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Handbook of Industrial Air Technology Applications

VENTILATION AND AIRCONDITIONING OF ELECTRICAL EQUIPMENT ROOMS Second, revised edition

Kim Hagström Jorma Railio Esko Tähti

February 2003

PREFACE This document is the revised version of the first pilot Application booklet for the Handbook of Industrial Air Technology. This text is based on INVENT project "Design Criteria for Ventilation in Electrical Equipment Rooms", done in Finland in 1991-94, reported in Finnish as INVENT Reports 36 to 39. It has been re-structured to follow the basic structure of the Design Methodology for industrial ventilation, also in order to test the methodology in practice. After being published as a draft manuscript in 1996 (INVENT Report 52), the text has been reviewed by Mr Martti Lagus (Nokia Telecommunications, Finland) and by Mr Peter Kiff (British Telecom). In addition, the described design methodology has been validated by several Finnish companies who actively apply the results of the INVENT project, either as end users of equipment rooms, or as suppliers of air-conditioning systems and equipment. The text has been revised after review by Mr Jan Gustavsson (Camfil, Sweden), Dr Paolo Tronville (Politecnico di Torino, Italy) and Dr David Shao (Ericsson Radio Access, Sweden). The English language of the revision has been checked and corrected by Mr Eric Curd (U.K.)

Helsinki, December 2002

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VENTILATION AND AIR-CONDITIONING OF ELECTRICAL EQUIPMENT ROOMS

CONTENTS PREFACE.......................................................................................................................... 2 CONTENTS....................................................................................................................... 3 SUMMARY ....................................................................................................................... 4 1. INTRODUCTION......................................................................................................... 5 1.1. Classification of environmental parameters for electrical equipment.............. 5 1.2 Typical environments of electrical equipment located in ventilated indoor facilities .......................................................................................................................... 5 1.3 Application scope .................................................................................................... 6 2 DESIGN CRITERIA ..................................................................................................... 8 2.1 Given data................................................................................................................ 8 2.2 Process description.................................................................................................. 9 2.3 Building layout and structures ............................................................................ 11 2.4 Target level assessment......................................................................................... 20 2.5 Source description................................................................................................. 36 2.6 Load calculations .................................................................................................. 39 3 SYSTEM PERFORMANCE....................................................................................... 41 3.1 Selection of system ................................................................................................ 41 3.2 Selection of equipment.......................................................................................... 53 3.3 Implementation design ......................................................................................... 62 4 COMMISSIONING..................................................................................................... 66 4.1 The construction schedule.................................................................................... 66 4.2 Checks .................................................................................................................... 67 4.3 Spare parts............................................................................................................. 67 4.4 Documentation ...................................................................................................... 68 APPENDIX 1 - BASIS FOR DESIGN FOR VENTILATION IN ELECTRICAL EQUIPMENT ROOMS, CLIMATIC CONDITIONS ................................................ 76 APPENDIX 2 - THE MEASURING PRECONDITIONS OF GASES...................... 77 APPENDIX 3 - REFERENCES..................................................................................... 79

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SUMMARY There has been a lack of "common language" for the design, construction and operation of air-conditioning of industrial electric-, electrotechnical- and control rooms. Requirements for the equipment and its environmental conditions are presented in different standards and guidelines in such a way that many interpretations are possible. For example, a given temperature limit can have been regarded by the end user as an absolute maximum, while the equipment supplier could allow it to be exceeded (within another range) for a short period. As a result of this, • in some rooms the environment is too severe, resulting in operational errors and equipment failures, which really can be worth more than the whole equipment • some rooms are conditioned unnecessarily well in relation to the actual environmental requirements, resulting in high investment costs, due to oversized (or unnecessarily double) air-conditioning equipment, or in high operation costs. An INVENT project was done in 1991-94 to tackle this problem area. The participants in the project represented different supplier and user groups such as: HVAC equipment manufacturers and suppliers, HVAC consulting engineers, electrical equipment manufacturers, process automation- and -control system manufacturers, and end-users from different trades of process-industry: pulp and paper, chemical industry, metal industry. A service product was also developed, in order to analyze the state of existing equipment rooms. This work was done in 1995, and the results can be utilized in commercial basis now, and several project references already exist. The knowledge gained in these actions has been the basis of this application. Modern electrical equipment containing electronics is very sensitive to their environmental conditions: temperature and humidity, chemically and mechanically active substances etc. In highly automated process industry a failure in process control equipment may cause losses in production that are many times worth of the equipment itself. Just to mention one example: a paper machine breakdown can cost up to 30.000 € or USD/hour. Minor improvements can be also done with low costs. Very often the tightness of the room can be improved so that the ventilation rate for maintaining over-pressure can be adjusted to a much lower level. A typical pay-back time for sealing the room properly is 0,5-0,7 years and investment less than 1000 € or USD/room respectively. The benefits from proper design, construction and use can be summarized as follows: • better operating conditions • prolonged lifetime for electrical equipment • improved reliability of the systems • efficient use of the systems • improved knowledge of the condition of the systems • improved skills of he maintenance personnel 4

1. INTRODUCTION 1.1. Classification of environmental parameters for electrical equipment The basis of the environmental classification for electrical equipment is covered in EN 60721-3-0 standard. International recommendations for environmental conditions in electrical equipment rooms are covered by the European standard EN 60721-3-3. To standardise design practice the above should be used in ventilation systems design. Environmental factors covered in EN 60721-3-3 have been divided in the following groups. • • • • • •

Climatic conditions (K) Climatic special conditions (Z) Biological conditions (B) Chemically active substances (C) Mechanically active substances (S) Mechanical conditions (M)

The environmental conditions in EN 60721-3-3 for electrical equipment room are covered in various classes. Electrical equipment manufacturers define the special requirements of each device according to EN 60721-3-3 in the following manner: A definition such as the following 3K1/3Z1/3Z4/3B1/3C1/3S1/3M1: The code -3K1

-3Z1 -3Z4 -3B1 -3C1 -3S1

Defines climatic conditions. In class 3K1, the target temperature value is 20 - 25o C in the range 18 27o C. The relative humidity target value is 30-60 % in the range 20-75 % and the absolute humidity ranges from 3,5 - 15 g.kg –1 Z-class describes the special climatic conditions, including the surroundings thermal radiation. shows the permitted air velocity if different from the K-class value. In this case it is 5 m.s-1. With special condition classes, it considers how a device reacts to water. describes biological conditions. Organisms or animals are not accepted in the 3B1 class. A demand that covers chemically active substances. This defines the permissible concentrations of corrosive gases in the space. Mechanically active substances. Defines the permissible concentration of particle contaminants e.g. dust, sand etc in the space.

1.2 Typical environments of electrical equipment located in ventilated indoor facilities Table 1.1.1 provides a general idea of the "environmental tolerance" of equipