C. Noise. 2. Looseshutter. 3. won pump. 4. Dirty strainer. 5. Air in oil line. 6. Transformerhum. 7. Draft control vibrates. S Motor couPlinS 'om. 9. Motor and pump not lined up cor:recuy. 10. Relay contactsnot seatingtishily. 11. Oil suction line restricted. 12. Motor nounting toose.

834

Mod€rn RefriSeration and Air Condiiloning

13. Tight motor beafnts. 14. Tank hum. D. Fuel oil consumptionis too high. 1. Nozzle is worn, 1oose. 2. Combusiion chamber is diiiy. 3. Too much combustion air (heat escapesup flue due to high flow of flue gases). 4. Poor mixing of air and oil5. Not enough draft over tue. 6. Air leaks into combustion chambei 7. Oil pressureioo high or too low. 8. Ovedired, as noted by a high stack temPerarure There are two ways to check combustion efficienry The tust is carbondioxide (COt analysisof flue gas.The secondis by the temperatureof flue tases. 1. Use a carbondioxide analyzerto checka sampleof flue gas.It should be 10%to 1270CO, without visible smoke. If the reading is too low, it means ioo much air: . With 6% COr, 155%excessair is used. . With 8% COr, 857' excessair is used. . with 10%Co,,50% excessair is used. . Wltl112% COj, 26Eaexcessair is used. 2. IJ the iemperature of the flue gas is too higl! a considemble amount of heat is beinS wasted. If the flue gas temperatureis too low, waier vapor condenses in the l'lue oi chimnel The small amount of sulfur will form suuurcus acid (H,SO3),which is very corrcsive, With a 10%to 12%CO, stackanalysis,combusHon efficiencyis as follows:

Temp. "F 1000 800 600 400

Temp. "C 538 427 316 204

Perc€ntageof efficiency 65 to 69 70 ro 73 76 to 79 82 to 84

These are flue tas temperatures minus furnace room air temPerature.

HEATING ELECTRIC

MODULE

21.31 ElectricHeat The useof electricityto heat homes,stores,commelcial buildings, and factoriesis steadilygrowing in Popu-

.

. . .

The eiectdc heating processalso has some disadvantages,however: ' . .

The cost per unit of heat is higher than for some other tuels. Humidity control problems may occur Added eleciiical circuits are required.

of ElectricHeating 21.32 Principles Electricity is a form of energy. Since one form of enefgy can be changedto anoiher form of ener8y,electical energycan be changedto heat energy. Heating with eiectdcity can be done either directly indirectly: or .

.

Direct heat. . by pa..Ltga l'edtint.acconplisl_ed Re5rstance (Air heated elemenl fluid over an electrically some urlits use water) the fluid, although is . Radiant heaiing, accomplishedby heating an elemeni to a temperaturc high enough to Sive . Thermoelectricheating.SeeChapter 18. Indirect heai,by using a heatpump. SeeChaPter24.

of ElectricHeating 21.33 Applications Electdcheating has a wide range o{ applicaiions.It may be used for heating oPerations in industdal processes.Examples would be Iast drying of Paints and melting of low+emperaturemetalsor metal aIIoys.It has been used for domesiic and commercial cooking and baking. It is often used for Providing hoi water' r;r reside,lrial use.elec.';.hertin8 hd. d growirS . .

hriry

of electricheatarei Someadvantages . Low fust cost. . Elechicheatingdevicesneedno oxygenand, therefore,no air suPPlY. . Hishest temperaturesneededarebelow ihe igniiion temperatureof most materials There-

forc, ihe system is considered safei than other heating systems. Due to ihe absenceof combustionand combustion gases, there is less danger of toxic conditions arising. No chimney is needed. Equipment normally requires less space than other systems. Individual room temperature control is easily obtained. Very clean operation.

The only sourceof heat. Supplementary heat, even though some othei system provide.mo{ oi ihe heat In lne re\iderLeTt i- al.o u,ed where the heal lodd ic low Hedf pump systems may use electric resistance heatinS' It is used \a'here the heating energy requiled durint cold weathel is more than the system can

supPly. .

Reiistance heating provides heat ii parts of a building that are not well-heated. It may be used in

Chapter2l

Healingand H!nridiiicationSyslems

83s

areas oI a building where heating by the standard system would be unsafe. Resistanceheating ajso may b€ used to heat additions to buildings. The presentsystemmight not have enough capacltyto heat the addition. Perhaps the extension of the present system would be too costly.

21,33.1 ElectricFurnaces Electricity may be used to prcvide heat for walm air or hydronic central heating systems.Thesefumaces have capacities rarying ftom 34000 Btu/hr. (10 kW) up to 120,000Btu/hr (35 kW). A forced-airfurnace that uses tubular heating elements is shown in Figure 21-94.This tumace can be installed for upflow do$'nflow, or hodzontal airflow The heating elements are used in stages o{ 5 kW or 10 kW. The elementsare sequenced(turned on one at a time). The electncal cfucuitsare shown in Figure 21-95.Note ihai the incoming power is 240 V while contrcts are

24v.

A hydronicboiler is shown in Figure21-96.This boilerhasa capaciiyof from 34,130Btu/hr (10kW) to Biu/hr. (24kW). It is a very efficieniunit. It mea61,900 suresabout10 1/2" wide by 21 3/4" high, and 23 3/4" long (aboui25cm x 50 cm x 60 cm).

Eigurc21-94. A farced-ai furnacewith tubularelecttic rcsistanceheatingelements.1 Warm air autlets. 2 lnsulatedjacket. 3 Fanantl linit contrcls. 1-Electric resistanceheatingelements.5 Operating controls.6-Fan outlet. 7 HeatingchanbeL q-Fan and motor.9 FiheL 10-Funace base.

.1,.

: trl r "-"-. ,|]

"JR.LA?.oNrAfisPDr

(CenetalElectricCo l FiBure2'f-95. WirinBdiagramol electricfurnace,withschematic.

836

Modern Reirgerationand Alr condiiioning

Relief

Oullet

DrainValve

Figure21-96. Electricallyheatedhydranicboiler.

Elect c tumaces designed for wam air usually have several heating elements. These elements vary ftom 5 kW to 10 kW (17,000Btu to 34,000Btu) each.They are usuallv sequencedby a relay Panel.The relay Panel energizesthem about 30 secondsapart, one after the other. Tlie thermostat is usually the low-voliage tyPe with two heai stages.These heat stagesare Put into oPeration ftom 0.5'F to 1.5"F(0.3"Cto 1"C) aPart. The total furnace output should be about 2070over the design heat load. The extra 20% car be wired and controlled to turn on to handle excessiveheai loads. It is used durint thosevery rarc iimes when the heat load exceedsihe desiSnload. HumidifieE are rarely needed wiih electic heat.

ElectricHeating 21.33.2 Supplementary Electricityis often used io heat building additions They may have a heating plant without enough capacity to carry ihe extra load. Also, it is used uhere extending - the presentslstem rdould be difficult. -nav be u>ed Varlou-type: o. -upplenelldry hedt for ihis purpose. Radiant heat Panelsmay be built into the wall. Baseboardheaiersmay be insialled.Resistance heaiing wire may be embedded in the ceiling or wall plaster. Added bedrooms, family rooms, and utiliiy rooms may be heat€dthis waY Units may be used either as a Primary heating sourceor as a suPplementaryheating source Aii enters al the top. A fdn lorce)tl_edir down overlhe elec.ri'dll) hedtedelenent.Alr lea\ecthe unit tluouBh lhe oser part of the grille. SeeFigrlle 27'97.

heatel Figurc21-97. Wall-mountedelectric resistance that may be usedfor eitherprimary heatingol supplementatyheatinS.Operationalcantrclsate on the Ieft side of the tap panel. (Marley Electric HeatinS, A United Dominion Comqany)

of ElectricResistance 21.34 Principles Heating ln electric resistance heahng, metals are generally used as heating elements. The metals are designed to permit a certain cufient to flow io Provide rcquired heat (This may be at either 120V or 240V) Someunits are designedto oPetateal blcanilescefit 'glor\rngrlen1perrfurec. SomFurlii. dremourled in Protic'ed .lbirer'. Tlpes of 'y.tem- u-ed are baseboaro units or wires installedin floors, walls, and/or ceilings. The systemswhich do not glow are descdbedas ttotritr.indescent temperabfte nits. The higher the heating element temperature, the smaller the space it must occupy.Some units are de-rBnedw:th hrBhienperaturehea,ingelemen|s.They hedtirtg energyand radiarl reled-eborhair {convecrionr energy. Electdcalenergyis changedinto heat energyin the following ratios: 1 watt = 3.415Btu/hr 100 watts = 341.5Btu/hr' 1000waiis = 3415Btu/hr. The voliate multiplied by the amperageflow in a .irc1lrrequalsthe !\attaBe.At 20 amPere'ma\inum input, a 120V circtlit wi]l Provide:

2400watts(20x 120= 2400)or 8196Btu/hr (2400x 3.415= 8196) [xample: A homeneeds50,000Blu/hr. for heating. ll'is homewill needlhe follosing Therelore. amount of electricity.(The amount is given first in kilowatts, secondin kilowaft-hours,third in amPercs.)l (Bfu/hr) bru/nr.=-wwaffs

laundry bathing, pets,and other soutces.ComParedto sourcesof heal that rcquire buming, electdc resistance water heatingproducesno draft.It doesnot pllll excess it with drierout5ide dir. r aporour.andreplace

21.34,2 ElectricResistance HeatingElements There are three iypes of electdc resistanceheating . . .

In better Iorm:

(8tu/hr)

437

Heatingand HumidificationSystems

Chapter21

oPen wire open ribbon. Tubular cased wire.

Figure 21-98shows some heatiry wire designs.Looped wires are used in some electdc resistance heating elements. Th€y transfer heat betier than straitht wires. A looped wire also helps ihe manufacturer get a controlled

|'bru/ffrI

L *"it I

50non Waits=-:14,b40 J.415

Then: 14,640(.atts = 14.64kilowatts To Iind the eleciricity usagein kwh, multiply by I hr as follows: 14.64kilowatts for an hour = 14.64kwh. To fu1d the electricityusagein amperes,do the following (assuming a 240 V supply): 14,644 Amperes = watis/volis =

244

For most computations,1 watt equais3.4 Biu/hr.

21.34.1 BuildingDesignfor Electric Resistance Heating Sometimesit is possibletoconverta coal,oil, or gasfired heating system into an electricresistancesystem. However, the bu dhg should be modified io reduce heat transfer and air in{iltration. The walls and ceilings should be insulatedas thorouthly as possibleto rednce heat losses.This will cut the operating cost io a minimum. Basementwalls or the floor slab of buildinSswith out a basementmust be insulated.Windows should be double-glazed. Wood or plastic windor4' and door ftames are prefe ed, rather than metal. Walls should have 4" (10 cm) insulation and ceilings,Z (16 cm). The tloor slab should be insulated 4" (10 cm) thick and 42" (107cm) deep. The basementwall should have 2" to 4" (5 cm to 10 cm) insulation. FoIIow the latest specfications availablefrom manufacturers. Solar heat can be used to supplementelectdcheat. When possible,east,south, and west exposuresshould Humidiiy control may require dehumidification rather than humidification. The building is likely to be very tight. Relative humidity builds uP fiom cooking,

The open wire type usualy consists of nickelchromium (nidtome) resistance wire. It is mounted on ceramic or mica insulaiion. The open \/ires must be carefully protected. Ihey must not b€ contacted by metal obiects and/or by humans or animals.This protection will avoid the danger of burns or electrical shock. Ribbon-type rcsistance heahng wires are made of the salne maielial as open wires. They are mounted m the same genenl way. The ribbon system,too, must be car€fullycoveredby a grid to preventburnsor shock.The dbbon design provides more surlace exposure for air The tubular heating element is similar to the heating elements used in electric stoves. Usuallt nickelchromium rcsistance wire is surounded by a magnesiumoxide powder. The wire and powder are en.losed in a heat-and corosion-resistantsteeitube. The tube encasedwire designprotectsagainstelec' t cal shock. However, the eiement may reach high temperatures. Tubular covered elements are sometimes placed in fin'type aluminum castings. This increasesthe heating surface, and rcduces ihe danger of hithtemPerarurewrnS-

c

-

heatinq Figure21-98. Threetypesaf electricresistance A Openwire.B Openribbon. elements. C-Tube-encasecl\ tne.

838

and Air Conditioning Modern Refriseratlon

Some q?es of electric rcsistance heating elements arc similar in shaPe to a tube'encased element. These heatins elements are usuallv made as follows: A helical-wound coil of resistancewire is supported bv ceramic insulatols. These oDen coils arc made of nickel chromium wire. They are wound on insulation (ceranic and mica). Ceramic disks shaped like doughnuts with the helicai coil passing through it A small-diametercoil of r€sistancewire is Insereo into a metal iube. Powd€r {orms the insulation. The metal Lubeis pre>ied.and the powder rmagnesium oxide) becomes dgid. Duiry manuJactue, these tubes are formed into many shapes. !\rhen heaied to 1550"F(840"C),the tubes become dull red. Metal Ioil is expanded to Iorm meshlike resistance heating strips. These opeBte on lower temperatures than the resistancetype wire (about1450'F[790f]).

windows. Figur€ 21-100showsa sectionof a baseboard heater. Another method is to use a stair-stePheahng elemenL Figure 21-101.This t'?e of heathg coil arrangement directs airflow so that the wall is cooler At the sameiim€, it provides more heat to the room. In most cases.a baseboardheatine rmii should be mounted on the wall. If built into the wall, dust in the heatedair from the unit may causesheaking.The wall will need frequent cleaning.It is important to keep the

ElectricResistance 21.34,3 Baseboard Heating Baseboardheating is a popuiar fom oI natural convection heating. It has the electrical resistance heating unit mounted in a casing. The casing is designed to €fficiently move air over the heating element by natural convection. SeeFitue 21-99.Air expands when heated, so warmed air is liehter and rises. The coldei a;f, which is heavier, settles td the lower openinS. It eniers the unit to reDlacethe dsins heated air. The units used are shaped much lile a regular baseboard. They are mounted on the wall close io the floor, usually under

electricheatingunit. Note Figure21-100, Baseboarcl the heatingelementwhere front cover hasbeen removed. (Marley Electric Heating, A United Dominion Conpany)

.9

.g E

. . _ _ ___' A m b i e n l A i r -_-_-- WannedAir HolAir

of baseboatd Figure21-99. Commonconstruction heatingunit. electticresistance nituralconvection (white-RodgersDivision, EmersonElectricco )

Fisure 21-101.

This three-element unit is used to

o6ain a differentairflow paftern.(QMatk,A Division ol MarIey Electric Heatin8)

Chapt€r21 Heatingand HumidiJicaton Synems

air passagesclear to prevent poor airflow The heating elementtemperaturemay becometoo high if the air Passasesareblocked. Each baseboardheating unit may be thermostatically operated.This permits individual room temperature control. The units are easyto instali, Figure 21-102" and take uD a minimum

839

may also be installed in ducts of comfofi cooling installations. Figule 21-103showsa unit, completewith conhols, that is designedfor a duct installation.

of space. Since there are no

moving pais, they are noiseless.Installation of a safety (limit) switch in eachunii is sirondy recommended.It opensthe eiectricalcircuit if any part of the heatergoes abovenormal temperature.SeeChapter26 for information aboutcontrols.

Figure2'f-103. Electricrcsistanceduct heatingunit.

21.35 ElectricRadiantHeat

Figurc 21-102. Baseboardelectric resistanceheatinq unit with decorativepanel rcmoved,showinBmaunting

Room temperature vadation wiII be greater using baseboardelectric heat than with ceiling cable heat. Temperature variation between ihe floor and ceiling with baseboafd heat can be 4'F to 15"F (2"C to 8"C) wiih about two heating pedods per hour. Cycles of five to six heaF ing periods per hour are recommended. Ceiling cable temperature variation between the floor and ceiling can be 4'F io 5'F (2t to 3"C),with about one heatingpedod per hour (the recommended interval). With ceiling cable heat, the floor above the cable is warmed, as well. Baseboard units are available in lengths mnging from approximately36" to 100" (0.9 m to 2.5 m). Some uniis have only one heatinS element. OtheE have two or more elementsconnectedin parallel. On most insiallations, ii is good practice to keep the current Ioad to 20 A or lessper circuit. The use of 240V circuits, where piactical is desirable.

Radiat t heat ls.ually is the infiared band oI light energy waves impacting atainst an object. Theserays are ai a frequencv oI 900 MHz to 2500 MHz, with a wave1en$h oi 4.0 microns or t€ss.The object absorbs the rays and becomes warmer. An example of radiant heating is ihe heat impact lelt when a tumace door is opened. This is felt even if you stand well back from the door The heat impact that is felt is usually an inftared ray impact. This principle can be used for comJort heaiing. The energy source may be any fueL Howevet gas-fued and elecirically heated elements are the chief sources. Electricradiant energysourcesmay be provided by a lamp, a high-temperature elect c elemeni, a ceramic soufce, or a low-temperafure electdc cable, Radiant heat rays, if focused on an individual who has several square feet of sufface to absorb them, will keeD that person quite comfodable. This is true even if theimbient temperaturc is below the comfort range. A largewarehousewith a few small areaswhere employees work is a typical example. Radiani heat is often used to good advantage in such areas. Radiant heat decreasesas tle square of the distance. That is, an object twice as far away from the mdiani heat source will receive onlv one-foufih as much heat.

CeilingHeating 21.35.1 Radiant 21.34.4 DuctHeaters Elecidcductheatersareprimarilya sourceof space heating.They arc often used as supplemeniaryheating for heatpump systemsduing the coldestweather.They also are used for auxiliary heatersin large air condi tioning lnstallations.Spacescan be heatedby installing electricheating elementsin existingduct systems.They

Radiant ceiling insiallations are most popular for homes.In theseinstallations,elecl c heating cablesarc enclos€din the ceiling plaster.The ceilint cablesrange in output ftom about 500 W (watts) to 5000 W (1700Btu/hr to 17,000 Btu/hr.).Theyhavea 1/E'to 1/4" (3 mm to 6 mm) diameter. Ceilingcablesusuallyrelease2.75W/ft (wattsPer

840

M o . l e r nR e r tr s e r a r i oann d c I C o . d i t i o . i n B

rt'"i' ,..** loot They "re .pa.edon-l_l_]^^t8J-' -0 rq0 \e cerl . Thrhenl' C rerrperah rF dbou. -surface (50'C) 1 1/2" centers on to about 120'F ing Wider spacing$'ill reduce the ceiling surfaceto about 100'F (40"C).Dry\'!'all uses lorver W/ft. ratings (about 2.2 W/ft.). About 60% of the heat released is by radiation. Floorcablesareheavier.They areraied at2 75W/ft, and are embeddedin a 1 1/2" to 3" (38 mm to 76 mm) ihicknessof concrete.About 45% of the heat releasedis radiani heat.

2.1,35.2 RadiantLampsand Glass PanelHeaters Some electiicallyheated fixtures use quartz lamPs that are either Vycor or metal-sheaihedSomeuse oPen resisiancewire or dbbon. SeeFigures21-104and 21_105. Quartz lamps usually consume 800 W to 2500 W (2700 Biu/hr. to 8500 Btu/hr.) of Power' The lamPs and \'vires reach tempelahlres of aPProximately 1200'F(650'C). Radiarli heat lamps mav hale 90' and 60' or 45" reflection. The-vradiat€ aboui 50 W/fi'? from at least

heatelementin a Figure21-104. Ihe metal-sheath ricliant heat lamp reachesextrenely hiih tenperatures Ihe healinglanp shaulclbe lacatedan aclequate ,:listanceton all funitLtreand clraperies. lHeattex

t$.o directions. Install one h'att for each l'F (05'C) desired above lowest expectediemperature (minimum 12 W/It'z). If the sourceis farther than 10' (3 m) from a person,add five percentfor eachfoot of distance When it'ese lamps are used outdoors, use lt'ind shields Also use abort two watts per degreeabove coldesttempem Q;artz tubes usuallv use a nickel chromium coil They are about 60%efficient.The air-filled oPeniube oP' eratesat 1500'Fto 1700'F(820'Cto 930"C).lt e',iis (8ives orfrirrrdredr.) - \^.rch drein lhe vi,rblFp"r! ul rr)e5pe.rum. A quartz lamp filled $,iih inert gas oPeratesat 4000'F(2200'C).ft u;es a tunssien coil and is about 8s% efficient.It emits infrarcd rays and visible rays in the yel' low part of the spectrum. panelireai.r-are .o a\dil.ble. l\e\ eife ofr C " "'. 'en flF trica abouro07 r"didnLard +0 0 con\e(rrorr the borosilicaie conductorsare installed on the back of The element surface glassand covered$.ith a rcflector (260"C). is glass surface The 6perates at about 500'F the (180'C). panel are used on heaters Glass aLout 350'F wall under $'hdo$,s. A useful applicaiionfor radiant heai in ihe temPerate zon€s is foi inorv melting Generall, an output of 100w io 200 W (340Btu/hr' to 680 Btu/hl) is needed for each squaretooi ot surfaceieniced C.r- m:1 al'o be u'ed ,or rdoi,.li he.lirS Cn* ed radiant heai usuallv is Provided by heating ceramjcelA reflectoris used to focusihis e ents io incandescence. heat. In 8as-firedunits, about 50% ol the heat energt'is coN.ertedinto radiant heai.Tlleseuniis oPerateat about 700'F to 1600"F(370'Cto 870"C)

HeatingCoils 21.36 Installing Electric heating elements must be installed accordins to electrical codes and the manufacturer's recommlndations. The electric heating insfallafion must be carefullychecked.Be surc;t is tire-safeand safefor human. and arrimah.ll rru-. d--obe etl:ciert air circuheatcrsmusthaveunhampered Baseboard dangerously not be installed must Ialion.Theun;theaters Furnaceunits closeto flammabl€materialsor surfaces. All heat-protected and elcctricall)' nrust be shiclded grounded. must be the units nretal parts of The elecidcalseivicemust use rvire sizesaPproPdto aie ihe voltage and amPerageof ihe circrdt.The circuii must be properltrtused.It should be Profided with adequatelimit and safetyconirols All controlsmust be designed for the correci voltate and current. FiSure 21-106shows electricalconnectionsbeing nlade to ar open wire and supplernentaryheating coil. The coil has heen installed in a duct.

ir.ti Fiqure21-105. Radiantheat lanlp Untt usese/emeti liie that usedin electricftnge Elementis callecla netal'sheathheatelement lAitkenPrcducts,lnc )

:ingHe.itingCoils

r': :'

Electric resistance heating seldom requires serYiceAtu passatesover the heating uniis musi be kePt clean

Chapt€f2l

3.

Fiture 2'f-106. Setvicetechnicianconnectingline to terminalsaf duct-mountedelectticresistanceheating

Grilles, ducts, heating coils,and Iins should be cleaned at ]east once each year. Brushing and vacuuming are recommended. It is extremelydang€rous1()use flammable fluids ibr cleaninS€l€ctric res;stanceh€atingunits. Check the terminals for tightnessand cleantiness. A voltmeter or ohmmeter can be used to check whether connectionsare looseor colloded. The ohmmeteris prefe ed, because it may be used with the electric power turned off. The themostat, Iimit control,and relay are possible service problems. IJ the circuit does not function, the fo1towing typical electdcal circuit diagnosis procedure is 1. 2. 3. 4. 5. 6. 7.

1.

2.

ls therepower to the fusebox or circuitbreakerbox? Is ihe fuse in good condiiion and aie the connections electricaly tood? Is the thermosiai operating?(Check opening and closing temperatures.) Is the limii switch operating?(Check opening and closing temperatures.) Are the relay coils in good condition and operaiing? Are the relay contact points clean and opemting? Does the electrical heating coil circuit have coniinuity? Someiroubles and possiblecausesare as folows: Blower turns on arld off. If heater strips heat and cool as the blower runs and stops, the thermostat is short cycling. Perhapsthe anticipator rating is too hith. . Limit con'rolmd) be openingand clos:nB. . Incorrectlow voltage. Motor overload may be opening and closing. Blower runs, but ihere is not enough heat. . Dirty filters. . Voltagetoo low. . Only some heaterelementsare energized. . OPen fuse or circuit breaker' . Elementburned out.

HeatingandHumdilicatlonSystems

84'l

Sequenceswitch not operating. Secondstage of two-stagethermostatnot oPcycle must add to heaF erating (second-stage ing capacity). No power or low voltage. . Seqlrenceswitch defeciive(open). . Thermostatopen. . Low line voltage. . Low transformeroutput voltage. . Motor not operatinS. . Defectivecapacitor. . Defectiveinternal overload. Proper voltage at motot . Defectivemotor (open circuii). . Defectiveoverload (open cfucuit). . Defectivemotor capacitor(shoried or open).

HEATING ALTERNATIVE MODULE METHODS 21.38 HeatPumps Air and geothermal heat pumps have becorne p o p u l a r h e a t i n ga n d ' o o } n g c o m b ' ) a r o n -i n . o m e areas.The operation of the heat pump is similar to that of a basic reftigeraior system. The coil mounted outdoors at times becomesthe evaporator.At oiher times, it is ihe condenser.This is accomplishedby the use of a four-way valve. ln cold weather, rhe ouldoor coil i. uced as an evaporator. After the rcftigerant has evaporated, ii is ,ompre5sed.fhi- produce' " hot refrigerant.The relr 8emnt releasesheat to the inside of the building through the condenser When the weather is warm, the evaPorator is changedto a condenserby a systemof vah'es.The condenser becomes the evaporatox This anangement removes heat lrom the inside of the building. The heai is dischargedoutdoois through the condenser.The major difJerencebetween a geothermalheat pump and an air heat pump is: . .

t\e air hearpump J:e: air ro chanSethe refriteF ant from one state to another. The geoihermalheat pump usesthe Sround or wa ter (Iake,pond, wel1,etc.)to changeihe refrigerant

For further inJormation on geothermal and air heat pumps, seeChapter 24.

21.39 CoalandWoodHeating In some arcas of the couniry an abundant suPply oI solid tuel exists.This is usually in the form of wood or coal.ln an effoft to conserveenergy,somehomeo$'n-

442

and A r Concliiioning Mod€rn RefrlBeration

ers are using solid Iuel. it may provide some or all of thefu heating enerty needs. Commercial systems are availablewhich replacenatural tas oroilheating sources with wood- or coal-bwning sources.This can be found in hydronic systemsas well as forced-airsystems. The use oI wood or coal may be more economical ir >one.itud!ion-.Hoherer. il r-Lally reqrirei a considerableamount of atention by ihe homeowner.Ii takes time io load the fuel, stoke the fire, and clean fhe ashes. Also, the flue and chimney must be ftequentiy and carefully mainiained. Solid fuels burn difiier than conventional Iue1s.This means there is more soot in the flue and chimney. A solid fuel heating unit is commonly used as part of a conventionalfurnacesystem.An exampleof this is a systemthat usesa heatexchangerin the fireplace.This h€at exchangeiis connectedin serieswiih conveniional heaiing systemduct$'ork in the home. When a fire is in the fireplace,the heat exchangerdraws latent heat. (This laieni heat is from waier vapor in the fireplaceflue gas.) The warm air is distdbuted through the forced air duct-

21.41 Cogeneration Many ]a€e industrial planis, commercial buildin8s, and shoppingmalls have installedcogenemtionsystems. These systemsboth generaie electricity and supply heat. This type of system has been lnstalled where there is a need for heatint year-round. Most installationsuse gas turbines, Figure 21-102 to generateelectricity.The wasteexhaustheat is used to prcduce steam for indusirial piocesses or building heat. The exhaust gasesleave the turblne at temperatures oI about 700'F (370"C). These tempentures are high enough to run a boiler at 75% of its usual efficiency. In someinstallations,the vrasteheatis used to drive absorpiioncoolingsysiems.Theseare calledon site 8eneraiing sysiems,combined-cycleplants, or iotal energy sl'stems.SeeChapter 24 for turther informairon

21.40 SolarHeating All forms of energy originate from the sun. The amount of enerty produced by the sun and the growing need to conserveIossil fueis makessolar heaiing desirable in some areas.Solar energy is used lor heaiing, cooling,and domesticwater heating.It is an alternailve to usrng other enerty resources. The use oI solar energy in heaiint systemshas developed slowl)r Solar heating developmentbeSanin souihem Califomia during World War L It was used ihere jn mfitary camps. It reappearedas a means o{ water heating in the 1930s.The use of solal energy expanded in the late 1970sand l980s. At thai iime, federalpro8ramsbecameavailablefot solar heating and cooling. In its simplestform, a solar heatinS/coolingsystem is one that redtces conventionalfuel consumPtion.So1ar ener8y heating systems use equipment to colleci, store, and distribute solar heat. The two basic tyPes of solar sysiemsare passiveand active.An examPleof a passiaesolat heaLingsysfem is the sun's rays entedng -outh \^irdo!( in cold we,ther Tlte.un'' r") - in. rease " the rcom tempenture, Actioe solat hedtitlg systetts have a number of different sections.Theseare necessaryto utilize the heai in a given area.The solar heat must be collected,stored, and distributed.The activ€sysiem is the concePithat is mosi used for heaiing and coolhg Solar heating and cooling has iicreased in recent \'€arsin areaswhere sun mys are availablefor extended periods of time. More detailedinformation on solar en' ergy can be lound in Chapter 25

Figure21-107, Simplecogenerationsystem.Wasteheat from Eastubine is usedto prcduce steam,whtch may be usedfar heatingar far absorptioncooling systems

MODULE HUMIDIFICATION 21.42 Humidifiers When af is heated,ii can absorb more water vapor. Human comfort reqrdres a relative humidity (RH) ;f about 35%.When ouiside air at 30'F ( 1"C) and 90% RH is heatedto 72"F (22t), its RH droPsto about 18% SeeFiture 21-108lor information ftom a Ps,vchrometric chart.

Chapter2l

843

Heatinsand H!midificationSvstems

t E

E

9 :

e

rrw Ky|t"

g

rj,.-q" B

E

i

100

+ DryBub TemPeralurc Figure21-108. Graph showingdecreasein relative hunidity. A-Startinq point. Air sample is heated fron 30"F(-1'C) at 90o/aRH,to 72"F (22'c)at IB% RH. E'_Result fot process carried out without adding any watet vaqor to air samqle.

A dry atmosphere causes dry skin and breathing dryness. There is a loss of moisture flom hygroscoPic materials. Examples of this are natural wood fibers (wood furniture and woodwork) and most foods. Dry wood cracks and fumiture joints tet loose. Dry air also creates static electricity .onditions. Moisture must be added to the air. T]?ical indoor moisture sources are plumbing devices, cookhg. and perspiration. In addition, moisture in the air can be incr€ased and controlled by using humidifiers. Humidifiers add water vapor (low+emperaturc steam) to the air If the rctum to a warm air furnace is about 60'F (16"C)arld 25% RH, and the furnac€ heats the air to 140'F (50"C), a humidiJier may be used to add moistuie to the warm€d air. This heated air is then mixed with the air in the room. In Figure 21-109, A to B indicates the air being heated. From B to C, this warm air is passing over the humidifier (total heat is constant). BetweenC and A, the heated and the humidified air are ml\ed. D indicates the final condition of the ai as ii is delivered to th€ conditioned space. Remembet it requiresabout 1000Btu to vapodze each Pound Most humidifiers in walm air systemsare part of ihe turnac€ or of the ductwork. Fture 21-110shows the operating pinciple oI a humidifier. Evapomtion takes place as the heated air passes through the evaporator pad. The pad is wetted by water metered thrcugh a solenoid valve. The waier is then distribut€d over the pad. Water that has not evaporated flows to the bottom of the humidiJier and is drained out. Humidfied air is then retumed to the heating sysiem and enterc the living area. This type o{ unit has a small fan motor and solenoid water valve. Figure 21-111shows ihe exterior of this tyP€ of humidifier.

140

DryBuLb Temp€€lure+ Figure21-109. Psychrometticchart depictswam air recirculatin7 heating cycle. A-Cold air return. A to B Heating in furnace. E to C Humidifying air. C to A-MixinB of air with roam ai. D-Final condition after mrxtnS.

*i',,1fu

SupplyIn

Dry

Cared ofl by Dain Hose

Figure21-110, Waterflow througha basic filter hinidifier. fhe flow of air is governed by the furnace blower and the opeztian af a small fan motor. (Aenercl Filters, Inc.) Some humidifierc use a vibrating object to atomize water (breakit up into tiny droplets).The vibrating object carlbe a piezoelectric crystal. This operates at a hiSh hequency of about 100 kHz (100,000cycles per second) See Figure 21'112. "Piezo" is pronounced "pea-ay-zo." "Piezoelectric" means vibraiion due io electric waves in a flat crystal plate. The unit produces moisi air that feels cool on contactinS ihe human body. This is becausePartiatty evaponted drcplets ar€ vaporized on contact with a wamer object. IJ air cools the body too muclr the air

844

Modern Refrig€ratloiand Air Condil onlng

d Figure21-11'l. Humidifier with evapotatorpad. Unit hasa solenaidvalveto evenl\/distributewater over pad and hasa motor anclfan fot air movement. (CeneralFilte6, Inc.)

must be heated.This occursilr the bdlding heating system before distribution. HumidifieE can be easily added to warm alr heat' ing q/stems. A separate cabineti),pe humidifier is neededlviih some heating systems,however.The]' are use.:t .ith hydronic heating,steamheatingsystems,and most electricheating systems.Theseseparatehumidifiers are necessaryif the needed relative humidity is to

21.43 Typesof Humidifiers Humidifiers of vaious typesareused-Thev includel . . . . . . . .

Plate ti/pe (low-capacity). Rotatint drum type (for rest cted spaces). Rotatlng disk ilpe. Fixed filier type. Fan type. Plenum/i{arm aft duct iype (slin8sthe water). Plenum/duci electrict]?e. Ultrasonic (piezoelecidc)type.

Ahu,lritlistat is .rsed 1^ a humidiJier to control the leve1of relative humidity Too much humidity may cause sweling of hygroscopic matedals ( .ood Products).It may cause condensaiion on cold surfaces such as wir_ dows,window frarnes,and doors.WatervaPormay also condenseon the firner surfaceof outside wa]]s. Excesshumidity should be avoided becausemold and rot can occur ai 70% RH. wei objectstake a long time to dry Wood frames rot from h'ater ddppinS off cold glasswindow panes. If outside air at 70%RH filiers into a building and is heatedto 72"F(22'C),this heatedair will have the rela tive humidity shown in Figure 21-113.If outslde air at 90%RH and 30"F( 1'C) is heatedio 72"F(22"C),it will have a relaiive humidity of 19%.If ii siats at 1007.and 30'F ( 1'C), it l\'iil be 20.7%at 72'F (22'C).A11$,aterservices in the home increase the relative humidity. Perspiration and respiration oI humans and animals also increasesthe relative humidity. Even if these moisture resources double the relative humidity, it would still be too low This is the caseexceptfor 30'F ( 1'C) outside air. The chart in Figure 21-113can be used at outside relative humidities other than 70%. Use the following

FelatlveHumid'ty(Psrcenl) InsldeRH SafcInsideFH Temperaturs OutsEonH 1 0 7 0 2 2 0 0 7 0 5 2 5 1 0 7 0 7 3 0 7Q i1 35 20 40 70 15 30 Figure2'f-I13. Chattsho$,srelativehumidity chatl]e in ai as it is brcughtinto buildin' frcm outside;also tecommendedinsiclerelativehunidity basedon outside tenperature.BuildinBinsidetenperatuteis 72'F (22'C) Exanple:0'F (-18"C) outsideair at 70% RH when broughtinto building aftl heatedto 72'F (22"C)will have RH of 5%. lt shouldhave RH af 25o/..

Drippirg

far crystalvibntesto breakwaterintomist.Notethatthecrystalplatesizeis exaggerated Figure21-112, Piezaelectric

Chapter21 Heatingand H!midificationsyftms

eaample .iih 100%outsideRH (conveting the first line of the chart): x InsideRH = 1.43x 2 = 2.86%. 100%/70% Humidifien arc used to add the neededmoisiure (watervapor)to the room air.A ranchhome25' x 60', with 8'c;ilngs,

has a volume of 12,000 fti. It will re

quire about foul (tight building) to 16 (loosebuilding) gallons oI added moisture per day. This depends on the number of changes of air in the buildingl . . . .

A tight building has 0.5 air chantes/hour. An averagebuilding has 1.0 air changes/hour. Anaverage loosebrilding has 1.5air changes/hour A loosebuilding has 2.0 air changes/hour

Figure 21-fl4 shows a humidifier with floai mechanism. It has built-in adjustablethemostat which senses duct temperature. It rvjll electrically tuIn the unit ofI and on to conirol the humidiJier outPut. Regular water (city mains or well water) contalns various q?es of foreign matter. II water is to be used in a hr.midifier, this forcign matter must be treaied ol rcmoved. The pedect water lor humidifiers would be disijlled water. Distilled water does not pui any foreign \.apors into the air. In additlor! it leaves no dePosits in the humidifier or in the duct systemThe quality of the water varies \4'ith its source: .

Sof ?rafel.Natural, untreatedwater with low mineral contenthas about 5 grains of hardnessPer gallon and no chlorides. The natural source is rain

.

Tu.tturis fteatedby the ion exchangeproSofte11ed cess (water softener). This removes hardness and minerals.The unwanted mineral ions (chargedatoms) are replacedwith water-solublesodium salis. Defiineralized ?rafel has been heated to remove

.

_/ ., Drain Figure21-1'f4. Hunidifler designedta fastento battam of supply duct. (CeneralFilters,lnc )

, Medirm hard water (well water)is untreatedwa_ ter with 5 to 15gains/gal. mineralcontent. . Very hn uater lwell waier) is untreated water wiih over 15 grains/gal.of minemlcontent.Hard waier is testedwith a substancecalled "green soap."Crcm soapwill noi Iorm sudsin waterthat h a . I 0 g r . i r s B d . o r m o r eo f m i n e r r l : .

21.43.1 ElectricHumidifiers Most heatedbuildings need humidiJyins. A watervapor-producing device is usually needed during ihe winter season in the temperate zones. An eleciric humidifier may be used for this purPose Blriidmts using s.eam, h\dru1ic. or wrr--iir heated equipment installations can use an electric humidifier. Warm air heating units sometimes are equipPed with a hr.midifier. It uses the warm air as a soruce of heat. Howeve! if the humidifier water is separatel]r heated, the amount of humidificatlon can be more accurately controlled. The electrichumidifief has the advantageof easeof installation and flenbiliiy of location. It has acculate retative humidity contiol. FiSur€s 21-115 ar].d 2a-116 show an elecidc humidifier desitned for use m a .iuct o. plenun lions. pro.es.b\ hhich the energvin. enerSy. fuel is convefted to A. heat B. iight C. elecirical D. Boiir A and Bamounts. 2. All fuels contain A. hydroSen and carbon atoms in equal B. h)drogendnd .arbon ?ro11i r varyinS C. oxygen and carbondioxide atoms in equal D. oxygen and carbon dioxide atoms in varying 3. The possiblecauseoI a yellora.flame is -. A. overbalance of primary air B. flashback du ng shuioff C, bumer overfiring D. lack of primary air 4. A possible remedy for a liftinS flarne would include A

in.r.,cino

o,.

R

nrdcicino

nrimin/

nrcqc,,rp :ii

C. reducing input gas or primary air D. AII of the above. I ftich of the following is not a basic component oI a forced-ai system? A. Combustionblower motor. B. Gun-type bumer C. Heai exchanger D. Combinationgas valve. High-efficiency tumaces A. have an AFUE ratint of 84% and above B. have secondaryheat exchan8ers C. use lessfuel and produce more heat D. All of the above. The "Complete-Heat"unit -. A. does not require a separatewater heater vent or vertical chimlley B. has a CAE of 90% C. coniainsthree modules: the heat module, the water module, and the air handlint module D. Both A and B. A modulating furnace can Fovide modulatinS rates A. 20%-'1407" B. 60%-100% c. 40% 104% D. 0% 100%

Which of ihe following is 1lofa concemcriiical to veniing? A. Capacityof tumace. B. Airflow C. Numberof elbows. D. Whetherthe piping must be vertically or hoiizontallyvented. 10. Which of the Iollowing is true rcgarding standingpilot fumaces? gasvalve. A. Thereis no combination B. The limit contol energizesthe gasvalve. C. The pilot light is maintainedby a thermocouple. wiihin ihe exchanger thefan D. As heatdecreases switch closesits contacts. HYDRONICRADIANI HEATINCMODULE 11. When using a concrcteslab floor with hydronics, the concrcie. ihe tubing is placed B. in C. above D. Any of the above. 12. \ 4rich of ihe following temperature control devices is used with water heating systems? A. Single conirol. B. Zone control. C. Indivldual mdiator controls. D. Any of the above. 13. Which of the folowing is ,of a means ot control_ ling a hydronic system? A. Zone valves are cycled and tuIn on the pump or heater. B. Pump is opemted continuously and the zone valves are cycled. C. Heat is on (oniinuouslyand the pump i5 cycled. D. All of the above are means of controlling a hydronic system. in the water. 74. Scaleis formed by B. corrosion C. sludge D. embdtilement Prior to putdnS a new boiier into service, you must A. use alkali to neuiralize acid B. boil oui the boiler C. add calcium carbonate D. None of the above. 16. Why must you llush ihe system before putting ii A. BC. D.

To remove salis. To rcmove t'hlxes, dirt, sand, and chiPs. To ensure there are no leaks. To heat the system.

Chapter21 Heatingand HumidlficationSvstems

17. To flush out a boiler, 1 Pound of trisodium Phosgallons of phate shorild be added for each hours. water and circulatedfor A. 5, 10 B. i00, E

c. 50,4 D. 10,1 18. Organicgrowth mav be contuolledthrough the use of -. A. chemicals B. sodiumpentachlorophenate C. phosphates D. AII of the above. 19. Ai what tempemture is the steam in a steam-heat system? A. 212'F (100"C). B. 102'F(38"C). c. 120'F(49'C). D. None of the above. 20. How often should a steam heating system be .hecked? A. Once per year B. Once per monih. C. Once per week. D. As needed. MODULE OIL TURNACTS &ai grade fueloi1is most commorily used in do21. \ mestic sun-tYPebumers? A. Grade 1. B. Crade 2. C. Grade 4. D. None of the above. pounds of air is required for each 22. About Grade 2 tuel oil consumed of ta11on A. 100 B. 1500

c. 106 D. None of the above. 23. \\4rich of the lollowing is flof true regarding oil A. B. C.

Oil bums best in a liquid form. Oil bums best when atomized. The most conlnon tl?e of oil bumer is the gu]l

D. LiL\e blower ihe oil mixes wiih ar. 24. Too mrch positive pressureis causedby -. A. not enough air B. a chimney that is too tall C. a faulty nozzte D. None of the above. 25. $'hich of the followint is a true staiemeni regardine sr.m-t\.rreoil buiners? li HrgF-pres,u-elpe,eeor oil at 200 p.i to 300 psi. B. Low-pressureb,?e usesoil at 1 Psi to 5 Psi. C. The nozzle on a high-Pressure iyPe must be carefullY centeied. D. All oI the above.

849

26. Which of the following statements is true regardine electdcal ignition? Ai It is comrionly used on oil bluners B. It includes a transfotmer and three electrodes. C. It must raise the oil temperatureto 1000'F D. All of the above. 27. Which of the following is not a cause of delayed ignition and puffback? A. Wrong posiiion of electrodes. B. Moisture in the oil. C. Poor insulaiion. D. Weak i8nition. feei 28. An oil storage tank should be ai least ftom the furnace. B.

10

c. 5.5 D. 12 29. \,Vhich items determine the mte at which tuel oil is bumed? A. Size oI the hole in the nozzle. B. Amor.urts of oil Pressure. C. Lentth of the nozzle. D. Both A and B. 30. Which of the followint is nof a resuli of air in th€ oil line? A. Flashback. B. Oil not being pumPed. C. Blowbacks. D. Flame failure. HEATINCMODULE ELECTRIC 31. The higher the temperature of the heating element, the space it needs to occuPy the B. larSer C. wider D, cooler 32. One watt equalsA. 3415 B. 3.415

Btu/hr

c. 34.15 D. None of the above. 33. In order to modify an oil or gas sysiem to electric resistance heaiing, -. A. have metal window fiames and insulate walls arrd ceilings B. have wood or plastic window frames and dehumidify C. have meial 'indow frames arld dehumidify D. have wood or plastic window frames and insulate wall, ceilings, floors, and basenent 34. lvhich of the folowing is ]lot a common t,?e of electric resisiance heating wire? A. Closedwire. B. OPen wire. C. Open dbbon D. Tube-encasedwire

850

ModernRefriseration andAir Condirioning

35. Which type of control is rccommended for use with

44.

baseboard electric heai? A. Relief valve. B. Safety limit switch. C. Flow switch. D. Pressure-reducingvalve. 36. The iotal furnace output of an electric fumace should be -percentthe desitn load. B. 10, under C. 20, over D. 5, over 37. Heating elements in an electric furnace vary fiom each. A. 10 kW to 20 kW B. 15 kW io 20 kW C. .5 kw to 1.5 kW D. 5kWtol0kW 38. Elect c duct heatersare used primarily as -. A. spaceheaters B. supplementaryheat sources C. auxiliary heaters D. A11of the above. 39. Radiantheatdecreases as the squarcof the distance. That is, an object twice as far away from the radiant heat source will receive as much A- one-fouth B. one-half C. one-eithth D. twice 40. Which of the Jollowin8 is true of electdc heat? A. Operates below ignition temperature of most materials. B. Humidity control is easily maintained. C. Operationalcostsare lower than other fuels. D. Increa.e ir to\ic indoor ai-rcondition5.

useoia_vatve. B. thermostaticexpansion C. four-way D. bypass 46. The term "geothermal heat pump" describes a system in which the evaporator/condenseris in

47.

48.

49.

50. ALTERNATIVT HIATINC METHODSMODUI.E 41. \ 4rich oI the Ioliowing is used for solid fuel heating? A. Coal and $s. B. Wood and oil. C. Oii and coal. D. Coal and wood. 42. Which statement is true about solid tuel heating? A. Ii is cieaner than conventional fuel. B. Ii is dirtier than conventional fuel C. It producesless soot in the flue. D. Both B and C. 43. What is the tunction of solar energy system equipment? A. To collect heatB. To store heat. C. To distdbuie heat. D. A11of the above.

Whena heatpumpsystemisusedfor cooling,what is the outdoorcoil? A. Condenser B. Evaporator C. Neithei of the above. D. BothA and B. Heai pumps altematethe flow of rcfrigerantby th€

A. the Sround B. a well C. a iake D. Any of ihe above. The outdoor coil of a heat pump can be used for the -. A, condensei B. evaporator C. Both of the above. D. None of the above. When the heat pump sysiem js used for heatin& what is the outdoor coil? A. Evaporator. B. Condenser. C. None of the above. D. Both A and B. How many basic types of solar energy sysiems are there? A. One. B. Two. C. Thiee. D. Four. Coteneration systemsare mainly used when there is a need for A. year-round heating B. year-rourrd cooling C. short heating seasons D

\h^rt..nlino

Gp:e\urely faslered belore ihe put place. Filler boalds are placed between in 1lnit is the uniihousing and ihe side of the window. They are

Eigwe 22-12, Winclo\( unit with indoor flush m;untine. The sheetmetalscrcwshold the side closure

usually sealedwiih spongerubber strlPs or Styrofoam. This i; held in place with sheei metal screws and with ,or}ne clips. I iaure 22'15 show' one nelhod of in-t"lling tl-"em.A t)pi-al 'nindo- unii inslalldtion in a casement wmclow Is shown in Figure 22-15 The inside mechanism is hea\.ry'lt should be moved usjng a dolly or special carrier' Avoid movinS or lifting

CL"pler 2.2 (oo i g d.d DFrum.difi ^8 \)cFr s

859

Sping Cabinet(TopVjew) Measore ThisDistance (X)

(X) Distance Fi9ure22-15, Fillerpanel betweenunit housingand Eigwe 22-13. Window ai conditioningcasing installed,showingrubber seal sttipsanclfiller Doards.

S il for

SashSeal

(Wedge behdeen Windows) Fi9lJJe22-14, Sponge rubber seal placed between upper edge of lower sashand upper sashof double-hun7 window. Sashbracket keepslowet sashlocked. the unit by using the tubing or coils as hand grips. Carry the unit by holding onto the bottom pan. Avoid lorcing the unit into the casing. As the unit moves into ihe casing, check that rcfrigerant lin€s and wiring arc ftee and clear The front grille, filter, and conirol knobs are easily installed. As a final step, checkall joints for tightness.Caulk seams which have lighi showing throu8h or they may not be airtighi. When making the electricalhookup, use a separate circuit. A polarized plug (one with a ground wire) is reqrllreci, Thermostats are used with most winctow units. They are adjustableto cut out between55'F (13'C) and 60"F(]6"C).The cui-in adjustmentis between77'F (25t) and 80'F (2fC). Their differentials vary between 3'F (2'C) to 8'F (4t). If a themostat fails, the unii will not start. To test the opemtion of a thermostat,cover the air outlet and ail inlet with a cloth. The air will now rccirculate inio the unit. The temperature will quickly drop to the cutout temperafure, Use a thennometer.

Figure22-'f6. Method of mountin7window unit in casementwindow A-Contrcls. B-Angle plate, usually enameledsteel,lastensto both casingand window frane. C-Machine screw holds angle plate to window frame. D Electrical cord. (Frigidaire Company)

Units that mount through th€ waII are popular in new apartment units. There is no intef{erence with windows, and comfort cooling can be provided as desircd. Figure 22-17shows a typical installation.

scribemost of the servicingopemtions. Some of the extemal seFice operations are as followsr . Semiannualcleaningor replacement of the filter (usually done by the owner).Figure 22-18showsa filter design.

Modenr Reirigeraton and Air Condtioning

860

C a r l k A l L a r o uSnede v e

AddedStud Shm

Sightlylo

Figure22-19. Window ait conditionetunit removed t,on .r . at",p .ad ,.adt o, , ledni1l. C"t'iF' ' o,pot"'ion \ub-idi.tr\ oi I '1'tPdlc l'noloc F'

S d ev i e w Eiture 22-17.

Typical through'the-wall unit in.rallation

Finned evaporato$ and condensersare difficult io clean.The fin spacingPreventsthe vacullm brush from reachingthe lint and dirt ln such cases,Plasiic blades p o h e r n r a c u L ms i l l ' e r o \ e m o - o t h e d i r l " rd r D r - , n i r - lb e r e m ^ \ e dl | \ < u r i t i ' l o c o r l i n u c d o \ i r t rvell. Never use metai blades for cleanhS, they may

( 2 0r 3 0 )

Figure22-18. Tj,pi.al fiher installatianfat winda\\ air

.

.

Annual cieanint of ihe evaPorator,condenser,fan blades, lan motot DNtor comPr€ssor/ancl casrng The unii is remoyed fuom its casint for these oP erations,as sho$,'nin Figlre 22-'19. hspeci fan motor or motors and lubricateihenl un_ less they have hermetic beadngs. Al*'ays wrPe awav excessoil. Oil nist on ihe fan blades collects lint and reducesair movement efficiencn

Place a tarPaulin or nellsPaperson riie floor Re-^\e ur lre b-.k ' url. llF o J?Pc' b. ore led"i-8 he unit. Use a commercia]model vacuurn cleaner wlth a brush-equipPednozzle to clean ihe cabinetinside

Servicnrg the unii outdoors is more desirable A po\4'erfu]water and dete+eni sPrai/ can then be used ior cleaning.Coils nust be cleanedthorcughlt: Fins, if bent, should be siraightened When sen'icing fan motors, rnake ceriain that fans are tight on the shaft They should be carefully p o n l i o r e di n L F - r r r ^ Jr l o r e f i c F _ l r i f n ' o r e n e t A \ o i , b e r d i r g r l ' e f . r b l r d e - ' , . $ i - . r , 8 r l , c n r 'A r off-balancefan \a.ill soon 'ear ott the motor beanngs It will be nois)' becauseof vibration RePla.ean abused fan. lnspect the drain. Ii must be clean. Remove lint from th; dra hole and tube using a soft lvire Check all bolts, nuts, and screus for tighiness Before replacing the unit in the cabinet, run ii to che.l fuf n^.F. r rnd l- -ou'Le"rd .l.p ,f F r'oi-e. Als'ays put a cloth o\-er the air conditioner ouilet when ii is firsi started after cleaning Looseneddirt not removedby the vacuum cleanerr\'ill be blown oui of the adiusiable srille. ' The wirnrg of a n'indor{'rinit is very sirnilar to oiher -Frriscrdlrrg.rril- ree fiSure 22-20.L\'"_ldl Flecfri' I ,e. i, ing p-"redure-.rreu-uJllv he ' rrre d: lor o ime' iic and aommercialunits exceptthe followitlg: . .

Fan motors usrially have two oi thre€ sPeeds Somesystemshave ihree caPaciiors:startingcaPacir.r. ru.ln:ng "pacilor nnd "rr m(.lor"'P"'iror

851

22 Coolins Chapter andDehumidrryins Systerns

conlacls ofi

f91..

* capacitor I

swilp[

Yettow

2

3

4

o

o

o

c

c

o

$an lS*5+i'.l

Bue

I \_./

t' :it '| --'-6| 1.9

-

E

-

SraningComponenrs Showi Dotledfor Foier€nce

Figjlte 22-20. Wiin7 diaEram of 120 V window air conditioner with 70A0 Btu/hr. capacity. Note tuvo-speedfan motol and fan caDacitor.(Fedders North America)

Shown in Figure 22-21 is a unit with a starting capacitor and a running capacitor. An arrangement with tluee capacitom is shown in Figure 22-22.Posiiion of the fan contrcl switch, thermostat, capacitors, and wiring are seen in Figure 22-23. Figllre 22-24 shows a wiring diaSram for a threesp€€dfan motor system.The systemhas a 21,000Btu/hr (6.15kW) capacity using a 240 V circuii. Testing of outside electrical parts is described in Chapters 6, 7, and 8. Fan and compr€ssor motor testint is d€scdbed in Chapter 7. AlI but ihe motor compressor can be repaired on-the-job. Before doing intemal service work, be sure the malfunction is not in the external circuit. Test Ior power Check the thermostat, the relay, ihe

capacitorc, and the overload protectors (both elect cal and temperature). Trcubl€s inside the unit may mclude: . . . . .

Lack of rcfriterant. Stuck compressor. lnefficient comprcssor Clogged refrigerani circuit. Short cncuit open circurt, or Srounded motor windings.

The motor condition can be checked with a conti nuity light or with an ohmmeter. To check for lack of refrigerant or clogged rcfligerani lines, installing service valves may be necessary This can be achieved by

M o d e r i R e f r i g e r a t ia o n dA i r C o n d i to n n g

862

@-

Slarting

Stmp

Figure22-21. Windaw unit sho\"/irylocationoi Pafts JUchas capacitors,conttal panel,ano relay

Fisure22-23, win(lo\+,uttit showin! locatianaf Nore rhe exparsioDside c;pacitarsand Ihermostat. panel.(CarrierCorporation,Subsidiaryof United Techno Iogi es C()Qoratian)

l\4ounlng

4 [4ounti.g

Siarl C oth

Figute22-22. Affan1ementof start,run and ian motot ctacilori. NoIe ihai ian notar capacitarand compressarcapacitorarc in the samecoDtatnet

p r e r c r n ue r b y u - : n gd ' s e . l o n \ . 1 \ t ^ l L r p n: n ' l J l a gaugemantold, as stlo\\ n nl tlgure lz'lr. Derernrirrg 'drr8rro.rn3'rr^uble i' e\Dldincd n C l r a p r " ^l ' " , a t = f t r e u r r ' l ' o u t d b e m o i e d o t l e need-rep"rr- ThPn_uto' .h.p ir lhr _1orufcomPre\>or

Fi9we 22-24. Wiin] dtagramot threespeeolan system.(FeddersNo!7hAnerica) ' arrbe replc,rdo" hr" .'wler_ Premi'e5tf LUn\pre.:or the unit iacks refrigeiant, locate the leak and rePair it before recharging.

C h a p t e2r 2 C o o l i n sa n d D e h u m l d i i ryg S y s t e m s

Bub

Lne

L o wS i d e

863

HighSide

' 270to 380lbs.

:

rr'ne

vEre

E /I

270io 380lbs

P,essure Tuscnarge

'Thesefiguresareiluslfative jor F'22 Theyw lLvarydue to equipment size ourside and nsideiemperalure condilons, High-presslre Liq! d I High,Press! reVapor E Low-Pressure vapor Low-P.essure Liqud I Figwe 22-25. Air conditioninB unit cycle diagran shawing gaule nanifalcl installed. (Cood man Manufactuti nB Coryoration)

Many window air conditioners se PSC (permanent splii capaciior) compressormotots. Thesemotors do not use a relav for startinS. If supplied \.oltage is lor\" (10% or more), they will start rvith great difficr ty. Manv servicetechniciansinstall a stariing capacitor and a relat to overcomethis problen1.The capacitor and the relay musi be exactly the right size for the The best wav to determinethe correctsize is to follo$, the manufacturer'srccommendation.If this is not ar.ailable,the table in Figure 22-26will help in selecting the correctelectricalstarting system. When the motor compressor reaches a sahstactory speed, ihe siarting capacitor needs a rela]'. This relay will open the starting capacitor circuit. Special starting kits are available lor PSC motor compressors. SeeFigure 22-27. Window units arc ofien removed durint the h'inier season.Howeirer,if this is inconvenieni,the unit can be winterized. The air inlet and the outlet grilles can be blocked with cardboard or flexible plastic sheeting.A storm sashcan be cusiom buiit to fit around the air conditioner.Pb\ rood held in placewith caulking or rubber grommetscan also be used-

Sp€cialSlarling (Add-on)' 2A 25 30 35 40

1a 1Aot 25 25 25 25 ot 45

50

45

'ir6t

Mdad€c spdit Micoldad Edng ol.p@ial sbn €pac'llor lor each of thek unlls. Foliow manulaclucr's speiii€l ons.

Figure22-26. Tableof specialstaftingcapacitotsizes to be usedon PSC(penEnent split capacitor) compressarwhen startingdifficultiesarefound. PSC motorsare introducediu Sectian7.8.3.

ReplacementcapillarytubesIor H'indo . units must Je"y a.'urrr.l) -ele.tedb\ .ize. Figure 22-28give, be correct sizes r^'hen R-22 refriterani is used

864

o n dA j r C o n d i t i o n i n g M o d e r nR e f r l g e r a t i a

4500 36in. x .042 5000 25 in. t .042 55oO 20in,x .042 6000 ,10'n. x .049 6500 35in,x .049 7000 4000 9000 10,000 11,000

2Ain. x 36 in. x 28 in. x 36 in-x 28 in. x

.049 .054 ,054 .059 _059

12,OOO 13,000 32 in. x .064 14,000 1 5 , 0 0 0 36 'n. x ,070 16,000 30 in. x .070 38 in. x 35 in. ! 2a in. x 40 in. x

FiEurc 22-27, A hard start capacitor desiEnedtar use \\,ih permanentsplit capacharnotarc' Ihis type af unit replacesth-. nlechanicalrclaysand sGrt capacitotto increasetarcpe ta the compressor'(SealedUnit Pans C().,lnc.)

If the window unit driPs water into the room, rt rs not conectl)' installed.Check the sloPeof the unit fiont inside io outside with a spi t 1evel.It musi slope to ihe outside (condenseredte) about 1/4". Condensaiewaier \,vi11 then run to the depressionof ihe rinit base under ihe condenserfan and condenser.Make sure the drain hole is open, then level the unit along its othei dimension. Finally, recheck the unit installation for airtight sealingin ihe I'indor{ oPening.

.075 .075 ,075 .080

80ln. x 64 h. x 52 in-r 75 in. x 65 in. x

.049 .049 .049 .054 .054

52 in. x .054 6 5 l n .x . 0 5 9 4€ in. x .059 5 0i n ,x . 0 6 4 68 in. x 56 in. x TAin-t 56ln- : 4a in. x

.070 .070 .475 -075 .075

65 in-r 55 in. : 48ln. x 58 in. x

,040 .040 -080 .085

figwe 22-28, Capillatytube sizesfar vtindow air cdntiitionersthat use R-22refriEerantCoil circuitsare the size of tubing in evaporator.Eachunit hasane capillarytube. (TecumsehPrulucts Ca )

packaged terminal air conditioner that Provides gas ieat. the unit has a sealed combristion funace that burns only the outside air. A solid state electronichot srirfaceisnition is used. Heattug is provided by a 8asfired heal exchangerwith ihe electronicallycontrolled pilotlessignition system.

22.3.2 PackagedTerminalAir Conditioners The packagedterminal air collditiofiet is a cofi' bined heaiilrg and cooling svstem lt is designedto ser\'ice an individual toom or zone This tyPe of unit is frequentlyuseclfor vear-arorindcomfort in instalaiiois .1.lude , " q r i t . g , o " " h F " t i n g. 1 o r o o l i r g l \ n r n p l e " -hoD.rrrd oL hoiel- iotel-. dp'1rren!-. dormit.-re' tices.SeeFieure 22-29. Manv o-fthe uniis are designedto fii through a siandard 42" ; 16"\\'al]space.This tueqtentlv rePresentsthe samesize thai $,ould be used for installing an electdcal resistanceor heat PumP unit Figure 22'30 lllusirates a

heatingand coolingsynem 22-29. Cambination Fis]':Je in officesancl installation ior commercial used t'rJquently Company) Manufactuting subuhan apaftments.

Chdprer22 Coolins rnd DFhu.rldify ng Sy(re.rl(

865

TopView

Seals

GasH€arI b

Exchanger

End View

Figure 22-30.

Packagedterminal heating and cooling systen. (SuburbanManufacturing Company)

Tle rcftigeration system utilizes a hermetically sealedrotary compressor.Airflow systemincludes an airflow fan and a combustionfan for the evaporatorand condensint units. Basiccontrols include a heating and cooling thermostat.A rotary control is usedfor heating,cooling,and fan opemtion-Units are nomally operatedwith natural gas or LP gas-Th€ systemusesa capillary tube meterint device.This t?e of unit is normally operatedwith R-22or R-134a.For seruicins.the entire unit will slide out of the wall cabinet.

22.3.3 MultizoneDuctlessSplitSystem Multizone ductless sysiems are popular for new and retrodt office use. They are frequently used in legal and medical offices, motels and homes without ducts. The basic components of the system include a single outdoor condenser, three independent evaporaton, and individual evaporator temperature conhol. The condensins unit is located outside on a slab. Th€ iines to the eviporators enter the building ai the desired locations, Fture 22-31. The new system now gives a ductless system owner four options for obtaining air conditionint. Theseare ihe use of the window uniL the wall unit, console unit, or the ductless unit. Some of the primary advantages of the ductless svstem ale as follows:

. .

. .

A single condensing unit is used with three indeDendent evaDoratols. iiach evapomtor temperature is maintained individually, providing different temperatures for three diJ{erent offices. Most units arc equipped with a remote wireless contrcl for iemPerafure. The units €an be installed in walls or ceilinss.

22.3.4 consoleAir Conditioners In console afu coflilitioflerc, entire systems are mount€d in a cabinet. They vary in capacity ftom 2 hp to 10 hp. Such units are olten used in small commercial establishments such as restaurants, stores, and banlG. Console models may have either wateFcooled or aircooled condensing urrits. Air-cooled models, needed in some localities because of rvater rcstdctions, must have air ducts to the outdoorc for condenser cooling. Ficure 22-32showsa water-cooledconsolaunit.Return at ente$ the lower grille. Cooled air is discharged at the upper grilles. Ducts can be connected to portions or all of the upper sections. These are needed wh€n Partitions inte erc with cooled air distribution. The condensins urlit is mounted in the bottom of the console. Air blowe$ are in the middle. The €vaporator is in the top of the cabinet.

865

Moderf Reirgefationand Air Conditonln8

unit A Thrce 5)saemsh/.h L,!csr tns/e outdaorcantlensing air condi{ronrng Fieure22-31. A nultizoneductlcss '"Eil tenperature ndependent rt matntaircd be ^"rriri ,rit' ,", ,ontratledb\' rcn.)tecann'is' Eachunit can Anerlca/tnc) Electronics (ButnhamCarporation) B-Rematenuttizoncheatpumpsystem(Mitsubishi

Chapter22 CoolinsandDehumidifyins Systems

867

Figuje 22-34.howsa consoleunil. tigure 22-35ihoss a large self-containedcomfort coolerwith an air-cooled condensei Water-cooledunits reqdre plumbing connectionsto both a water supply and a drain. The dtain alsoreceives mojstu€ condensedout oI the air by the evaporatorin surnmer.Suchunits usually do not provide winter conditioning facilities.

Figurc 22-32. Self-contained console air conditioner has water cooled condenset. Upper grille is cooled air

Console units also have adjustable fresh air intakes and evaporator b]?ass controls. See Figure 22-33. A11 musi have drains io r€mov€ the condensate tlowing from the evaporator. Most of ihe console models have a complete rcfrigerating system, filtering system. and evaporator

Figure 22-34.

Drawing of console ait conditioner.

Console 1udls tt?icaly us€ a hermetic compressor. The relrigerant control is usually a thermostatic expanThe unit should be thoroughly checked. Air iemperature (both inlet aJld outlet), electrical load, and operating pressures should be checked. The data should be recorded for fuflrre reference.

following: . . . .

Figure22-33. Air ciculationin consoleair conditioner.

ReplacinS the filter or cleaning it. Cleaning the evapontor and fins. Cleaning the fan motor al1d oiling it (unless it has sealedbearin8s). Clearring the drain pan and drain tube.

The inner lining of the cabinet sometimes gathers lint. This shordd be removed by vacuundnS. Servicing

Modern Re{igerationand Air Conditioning

Fisure22-35, Consoleunit \vith ai-cooled condenser'A-Contdls. B-Heating coil C-Evaporator' D-Comprcssor. ail C pondenserfan H-Evapotatorfan I Ventilating conditionedairdiverters. F Filtered {Nr-cooled condenser. duct.J-Dischage grilles. K-Air filter. L-Return ait Stille. of ihe refriSeratin8 unit and the condenser water circuit r' erolainedin Chdpter15.Il i. imporlanito checkthe rerriderantcharge.tire operationof-the thermostafiLe{valve, and the water flow Dansion ' A rcgular maint€nance schedule is necessaryto ensure longlnd satis{actory seffice from the air conditionine s\stem. DiJferent pdrt( of ihe syctem mu't be ct,"".tia -ore frequentlt lhdn others A record should be kepi of a[ checks including both the data and the date. aheck the following weeklyl

. . . .

Fanspeeds. PumpsPeeds A[ standbyunits. Waterleaks.

Controls (pressur€, iemperature, and airflow). Lubrication. Canvasconnectorson ducts. Cooling tower. Water treatment. Bleed off. Monthly checks should be made on these: Refrigerating system (charge, Purge, test {or leaks; check strainerc and d ers). Filiers. Humidifier Safety valves. Coolinq tower PumP. Duct dimpers, regislers and diffxsers. Piping (insulatioD vibration, anct wear).

Chapter22 Coolinsand DehumldifyinBSyrtems

869

Everysix months: Cleanfansand casings. Cleanductregiste$and diffusers. Everyyear: Efficlencycheckof compresso$. Efficiencycheckof pumps. Damperopemtion. Cleanwater circuits. Opente all hand valves. Every two yearc: Inspectcondenserwet surfaces.

22.4 RemoteComfortSystems Service

Relrigerating equipment in remote air conditioning systems is located away ftom ihe conditioned space. These units vary in capacity 1lom tvro tons to thousands of tons. Sone uni-. do not use long refrigerart pioint runs. Figure 22-36. Conditioned air is distributed by ducts to the spaceor spaces, A water-cooled sysiem is shown in Figure 22-37, The system has se ice valves, a tube-within-a-tube condenser, and a water valve. Figur€ 22-38 shows a chilled water system used in combination with a duct distribution system. Chilled water lines are run to evaporator units in each room to be ai conditioned.Each room unit has a themostat. A solenoid valve usually controls the tlow to each unii. This valve is connectedto ihe room tempemtwe control and conhols both a fan and the solenoid coolant valve in the room unit. Chilled water flows to the room unit when the fan startsand shuts off when

FiEurc22-37. Watercooleclcondensingunit.

tt lrSupply

Figure22-38. Controlof spacetemperatureby chilled Aatcr .ail. ,Reprintpdb\ oermi,,ion of the Ar"e,icdn Society of Heating, Relrigerating, and Air Conditioning Engineers, Atlanta, Cearyia) the fan stops. Air filters are also sometimes installed in theseuniis.

22.5 DehumidifyingEquipment A mechanism that dehumidfies (removes moisture) is known as a dehrmidifier Such equipmeni depends upon a cold coil over which air is blown. Moisture is condensed out by coming in coniact with the cold

unit for duct Figwe22-36, Air-cooledrcftiqerating blower areused heating ducts and Central distributian. refrigerating ta right side on right side in addition blower.lFeddercNotThAmerica)

When coil surface tempeHture is below the dew poini of the air, moisture will condense out of ihe air. The coil surface tempeiatue must be kept above freezing. Frost or ice formation would block airflow. A dehumidi{ier, as shown in Figure 22-39, is usualty a small hermetic refrigeraiing system. It has both a condenser and an evapoEtor in a cabinet. Many oldet sysiemsuse R-12or R-500.The newer units use R-134a The device is used to "dry" ihe air. lt is usetul in basements and other damp places.Air is dra n over the

870

Modern Refigerahonand Air ConditLoning

In some i$tallations, cetain chemicals ale used to absorb moisture from ihe air The chemicals are usually cycled so moisture ftom the air is 6rct absorbed into the ciremical. Thm the chemicals are heated. Moisture diven from the chemical is exhausted The chemicals ar€ ready to absorb moisture once more

22,6 Reviewof Safety

Figure22-39. Outsideview of dehumidifier.Air ente6 in fnnr of cabinetand is forcedout at back. Note atrows. (Frigidairc ComPanY) evaporaior. As the air touches the cold evaporator surface, it cools below its dew point. Water condenses out of ihe air and collects on ihe evapoFtor. The cooled air is then moved over the condenser.It rcheats the air to a reasonable relatlve humidiry These units usually have a hufltidktat. This rs a device that sensesmoisture in air. A container is used to collect the condensate or it is removed through a drain iube. Figure 22-40 shows a hunlidistat and other

All of the sa{etypracticesdescribedin chaprerc 12 15 also apply to comfort cooling units and Window units should be handledwith care. Heavy units shoutd be moved and lift€d wilh hand trucks and lifts. Many window units are installed in upper floors. With double-hungwindows,lhe upper sashis loweredto the air conditioner.This helpskeepthe air €onditionerin place.sometimesthe upp€r sashis openedaccid€ntally. Sincemost of the air conditioner'sweight is oulside the building,lhe unit may fall. lt shouldbe securelyattached to th€ windowsill and braced. be carefulnot to drop when removingmechanisms, Safety sho€s are recomslippery. They may be them, mended. Carefully Iollow installation instructionssupolied bv the manufacturer. Remotesvstemsshouldbe sturdilvmounred.suction tinesand liquid lines shouldbe protectedfrom abuse. Eefore performingany serviceor installationwork on larger units/ alwaysreview instructions. window air conditionersare usuallyavaildblefor use on either 120 V or 240 V circuits. lt is advisable-_particularly with the higher Btu ratings-to usea 240 V cir' cuit becausethe voltagedrop betwe€nthe power pan€l and the air condition€rwill be lesswith a 240 V motor.

AC Systems,Coolingand Dehumidilying AILclr1agtao_pqn_ L-4Open

FanConi

Sping

cm *-

^--splce Switch

Figttre 22-40. Wking diagram for dehumidifier. Note selectorswitch, hunidistat, and bucket switch'

Chapter22 Coolingand Dehumidiiying Systems A separateair conditioner circuit should be provided. Make certainall systemsare prop€rly grounded. When addingrefrigerantlo a system,alwaysb€ sure it is the sameas the refrigerantalready in the unit. Alwals wear goSgleswhen testingfor leaksand adding refriserant. Much ofthe sheetmelal usedin air conditioninehas ver\ \harp ed8es.You musl be careful not to cut h;nd\ or fingerswhen making repairs.

22.7 Iest Your Knowledge Pleasedo not write in this text. Placeyour answerson a conir:ro

etrppr

^f

nrna,

1. Which of the following is r?0,a rcfrigerant control commonly used on air conditioning evaporato$? A. Capillary tube. B. Low-prcssure float. C. B) pas, automdfice\pan.ionvdlv(. D. Thermostaticexpansionvalves. 2. Air leaving the evapontor possesses-% humidity. A. 70 B. 20

c. 100 D. 50 3. How can af be dehumidiJied? A. Chemicalabsorption. B. Filtration. C. Cooling. D. Both A and C. 4. air is used to cool the condenserof an aircooledcomfort cooler. A. Ouiside B. Inside C. Recirculaied D. None of the above. fan(s). 5. Most common window units have B. four C. no D. two in a dehumidifier. 6. Air passesover the A. evaporator B. compressor C. condenser D. evaporatorand condenser 7. I rhich component of a dehumidifier is often used to reheat the air after moisture is rcmoved? A. Evaporator. B. Chiller. C. Condenser. D. Compressor.

471

How are the installation joints sealed on a window unit? A. Filer boads. B. Rubber seal strips. C. Caulking compound. D. All of the above. 9. How should a window unit be piaced? A. Slant toward the inside of the home. B. Slant toward the outside of the home. C. Level. D. None of the above. 10. The normal cutout setting of a window unit thermostat is between -, A. 56"F and 60'F (13'C and 16 "C) B. 60"Fand 70'F (16t and 21'C) C. 52'F and 72"F \'ITC and 22"C:) D. 50'F and 55"F(10'C and 13t) 1 1 . What is the dew point? A. The temperature at which moisture freezes. B. The point at which dew forms. C. The temperature at which moisture firsi stats to condense ftom the air. D- None of the above. 12. What may happen iJ a window unit is shut ofI and then immediately tumed on aSain? A. Ii may stall. B. The motor compressormay be damaged. C. It may not start. D. A[ of the above. 1 3 \ /hy should you avoid bending or twisfing fan blades? A. It will cause ice-buildup. B. lt will wear out the motor bearings and be noisy. C. It may slice the suction line. D. All of the above. 14. How many capaciio$ doesa window unit have for its motor compr€ssor? A. 3or4. B. 2or3. C. 1or2. D. None of the above. 15. A multizone ductlesssystem used for three independent offces uses-. A, one evaPorator B. one condenser C. three condense$ D. thrce compact units, each with an evapontor and a condensel 16. Whai air chamber is located in the upper palt of a consoleail conditioner? A. Condenser. B. Compressor. C. Refrigerantreceiver. D. Evapomtoi.

872

ModemRefri8eratron andAir Conditioning

17. The condensatefrom an air-cooledcoEfort cooling systemgoesto A. the evapoEtor B, the condeflEer C. a drain D. None of the above. 18. lvhich compon€ntsof a window unit should be cleanedannually? A. Evapo6tor and condenser B. Motor compre€sorand casing. C. Fan bladesand fan motor. D. All of the above,

19. Console air conditioner6 vary in capacity ftom -hpto-hp. 4.. 4,8 B. 2, 10 D. 5, 10 20. \ Ihenservicingcon-sole ail conditioners,it is impoF tant to checkA

F+iaarnr.hrrrc

B. op€rationof the therErostaticexpansionvalve C. water flow D. A11of the above,

AIR DISTNBUTIOA/, MEASUREMENT, AND CLEAN/NG Modules: A i rD i n r i b u t i o n . .......A73 Air Measurement andCleaning . , , , , , . . . . . . , . . ,900

KeyWords; balancing darnpers diffusers ducts

electrostaticfiker grilles registers stratification throw water spray

LearningObjectives: After studyingthis chapter,you will be able to: .(' Cive basic ventilation requirementsof conditioned space, a Listand describethe typesoi air duct systems. lo dJ.r ciTingano d$rgn. a Relatelir oislribLlion it Sizeand constructductsfor a balancedsystem. 'a Computetotal pressuredrop in a ductedsystem. O D scusstl pesand cld.(ificaliors o fans. a l \plrin prin{iplesand n ct\ods for cleaninS d r. a Servicedifferenttypesof air cleaningsystems. a Demonstrateproper lse of various instrumentsin checkingairflow and draft control. l} Follow approvedsafetyprocedures.

Air conditionine mechanisfirs condition the air and dishibute it. They are desitned to distribute atu to the proper space, in the proper amourlts. This should proyide the most comfort to occupants of the conditioned space, When a radiator or a room convector system is used, air distribuhon is simple. (Examples of this are steam heating or hot water plants.) The heat exchange units are located along the outside walls. During the heatins season, ihe heated ail rises from the mdiator a]ory ihe wall. Ii mixes with the cold air adjacent to the cold wall. Then natural ak cunents (convection) move the air mixture throuthout ihe rcom. Many heating systems use moior-d ven {ans to help chcuiate the air. A good air conditioning system delive$ clean air to the spaceberng conditioned. Air quality control is becoming one oJ the most imporiant pats of air conditioning. Chapter 19 describes the impurities found in air.

AIRDISTRIBUTION MODULE and Behavior 23.1 Air Properties Beforc designing or installing an air distdbution system, one must rnderctand th€ basic properties oI air. If the beha\/ior of air is not considered. a poorlydesigned system will result. Some propertles of interest include the weight of air, the manller in which air abso$s heat, and the way air separatesinto layers.

23.1,1 Weight Air has definite weight. Although they are invisible, the tases that compose air have a definite mass. Figure 23-1 giv€s the weight of air under various temperaturc and relative hunidity condihons. One lb. (0.454 kd of dry air at 70'f (21"C)al slandard dtmo-sphericpressure will occupv a spaceof 13.35ft' (0.378m'). If therc is 50% relative lirimiairy 13.51 ft3 (0.3$ m3) of air and moisture mixture \nr'eighs1 lb. (0.454kg). Since air is a 8as, it obeys Boyle's and Charles's Laws. Thercforc, as the

873

Mode,n Fefri8erationand Air Condrtioning

474

DryAn Dryair

0

11.58 12.U 70 13.347 100 1 4 . 1 0 120 14.60 150 1 5 . 3

204

.08635 .07786 .a7492 .0709 .0€85 .0652 ,0600

50%

11.585 12_915 13.51 14.585 15.55 17.7

5op,t

1o|r,t

.08632 1 1 . 5 9 _0n4 1 2 . 9 9 13.68 ,074 .06856 15.07 .0643 1 6 . 5 0 .056s

100%

.08628 .0709 .0731 .06635 .0606

and Fiqure23-'f. WeiShtof ai at varioustemperatures less than an weighs Water vapor humidities. relative equal volumeof dry air.

iemperafurerise-, ii take! more cubic feel lo weiSh one pound. As the pressuredroPs il taker more cubiL feet io weieh one pound. As relative humidib increases,iL take. irore cu-bicfeel to weigh one pound Eachwaler molecule weighs less than each nitrogen or oxygen molecule.A qas hade up only of waler molecul$ hould neigh 0.o-1times as much d. an equal volume of dry all, provided that the pressure remains constant

23.1.2 Heatin Air Since air is a physical substance, ii can carry heat Ii will remove heat from or take heat fo a sPace. Psvchromekic prcpertres studied in Chapter 19 show liow heat contint_changes as the temPeGture and relaiive humidity change The sPecificheat of dr) air is 0.24Btu'lb."Fr1.004k]/kg"C)The ddditionaihedtdue to ihe moisture in the air varies considerabl)r It will depend on the amounl or salurafion For e\amPle,from 0'f i- tA'Ct to tOO't,$'Ct. 24 Btu are dddedto I lb of dr) air. There may be 0.04293lb of moisture added to ihis 1 lb. of dry a to sahllate it, but the heat in this moisture is 47.4 Btu 0atent heat and sensible heat, ffom steam tables).The total heat in 104293 lb. is 71.4 Btu Howevei, where distributing the air is concemed, only sensible heat needs io be consid€red. This is because vapon/ing or condensingof waler should not takePlace inihe dLrctr,nor should it occur in {he room being conditioned. To find some of the above values in met c requfes accuracv in rounding nurnbels The temP€rature differ_ ence is from -17j71C to 37 n7'C, which amounts to 55.555"C.The calcuiation is done as follows:

be released.The temperaiureof the air delivered to the condirionedspacemiy be changed.lt may causea fail ofthe equipmentOnly 'e^sibleheat urein tle oDe;aiion 'hould tale placeouLideo{ thehealingor coolchansec ng system.

23.1.3 Stratification WaIm air tends to rise Cold air tends to settle. ft air is not deliberately moved, the air will assume levels dc.ordine to ilr lemperafure See Figure 23-2. This i! calledsiatifuatiot. Nr in.n oLcuPied'Pdce muct be kepl moving m order to elimmale slraolicaiion fherm;stats and hrfiidi5laF must be placed aLihe uoper level becauseof stratification Stratificaiion tends io make smoke haze hover in layels. The layers make it difficult to get dd of smoke. Lnfortirnatell, somegrilles are Poorly located. fhen arr movesor \, in cerlain parls oi ihe room dnd becomes stagnant (not moving) in others. Furnishings also obstrict air movement. For this reason, some griJles are located 6' high in the room or in the ceilings. In these locahons, the grill€s must be athachve in apPearanceor concealedenti;ely. ln Figure 23-3,a diftu'ion Srille Promot$ mixjnq of some room air hrih enterint air' The mixing pdnciple is shown in Figure 23-4.

Celing

Fiqure 23-2. Various temperature levels (stratification) found in roon with little ar no air circulation

x 0.4s36 kg = 25305kI kJlkg'Cx 55.55s"C 1.00416 The numbet 1.00was obtainedas follows: 0.24Btu/lb."Fx 1.8"F/'Cx kJlkg"C (kl/kd /\Btu/lb.) : 1004158 2.32444 Thereare 7000gains to a pound lt rcquiresabout 1000Btu/lb. (2324kllkg) to chan8ewaterto watervato vaporrequfes grainof $aterchanged DorThus,each or 0.141Btu Per$ain One ; hLeniheatof-1000/7000 erain weighs0.0b5grams lf (onden5ationoccuJrin someheatlvill :ooleddir'ductcor on outsidesurfaces,

air in all Fiqure23-3. Ceilingdiffusiongrilledistributes (Anemostat Div ) Products diectionsin occupiedspace

Chapter 23 Air Distriburion, Measufement, andCleaning

875

depends on the number and size of the air i €t grilles. It also depends on the velocity of th€ air moving ihrouth

Figure23-4. Airflow and air mix of ceilinggrille. Black atows indicate aiilow from duct. White aftows indicate toom ait matin9 inlo Erille to n;\ ,'nh dutt ai!. lAnemostatPrcductsD iv.)

23.2 Air Circulation In walm air heating, three basic systems are used to circulatethe air . . .

Craviiy. Intermittent forced air Continuous forced air.

The gravity system is no longer popular Too much energy is lost beforc ihe air geis to ihe room being heated. Most installations use the intermittent forced air system. A thermostat in ihe fumace plenum chamber is used to control the fan. BecominS more popular is ihe continuous blower system. It provides a more constant temperature in Systems desiSned to pmvide cooling as well as heaiing need additional capacity to move air A cubic foot of cooled air will not changeroom temperatureas much as a cubic foot of warmed air. The rcason for this is the temperature difference. Warmed air comes out of the duct many degrees wamer than the rcom air it is rcplacing.Cooledair is not all ihat much coolerthan the rcom air it is replacing. Therefore, geater quantities need to be moved into the rcom to get the desired effect. Also, ihe cooled air has a high relative humidity. People have difficulty getting cool when the relative humidity is high. More ai low is needed to cool than to heat. The high volume of cooled air needed is somewhat offset by the lower cooling load. ln average conditions, a 30% to 50% airflow increase is required. Either of two methods will incrcase the airflow when needed: . Use a two speed blower motor (for directly-driven blowers). . Install a two-speed pulley on the motor iJ a beltdriven unit is used.

23.2.1 RoomAir Movement Air entering a conditioned space thio11gh ducts must circulate without causing annoying drafts. This

Air delivered to the room from the supply duci, moving aL a velocity of 150 ft. per minute or more, is called pn nary r. T'l1eprimary air pushes against and mixes with afu already in the room. The distance the air from the gille tavels before it slows down to 50 ft. per minuie (terminal velocity) is called the fhlo?r. The outlet velocity is the speed of the duct air as it l€aves the gdlle. The overal siz€ of the grille is not impotant. The total arca of the air openings in the grille determines the giille capacity. The spread of ihe air that leaves the grile is very important- R€tun air gdlles should be locaied where room ail has the slowest movement.

23.2.2 ReturnAir Ducts Retum air ducts are important. Airflow through these ducts is almost always from the "pulting" action of a fan or blower. If the return aiflow does not match the airtlow into a room, the flow of air will not be proper\ balanced. lf ihere is morc return air than entering air, the room may have a negative prcssure. Thus, more entedng air will be needed by this rcom. ln tum, other rooms may starve for air, Dudng the heating season,rcoms staffed for air will be too cold. Duct return grilles should be placed in the stratified (stagnant) air zone of a room. Durint the heatinS seasoD this area is along the floor. During the cooling seaso& this plac€ is near the ceiling. Idealy therc should be two places for retum air grilles. In all cases,the place is ihe maximum distance {rcm the inlet grilles.

23.3 BasicVentilationRequirements As noted before, air is a mixiure of tases. Normally atucontains about 21% oxygen- A human system requires that a cetain oxygen content be contained h the air: . .

To maintain 1ife. To be comforiable.

lf a room is tightly sealed, any human in that room would slowly consume the oxygen. The amounts of carbon dioxide, water vapor, and va ous impurities would also increase.This could caus€drowsiness or ev€n death. Human livint spacemust have air with a good oxy gen content. Tlis air must be kept at a Ieasonable iempelature. It js very important that fresh air be admitted io prcvide the oxygen. In the past, this ftesh air entered the spaceby inJilhation (leakage). Infilhation normally occws through door and window openings and cracks in the structure. However, modern constmction is reducing this air leakage. The air conditioning apparaius, then, must turnish 6esh air. Modem units have a controlled fr€sh-air intake

o/o

on andAir ConditloninB ModernRefrigerat

This ftesh air is conditioned and mlxed with the recirculated air before it reaches the room. Some conditioned air leaves a building through doors, v,'indows, and other construction joints. Some also leaves through the same openings (exfiltration). Any l.ind of eyhau-r fdn removescondifionedair. It is b€st io bring in replacement fresh air through an air system. When this is doner the air can be cleaned and cooled or heated; a positive pressure can be maintained in the building to help keep out airbome dirt, dust, and po11en(a neSative press$e reduces the efficiencv of exhaust fans and of a fuel-fued furnace); and a definite amount of fresh air (makeup air) is brought in Ior health purposes(oxygen content). Certain building arcas should have stghtly less positive pressurethan the rest of the building. A lower positive pressure(10% to 15% less than the rest oI the Luildingi reducesthe spreadof odors.Suchareaswould include the kitchery lavatories, and where certain industrial oDerations Droduce fumes. T; calculate fresh air rcquirements and air changes per hour, the following {actols must be considered: number of occupants, use of the sPace, dry bulb temPeratures, relative humidit, amount oI fresh air admitted by infiltration, and efficiency of unit. One basic rule, when a systemis in a cooling mode, is to Provide at least 15 cfm of air per person. This will provide enough oxygen alrd will remove carbon dioxide. Six people occuPying a 10,000ft3 spacewould need 90 cfrn of fresh air (6 x 15 cfm = 90 cin). It would take 10,000/90= 111minutes

PositiveAir Pressure

(1.85 hours) to completely replace the air in the space This is mthet slow Remember, however, ihai the PurPose ls not to rcplace ihe air quiclily. lt is cosily to use heat as fast as needed to replace the air innediately. The air can be handled either to produce positive or negativepressurein a building. {PositivePre.'ure is IxBher than atmospheri( Pressure.Negarive prcs"ure is below atmospheric pressure.) A positive P€ssure will eliminate inliltrahon oI air ftom outside or fiom other sDaces. ll r! done bv Lrsinaspecialair in lale. io the blowll'al all air enterinBa eis. A po"rtive pri.tut""rort". building can be hltercd. It is cleaned before reachinS the occupied)pace.Neearivepres5ureincredsesihe inJiitrar'"n',t windou ' a;d door". lhis air b unbealed and may be dtty. Residential homes that use fuel-buming fumaces need air Ior combustion. Combustion air, leaving lhrouth lhe chimney, mitht creale a .lightlv negah\e inside ihe house.SeeFigure 23_5. Dressrre _ The amount oI impudties in the air may be great enoushlo requireair cledning(Odor.'mole and ba(The remedyma) teriamay be iparr of suchimPuritje5.) be either ventilation, using fresh ait or imProved air cl€anins. Veiiilation is usually based on air chan8esPer hour ror the conditionedspdce.lna 1000tr -Pa(e,for e\dmPle. lhree,hanBe5per hour trould mean 1000ft" hour or 50 cfm. Three changes every hour is the minimum for a rcsidence during the heating season As hiSh as 12

Air Pressure Negative

indicate Fi&re 23-5. Sinptified diagran of airtlow into andout of a building during the heatinl season Redarrows

and cl€anlng Chapter23 Alr Dlstribution,Measurement,

changes per hour (in the above case, 200 cfm) are recommended for cooling in public assembly.Figure 23-6 shows i}?ical an changesfor both the heathg and coolrng seasons.

477

attic fans may alsobe used to bring cool eveningair into a building. These fans have large capacities ranting from 1000cfm to 4000cfm. lt is desirableto have a fan large enough to make the needed air changes.A complete changeof alr should be made in the building every 8 to 10 minutes. Example: A building measuies30' x 60' with an 8' ceiling. Volume = length x widih x height :60'x30'x8' = 14,400ft3 An exhaustfan of 1440cfm capacityr,{ill chante air every 10 minutes.

Figure2l-b. Re,onn.nled atr 'hnse\ tor \dtou, ttpe. oi a' rL1p.4t ^uh t0A0n oi -pd,p pp, toom.

I i - 8 o o dp r a c r i crpo l e e p r h e . i . b l o a e i , r u r r n r n 8 all the time. They provide good ventilation to all paris of the building. Variablespeedblowers are sometimes used. They provide more air movemeni when the heating or cooling systemis running. Lessmovemeni is pro' vided when ihe systemsare off. An adequateair supply is the besi way to control comfori. Body comfo is controlledby evaporation,convection, radiation, and respiration.Therefore,the temperaiures of the walls, floors, and ceilings must be controlled.Enouth air must also be supplied to promote good respiration,evaporation,and convection. Where specific-condihons are unknown, it is bestto designlor 2 cfm/ft'or 12 changes/hi.It is importani to remenber that peopleoccupyinga closedspacegive off considerableheat.A sleepingpersongives off about 200 Btu/hr., lvhile a person doing heavy work gives off up to 2400Btu/hr. One Btu = 252 calories. It is important for the iechnicianio rcmemberthat local and state codesmust be consideredin all installations and selvicing.In someinstances,the local municipality code may be more sLringentthan that of the state.

23.3.1 AtticVentilation It is important to properly ventilaie the attic space. The air wiihin the attic affectsthe conditionsofthe struc iure. Tlrc attic may de\-elopa mildew odor or becorne extremelyhoi. To prevent this, some type of venhlahon is required. An unventilatedattic could reach 150'F(65'C) on a hot summer day. This would make it diflicult to mairtain comfortabletemperaturcsin the shtcture. A common method of ventiiating an attic is to use louvers or venis. This allows the fresh air to enter and the intemal air to escape.At the same time, water, in.ec.-.dnJ orLer"bje.l- dre Dreverledfror en'Fr'18. Man)' buildings use exhaust fans. These tans re move extremelyhot air that collectsin attic sPaces.Some

ft3 of space/cfm = 14,400ft'l1440 cfm = l0 minutes/change

23,3.2 BasementVentilation Basementstend to be cool and damp in the summei Therefore,mold and odors are problems.An ex' haust fan will reduce the dampnessand mold growth. This fan should removebasementair from the floor level and eahaustit outdoors. One method of installing such a fan is to rernovea basementwindow pane and install an exhaustfan with an inlet duct leading down to floor level.

23.4 Air Ducts To deliver atuto the conditionedspace,air carriers are needed. These carriers are called dr.ts. Ducts are made of sheetmetal or somestrucLuralmaterialthat will not burn (noncombristible). Ducts work on the principle of ail prcssure difierence. If a pressure difference exists, air moves from higher pressure areas to lor{rer pressure areas. The greater this pressure dif{erence, the fasteJ the air will flovu-. Ducts are made of many materials.Pressurein the ducts is small, so materialswith a greatdeal of strength are unnecessary.OriSinailt hot ail ducts were thin, tinned sheei steel.Laier, galvanizedsheet steel,alumi num sheet,ard insulated ducts \,'er€ developed.They are made from maiedals such as fiber board. Passageways formed by studs or joists are sometimesused for reium air This canbe done where a fire hazarddoesnot Thereare three common classificaiionsof ductsi . . .

Conditioned-af ducis. Recirculating-airducts. Freshair ducts.

Ducts are round, square,or rectangular.SeeFigure 23-7.Round ducts are more efficient.That is, less material is neededfor the samecapacityas a squareoi rcctangular duct. Resistanceto airflow is also less. Since

478

Modern Refrigentionand Air Condirioning

Solution: Pelimeter

=2x17'+2> rrom ll'e .ho bo llF- to mi. ar lhe n iiine of the iuo ga.e. orm- d *hile -mo.F thdthasa densi6' not much g-reaterthan ihe density of air' The liquids used are dilirted hl'drochloric acid and aqueous amnonia. The smoke formed is ammonium chloride Caution:Both hydrochloricacid and aqueousammonta are danSercusto us€.Wear goggles,rubber gloves,and a when handingthis nratefial. resDirator A mixture of titanium tetrachlorideand air moisture forms a dense,lasiing \^'hite smoke.It can be used for checkingair movement and air leaks The mixture is toiic. Wear goggles,gloves,and a respirator.

Figure23-59. Digital micramanometerthat uses re, record, electranicsto measu m-icroprccessar-basec! and stotediliercntialptessurcand air velocit\/in system tAlnor lnstrumenlCam?any) Man]' of these air-measuringinstrumPnts are explained in Chapter 19, along with suggesiedpositions for air-measuringinstrumentsover 8rilles. To deiennirleflow mte, both ihe air velclcityand the size of the opening are needed.The gdl1emesh or bars are not considered{,hen determiningthe sirreThe Srille openingis sinpl]r measuredalong its lengtl and heighi, FiSure 23-60.

A

B

figure 23-6'1. A sinpliiiecl smakeSeneratorusedin deterninins airflow.A-Hydrcchloric acid container' B-Aqueaus ammonia.C-Rubber aspitatorbulb Snoke is releasedat nazzle D.

Chdpre 'J

A r D -'iour o

ved5 r._le-l rrd C P"ni I

901

A zinc stearatepowdet when mixed with air, may also be used.Ii also foims a white, small cloud. This can be used for checking air movement and air leaks.The mixture is not very toxic, Other devicescan be used to add smoke to the air: . . .

Smokesticks. Smokeguns. Smokecandles.

Sticks and candles are igniied and placed in the air distribution system intake with {ilter removed. Distribution of air and air balancecan then be observedin the system, A three-minuie candle will generate 40,000 ft3 (1132m3) of visible smoke.Haif-milute and five-minuie sizesare also made,The smokecanalsobe used to check for rvindow and door leaks.Refrigeraiordoor and window sealsmay also be checked.The smoke is nonioxic, but long exposureto it is not recommended.It is harml€ss to clothing and building contents. Avoid using too The smokeis producedby a zinc chloridemist with a trace of carbon in ii. While they usually produce white smoke, candlesproducing yellow or orange smoke are also available.

23.7,2 lnstruments Draft Control Efficient,safecombustionin a fumace requiresaccuratedrafi control (controlof flue gas movement)-nue gas llow dependson t\'vo things: . .

Figure23-52. Draft indicatorfot residentialand conmercial heating systens.lt is used ta iclentifyclraft prcblems.lBacharach,lnc.)

The density of flue tas as comparedwith the densitlr of the air. The pressuredifferencebetween ihe inside of the buildin8 and the outside of the building.

Flue gas conditions vary accordhg io the type of tuel (oil or tas) used. High-efficiencytumacesrequire a flue gas flow becauseheat must not be lost up the sma11 flrie Adraft gaugeis generallyused to determinethe ef_ ficiencl' of flue gas (combustiontas) flo '. Figure 23-62 sho$'sa draft tauge being used. The stack temperaiure is alsoan indicatorof draft efliciencyStacktemperatures vary ftom 300"Fto 900"F(150"Cto 500'C) Figure 23-63 shows a stack thermometerbeing used to find the flue gas temPerature. Combustion Efficiency Combustion efficiencycan be determined by mea surint the amount of carbon dioxide (COr) in ihe flue gas.A combusiion gas sampleis exposedto a chemical that absorbscarbondioxide only afIf 10 cmr ol ihe flue gasrcducesto 9 cm3 of gas 'l ter exposureto the chemical,the flue gascontained .m' or 10%carbondioxide. If the tas cools dudng testing,its volume re.luces. The technician$'ill gei a readint that is too high. The flue gas tempelature must be known before and afier

Figure23-63. Stackthermanetetuseclta determtne flie Eastemperature.Nate smallhole made far puttin!

testing.A corection must be made fol accuratercsults Tablesare provided by equiPment anufa.hrters Systemswill vary in CO2content Someare opelating coirectly with as low as 8% CO2.Someopente correatly wiih as high as 12% COr. The manuJacturer's servicemanual will give the correctamouni for the system being test€d.Remembet a clean flame is essential iogether with the co ect COz reading Figure 23_64 sl1-owsthe percentage of CO, and ()2 conteni of the flue gasesand excessair Excessair is the Percentof air ihat is greater than thai required for comPlete.ombustion

on?

and Air CondiuoninB Modern Refrigeration

RelationshipBetween 02, CO2and ExcessAir 18

Theprobeof a portabledigrtalaralyzeris hserled hto rhedir oeinS-drnpledAnrlyzersarealsoavaildble that display carbonmonoxide levels. SeeFigure 23-66. Theseanalyzen digitally display readingsof the carbon monoxidelevels.

16 E 1 4 o

3 8 . g -

WS

o

40

60

so 100 120

Figure23-64. Oraphshowschangesin stacl.cahon di-oxidefor variousfuelsand the amountof orygen as the amountof excessair chanqesfrom 0 to 140o/a. (Bacharach,lnc.) The $aph shows these percentages for five different tt?es of fuel. \ 4'ren the CO, amount has been determined, the technician can {ind the stack tempeGture next. The combushon efficien€y of ihe tul:rtac€ is d€termined though the use of an efficiency calculator' See Fiture 23-55.

Figure23-65. Servicetechnicianmeasuringcarbon m-onoxidelevel of residentialplants.(Bacharach,lnc )

Sone analyzmginstrumenl>u.e elecEonicsensors. circuits, alld indicatorc. Figure 23_57shows a Portable air quality monitor. It is capabie of reading carbon monoxidi, sultur dioxide, temperature, arld humidity

efficiency slidecalculatars fiqure23-65. Combustion a;e usedto deternine the efficiencvof differenttypesof fuel. Thethree chansshownare to be usedwith coal,fueloil, andnaturalgas. anthracite (Bacharach, lnc.)

SmokeTest A smoke test is an excellent way to check combustion efficiency. Air-tuel ratio, primary air, secondary air, and draJt are checked. Several diJfermt tests may be usect, The first test is an empirical test rather thart a scientific rule. (An empirical test is based on exPe ence and obse atron.) A white filier PaPer is inserted in the flu€. The flue gas sample is drawn thiough the filter The smoke deposited on the paPer is comPared with a chart as a standard. sample -AJIoLher method i- ihe Lrseol d -maLl hand-held smoke tester Figure 23-68 shows an oil bumer combustion testing kit. These instrumenis are used to tesi for air pollution, boiler efficiency, and stack gas analysis Thei use thermal conductlvity and a combustion chamber with catalysts to measue the tas samPle. The technician inserts a tube in the flue. An asp ator bulb Pulls flue gas sanples through a fiiter mornted in a fixture.

andCleanins Chapter23 A r Disiibution,Measurement/

903

todng system is shown in Fiwe 23-59. The reflector can be mounted in chimneys from 1.5' diam€ier to 10' diameter. The photoelectric signal is amplilied. The Ringelmann Scalereading is shown on the upper left in$rument, The reading can also be recorded. An alarm signal is given when the smoke density reaches a preset maximum. This unit can also shut down the syst€m or start up Ilue blowe$ or afterbunels. In no caseshould therc be smoke appearing at the chimney exit.

FiEurc 23-67. lndoor ait quality monitot. Interchangeable sensos may be used to measurc various pollutants.Unit may be usedas a data loggerto monitor air quality trends. (Metrosonics, lnc.)

(About 30 aspirator bulb squeezesare made.) The smoke deposit on the 61ter is then compared to a master compadson scale. This scale (ihe Rintelmann Scale) rates smoke samDlesbv numbers from 1 to 4. Photoelectric cells may also be used to check smoke density in large systems or laboratodes. A smoke moni-

Figure23-69. Photoelectricsystemmeasures smoke densityin chimney.A-Chimney. B-Photoelecttic cell and beamtube.C-lndicating instrumentcalibratedin RingelmannScale.(Fireye)

23.8 Air Cleaning Air may be cleaned in many ways, depending on the for€ign matter contaminating it. .

To rcmouesolidssuch as dust, soot,and slnoke,onefiaV . . . .

Figure23'68. SeNice technician'soil buhel combustiantestingkit. lt is used for testingoil buner efficiency during installatian ot seNice. The test kit contains the followinq items.A-C02 indicatot used to examine flue tas contents. B-A flue testpapet strip and testpunp. C-Slide rule used to detetmine combustion elficiency and sack loss. D A dial thermometer. E and f-The 6-hr.dralt gauge(Bacharach,lnc.)

.

CentrifuSal Iorce (for large partides). Washing the air. Screens(to block the larger particles). Adhesiv€s. The air st kes against a filter coated with a material that causesmatedal in the air to stick to the adhesive. Figule 23-70 shows a lilter aii cleaner which has a humidity condition indicator. It indicates when the 6lter should be changed. Electiostatic (elecdcatly chargint the particles and adhedng ihese particles to an opposite charge surface). Most of these cleaners have a screento tmp large particles, an electronic unii to rcmove particies as small as 0.001micrcn.

andAir Conditloning ModernRefrigerarion

904

/i-;\

{oo o)

s:

;}ffi:i:;# """'"',.' i-R:ir*A;+#i--: Yze9t,

\#*.'"-:*,,r.,...

TobaccoSmoke

Greaseand Sool

saot,tobaccosmoke,andothetforeignair pollen andmold,dust,grease, Figur€23-70. Ai cleanetthatremoves (Ceneral Filtes, lnc-) pollutantsand iritants.

,

A mai is used to tmp ihe electrontreatedParticles. They are usually equipPed wiih a Pressure drop indicator and conhols. Figure 23'71 illrctrates an electronic air cleaner with a water wash system. This uses hot water to wash the unit through a sFay maniJold. Water is released into the maniJold and forced through a series of spray jets. The dirt is flushed off and drains to the bottom of the unit. liq itls: Ta rcmarJe . Liquid absorbents(chemicalsto absorb or reaci with the liquid). . Deflectorplates. . Settlementchambers.

,

Ta rcmoxegasesand.laporc: . Condensation(cool the coniaminantgas io its dew point and rcmove as a liquid). . Chemical reaciion (io react with the gas). . Dilution.

Ii is possible to remove almosi 100% of ihe contaminants in the air. Doing so, however,is very exPensive. Removal ot 90Eato 957. is much morc common and Dractical. iilter efficiency is measurcd by: . . .

Total weight of dilt it collects Size of the smallestParticleit will rcmove. Checking for discolorationon the exhausi side of the filter being tested.

Many rooms gradually collecta brown-yellow color on walls, windows, and liShi-coloreddraPes.This deposildoesnol comeIrom the furnaceor duci< ll is cdrned in thc vapor' irom 'molind and oPen cookinS meats. These tases and small Particlescollect on the cooler sufaces oI a toom This occurs esPecially when ai movement is slow.

23.8.1 Filters There arc four basic filte$: . . . .

air cleanet. Figure23-71. waterwashelectronic filter. B-An after manifolcl. Alwarcr wash (Elect o-airANh ite-Rodqe rc Di vision, EmersonElectticCo.)

Standard throwaway filiers. Adhesive Iilters. Electronic air cieanels. Carbon filters.

Each type servesthe samebasic function The major differcnce is the amount of Pollutants ea.h removes irom a sDecificarca jn a given penocl fiiterc arerneffecli\iagainslg,5e' Acfi\aledcharcoal will adsorb gases and so will suitable liquids. Water rcmovesgasetsuchas SO2and NO2 effechvely.Water saturaiedwiih calciumhydroxide rcmovesCO,. At least 99.680of the CO, is removed Throwaway Filters-Servicing Filiers should be rcplaced when they lose iheir efficienc)'. They should be discarded when they are

and Cleanng Chapter23 Air Distribuiion,Measurement,

905

clogged. Clogged filte$ produce too much pressure drop across the filter. Visual inspection is one way to decide ihat filte$ need replacement.The filter should be replaced: . . .

If they have turned black. If the frame is bent or waryed. If the filtering medium is punctured.

lf the housint shows signs of corrosiorycleanit by sandblastint and rcpaini. Checking ihe prcssure drop across the filter is an other way io decide whether ihe filter should be replaced.When the pressuredrop acrossthe filter is more than 25% of the pressuredrop acrossthe fan, the filter should be changed. Always replacefilters with the anows (pinted on the frame) pointing ln the dircciion of airflow The side towards the blower has more adhesive.It must be on the outlet side of the filter. If this is not done, ihe Iilier will quickty load with dift and clot. When replacingfilte6, make thesetwo checks: .

.

lnspect the filter for tears or holes-Place a stront light on one side of the filter. Then look through the filiei from the oiher side. Use a manometerto checkthe pressurcdrop.

The more common filte$ are ifuowaway filterc.See Figure 23-72.Thesefilten should be renewedtwice each The ) edr.lhev md) needLoberene*edmorefrequen.ly. sLeelor cdrdboard Jramc-"re u,ral y mddpof ru5rproor with wire reinforcement. Figur€ 23-73 shows how a fiber filter is installed in a funace.

tigfie 23-73, Hilh-efficiency furnace filter system. A The 30% prefiltet rcmoves large pafticles- B-The final filter is 95% efficient. (AirBuatd lndustries, lnc.) Adhesive Filters Adhesive filters are made of various fibers 8lass, coiton,syntheticmatedal.and alumnlum Thereare two classesof thesefilters. . .

Class1 Fire resistancewhen clean. Class2-Nonfire resistani.

Most homesuse Class2 filters. Fibe$ oI adhesive Iiliers are coated with adhesive tiquid or oit. AiI is forced to changedirectior and lose ltfough the filler The Particle,of lint 5peeda- ii pdsse> oita ar" ui" trdpp"dd' !he) corrrc tle ddhe'ivesJrIaces.The filter matedal is also Packed tighter at the oui let side of the filter This improves its di -holding '

C o d AI

l xcharser F o r c e d A i rH l oe a E

DepthLoading Figute 23-72,

Thrawaway paper iame glassfiber filter'

Tiese filters will removeas much as 90%of the dirt. This e{ficiencyis decreasedif they become"loaded," or if air veiocity is too high. Anoiher method to determine if a filter needs repldcerrentis lo u.e d waLermdnometer'The two malhe dirflow to mea'Lrre norne.eropening.are connecled The filter should of ihe filter. sides on the two opposite water across exceeds 0.5" of pressure drop if be replaced ihe filter. The svstem is usually designed to allow the filter pressurediop (resistance)iobe;bout a fourth of the todrop (pressure rise acrcss the fan) ia1 pressure ' lor exampfe:ihe total Pressuredse acrossthe fan is ,1.0"(10 cm) oI water column. The ailowed pressure drop aclo.- theriller i' l 0 ofwaer.olumr' l\ese Pre'w:th a hdter n'anometer sure. are n'Fasured in labomtories.They can also be arc iested Filters testedon the job. One iest determineshow many 0.3micron sizeparticlesthe filter canremove.This testis made by measuring the interference with diffused (scattered) light. To increase filtering surface or area in filieis, many different designsare used.APoPulai method to increase the arcais to usepocketsto traP the air.SeeFiSure23-74'

905

and Air Conditionlng Modern Relrigerauon

Eleclical Charg€ Filteing

Materlal Glass Human Hair

sitk

BrassSilver Odon

rigute 23-74. Pocket-type dispasable air filter. Air packetsincrease fiheting suiace. (Faft Co.)

Electrostatic(tlectronic) Theory of Cleanin8 Static electricity is created by iwo surfaces rubbrng and then separating.Ii has an imPortant effect on dirt and dust clin8ing to walls, draPes, and ceilings. Rubbing a cloth on a nonconducior wlll build uP surpius elecironson one of the nonconductots(negative chaige). The oiher matedal will iack electons (Positive charge).This excessof electronsis called static elect c_ ity. When this static electrical charge jumPs an air gap, a spark results. This spark can cause a fire or exPlosion Static electdciiy also attracts dirt and dust to vertical and overheadsudaces. Ionizing the air will neutnlize this static elecidcal charge.(loniing means to brcak it down into Positive and negative particles or charges.)l rhen this is done, dirt and dust will settle to the floor The danger of a staiic electricityspaik is removed. Instruments are used to measure statia electicity. They can "read" boih a lack of electrons (Positively chaiged)and a surplus of electrons(negativ€lycharSed). Matedals vary in their ability io generate static eleciriciiy. Figure 23-75 Iists a vadety of materials and their abilities to generaie staiic eleciicity. The farther aPat the subsiances arc on the llst, ihe greater th€ir abllity to geneEte static electriciiy. The maierial at the top asiumes a positive (+) charge.The material ai ihe bottom assumesa negative( ) charge There are ihree ways to ionize air: . . .

Power-A Power unii is ihe electfoni. filier' Nonpower-A nonPower unit usesmeta 1to remove the static electrical charg€. Nuclear-A nuclear power unit gives of{ a double positive or alPha Particle.

Figurc 23-75. Ability af various materials to Eeneftte elictricity. Materialshigh on list, when brcughtinto contactwith materialslow on list, ptovide efficient Benetation of static electticity. Cantact requies lrictian Basically,the electrostaticftlter Pnts a static electrical ,harge on dLl Parlicle' PdhFr-hould frve " rtrdire' Airflow should be evenly distributedacrossthe face of the air cleaner for maximum efficienc\r' lf the unit is near an airflow elbow, use movable air vanesor baffles Excessivelint interfereswith electronicair cleaner (EAC) operation.A fine-meshscreenor filter sho ld be installed ahead(upstream)of the filter. Servicing Electronic Filte6 Fleclronicair cleaners(EAC)need seNicein ihe fol lowing situaiions: . . . . . .

Unit does not arc. Meter (if used) readslow Trouble lighis remain on Strong ozone odor is detectecl. Rooms are dusty and dirty. The unit arcs consiantly.

C h a p t e2r l

A r D i s t f i b ! t i o nr,\ , 1 - " . s ! f - . m ei nndt , C e a n i n g

909

Check \^.ith the owner on the last cleaning of the filter Be sure thc poser doors or panels are closed.Be sure tl-Lcpo$rcr su,iich is on. Check thc fuses.Check the meter rcadinBs oi operaiing indicator. (Refer io the Mete$ or indicator litht rvill show if: . . . .

Conditionsare normal. Filter is dirtl'. Filter is wet. (Opcraie"drv" switch or blower.) Thereis an clecidcalfailure.

Some meters sho. if elech'icalirouble ls in the porrer souce clrcuit or ligh |oltaEiecircuii. lf the trouble is in the hlgh-!olta:te circrdt:Inspect and electricallytestthe "powcr pack" capacitorsand colLectingccll ionizing \^.ires.Figule 23-83shows an elec, tronic filtcr s/ith the collectctcell and power factorbeing checke.:I. A kilo|oltmeier probc is being LLSed to check the high l oltagecircrlit. This is donc kr Lletermineif the cell is shortedout.

af Usedlo CheckHiqhVotage

rRq

ffi \v

€'Long wlh AlligatorClips Atlached to Each End Volt-Ohm-Milliammeter Used lo Check Low Vo tage InpLrt(AC/DC),Amps (DC) and F€sistance(Ohms)

Fi8ure23-8,t. rritrlrr)crli, /cads,ai)d tooli lred to test ele.tical ci.uit\ af cbctrcnic eit iilter. iA \t\'.Spe'|ylnsrunentt,lr..)

Elecironic air cleancrs shorild be cleaned on a planned schectule.Frequeni washinil of a urit is not harmful. A neglecicd unii, ho$'er.t {ill not clcan air

Figure23-83- Electrani.in cleanetilltet bei.3.heckeLl. Note fejt /endJfrf)rr p.rL|et packta ollecting.ell Make .Lirc thal poh,er pa.k is iuu.ttor)tngptiot to tettilS cd lcctingcel l\\'hitp Radt€$ Dirisian,tr,etsantlecttic Ca.) rf t, por a p..l | -fr. rL.lo\.-rda .. J-i.g d krst lilihi or yolhneter.Testeach part, starting $ith the r!'all olLtletof po\ler s.rurce.Figure 23-84shows iools anclinstrum€ntsLrseddurint servichg. ln the collecior section,inspcct for thc foLlowingi bent plaies,platesout of position, ctirt bridging thc gap betweenionizing wircs and theplates,brokennruhiors, anclbroken $ircs. Platcsmust be straight.Iiemole and ?l d . LJo.F '-.,1,r", ' .l ri./ r. \ i,. .. The building and the completeair-handlhg s)'stetr should be irsfectell. New .aryeth& for examplc,]nat terrporaiii' causeanoverload o. thc filter.Lcaking duct svstemsand untreated concletefloors ar€ all unusual high-loadconclitions.Dust)' consiructio. work in thc Yicinit] n1a\'also ovcrload the unit.

The lilier \\'ashing procedurc for units $ithout buili-m wash slstems is as follows: 1. Tun th€ electronicaif cleane{.fumace,and blower Remoye lint screensa.cl iorljri.g collecting cells. Do not run the svsiem withor.rt replacjng thc screensand cells. 3. Clean,using lrot soap) waier,and dnse thoroughl\'. .1. Replacelint scrccrlsand ionizing collecting cells after the)' have dried thororighl),.If thel' ale not properll dried, elecirical arcing m.r)' occur $41en svsternrs turnco o11. A properl_v operatingunii wi11beindicaiedbv bla.k w aterwhen the cellis cleane.t.A prcperlr operatingrmii allows onlv fnrc lvhite dust to leave the ctucts.Tf a cheeseclotbplacedover a grill€ becomesdiscolored,thc EAC is not ulrking properh: 2.

A iilter ma.le of actiYatedcarbonr!,ill removesolid particles,odor-causinggases,and bacteda.This t\pe of t i l l ! i - . p r t - r d | . . o r . l i t i ,n " = . r r . l i L , i r i : c r r . tors. Figure 23-85 shows an activated carbon ijlter

910

andAlr Condirioning ModernRefrlgeration

Ideally, the fuhlre of residentiatliving will include

aii cleaning similar to "cl€an room" siandards Home computels rcquire ciean condihons

23.8,3 WatelSprays

Figure23-85. Activatedcarbonfilter and air purifiet. assembly.The carbon in activated charcoal form is made from various substances,including such mat€dals as car_ bon from refining petroleum and coconut shells. This charcoal will adsorb as much as 50% of its weiShi in Ioreign gases. It is possibleto recycle used carbon fiLters.Howevet this is usually done by the manufacture$. They remove tlle carbon and process it for reuse.

23,8.2 Dirt on Wallsand Drapes Dirt collecting on walls, ceilings, and dnpes in a conditioned space is always a problem ln most cases, this dirt does not come from the ducts. It is already in the room. Room af movement (convection air currcnt) is responsible for carrying it to the rcom surfaces. The collection of dilt around warm-air gdlles is called,thenlal precipitatior. Warm air comint out of ihe trille picks up dirt from the room air. As this air hits cooler surfaces, ihe dirt seitles (pr€cipitates) on the surfaces. This precipitation iakes place on wildows also. The cooler ihe surface, the more dirt it collecis. Therefore, insulation and storm sashesreduce the amount of diri settling out of the air. Clean rooms are now in use for surgery and rcgerrch.The) are also used for manufaciurin8.repairing and seNicing cdtical iiems such as instruments. Compuier disk drives benefjt from clean roomi. A clean room maintains the "ciean" iequirements in four ways: . . . .

Extremely high efficiency filterc. Laminar airflow Anti-contaminationdevices. HiShei Pressure in ihe clean room than outside the room.

Large air conditioners use Taater sprays. These rcmove wettable solid coniaminants, liquid contaminants, and water-soluble gas contaminants ftom the air. Some of these gases are sulfur dioxide, nitrogen oxides, and carbonmonoid€, Water do€s not remove soot, Usually the water is sprayed in a pattem that produces 100% duct cross-section coverage. A drain Pan catches the water. Eliminator plates in the duct coll€ct any water droplets which travel down the duci. The water dmin pan is usually equipped with a float-controlied makeup water connechon A continual overflow drainoff is used. lt rcmoves dust and dili as it collects on the surface o{ the water water in the drain pan is rcciiculated by a centrifugal pump. A screen is located at the PumP inlet to prevent dirt particlesfrom clogging the sPray nozzles.Theseair washers are popular dudng the h€ating season. Care must be taken to avoid fr€ezin8 temperatures in ihe spray chamber. A preheat coil is usually used to keep the temperatures above freezing The waier spray. in addiiion to cleanint the air, also serv€s as a humidifier. Comfofi cooling sysiems that condense moistur€ out of the air use wet evaPomtor su aces for filterint. A rinse device is used to remove the collected d t.

23.8.4 Odor \apors and odors frequentlv form a ldrSe Part oI almosphericair contdminanls.\4ost odors are 8ase..dnd filiers (even electrostatic ones) will not rcmove them. Some odols can be removed by cooling the Sases to their condensatlon or freezing temPerature. Some are removed by oxidation (and by uliraviolet ray trcaimenD. Others can be removed by combining them wiih other chemicals. They may be diluted with air. or absorbed into a liquid. They may also be adsorbed into a solid. Both vapors and odors can be removed with activated charcoal. Aciivated alumina with potassium Permanganateis also used,

23.8.5 Ultravioletlight Ultraviolei lighi of 14,000 microwatt/cm'? (duct cross section) will kill most bacteria. One should avoid looking aLor being e\posed lo $e-e rd)s the effecl' dre harmful $ hen one ir e\posed lo Lhemfor any lenSth of The ]amps are installed in ihe reiurn air duct Acc€ss doors must be equiPPed with safety shut-off switches in casesomeoneopensthesedools The lays must cover the full cross-sechonof ihe duct to be effechve.

Chapter23

Air Djstdbltion, Measurement, and Cleaning

911

Uitraviolet lights areused to reducebacteria,mold siores, viruses, and other microorganisms.T)?es of microorganismsand quantity killed depends on the length of exposureto the ulhaviolet iays and the output or intensitv of the lamDs. Ulhavioiet light duct fixtures may be usedfot rcsidential and commercialapplications.Residentiatunits may include dhaviolet ray fubes.Commercialsysiems often containmultiple tubeswhich areusedinside large afuhandling applications.SeeFigure 23-86.A commercial svstemiistallation is show1lin Fieure 23-87.

of a multi-tube ulttaviolet ray Figure23.87. lnstallation (Steil-Ai re,Inc.) assenbly. at leasi 99%in hospital operatingand recoveryrooms. Systemsthat removemorc than 99%of tl€ bactedaare more expensiv€but may be required for the protection needed, Theusefullife of a Iamp varieswith output but may be as high as 9,000hours. For best resultsand longest Me, an ultaviolet lamp ghouldbe independendytested to provid€ output no lessthan lo"Wcm'zper inch of arc length in a moving airstreamof at least 500 fpm, at a temperature of 45"F (7.2'C).

23.B,6 Air Curtains Air curtaifls are olie lsed at garage doors, delivery docks, little used doorways, aJld similar boundaries. Air cutains may be used on doors opened frequently. A powerful blower is connected to a source of walm or cold air. As a door is open€d, thrs air js direcF ed through openings. These openings provide narow sheams of warm or cooled air acoss the enfue door arca. This air flow stops any natwal flow of air ftom ihe building to the outside. Ii also stops any natural au flow ftom the otltside air into th€ building. Figure23-86, Ultravialetfty units designedfor duct A Singletube unit. B-l\,4ultituberack tor installation. (Steil-Aire,Inc.) cammercialinstallations. Units are normally equipped with lamps thai do not produce ozone. These units provide boih odor conirol and germicidal prctection. Cooling coils and diain pan a1€asare ihe corect locahons for lanlp installatior! as these are lhe areas of highest contamination. Used in theselocation-g,the lamPs c; rcduce or eliminate the ne€d for chemical coil cleanin8 a8enh. Additjondl fight fi^fures rnay be in-id]led in the dLrcrwo_liJ hea\rycontaminatione\i)ts brrere. Lamps should remov€ 80-90% of the bacteda in domestic alrd commercial systems. They should rcmove

23.9 Reviewof Safety It is especiallyimporrant to rememberthat conditioned air musl contain enoughoxygen to support life. The carbon dioxide conlenl must be kepl lo a minimum. Always be careful when working with or handling metal duct material.Use gloveswith metal insertswhen handlingthemarerial.Usestepladderswithnonskidbases. Be sure lhat the Dressurein a duct is low before opening a duct door. lf th€ door bursts open, it may iniure someone. Fans,motors,and belts are potentialsafetyhazards. When these unils are operatin& protective shields or guardsshould be provided for prole(tion. When adiusl_ in*, be 'ure lhe main power lwilrh i\ off. lt mu{l be loakedin the off posiiion beforehandling.

912

and Air ConditioninS Modern RefrlSeration

B€ careful that obiects do not fall into a revolvint fan. The obiect (nul, bolt, tool) may becomea dangerous projectile. Before turnint on the power/ always spin a fan by hand. This will help check if il is free to Electrostaticair filters requirehigh voltageto charge the dust particles.BeforeservicinSel€ctrostaticair filters, be sure that the current is turned off. Be sure the resistors have dissipatedlhe capacilorcharge. All air conditioning equipment is provided with safety controls. Ihese cut out th€ burner if the bonnet (plenum€hambedtemperaturesget too high. llfilters become cloggedfthe airflow may be reduced This may causethe temperatur€limit control to cut off the heat source. Fanbelts and fan motors sometimesfail. A failure in the fan drive will result in an overheat€d{urnace.Check to make sure that the lemperaturelimit conltrolsar€ in satisfactorycondition. Avoid €xposureto ultraviolet lights. Eyesmay b€ damagedby ultraviol€t light. Always determine the pr€ssurein the system part on which work is to be done. Always measure the temperatureof the systemparts which will be repaired, adiusted,or touched.Do nol guesspressureor tempera' Use instrumentsto check elecrrical circuits. Nevet assumethat the power is off. Usea masterinslrumentto checkanytest instrument that has b€en dropped. lf necessarthave it repaited. Carbon monoxid€ (CO) is dang€rous!lt is always presentin the combustiontases,especiallyif combustion h not complete. Palladiumchloride may be usedto measurethe presenceof CO. To useit, placea smallamounl {the size ofa dime) on 2" x 2" plastictabs. The substancewill dark€n when exposedto Co. Amountso{ co can be determined by color: 30 pprn to 70 ppm will causedighr darlening. 80 ppm to 120 ppm causea grey color. Over 130 ppm result in a black color.

23,10TestYourKnowledge Pleasedo not write in ihis text. Place your answerc on a sepamiesheetof paper.

MODULE AIR DISTRIBUTION a comfort cooling air duct has condensation 1. When Lle inner duci air its oLlle>urfa(e, on B, C. D.

is wainer has moisture AI1y of the above.

2. NeSativepressureis -. A. excess humidity which causes constant dehrmidification B. a room or building with presswes slightly aboveatmosphedcpressure C. a room or building with Fessure slighdy be low atmosphed. pressue D. None of the above. 3. What is the voiume of 1 Ib. of 72'F (22"C) air at atmosphedc p-ressureif it has 50% relative humidity? A. 13.05ft". B. 13.55ft3. c. 7.54F. D. Non€ oI ihe above. What is the specific heat of dry air? A. 11.58Btu/lb.'F. B. 0.08645Btu/Ib."F.

Btu/lb.'F. c. 14.10 D.

None of the above.

5. Should blowe$ run consiantly? A. Only in humid conditions. B. Yes. C. No. D. Only in weather above70'F (21'C). In a six-duct outlet system, what is meant by a toial 'Dressuredrop system? e. The fan pressure drop to each outlet will be ihe The Ian pressur€ droP to each oudet will vary with the last one being less. C. Therc will be no air movement, Prcssure drop, at last outlet. D. None oI the above. 7. Smaller ducts may be used to disiribute heated air and maintain tood heating season t€mPeratures by B.

A. increasing the raie of flow ihrough the ducts B. using larger regrsiers C. providingaddilrondl.leararlcefor air in the ducts D. Both A and B. draft is air movem€nt caused by creating a 8. rpduced pre-suJe within an air blower. dmft is air movement caused by an increased Pressurc produced by an air blower' A. Induced. Reduced B. Induced, Forced C. Forced,Induced D. None of the above. 9. Air ducts cany -. A. warm ai( or cooledair B. fresh makeup air and exhaust air C. air from the conditioned spaces back to the conditioned system D. All of the above. 10. How can galvanized steel duct be prcPared for Dainiins? Treit with vinegar or weak acid. i. B. Sand with a fine Srade sand paPer' C. Use a pdmer. D. A11of the above.

Chapter23 Air Disrribltion,Measurement, andCteaning

AIRMTASUREMENT ANDCTEANINC MODUTE 11. What is th€ voltageof the ionizing wires of an eleciric air filter? A. 120V B. 12,000 v

c. 1,200 v

D. Any of the abovemay be used. 12. \{hen clean, 1" adhesive filte$ are _% efficieni. A. 70 B. 84

c. 90 D. 100 13. The principal impurity rcmovedby an aciivated carbonfilter is A. B, C.

carbonmonoxide moisture solid paticles and odor-causint gases and

D. All of the above. 14. How are most electrcnic filte$ cleanecl? A. Simply vacuum. B. Clean with R-12. C. Both A and B. D. Wash with a water and detergent solution. 15. What is the CO2 content of oilfrnace flue gas at 1007oexcessair? A. 10Ea. B.8qa. c. 100%. D. 25%.

913

76. -

may cause the femperature limit conkol to shut olf the heat source in an electronic air filtex A. Lack of heat B. A faulty circuit C. Poor air flow in the system D. A11of the above. 17. Ultraviol€t lights are used to _. A. kill bacteda and mold B. kill Yiruses C. remove odors foom ducts and duct air D. A[ of the above. 18. When usint a CO, indicator to measure combusfion efficiency by a reduction in volume, how will the contraction of the flue gas impact the CO2 reading? A. The reading will be hiSher than a hue reading. B. The reading will be lowff than a tlue readine. C. The rcading will be accurate. D. The reading w l fluctuate due Lo e\pansion and contraction. 79. A dlaft can be detected -. A. through the use of an elechonic draft detector B, with a smoke candle or smoke source C. by positioning oneself in vadous places around D.

Any oI the above.

20. Water spEys in a large air conditioning unit are used to -. A, rcmove contaminants Ircm the air B. increase the rclative hurnidity D.

Both A and B.

914

and Air Conditloning Modern Refrigeration

Thegeothermalfuel sourceis infinitely renewableand readily accessible.A typical suburbanlot containsplenty of eneGy rc heat an.Jcaol a home. Three diftercft Seothermal loap svstemsarc displayed above From left to right: a pond loop, a horizonal closed loap, ana a vertical closed loop. (WaterFunace International' lnc )

AlR CENTR,AL CONDITIONINGAND HEATPUMPS Modules: ........915 H e aPt u m p s . . . . . . . . . . . . . . .936 Air Conditioning systems Central ......949 L a r gSey s t e m s .

KeyWords: absorptiontype chiller air coil chillers chiller compression{ype districtheatingand coolingsystems geothermal(ground)coil geothermalheat pump

high-pressure chiller liquidfloodback chiller low pressure naturalgasheat pump feversingvalve

water coil

LearningObiectives: you will be ableto: thischapter, AfterstLrdying of a heatpumpand list a Describe the basicoperation its princlpalparts. of _hehedlpumote\ersilg a L\pld.r lhe ope-dlion valvein re thechanges a ldentif,on a heatpumpdiagram, valveis switched frigerantflow when the reversing fron hedlinS modeto , oolnBmode.or viLe\ersd. a Discuss typesof outdoorcoilsandtheirapplications. a Explainthe differencebetweengeothermalheat pumpsandairsource heatPumPs, and Serviceon heat a Performroutinemaintenance pumps. 'a Describe systems. airconditioning residential a ldentifythe threemethodsusedto installcentralair conditioning. a ldentifythe basicfour stepsfor installingcentralair systems. conditioning on residential centfal a Performroutinemaintenance systems. airconditioning a Listthe typesof chilledwatelsystemscomponents. a ldentilythe chillersystem a Explaintotalenergysystems. a follow approvedsafetyprocedures.

MODULE HEATPUMPS 24.1 Heat PumpTheory Heai pump theory lests on the Principle that heat will mov€ from a ftErel tempemture to a lolrel temperdture. Thus, a hear transfer co lePi at a io\er iemperaturelhan it5 surroundint- h ill pick uP heat. I1 the evaporator of a refriSeraiing syst€m were mounted outdoois and opeiated at a refrigerant temoerature of 0'F ( 18'C), it would remove heat from the air even iJ *re outside iempemtue werc only 10"F to 15'F ( 12'C to 9"C). ff the evaPorated refrigennt is to a temperature of 120'F to 140'F (49'C tien compressed -the hot reftigerant will rc1easeheat to ihe into 60"C), door space where the condenser is located. The evaporator and condenser functions can be switched usint a system of valves- l rhm the condenser becomes the evaporatot heat can be removed ftom the iivint zone durint hot w€ather ard discharted outThe evaporator and the condenser are both heat_ transfer devices. They can be used Ior cooiing (picking up heat) or heating (releasing heat). The idea of using a rcfrigeGtion unit as a heaiing mechanism was fust Prcposed bv ihe Scottish scientist Williarn Thorson (Lord kelvin) more than 100 yeals ago. A Period of more thalr elapsed before such a d€vice was actually built. 30 years _ -r€verseThe heat Dumo is somedmes called a cvcle" mechaniim. Howevei, the cycle is not actualty rcversed. Only the evaporator and condenser functions aie interchanged. Thereforc, ihe name "reverse_cycle" is not technically corect.

24.2 Typesof Heat Pumps Two t€rms are used in ieference to heat PumP souice of operation. They are aiFto-air heat PumPs, and geothermal (ground source)heat PumPs T\e aiFio-di hear ptimp ;s ihe most poPular l)?e. Its source oI heating and cooling is the outdoor air' Its

915

916

Modern Reirigeration and Air Conditioning

exteriorappearanceis similar to that of the conventional complete air conditioning system. The geotheftfial heat pffirp uses the underground (earth or water) temperaiure to produce the desied temperature. Although outdoor temperatures may vary the underground iempemtures remain relativeiy constant all vear rcund. This allows a teothennal system to prcduce the desired heating and cooling iemperature yeai round. The terjn enoirafitke fal comfoft systemis sometimes used to descibe heat pump systems. This is because a heai pump operatesby using the natural heat storage ability of the ea h and/or groundwater to heat and cool space.The eafih absorbsand storesheat energyfrom the sun. To use this storedenergy,the heatmust be exiracted from the earth using a liquid medium (groundwateror a refrigerantsolution). A heatpump transfersheatfrom one locationto another by changing the state of a liquid. A water-based geothermal heat pump sysiem circulates a water-based nuid ihrough plastic lubing in the Bround. A dileci erpa sion slste fD& circulates retuigerant through copper tubing in the ground. Components consist of a continuous sealedunderSround heat exchangecoil, a standard rcfrigeranFto-a heat exchanger,a compressor, a revening valve, and Iiquid and vapor refrigerant f'low controls.SeeFiSur€ 24-1. The chart in Fiq.lrle 24-2 deiails both open and closed-Ioop geothermal systems. Open systems use wells or lakes as their water source.The weu or lake serves as both the supply (lulni a\A discharye G np) source for the system. This is un1ile closedloop sysiems, which recirculate their water- or refrlgemnFbased fluid. Ninety-five percent of geoihemal heat pump systems ln the Uniied States are water-basedsysiems. Therefore,this text will deal pdmadly with water source technologyin this section. The heat pump may be used {or many purposes. Water heating and heat recovery from industrial processesare two examples. Defrosting evaporatorc by means of the hot gas method is a form of heat PumP application.Both compressionsysiems and absorytion systemscan be adapted as heat PumPs. Figure 24'3A illushates a typical geothermal heat pump installation operating on a heating cycle. Figure 24-38 shows ihe same heat pump operating on a cooling cycle. The basic p nciples are described in Chapter 20. Self-contained (single-package)units of 1/2 to 25 tons are common, and large systemsof 100-ton to 1000-toncapacityare in use. Window units of 1/2-ton to 2-ton capaciiy are also available.

24.3 HeatPumpOperation OperationoI the heatpump is iike any othercompressioncycle.The principal parts of the systemsarc: . Compressor . Condenser. . Liquid line.

Figure24-1, Diagramsshawinga direct expansion systemin the heatingmode (A) and in the cooling nade (B). (ECRTechnalogies,|nc.) . . . . . .

Two expansiondevices. Evaporator. Suctionline. Motor control. Reve$ing valve. Two check valves (usedlessfrcquentlyand may be fi1its with bi-flau et eliminatedall higherperformance pansianvaloes) .

Notice that a reversing valve and two exPansion devices are needed in the heat pump. This ailows the unit to change fuom summer cooling to winter heatinS. Figure 24-4showsa heat pump in the cooling cycle.The reversingvalve allows the unit to opemte in a conventional cooling mode. High-pfessure vaPor is emitted from the compressorand then travels to the condenser. It then passesto the evaporaiot where it cools the indoor area. It Iinally retums to the compressor. In the heating cycle, the four way valve reverses th€ path. The compressedvapor is emitied io iheindoor coil. This provides warm air to the heating system.

24.3.1 HeatingandCoolingCycles The heai pump operatesin two different cycles: . .

Heating cycle. Cooling cycle.

C h a p t e . 2 , +C e n i r aAl r C o n d i t i o n i nagn d f e a l P u m p s

Closed-loop (water-based)

Water-based

9'l7

1. Fluidis lowcost. 2. Freezecontrolmustbe provided. 3. Oxygenmustbe .emovedfromcirculating fluid.

Water'based antifrgeze

1. Extends operating tempeaatures overwater-based solulions. 2- Coffosbnandsafetyol antif.eezemustbe considered.

Closedloop Directexpansiohof (reffigeranlbased) reffigerant underground

1. Comprcssor circulatesrefdgerant throughthe closed loop,thuse'iminating the needfor a secondaryloop circulation DtimD. 2. Coppergroundheatexchangers are required{corfosion etfectsp.evenlionmuslbe providedfor somesoils). 3. Designmustensureoil returnin the refrigerant loop.

Openloopsystem Waterwellwith surface discharge

1.Watersupplymuslbeplentiful. 2. Waterqualitymusibegood. 3. Disposal is required throughoul theyear-

Watersupplyand dischargewel'

1. Commonlyreferredto as a pumpand dump. 2. Discharge wellfiust be capableof retumingthe waier overan extendedperiodof time.

Standingcolumnwell 1. Singlewollactsas supplyand dischargewell. 2. Boremustbe clean3. Watermustbe non-conosive. Surtacewatersupply 1. Filtration maybe reqlired. and return 2. Waterqualitymusibe good. Figure24-2. Cui(le describingopen- an.l closedloap geathermalheatputnp systens.llnternatianalCrcunci Source Heat Punp Associattan) The samem€chanisrnis used lor boih cvcles.Houever,the traYelof refriterant is reversedio changefrom cooling to heating.Figure 24-5sho!\'sa basicllcai pump svstem. Hand valves or thermosiaiically controlled vah es may be uscd to reverseihe cvcl€. During ihe heaiint cycle,heat is removed ftom the ambi€nt (surroundnrg)air It is releascdrnsideihe build ing. Heating is not usually neededunulthe ouidoor temperaturc is less than 65"F (18'C). For example, ln the conditionsshorvnbelol{',the outdoor coil \\'i]] aci as an eyaporaior.It will pick up heai irom ouiltoors.This hcat is releasedin ihe building, as shos.n ill Figure 24-6. Outside (Ambient) Conditions Tenrp. Humidity

50'F(t0'c) 80'i

Inside Conditions Tcnlp. Humidiiv 72"F (22'C) 50--i.

The heai pump heainrg cyclc becomesless efficient as thc outdoor t€mperatur€drops b€loh' freezing.

As the outside temperature decreases,heai ]oa.l in creases. This creates problems in colder cli aies a'herc ienlPerahrresdroP to 20"F ( rC) or lor{'er. Fig]ure24-7 sho\^'ssuch a condition. Ihe oriside temperature at 20'F r€quires a refrigerant ternperatureol 0"F ( 18'C). \oie that Poini A has increasedwith very little incr€asein B. This means thai the ener$' efficiencyratio in heat units (EERd is lessthan in Figure 24-6.With the refrigerant boil g at 0'F ( 18"C),the evaporator rvill fiost rapidl_v.Somemeansof tequent defrostint h'ould Whei ambientconditionsare l\'ithill 10'F (6'C) and 10% relative humidit] (RH) of ihe inside conditions, very 1itt1etreaiment is needecl.This is due to the heat lag and time laE in controlting ihe vadables. For ex ample, the sutl's heat on a south wall in the moning mav correcta problem of low temperaturebv afternoon. Ternperaiureand relative hrmidif in a ver,vlarge room may hold to desired leve1sovernight. Howcver, if the

9r8

a.d Air Condltioning Modern Refrigeration

Horvua|€r(j-

Jlcder*or

Hoiwhl€,()-

licomp|Nr

HealAdd€dlo lhe R@rnAlr ls Wn|d€wn lrcm thl Cldlatng FluldIn th8 GrcundL@p

Figure24-3. Ceothermalheatpump operationin cooling mode (A) and in heatingmade (B).(lntenatio I Cround SourceHeat Pump Associatian)

ambienttemperatureswere to increaseover this amount, for examplei

Outside(Ambient) Conditions Humidity Temp. 85"F(29'C) 75%

Inside Conditions Temp. Humidity 72"F(22'C) 50%

a cooling cycle would be required. Heat and moisturc would be removed from ihe inside of the house.This would thenbe releasedoutdoorsasshown in FiSure24-8. On ihe psychromefficchat, the aPparatuswould affect the air conditions as shown in Figure 24_9.Point A is the condition of the ambient (surrounding) air. It represents air at 85'F (29"O and 75% RH. The line tuom Aio B shows how the air is cooled to 100%RH Line B to C shows how the air is further cooled.It also shows how moisture is temoved Ircm the air.

If 100%fresh air is beint resentsa leaving the e1'aPoratorAs the the air in the house, or as it mixes with air

into the duct system (reciculated ai) reached,

point C rep-

mixeswith int brought point D is

24,3.2 Etficiency Geoihermalheat pumPs are also Exchangeheating and cooling systems.Ac Environmental Protection Agency, Geo most energy-efficient, environmentally effective conditioning system available.

heat pumps can reduceenergyconsum sionsby over 40%comparedto ai

to as Geois the

. and costchange and emis-

heatpumps,

heatint. In and over 70%comparedto eleciric iechnologies, other fuel comparEonto all syst;ms are48%more effioentthan the be gasfurnaces on a source-fuel basis, and 75% or mole efficient ihan

Chapter24 Centra Air Conditioninsand Heat Plmps

ve

919

U H gh-Prgssure Vapor I H gh-Pressure Liquid Low-Pressure E Vapor

I Low-Pressu€ Liquid

EiSwe24-4. Heat pump. Both heat transfercails arc blower cails.TEVrefrigerantcontrolsare used. Notefour-way reversinqvalve.Systemis operatingas camfott-caolingunit with autdoar coil as condenseranclindoor coil as

Coi F --...;-

t

V av €

E I

conpr€ssor l€-

\-,/

rev zl

CoilE

service

rre,m"o"-

Y_r E{pansior

E Vaive2

Bub Figur€24-5. Ea y desi1nsof heatpumps requircd the useof hand valvesto manuallychangethe systemfrom heating to cooling. Coil F is the outside coil and coil E is the insideheat transfersurface,During coaling season, valve 1 is open, valve 2 is closed, valve 3 is clasecl, valve 1 is open. Check valve 1 is open, check valve 2 is clased. TEV 1 is not warking, TEV2 is working. During heating season, valve 1 is closed, valve 2 is open, valve 3 is open, valve I is closed. Check valve 1 is closed, 4 check valve 2 is open, TEV I warking, IEV 2 is not working. (Alco Controls Div., EmersonElectric Ca.)

Figure24-6. Pressure-heat chart for heatpump setving as heating systemwith autside temperatute at 50"F (1A"Q. Reftijerantis evapotatin!at 30'F (-1"C). Refigerantis candensinsat 1lA'F e3'C). The Btu ratio of B to A is EnergyEfficiency Ratio in Heat Units (EERd. EERais B/A, which is about 4.

qln

Modem Reirgeraiionand Alr Conditioning

fr:

d o

LE

DryBuLb Temp€ralure Fi5we 24-7. Pressurcheatchatt oi heatpunp heating cycle in opentian wheDoutsicle(anbient)tenpenture is 20'F ( 7"C). This rcquiresa 0'F (-18"C) reftigerant tp.perotdtp.\ore ;a, .ed,ein hc"r af (onprcs'ian compareclto Figure24-6, EERa,which is E/A, is less than that tor Figurc 21-6.

Figure24-8. Pressureheatchart showscaoling cycle fot heatpunp. A identifiesthe heatenegy of compressian.C sha\rsthe heatenergyremavedfrcm ail (caolin! and dehumidifyinB).Note thatA is about 1/3 af C, meaningthat 3 tintesmate heat is moved than is used ta pump. Ihis is a Coefficientof Peiormance(COP)of 3 t1 .

oil fumaces.The mosi efficientCeoExchantesystemsexceed the best gas technologyby an averageof 36% in the heatillg mode and ,13%in the cooling mode. This amounts to a savinSsto homeownersof 30% to 70%in the heatint mode, and 20% io 50% in the cooling mode in comparison to conveniional heatint and coolint Analysis by ihe Enviionmental Protection Agency determined thai ground-sourceheai PumPs had the highest source heating sensonpetfutmace fnctat (SPF) The next highestperformersin the areaol heating were the gas-fired heat pumps. The ground-source heat pumps aiso had the highest cooling SPF Cround-source

Figure24-9. Psychrometricchatt shawseffectan air in housewhen usingcoaling cycle of heatpump. heat pumps and gas-firedheai pumPs had the lowest annual operatingcosts. to calculateihe net benefits Utility cosfeffeciiveness of replacing "siandard" technologies with hiSherelliciencyemergingtechnoiogiesis calculatedusing the Cost(TRC) test. Cost-effectivenessis meaTotal Resources sured as both a raiio of total benefits to total cost and as a net prcsent va1ue.Ground source heat PumPs were highly cost effective as rePlacementfor ele.tri. resistance and air-sorlrceheai pumPs. They were also very cost effectivecomparedto standard gas furnaces/standard air conditionint in milder climates.Cas-firedheat pumps were cost-effective substitutes for standard iechnoloiies in all locations.Advanced gas tumace/high efficiency air conditionerswerc most cost effectivein the colder climates. The EnvironmenialProtectionAgency and the Department of Energy have developed a system of label.osl-avin8 Produ.!i T\ 5 .) ' em iing ener8y-pfficrent. caUedihe Energysrar. llem5 rreFlinSthe tnerg) S.ar guidelines (seeFigure 24'10) can save consumers10% io 40% on heating and cooling costs.Residentialeneigy accountsfor 20%of all U.S.energyconsumPtionNearl]r hau of all energy used in the home is for heating and cooling. Purchasing ene€y-efficient heatint and cooling equipmentcan reduceenergyuse,savemoney,and benefit the environment. AFLE (Annual Fuel Utilization EIficiency),SEER(SeasonalEnergyEfficiencyRatio),HSPF (Heaiing SeasonalPe ormance Factor), COP (Coefficient of Performance),and EER (Energy EfficiencyRatio) are all measures of heating and coolint efficiency. The higher the number, ihe more efficieni the product is (e.t., a 13-SEERair conditioner is more efficient than a l2-SEERair conditioner).

24.4 Heat Pump Systems Use of heat pumps, Figure 24_11Ior residential heatingand coolingis increasingHemeti. units have beendivelopedin manydesignsandin a wide rangeof

C h a p r e2r , 1 C e n t r aA i r C o n d i t i o n i nagn d H e a iP ! m p s

q)1

The "outside" coil is not always locatedoutside the structure.Ii mavbe locatedinsidebut ducted to the outside (if it is an air coil). SeeSection24.4.4.

24,4,1 Compressors

Figure24-10, EnviranmentalPrctectianABency(EPA) Enegy Starguidelinesfar heatinBand coalinBequipnent

Heai pump compressorshave a standardconstmc tion. Units up to 5 hp use compressorsof consiant ca pacity-Largersystemssometimesusea moduratingiype. The trend is ioward hermetic systems. The pumping ]oad vaiies greatly dudng the day and with ihe change of seasons.Therefore, \'ariable capacity compressorsare being used in larger systems. Thesecompressorschangecapacityby operatingvalves. The valves u oad one or more compressorcylinders inio clearancepockets.SeeChaptels 4 and 13. Heai pump compressorsmust operate dudng the LrrLr)ua.(ondirion. ir\olved ir re\erring rhe c\.1e. Motors should be protected with inienal temPerature thennostats. The compressor must be designed to handle some liquid slugdng without injurv Cnnkcase heatersprotect the compressorftom liquid rcftigerant buildup during low-temperatureoperatingperiods.Suction line accumulato$ protect the motol comPressor Two-SpeedHeal Pumps Two-speedheat pumps achieve a higher seasonal energy efficiency laiio. For normal heating or cooling loads,ihe compressoroperatesat loi\' speed.When ihere is extremeoutdoor heat, the compresso|will oPerateat high speed for maximum cooling. When the outdoor tempelaiureis very low, the compressorlvill oPerateat high speedfor n'uximum heating. One najor differencebetween a single-speedmo tor and a tr,{o-speedmotor is its adaptabiliiy.At high speeds/it opemtesas a two Pole motor. At loi{ sPeeds, it is a four-pole motox

24,4.2 Molors

tigure 24-11. Heat pumpsprovide customizedcontrol that can siqnificantly decreaseoperatinE costs. (Carrier Corporation,ResidentialProducts) Hermeiic systemsare ideal for heat pump installaiions, becausethelr are so simple to install. Some are equipped with se ice valves/ suction and discharge muIflers, and other special features. These systems Pfovide quiet, reliable operation,and long life. The coil that is mounted inside the house 1susually a standard finned type *-ith a blower The outside coil comesin various designs.The choicedependson the medium (substance)in which the coil is placedrair, wa-

Heat pumps of 1/3- to l-ton capacityuse standard single'phasemoiors. They usuall)i have a starting ca' paciior Single-phasemotors should be operated at 240V This permits the use of smallerwires.Three-phase motors are preferred in units over one{on caPacity, mainly for electricaleconomy. Motors ir hermetic systems are usually well insulated. They can tolerate some voliage change. protectorsare buili inio the motor Temperature-ser$or windings. Motor Controls A double sei of automatic conirols is usuallv requircd for the heat PumP. One thermostatmust be designed lor heating dr.rring cold weather conditions. Another is needed for warm-weather coolinS.In most cases,these two controls are mounted in one caseol housing. Humidistats are not used on all models They d/€ needed,however for completeauiomahc control. Lines are normally fitted with brazed or welded connections.Brazing is ihe most popular. Rexible connectionsare usually installedin ihe lines at the compressor This eliminatesnoise and absorbssome vibraiion

o'r',

and Air Conditionlng Modern RelfiSeration

Often, a receiveris used to hold the extra refriSerwhen the systemis on a cooling cycle.An needed ant accumulatoris often usedon the main suctionline This minimizes the chanc€of liquid refrigerantreachingihe comPressor.

24.4.3 RefrigerantControls A heat pump is unique in that it provides both heating and cooling. It is important to remember that heaf ing output js dirctly related ro ambient temperaRue.A hedt pump is mo-i efficientdurint hjther ambienl lemperature.\ /hen LheambrenttemperafuredroPs. ouiPut is reduced.and supplementaryheat mdy be requiredto maintain design conditions. Conhol systems aliow the owner to maximize the heat pumP usate during pefiods of high-e{ficiency heating, using suPPlementary heat only when needed. Electric heat is commonly used as a source of supplementary heat. The controls descdbed below will be those which ar€ comPatible with electric heat as a supplement. TemperatureControls Previous chapte$ describe the basic oPeration of a room themostat. HeaFpumP thermostats provid€ the followint functionsr tuming system on and off, mitiaiing coolinS or heatinS mode, initiatinS auxfiary heat, and initiating fan options. A wiring diagram for a heatDumD thermostdt providinq the above function! ia :ho;n in Figure 2&i2. The trlem switLh seleclrejlher heat or cool. If the Ian switch is in the l?rlo posihon, the

indoor blower motot and compressorwill ing either the heat ot cool mode The ot m;intain continuous operatlon of the insi(

tor. If the heat PumP is not rcsPonding, substitutethe auvjliary heai for the the systemswitch to energmcyhcat DefrostControls During the heating cycle, moisture door air will condense on th€ outdoor tempemture reaches32"F (0'C) or less,

will tum to frost or ice. Such frcst or airflow acrossthe coil. This wiII reduce of the system.Various tyPesof deIrcsi to begin the defrost Processand io com systems i clude temPerature initia iermiirated cycle, time-initiated / temPe deftost cycle, pressure- and time-initiation

te ourition will blowermoowner can by moving

the outIf the coil restricts the

it. These

temination cycle,and solid-statelogic The temDeratue-initiated/ temperatu relerminated control complrcs th€ temPerature of the outside coil with the tempemture of the air ente ng it. Incrcases in rhe difference signal the defrost cyde. The timetemperatffe control uses a timer that reqigires defrost-

inp,;veryl0 minutesduringcompre"'oroperafionThis be below sr>temalsorequirestlat thecoil temperafure The thermosta! lo close. 2;'r-3"Cr forlhe terminahn8 pressure- and time-initiated/temPerah and conhol opemtesbased upon differential

det€rtime lor initiation of the cycle. CoiI (see module solid-state logic The terminaiion. mines thermostat Figure 2&13)usesa demandsi8nalfrom

as weII as input temperaturesignalsfrc indoot outdoor, discharge,defrost, arrd liquid line to detennine conbol sequences. The low ambient contol is used to pressor circuit during low ambient tem point a[ heating is pelfolmed by the source. This sethng is usually

manufacturer(usually 0'F, -18'C), but

out dre comtur€. At ihis by the be adjusted

by the teclulician to me€t local tempem

Fi*trc 24-12- Wiring diagramfot a typical heat'punp Division) thbrmostat. RheenAi Conditioning

logigmodule Figure24-13. Heatpumpsolid'state (Rheem Division) Ai Conditioning

Chapter24 Centa Air ConditioninEand HearP!mps

24.4,4 ReversingValves Many different i]?es of specialreversingvalvesare used in heat pumps. Th€ specialreversingvalves may be operated automatically, manuallt or electrically (through solenoids).If reftigerant flow is reversedby h d n d , a t l e a < t-

o n e - \ r d \ v a l v e ri( con5idered Commercial and industrial systemsuse morc elaborate controls due to the lartei flow of fueL Flame sensoIS are generally used. These shut off the system by reacting ;ery rapidly should a flame lail (They will react in Jfraciion of a second.)The sensorsar€ electronic They use a flame rod and a Photocell The Photoceti is eith;r sensitive to the radiant energy or to the ultraviolet

specific lor a typicalhomeHVACsystemEachblockreprcsents Figur€26-58. Controlsystenblockcliagram electroniccircuitry

Chapter26 Air Conditon n8 andHeatingConlrolSystems

1007

M llvoli

Salely

MuslBe N.E.C.CLass 1

Limt

cLt-oli

GasValve Figure26-60. Schematicis for low vohageelecttical circuit usedon gas furnacewithout blower.

Figure26-59, Electricalcircuitsused with gas controls. A-Millivalt circuit. B-A 24 V circLtit.C A 120 V cncuit. A hiBh limit control is usedon each. (White-Radgers Division, EmerconElectticCo.)

rays of the flame. Someinstallationsuse a lead sulfide cell. It respondsto the infrared rays ftom the gas flame. Electric ignition for gas systems is used when the gas fumace is located outside the building. It may also be used in hard-to-reach locaiions. In this system, an elecirical spark ignites the gas at the main bumer It also automatically shuts off the main bumer gas supply if the buner does not ignite. The main gas line to a gas fumace has four valves: . . . .

Hand shutoff vah'e. Pressure regulator Cas flarne sensorsafety. Automatic gas valve operatedby thermostat.

The flame sensorprobe detectswithin a fixed pedod of time whether the flame is operational.If not, it closesoff the flow o{ gas.The ignitor is also tumed off, and the controlsiock out the system.Figur€ 25-61illustratesihe completegas bumer control.

Figure26-51. Solid-stateelecttic ignition systemfor Eas lurnace burner. (White-RadgersDivision, Emerson Electtic Ca.) Originaliy, the Iour valves listed above were separate units. Prcsently, the attomatic gas valve is made into a sintle unit for easeof installation.Figule 26-62 shows a combination valve. The combination gas coniroi is often called a "CCC." Figure 26-63is a crosssec' tion of th€ combination gas valve. The automaiic gas valve portion may be opemted by a solenoid.lt may also be operatedby an electrical bimetal blade. A sensingbulb, capilresistance-heated lary tube, and bellows combination (hydraulic ihermal el€ment)may also be used.

Moder. Relriserailonand Air Conditionng

1008

ihe {lame to temPeratule differences The system's three main control paris are the thermostai, an amplifier, and a modulating qas valve Figure i5:64 illustrates a wiling circuii used \a'ith a makeui air svsiem.The 120 V ac power is reduced to 24 V ai, usini a transformer. A rcctifier in the amplfier changes this-current to dc. Three control devices arc

Solenoid Adjustmg

. . .

A remote temperature selector' A dischaigeair sensor. A duct stai (for safety).

These contrcls siSnal the amptfiei The amplifier on thenoperale.rhesolenoiddnd modulatingregr-lalor nPlithe a 26-b5 ,hows liSure ga. line burner n;m the tier unit. lt hotds the rectifiers and solid-siate comPonents for the control cicuits- It also contains an adjustable Poteniiometer for calibraiion

Figure26-62. Combinationgas valveand autamatic piat. (white-RodgesDivision,EmersanElectricCo ) Electronicstechnolo8y,alon8 with safety regulations, has resulted in many advances in tas furnace control systems. Electronic circuits. someinnes used to contro'i heaiing systems, can vary (modulate) the u'e' d -olidBd. Ilame cize. lhe modula.rngs\5lem iia,e thermo"tat.lL also u'e< a hermisor dnd several transistors. The gas flame size depends on a temperature difIerence b6tween thermostat setting and room temPerature. The flame is larger with a Sreater temPerature difference. It gets smaller as room temPemture aPp"oa,heslhe thermo-iatiefting The unil >ldrt5up lhe hn-e at ,bou' 20^oio q0%of caPdciryThen il adiust'

!

r,:eo*

m

Pressurzed

Figure26-54. Wirin1 diagran shows indiect-fired nakeup air application (Maxittol Conpany)

l',4ain Conlrol S o l € n o d GasOitice

A'

I

oulet

I ) Diaphragm

[4ainvave outl€tscre€n

lt hashanclshutoffvalve,pilot lightcontrol,bypass'operated 2G-63. Combinationgascontrolin crasssection. 'rTi-ilri, Fisur€ ElectricCo) Divisian,Emersan undpr"ttur"re!;labr' (white'Rodgers

Chapter26 A r Conditioningand HeatingControl Systems

The remoieiemperatureselectoris shown in Figure 26-56.This unit containsan adjustabiepotentiometer.lt sets the temperaturc level of the discharge air. The dischargeair temperatureis being sensedby a thermisior located in the dischargeail sensot Figure 26-67. The modulator/regulator valve is shown in Figure 26-68. This is the valve which vades the eas llow' In

1009

addition, an automatic solenoid valve is needed to completely shut off the tuel supply. Direct currentto the modulator controlsthe amount of gas f']o .. The less the current flow ihe higher the flame. A duct thermostat is connected in sedes with the solenoid valve. It is used as a safety device iJ the duct temperature becomes too high. Spaceheating is obtainedby combinint the remote temperature selector and discharte air sensor It is com, bined into a single wall-mounted uniL shown in Figure 26-69.

Figure26"65. Solid stateelectranicamplifiermay be placed at any convenientlacatian.lMaxitrol Company)

murnAdjusling l'.4ar Screw

FiglJre26-66. This rematetemperatueselectol temperature-sensitive and nay be placed in any convenient locatian.(MaxitrolCompany)

EiglJre26-67. Dischar]eair sensar.lt sendssignalsto the amplifierof any temperaturechanqefrom setpoint. (Maxitrol Canpany)

valveperformsboth Figure26-68, Modulator/regulator regulation and modulation to vary burner flame size (or buming rate). A Exterior view. Note 8as /lne cannection.B-Cutaway of sane modulator/regulator valve. Noteadjustingscrewsused to vary the amountof ptessurercquircd ta operatethe valve.(Maxitrol Company)

1010

Modem Refrigentionand Air Conditioning

Figure25-69. Combinationmodulatingmakeupair thetmc)stat and selector.Note temperatureis in degrces Fahrcnheit. (Maxitrol Conpany)

26.18.2 Oil FurnaceControls In the gun-q,pe oil burner, a primary control usually starts the burner motor. The control can also stop the unit. This occurc if the flame goes oui or iI the flue temperature becomes too high. Some p mary units are mounted in the flue. When ihe ihermostat signals for heat (closing of points), the primary conirol sia s the gun-type oil bumer motor It tums on the ignition. This contrcl is shown in Figure 25-70.It has a temperature sensint element. The element wil shut doun the unit unlessthe flue temperaturerises in a few seconds.(This will indicate that the oil is bunmg.) This same sensor will constantly check for flame temperatures. It will shut down the system if the flarne goes out. Ii will also shut off the systemif ihe themostat or one of ihe limit controls opens the circuit.

A

Power,lgnilion, and MororConnectons Filute 26"70. Oil burnerptimary cantrol. This control will cycle burner, operate electric ignitian system,shut off unit if ignition fails, and scavenge unit after each

Many commercial heating and process bumers using gas or light oil fu€ls employ a modular bumer management system. Flame monitoring is done by ultraviolet scannels or flame rcd/photocell detectors and plug-in amplifiers and programmer modules. These are connectedto a standad chassisand wiring base,Interchangeable prcgnmmer and ampliiier modules determine the control methods. In the event of igniiion {ailure (or Iollowing a safety shutdown), the unit locks out- This aciivates an aiam. Vadous programmer modules are available,depending upon the type of installation, Figur€ 26-2.

B

A-Extetiar viewof tigurc 26-71. Flame-out safetycantrolmonitarusedwith commercial oil andgasfurnaces. solid-stateflamemonitor.B Manitot with cover removed.An amplifiermoduleprogrammeris being insettedinta the

Chapter26

The ullit's operation is based on an ultraviolet scanner It is located within 18" (46 cm) of ihe flame to be monitored, closer if possible. The scainer musi not sight the ignition's spark directly. SeeFigure 26-72. New models of oil bumers use solid-stateconhols. Ignition (electrical) may be either continuous or intermittent. Figure 26-73 sho\ .s a gun-i)?e oil bumer with a pdmary control and ignitor \ Ihen the thermostat calls for heat, the gun oil bumer motor tums on. The oi1pu]np siarts, and the ignition is tumed on. If tuel does not ignite in 15 seconds,the flame detector stops the bumer motor AJter the tdal for the ignition period, the control provides a s-second to 10 second ignition overrun time. If the tuel does not i8nite within 30 seconds.the safety switch must be manually reset. The flarne deiector siops the bumer motor and closes down the system. It then attempts to re start. Fiture 26-74 shows the circuit. A solid-state primary control is shown in Figure 26'75.It can be used as a replacementfor older model primary controls.Thetechnicianmust be absolutelycertain that th€ power is off before installingthe unit. The control is wired as shown in Figure 26-76.The cadmium cell must be very carefully mounted-The cell must "see" the flame. The correct mounting is shown in Figure 26-77.Another photocell flame detectormounting is sho$'n in Figure 26-78.The flame detector must be lined up with arl openinS in the static pressure disk to be able to "see" the l'lame. The hansforme$ have a primary winding of 120 V 240V or 208 V The secondary winding usually provides 10,000V Somesystemsuse 12,000V When a 10,000V transformerneedsreplacement,a 12,000V unit should be used. This is especiallyadvisable in cold air or cold oil situations.lt is also advisable when line-voltagedrops are known or suspected.

Air Condiiionjngand HeatingControlSystems

10 1

Figurc26-73, Cun type ail burner.(CarlinConbustion TechnoloByInc.) or may be corurected in parallel with the heating element. Central systems normally use sequence relays as primary controls.Blowers operatethe sameas on baseboard units. In addition, a safetycontrol is usually p/ovided. This shuts off the heating eiements iI the blower fails to operate. lt will also shut them off if air fails to

26.18.5 InfraredHeatControls 26.18.3 ElectricHeatControls rnits usuallyhave indi\.idualthermoBaseboard stats.Pdmaryconholsare most oftenrelaysand limii controls,Units usingblowersor fanshavefan contols. Such controlsmay operatehom a separatethemostat,

Electric inJrared heat lamps may require as much as 32 kjlowatts (kW). The heating unit may have as malry as 16lamps of 2000W each(32,000w). Eacheleciriccircuit has a contactor.At 240 V ac, the line capacity will need to carry 175 A. The 175 A main circuit is usually divided

ThernaxmumUVsigna! lronrallameis loundnlhe i rstonethrd ol ihe vlsbl€ iLame iakenlromtli€ poinl wherethel amebeginsThe scanners ghl pipeshould

A-Typical scannerinstallationon burner.B 5cannettSht pipe amed Figurc26-72. ultaviolet scannerinstallation. affirst 1/3 of visibleilame.Thisprovi.lesmaximumUv signal (fieye)

1012

Modern Refrig€fallo.and Air Condltionins

OFANGEWIREFFO[4.02CONTBOL CONNECT INSERTRELAYCONTACTS CUTJUMPER 1 2 0 V A CC O I L 3900OHI,ISMAX io a difierenl NoTE:Th€orangowireis connected tsrmnalihana normalhookup.

-1'Fh I rrrir--E: ,1n',i-- -i

THEBMOSTATUSED W|THFONCEDAIR OB TO ZONE SYSTE'\I RELAYS CONTROL

twowir€sirornl€rminal Remove t l r g e l m e r c o n r raos 4on posp shown.(Twowtss mayb€ on logeiher' Leavewiresconnecied

2. Conn€clisoaiion€lay coil

belweenTl &T2. Conn€ctnormally openconlaclbeMe€nT1 & 4 (s)

oil burnerprimarycontrolandiSnitor'A-1 20 v ac coil with 3900t) ior electronic Figwe26-74. Wiringc)iagrams teminals.Notelocationof oil burnerand ignitorin relation to thelow-voltage B-Thermosta{isconnected reZistance. lnc ) TechnoloEy, (photoelectrid celt Carlin Combustion andcad to the thermostat Cad C€l

N-N Y

I

@@ Fiqrfe 26-76. Schematicwiring diagramfor solid'state pinary control for gun-typeburner' Nate that 'Ltrent is suppliedta motar and iqnitorat samettme.

primarycantroltor 9un type Fisure26-75. Solid'state E-Cadmiumcell flame control. A-Prinary oi burner. backetand mountinB cell (letector. C-Cadmium ng I e acl f ittings. D-Ca nnecti

into four or moie s€Parateckcuits Each cfucuit has a re_ (coniactor). lav ' Either thermosiator solid-statesensorseneigizethe oDeratinq coil of ihe contactols The contactorc are usu_ so that only one closes at a time (Seaily "eqi"rrced quencing means that the contactors are set to 'lose one

C h a p t e2r 6 A r C o n dt i o r r i n ga n d F e a t i n gC o i l r o l S y s t e m s

BumerHousing

1013

1/4 Hol€D lled in BumerHousing

SiallcDisc

Figure26-77, Method ot n()untinE photaelecttic ilane tensotin SLtn-type oil btlrn,.r.

P rm a r yO B u r n e r C o n i r o lg. tionE ectrodes S l a cl P r e s s u € Dsc

Oi Lre

Figute26-7A. Flant sentd d.-'le.larnounted in Sun lype oil l)LtneL iwhite-l?ad1ersDirtsian, Entercatl Electrica:a.) aiter the other, raiher ihan all ai once. This is usuallv .,'I

o).

r r .J - a ! ^ ' - J

r . o r . \ . ' i r. i i . . l \

rr"l-

eratesthe coil of thc nc\t contactor.) Soli.1state temperattlr€conirols nrodllate the curr€lrt tlor!' \\.itl1 thermistorsand triacs.Thev reciuccpart of each sine r!'ave oi the ac flo$'. This mairltnins a constant telnperature.SeeChapier 6.

26.18.6 HydronicSystemConttols lrimary control feaiuresin rvaier or hydronic heating svsternsare ,aterlevel and temperaturecontrol.l{a ter level controls arc cspecialy important on steam

The control is tenerally a switch turned on and ofi b)' a float. If the rvaterlevel drops near the danter poht, the noat will drop. lt drops far €nouth to open the electdcal circuit io the operating controls. This sbps ihc boiler. The sli,itch gcnerally operatesin tlro stages.Lo$ering of the float ill trip a sl\it.h. This $'ill turn on ihe feed lvat.r punp or ieed water solenoid vah'e. If ihe float drops still more, ihc lystcm is shui ofi. Som€waterlevel ccnrirolsare oi the probe type. This iD the u,ater A sm.l1 curtype inmerses trro elecLrodes ient flo$,lng in the !{ater betb'eenthe i!\'o $'ill energize a holcling rela)r The svsternwill be allolved io run. ii ihe water level falls below the upper probe, the current flo(. will ceasc.The operatingc.ntrols $.ill shut !:town. The opcrat g principl€s of the h{o types of water level control are sholvn in Figure 26-79.Avoid air 1r1the s,vsien,$'hich .ould causethe contfols to rnalfunction.

26.18.7 ComfortCoolingControls Conhols for comfort cooling ar€ oi ihe same basic tvpes as those in heaiing. There are opefatjng controls, primarv controls,and linit controls. The operating coltrols arc ihcmostats, prclsurestats,and hunridistais.lidmary .ontrols include motor staricrs and starting relays.Lnnii conirolsinclude over load circuii breakcrs,thermal overloads,internal motor overloads, refrigerani pressurc limit controls, and oil pressurelimit controls. \4ost oi thcse controls are d€ scribedin ChaptersI and 13.The h\:o nost PoPrilarreftigerant controls are the thermostaticexpansionvalve (TEV) and the capillari, iube. These controls are de scibcd in Chapters5 and 13. The schematicdjagram in Figure 26-80is for a cir cuii us€d in a co fort cooling !nit. This s,vstemusesa

1014

Modern Refrigeration and Air Conditioning

A 120v Fi9we 26-79. Two types of water level contrcls. A-Float control. Float valve will open makeup watet valve when water level drops. Some valves are connected to electric switches that will shut off the unit if water level gets too low B-Probe type water level control. Solenoi.l opens when current stopsttavelin| acrcss electrodes.

1 Hp.orGrcal€r Diagram u6ing a largs€ligeEtionuni. Compressor Molor 1 Hp.or Less

hasa blower,il is usually Itth€installalion durinolhscooinq wir€drorunconrinuously

combinationfor small comfortcoolinEunits

Figure 26-81. Wiring diagtam is for a comfoft cooling unit that useshigh-ptessuresafety cutout and motor starter. (White-RodgersDivision, EmersonElecttic Co.)

Iow-voltag€,two-wire thermostat.The thermostat controls a rclay that will closethe motor circuit. If the motor cannotbe connecteddirectly to the line, and pressure safetydevic€sareto be put in the system,the wiring will be somewhatlike that shown in Figuie 26-81.The highpressuresafetyclltout is wired in seriesv/ith the starter coil. lt will openthe circuit iJ pressuresbecometoo high. Somesystemsrycle on cotnmandfrom a low-side piessure contlol. The thermostat oPeGtesa solenoid

valve mounted in the liquid or suction line. When the thermostat temperature is satjsfied, the solenoid valve will close. lvhen the low-side pressure drops enouglu the motor circurt will be opened. This is done by means of the presgure control connect€d to a matnetic starter. See Figure 26-82. The unit will then stop. A hiSh-side switch is also prcvided in this control. This conhol will stop the compressor if the high-side pressure exceeds a preset limit.

Figure 26-80.

Wiring diagran of thernostat rclay

Chapter26 Alr Cond tioning and HeatingControl Syslems

1015

Figure26-82. Comfortcaoling systemwirinE diagran. Note that thermastatoperatesthe salenaidvalve.System cycles as low side pressuresvaty.

The controlsfound in comfort coolint systemsarc: . .

. .

Thermostat (24 V ot 124 V) or thermistoi sensor (one-stageor iwo-stage). Evaporator icing control (freeze-upconircl), t$'o' wire 21 V or 120 V to control dampers/valves, or compressors when evaporator temPerature aPproaches32'F (0'C). V u l l i p l e . o m p r e * usr c q L q r c5el . r : 1 8 c o n ,o l - . Vulu, ) linder Lonores5o LrnloadinB.er uelcing controls.

Generall, Iarge air conditioning evaporators use the thermostaticexpanslonvalve for refrigerantcontrol. Someinsiallationsuse seveml such valves on one large evaporator io get maximum efficiency. Self-contained siEtems especiallythose hermetically built-may us€ the capillary tube refrigerantcontrcl. Theseconirolsare describedin Chapier 5. In addition to the rcftigerant control use.t on auto matic sysiems,a solenoidvalve is someiimesPlacedin ihe liquid line. This will auiomaiically siop the flow of refrigerantto the evaporaiorthe instant the condensing unit stops,or when the iow-side prcssurecontrcl opens. This is done so that the evaporator will not become flooded with reftigerant o'hile the condensint unit is idle, and 'illbe pumped down. Figule 26-83illustraies a solenoid refriSerantcon trol valve. This valve uses 5 W at 120 V ac. It has an odfice 0.1"(2.5nlm) in diameter.At a 5lb. PressuredroP acrossihe orifice, the refri8eratingcapacityis 1.3 ton for Rl2. It is 2.1 ion for R-22.For R-500,it is 1.62ton. In addition to the operaiing controls (thermostats), comJortcoolingsystemshave primary controlsand iimit Largerretuigeratingunits areusually equiPpedwith pressureconirols.The low- and high-Pressurecontrols are usually desiSnedto iock the circuit open if any unusual pressuresoccur.The operaiormust then manually iurn the systemon. This allows a carefulcheckfor faults.

Figure26-83. Crosssectionof salenoidrefri'erant contrcl valveused in liquid lineson ait canditioning systems.(SpotlanValveCo.)

The internal constructionof a combinationlow-Pressure and high-pressurecontrol is shown in Figure 26-84. Comfort cooling systemsuse severaliypes of limit . . . .

Motor limit controls. Pressurelimit controls. Temperaturelimit conirols. Fluid flo\^' limii controls.

Motor limit conhols are descdbed in Chapter 8. Suchcontrolswill stop the unit iJ curent dmw becomes too high. They will also stop the unit if ihe motor temperaiurerises to a dangerouslevel. The anti icing control is another t)?e of temperature limit contiol. (Thls is in addition to the motor ther' mistor or bimetal protector.) lt is located on the evaporaior.Shouldice accumulatethere,this controlwill oPen and stoP the system. Fluid flow controls stop the system in the event chilled water flow ceases.They will also stop the system if conditioned airflow stops or slows io inefficient amounts. Figure 26-85 shows an airflow signal switch or shutoff switch or both. Apaddle is moulted on a Pivoted arm. If airflo . is too great, it will move back through a small arc. It will trip an elecirical switch. Figure 25-86shows a similar switch for liquid flow, such as chilled watei or condenserwater.

25.1B.BHumidityControls On smaller units, humidity control systemsare almost always electric. Pneumatic systems aie usually usedfor iarge installations.Hurnidity is most often made higher by adding water vaPor to the air. Ii is most often lowered by cooling air belolv its clewPoint temPemture Thls condensesmoisture out of the air'

1016

Modern Refrgerationa.d Alf Conditionin

DlalKnob

Bolh Low and High

ar€norro b€ Disiurbed High-Pressure ior D.C,

1/8"Dia.CapiilaryTube

Fisure26-84.

motar cantrol lRanco NorthAmerica) lnner mechankmafair conditianing candensingunit pressure

{

}

(sz) l - l

t

l

Fisure26-85. Anflow siSnalswitch prcventsdamaget') sv;Em iom toa'high ai velacities lf dacity Eetstao high,it \\,ill nove the padclle,trippingthe electrical switch.(uI McDonnell& Miller) The electrical system uses a humidistai control aJld an electricalpower source.Iither a solenoiclor a motor operatesa valve or damper.The Pneumaticsystemuses a humidisiat control, piping, ancl a vacuum or pressnre source. The controlled vacuum or Pressure ihen acis upon a diaphragm_oPeiatedvalve or a diaphragm_ operateddamPer'

F i e u r e2 6 - 8 6 . l q u i d l l o r ' ^ ' t ( h t ' h t t l a l 6 1 ' r 6 ' tioA i. not 'utti' FFt th^ L''it ^ilt tla',,i,ro",, ",,", " . signalcitcuit, shut ofi the unit- or bath

llTT McDonnell& Millet)

Chapter26 Alr Condltioningand HeatingControl Syftms

1017

Humidistats A h 'llidistat is lsed as ihe contrcl device in a hu-

midity control system.It respondsto changesin humidir) : in doing so. il opens or clo-p. a .ontrol s) \lem. The sensingelement of the humidistai is called a hygtoscopicelement,S\ch an elementwill siretchas the moisture content of the air increases.Commonly used hygroscopic elements arei human hait wood, nylon ribElectronicsolid-statesensorsare also used. In elechonic solid-statesensors,the sensorresistancechanges as moisture content of the air chantes. Some sensors

. .

Hygoscopic salt (fof example,lithium chlodde). Carbon particles imbedded in a h),groscopic matethe resisiancedecreasesas rial. In ihesesubstances, humidiiy increases. the

The changein size,shape,or elecidcalresistanceof the sensing element is used to operate a switch or a pneumaiicsystem.Figure 26-87showsa humidisiat that usesa muliiple hair element.The conirol should be kePt dust-free. The covff must pemit free air circuiation over

Figure26-88. Electranichumiclistat.Elementvaries resistancewith changes in humidity. (Actian lnsttuments,lnc.)

The el€ctronic cleaner is connected into the electrical ckcuit of a heating/cooling system.It uses a single speedfan. Thereis 120V seffice io the cleanerand 240V sewice to the fan motor. This is shown in FiSure 26-91, The automahc water-cleaning system has a rvashing cycle with deterteni, a rinsing cycle, and a drying cycle. SeeFigur€ 26-92. SeNiceto electroniccleanersincludescheckingrectfiers and high dc voltage. High voltagesare used in th€se eledronic cleaners.They should be servicedonly by someonewith specialtraining on the model being serviced.Figure 26-93showshow the rectifie$ are rcmoved and the high voliage is checked.Note the heavy insulatoIS on the meter leads.The]' protect against this very dangerousvoltage.

25.19 AirflowControls Filute 26-87. A humidity control. Operating mechanismis sho\rn. Figure 26-88sho*'s a typical electronichumidistat. Its output amperage vades, based on an intemal res$iance that chanSeswiih humidity. SeeSection19.3.1for more infoimation on humidity measurement.

26.18.9 EleclronicCleanerConlrols Eiectronic cleanerc have an electrical circuit that converts 120 V ac io about 9000V dc. This circuit also has safety devicessuch as door interlocks,and seNice devices such as automatic washing and diagnosiic circuits. Figur€ 26-89 shows an elecironic cleaner electrical circuit. Note the two step-uptransformers,ihe door interlock, the fu11wave rectifiers,and ihe neon light circuit. The actual wiring diaFam is shown in Figure 26-90.

Airflow conhols constantly regulate air volume and temperature.If outside air is too cold, ihermostatswill causepower-operaieddevices to close the outside air damper. Thermostats also react if the recirculated air and outsideair is out ofbalance.They will open one damper and close the other jusi enough to produce the co ect mix. Damper motors are usually used-However,heated vapor elementmay also be used,as mav a Pressureor vacuum (pneumairc). lf air temperature is too high or ioo low (in the airflow to the foom, in ihe recirculated air, in the {resh air, or in the exhaust air), the thermostai will react. It will properly adjust the dampers. Pneumatic moto$ are used io vary the air supply as outside t€mPerature changes. One motor for operatinS dampers uses Power to open the damper. It works against spring pressurc, holding the dampers open uniil the thermosiat Points open. Spring pressure then closes the damPer' The motor opemtesthe damper through a gear ieduction train Figure 26-94 shows such a damPer-controlmotor and shaft.

Modern Refigefationand Air Conditioni

29.4MEG.

A-Iransfarmers B Door intetlock(safetyswitch) Figure26-89. Wiringcicuit fot an electronicai cleaner. .' (HoneywellInc.) C Rectif/ers. Conirol devicesthat reSulaieair volume in a distri_ bution system are called vadable ai volume (VAV) controllers. These devices use electronic components. They are Llsually part of a larger computer-controlled FryAC system.

.

24 psig sysiem = 30 psig io 35 Psig (45 psia to 50 psia or 310kPa io 344kPa).

Air pressure conhols are ofien used in large commercial and industrial systems. These cont(ol systems should be thoroughly checked each month.

26.19.1 PneumaticSystems Pneumatic(air) systemsare often usedto.ontrolair conditioning. Thermostais control a Prcssurized air line. Air in this line call operate pneumatic motors (a piston and cylinder or a diaphragm).Motors, in tum, oPerate dampers,valves,aJldswitches. The system's two main pads include sensing devices and pnerlmahc conirollers. Main LinePrcssures used are either 12 psig or 2,1psiS (17 Psia or 39 psia [117 kPa or 269 kPa]). Some systems operate at a The 12 psig systemactuallyusesan oPeratingPressureol I psiBto lc piiS , 8 P.id to J0 Ps a or 24 kl'a to 20- Lla) the 2,1p-i s)sremdcrudll)usesan oPerdtint pressureof 3 psig to2Tpsig (18psiato42Psia or 124kPa to 290kPa). The regulator reduces the suPPly air Pressure. The supply air pressurefor thesesystemsis as Iollows: .

12 psig sysiem = 18 Psig to 20 Psig (33 psia to 35 psia or 227kPa to 241kPa).

26,2O DistributionControls The heating and air conditioning control systems reviewed so far must have a method for controlling the distribution of the ar, watet or whatever medium js ,)sed. Distib tioll conttuts help to ever y and efficiently iransfer the headnS or cooling medium to the area where it is needed. These contiols ensure that steam, water, or ai is proPerly circuiatinS in the svstem In sieam systems, the zone control valves are oPerated upon a signal ftom a thermostat ln hot water (hydrcnic) syst€ms, pumps and valves must work in proper rem5 \ ide independent in greater depth. lirere, actuafheat-load calculations are *""1 165.onLrol i5 pro\ided at a relaiivel\loh (o-L discussed. Each local controller is independent-lt controls its specific system and has no interaction wiih any other conholing device. Ttpical localized controllers inciude:

System 26.22 EnergyManagement andFunctions Types

There are three general tlpes of ene€y manatement systems.

.

Time clocks.

.

Localoptimizarionde\ice)rfor e\dmPle lho'e lhdi confrolbamper) basedon zone iemPerafures)

Chapter26 Air Conditioningand HeatinSContml Sysiems Localized conirollers are used for relatively

simple

HVAC system control. SeeFigure 26-103.They are used . . .

lnstallaiion time allowed is minimal. Individual system eficiencies are more important than ioial systemmanagement. Minimum cost is desirable.

1027

The newer remote controllers are programmable through the use of microprocessors. SeeSections6.6.12 and 6.6.14.It is the most common lype of toial enerty

management systemin usetoday.Thisis due to the number of uniis typically controlledand the lower cost of themicroprocessor devices. An illustrationof thistype of controiier is shown in Figur€ 26-105.

figure 26-103. TheseHVACcontrollershaveavatiety of diBital,analoe,and universalinput/outputs.Theycan operatea5standalanecontrollersornlay be linkedwith atherdevicesana netwotk.(SiebeEnviontnentaI Contrals)

26.22,3 RemoteControllers A renote collttollet operatesdifferently from a localizedconiroller.More than one energy'consumingdevice can be controled. It can also be iocated some distancefrom the devicesit controls.Thesecontrollers, Figure 26-104,are used to minimize overall energy de-

Figure26-105. Thisstand-aloneeneryymanagement and tempetaturecontrolsysten hasdirect digital contrcl capabilities.(Landis& Cyr Pawers,lnc.) Functions normally found in a remote controller include: . .

. . .

.

Figure26-'f04. A temateenergycontroller.Many eneryy-consumin!devicescan be controlledat the same time. (Control Systemslnternational)

Retflotestai/stop.The controllerturns systemsand deviceson and off at certaintimes. Optitfiized staltlstop. Devicesare controlledbased on .ome prepro$dmmed{hedule to nrnrmne creryy use. Status monitoriflg. Used to indicateif the systemis operating. Alarms. Devicesthat indicateif a systemis operat int incorectly. Defiafld .oftttol,'lhe overall demand for electrical power is moniiored and modified for minimum energy consumphon. Dttty cycling. Tvfii]1g systems on and off in cycles. This mainiains minimum energy consumption with th€ least effect on the building's users

A remote contrcller is used when multiple functions and systems (approximately 50 maximum) require

lo2a

on and Air Conditoflng Modern R€Jrigerat

26,22.4 CentualizedComputerControl The centralized computer control system is the most elaborate of the Total Eneryy Management systems. One or more centralized comPuters make control decisions These are based on opemting data, programmed information. and data aiready stored in the comPuter memory. This is the most costly of the three t'?es of TEM svstems0ocalized,remote, and ceniralized computei ;ontrol). Howevet it does olfer the widest range ;f control functions. In large complex strllcturcs, this ceniralizedsystemresultsin ihe bestoverall total enerty consumption conirol. Figute 26-106 shows a central control site for this ilpe of Total Energy Management ' The centralizedcompuier conirollei is used in most neirlv,on to u-e heat 6ao by a' much as glasstinted a bluish Sray to reduce the solar glare and cooling 1oad.

Roo{extensionsover a window will rcduceth€ area exposedto the sulr. Double-glazedwindows exposeclto sun ravs reducesolar heat absorptionby 15% Awnings to shade glass windows exPosed to the sun can reduce the heat load by 55%. Humidifier Heat Load During ihe heating season/water vapor must be added to the aif for comfortableconditions Heai to Produce ihe water vapor may come ftom heated air, fumace heat, or electricheat. The amount of heat needed is figured as followsi The number of volume chanSesPer hour musi be known. Generallt one changePer hour is satisfactoryfor homes.The number of gains to be added per Pound of ait to obtain the required relative humidity must be known. SeeChapter 19Formulai Pounds of air per 24 hours x increasein Srains: grains/day =lb of water/day gt./Ib. $./day/7A00 ]b. of water/day/8.34 lb./ga|: $I /day To calculate: \olume

' charg ' e- hr

ln.

d-;;= o/^) JJ,UUU

-

Example: A homehas12,000ft3.Thegrainsto be addedPer poundof air to changeihe air ftom 35'F(2"C)and 907" iiH to 72'F(22"Oand 40%are20.Find the totalgallons of waterto be evaporated Perday. Solution: z 1 20 :12.000 :. 33,000

240,000 - -. . Jg a, l .,d a y 33,000

Heai Loads Energy

Btu/hr,

Ee c l r c in Foom Morors, E eclric;/Hp Oul oi Foom tvolors,Electic/Hp

8il /dd)

UPIA 112 U P T O3 U P T O2 0 UPJO 1/2 I.JPTO 3 UPTO20

3415 4200 3700 2950 1700 1150 400 3415

1020 1230 1080 880 500 340 120 1020

1100 550

320 160

300 675

88 198

36 400

10 120

800

230

140

Slnirg Dancng

110 370 700-1500 204444 590 2000

by variausenegysourceswithina building figfie27-22. Heatreleased

Chapter27 Air Condit onlng Systems Heatn8 and CoolingLoads

The amountof heai(in Btu/hr.)neededto evaporatethe wateris found as follows:

the shade)have a U-value of 1.25.Ifthe iemperaturedifferenceis about 12"F(7"C),the multiplier becomes15.

Formula: Volumeof house \ ( h d r S e i p e r h o uIr3 . s qf r o f a l r / l b . x (Br./lb.indoors- gr./lb. outdoors) x 970.3Btt:/lb./7D00gr,/1b: Btu/hr. - sr, n" volume chdnge..hr. F^-iL

12x1.25-15 Thefollowingis a way io makea roughesiimate. The chart identifies COP, which is the ratio o{ output divided by input. The output is ihe amount of hear absorbed by the system. Input is the amount of energy put into the system. Remember iha! on the average, a medium-size room needs 5000 to 6000 Btu/hr oI cooling.The averagewindow conrJortcooling unit will adequately handle the cooling bads as follows:

Example: Using the samenumbers as beforc, the volume is 12,000 ff. Thegains are20.Find the requiredhear. Solution: 12,000 1 20 _ 240,000 ^,-- - , r,. hh, hr 97.75

= l/2 L|P.,COP = 4.71 0-6000 Btu/lt 6000-9000Btulhr. = 3/4 hp., COP = 4.71 9000-11,000Biu/hr. = t hp., COP :4.32

97.75

Air Conditioner Heat Load Figure 27-23is a form used to calculatethe coolinS heat load for a room. By multiplying the area of the floors, walls, and windows by multipliers, the amount of required ener8y can be determined.The nultipliers are obtained by multiplying a typical U-value by the temperature difference. For example, the wnrdows (in

27.1.3 TotalHeatLoad It is best to set up total heat load calculationsin table form. Figure 27-24shows a iypical heat load calculation for a 24' x 32' (7.3m x 9.8 m) house.Refer to Figure 27-7, Note that the temperaiure difference Ior the ceiling is only 35'F (19"C).Also consider that ihe roof

EnefgyRequlredlor Cooling

Heighl: No.r-

Sze:-

Facinal

x -

suf exposed( rteror shad€s) 60=-Blu/hr-watis 40=-Biu/hr-wans

Sunexposed(awninss)

35=-Biu/hr-wans 1 5= - B l u / h r . - w a t l s

East,Nonh,or shaded:

f i .x 8 = - B 1 u / h r . - w a t 1 s s q .f r .x 5 = - B 1 u / h r , - w a f t s T h n w a l a l e x p o s u r e s -: Blu/hr.sq.fl. x l0 = -sq.fl.x 4=Biu/hr. Blu/hr.sq. n. x 10 =

wails walts walts

Btu/hr.BtL/hrBtu/hr

walts walts walls

Souih,Weslexposure: - s q ,

3= 8 =2 0 =-sq.ft. -

x

4=-Bl!/hr-wans

sq.l x 400= -

Blt/hr

wans

x 3.4=-Btu/hr.-walts =-Biu/hr.-walts Total: -

Figure 27-23.

1045

Btu/hr,

walts

This table can be used to cletermine the cooling needed for a typical residence.

't

046

M o d e r nR e f r l g e r a t iaon d A l r C o i d i t i o n i n g

Figli]e 27-24. Typicalheatload calculationfor 2r' x 32' hane havinBan 8' ceiling heiSht.

servesas added insulation. it keePsthe attic temPerature higher than the outdoor iemPeratureThe attic temperatuie canbe accuratelycalculatedby makint theheat leakinginio ihe attic in winier equalthe heatleakingout

x Ceilins - area x (70'F [attic temP ]) U. = Roof area x (attic temp. 0"F) x U.. WhererU. = U-value of the ceiling U, = U-value of the roof Note that most homes have an 8' (2 4 m) ceiling heisht. Manv homesmay have 9' (2.7m) or 10' (3.0m) tusi floo' ceilings. Va.lt;d ceilings require that the total wall areabe calculatedby adding the dimensionsol the entire wall, including the "iiangle area" at the top of vaulted rcom's walls. The lorver ceiling helPs Prevent trapping hot air near the ceiling The hot ceihlg ail can be used for heaiing Eachheatleakagevalue is obiainedby meansofthe Iollowing formula: Heat leakage= area x U-value x temPeraturediJference -odd' s A qu'cl nethod u"ed to eshmitetotalhFar Jrown in Figur€27-2q.\ote thar lhe hed!load i' brsed

ResldenlialForcedAirsyst€m DesignGuide(For EstimatlngPuQosesOnlv)

rzoo 6

r3oo P

bated on valumeoi conditionecl Eigurc27-25. APptoximateheat laadchatt far winter heatinSand summercaoling is space.lDetroil EdisanCa.)

I hdper2

a i r , o n a i r o - B ( ) ' l F m - l ' F a l_ g " n d ( o o l ' r S l o d d

1047

Residential ForcedAir SyEtemDesignGuide Air Distribuiion sizes Outlel(ln.)

Supply D uct(ln) (Da.)

200 300 400 500 600

4

700 800 900 1000 1100

5 5 6 6 6

1200 1300 1400 I500 1600

6 6 7

6 x 5

7

8 x 5

1700 1800 1900 2000 3000

4 1 1 2t 4 1 1 2t 4 1 1 2x 4 1 1 2x

3 3 3 3 2 1 1 4\ 1 0

5

8 t 3114

2 1 1 4t 2 1 / 4x 1 4 x 2 1 1 1 4 2 1 1 4\ 1 0 x 3 1 / 4 2 1 / 4\ 2 1 1 4\

10 10 '10 10 12

4 x l 0

2 1 / 4\ 1 2

9 10

10000 12000 14000 16000 18000

l3

x 1 0 r 1 0 x 1 0 x 1 0

6 6 6 6 6

6 6 6 6 6

x x r x x

l 0 l 0 l0 1 0 1 0

6 6 6

6 x 10

7 I I I

6 t

I 8 8 8

4 x 1 2 4 x 1 2

Eouv.

8 x 6

I ^ 11

13 8 I 8 8 8

x 8 x 11 x 1 3 t14 x 1 6

14112 15 16

a 8 4 8 8

! 18 \22 , 2 4 r 2 6 r 3 0

24\24

18

8 x 3 4 8x39

111t2 12

(Dia.)

6 6 6 6

12x6 14xo

x 6

T 112

6 6 6 6 6

Grille

1 0 , 6

7 7

4000 5000 6000 7000 8000

20000 25000

Ceilinq (Dia.)

Equiv

6.t24

6:30 8x30 8/30

l1 12 13

8 x 1 8 8x22 8\24

1 8 x 1 8

15

18r l8

8x2a Sx36 Sx46

24/30

16 18 20 20 20

24x30 24t30

22 22

8x60

valuesfaund in Figurc27-25. (DetroitEdisanCo.) Filure 27-26. Duct sizesbaseclan estimatecl on room volume. The table also includes cooling. A method for estimating duct sizes is shown in Figure 27-26.This tableis used as a companionto the heat load table. For a given rcom volume, a recommended supply and retum duct size is 8iven. Outlet and retum 8rille aleasare also shown. More information on the calcula iion of Droper afu distribution svstems is found in Chapterb. Standardworksheetsaie availableIor calculating total heat load. SeeFigtre 27-27. Heat gain calculaiions to determine the total building cooling load are similar to heai losscalculations.The temperature difference is based on the localiiy being considered. Indoor tempefature is usually designed to be 75"F (24'C) at 50% relative humidiiy (RH). Therefore, if the sujnmer design temperature is 100"F (38'C), the temperature difference is 25'F (14'C). This temPerature

dilference is for Ioad calculations only. In practice, a 20"F (11"C)differenceis recommended. Other heat sources must be considered. Sr.mload, electricalload, and occupantsare ]arge enough sources of heat to be included in the heat load calculahons.

27.2 DesignTemperatures Contactthelocalweathetbureauor lo€alchapterol the AmedcanSociets/of HeatinS,Reftigerating,and AirConditioning Engineers(ASHRAE)for data on desiSn rcmperarufes. Always choosethe outdoor desiSn temPelatures (ODT) on the low side. Heaturg plants that are overstackand chimneytemPeraturcs worked causeexcessive

Modenr Rei'iseraton and Air co rdltion ng

1 048

Besidential

WholeHouseWorksheet WINTER:InsideDesignTempOulsideDesignTempSUMTIEF:

Zp State'F-OutsideOesignTemp'F-lnside DesignTemp-

COOLING

COMMONDATASECTION

HEATING

'F )F

'F = HealingTemPDitrerence"F = CoolingTempDitlercnce-

SUBJECT GROSSWALL

DOOFS & W I N D O WfSi a b e A o rB ) NETWALL CE L]NG

FLOORS

-,!"TXT="!ttitt"

ffit'f,

001833 :

x

x 0 18333 SUB-TOTAL BTUNLOSS(per10 F) FACTOF(Tabe C) ADJUSTMENT

x

TOTALBTUH LOSS

pEopLE-

JooBruHGer

1}i!g5,"'"',;'l'""' '

.

.

.

. 1200

BTUH APPLIANCES only) SUBToTALBTUHGAIN(roomsensible (TableF) DUCTLoSS/GAjNFACTOB (Sensb e Gai.) sUB-ToTALBTUH (s!b lola x 1.3) F EI'IOVAL L4OISTUFE

x 1.3

TOTALBTUHLOSS/GAIN & WOODFFAMEWINDOWS TABLEA.HEATING-OOORS ( P E F1 0 . F ) Fors idingglassdoors- uselactorsforthesamelypewfdow

slls e Pane

& WINDOWS TABLEB-COOLING-DOOBS Factorsassumewndowshavensdeshadngby drapeiesorvenenan blndsard sidingglassdoorsarelreatedas wndows

9.90 1 0 . 4 51 1 5 5

4 . 7 5 5 . 2 5 6.50 6 0 9 7,25 3 . 4 1 3 3 5 4.90

3.80 4.39 5.46 11.0

5.0 Skylghls

TOTALS

1 1 . 0 71 1 . 6 912.92 6.65 7 . 3 5 4.75

MULTIPLIEBS TABLED_INFILTFATION winterAir changesPer Hour

4.60 3.20 1.90 (F-5)W/Slorm

1_70

SummerAir ChangesPerHour FACTOFS{HEATING TABLEC-ADJUSTII,!ENT 50 5

30

page) Fisvre 27-27, t-Jsethis ||atksheetto catculateheat tassesand p.ains.(The Tnne Canpanl lconLinLled,next

Chapter27 Air CondirioningSynems-Heatingand CoolingLoads

1049

HEATLOSS& GAIN FACTORS TABLEF

TABLEE CONSTBUCTION FACTOBS HEATING & COOLING

ryPEOFCONSTRUCNON

Calcuale only I duct s localadin 6n unconditonedspaco

DUCTLOSSMIJLTIPLIEFS

1 5 . 20. 25'

CaseI " SupplyAn Temper.tuE6Below120!F

Walls-woodtramew/ sheering& siding, von€s or otherlinish A) No islaloi rr2 GypslmBoad OpenCcq soaca a2

B) Frr cavib/ns!aroi + r'2 GypsumBoad c)Ri3cEvryhsurarion Dr F 13caviyinsdario^ 3/4 Beadeoa'n(R 2.7) E) Rrecavry i&aron + r2 GypslmBoad F) Fnscaviv nlaron + 3'4'EntudedPoy

a) AboveEade No ns!aror

D) Beronqrade No 6u roi

CEILINGS(Use Sq. Ft.)

Dl 5rr 6rr, rnsuraron F 1e

DUCTGAINI\iULTIPLIEBS

i) carhedEtpe No nsraron(rcdrceiiqconbnaron) 4 carheddryp€ Frr l,oorcains..ffbiaioi) () carhad'a\ipe u le (,ooite rnq6mbnaronl rype F 22tootcerhq.onbnaion) L) Carhdd,a Mr caihedErtpe R.26(rco'tsnocombmrioi)

FLOORS(UseSq.Fl. OF LinearFt.) FrooE ove, unFndrionsd spa€ ($.3q. h ) spa.e liorveiiad] Al owba*medo,endosedc6w

B) SameasA + Rrr isuaroi c) samsas A +Fieinsuraroi D) oYe,v4rEd spa€ or saraqo E) overvenred spaceor qaGqe+ a 11insurarion F) o€r!6id

remenbprlhdl a 5hon belt life or " broken belt may be the result of an unusual overload (excessive

the fouowing method€: Tlace chemicals. Halide torch. Ultraviolet fluorcscentleak deiector' Electronicleak deiecior Foam leak detector (soapbubbles). Pressuredse method.

Tlese leal-testing techniclues arc described in Chapters12 and 15. Some technicidn-hill pui a relriEerdntcolored with reddish dye into the system.Then, red discoloraiion on the metal surfaces $'i11reveal the source of the 1eak. Use of a halide toich on R-12 systemscan locatea leak that amounis to I lb (045 kg) in abour fourieen years.When using a halide torch, an exPloringtube end iniffer is placednear the joint being checked tf ihere is a 1eak,some escaping refrigerant is drawn uP the tube. It passesover a PfoPane or acetyleneheated coPper element. If there is refrigerant vapor in the all samPle, the flame will tuln green. Danqer: whet R-12 i. burned, rery poironous pho'eene-gasi. produced.Atoid brealhingfumc< trhen sslem rilh a lor(h hpe ieaLie'ring an air conditioning tester.

1080

and Alr Conditioning ModernRefriseration

The ultraviolet fluorescent leak detection system is used on rcsidential, commercial/ and arltomotive systems. Mosi ultraviolet iights used for automohve service use a 12-volt ultuaviolet light that can be directly attached to the vehicle's batiery. Figure 28-45 shows a t]?ical kit including leak dye injector tool, quick-connect fittings, ultraviolet litht, and ultraviolet glasses. SDeciallv formulated f:luorescent addiiives are used to find thesmallest Dossible leaks ln ihe svstem. It is effective on leaks as shall as 1/4 ounce par year. It can be us€d on any iype of reftig€rani. A technician inserts a premeasured fluorescent additive into the refriSerant system with the mist intuser Then the lamp is used. Ii pinpoint, eak. in Lhefrltings,tubin8. .oils. or.omPre* sor.The add:ri\e -ernain. in the sy'lem, d]]o$ in8 fuiure leak inspection. Frequently, leaks are found by the use of arr ele€_ tronic leak detector This is a hand-held elecfronic device with a pulnp that is calibraied for detecting the reftiterant used. The most sensitive models can detect leak that would amount io 1 lb. in forty years. A technician moves a hand-held probe across the area being tested. ArL air sample is drawn into the device by a sma[ ptmP built into the detector. II refriqerant is detected, the leak detector alerts you wiih an iudible tone The tone increasesin intensity with the amount of reftigerant being detected.Mosi models deteci both R-12 and R-134a Leaks caJl be deiecied when a vacuum is being drawn. With the vacuum Pump mnning, shut off the vacuum valve on the maniJold. If the vacuum $uge

needle starts to creep back toward zero (atmosPheic prcssure), there is a leak in the syst€m. The leak must be corrected before completint the vacuum operation for drying out ihe system. This test is a good practlce when evacuating a system. It can help conseffe r€frigerant and needlessventine into the atmosphere.

wear of the compressorbearings, Pistons. dngs, and valves. It will also cause scoring of the shaft seal. Therefore, ii is importallt to maintain the corect amount of oil in the system. Mosi refrigerant reclaiming stahons Ior R-12 oI R-134a contain provisions for measuring oil removed frcm the system. The amount of oil rcmoved during evacuation or reclaiming of refriSerant should be caretu11ymeaswed. It should be replaced during charginS Always check the manufacturer's service manual for the corect oil io be used. When system components are rePlaced, they may ne€d some additional oil. Therefore, ihe ieclmician should check the selvice manual for the correct amount of oll in a system. Additional oil may also be needed if the system has been raPidly discharged This occws when a vehicle is involved in a collision.

Figure28-45. Ultraviolethght ktl use(lfot leakcheckingaf autamotiveai conclitioninSsystemsThe ultravioletSlasses dt' Tlllnr',ur"nu tn, t al uo,escpnr orotide beLLpr,ub,t,Lt

ng Air Condiuon 2S Automotive Chapter

SiglrtGass

Somecompressorsallow checkilg of the oi]. Some must be removed from the vehicle to checkthe oil level, while others require a dipstick. The t'ire dipstick is inserted through a bolt hole in the compressorcrankcase to checkthe oil le\.eI.Check servicemanual procedures if in doubi.

The compressor must pump e{ficiently. If the compressor capacity deoeaset maximum cooling will not be obtained. A compressorshould pump vacuum to 15" Hg (381mm Hg) in a short time againsi normal head pressure. If this camot be done, the pistons,rings, or intake vah'esare leaking (wom). ReiriEierantis used for testing lor compressor ieaks.A carefulexaminationof gauge pressuresis used to evaluate compressorpumping capacity and valve Notel Neil?rruli i ca lressor nlessit lns the correct dnaunLaf clen rcftigennf ail. Some compressorsha\re a screeninstalled in the compressorbody under the suciion line moul1tirg. This screenremovesforeign particlessuch as dirt, sand,and metal chips. This prevents damate io the comPressor. The screer should be inspectedea.h time the refriSer ant is removed from the system.It should be cleanedif necessa4..If the screenis blocked (clogged),or almost blocked,the systemwill not refriSeraie.Ir addition, the compressorcrankcase\{ould be under a vacuum. Low sjde pressure would be abo\.e nomral, and high-side pressrrrewould be belo$' normal. Liiile or no reldgerani would circulaie.

Charging and testing of both R-12 and R-134a systems arc very similar When opening a system for servicing or refrig€rani disposal, certified rcfriSerant recoveryequipment must be used.SeeChapter 10. Someautomotive $Tsiemshave a sight glassto aid in charging ihe slrsien- See FiSure 28-46.No bubbles should appearin the sight tlass after the systemhas operatedfor a few minutes.If the systemis short of refrig erant,bubbleswill appearretularly ln the siSht glass.A slrstemlvith litt1eor no refrigerantwill not have enough liquid to folm bubbles. An overchargedsystemmay be detectedby exces sive head pressure.This conclitionlvill not show in the -'ghr gla--. l'igL -).tem hedd pr"-+rre trtl1be .\o*r u Le hiqh -r.reg;uge.Chp l l, -ehouldcon{aina filler drjer in A. the suction line of the system B. the liquid line of system C. cylinder inlet D. machineinlet

Refrigemnt must be removed ftom the condenser outlet when -, A. the evaporatoris leaking B. the compiessoris not operating C. the condenseris overhead D. the condenseris below the receiver Once liquid refrigerant has been recovered, any vapor which is left is -. A. bled to the atmosphere B. pumped into the high side C. pumped into a recovery unit D. condensedby the recoveryunit Refrigerant can be removed from the condenser when -, A. the compressor is not working B. the condenser is mounted above ceilint height C. no receiveris present D. no dischargevalves are present

4.

Operating pressure may be below aimospheric Pressure. B. Becauseof the re{rigerant's low boiling polnt. C. Non-condensables in the system. D. Chiller may be openedfor maintenance. One method of recoveringrcfrigerantfrom a chiller that is cost effective and meets EPA requirement is A. vapor rccover B. use a liquid pump C. rccover liquid firct, then vapor D. recovervapor fust, ihen liquid When rcmovin8 R 11 or R-123from a system,rcmoval starts with A. vapor removal B. liquid removal C. liquid/vaporremoval D. oil separation The maximum pressure of nihoten when leak testino.Fnrnf,,o,l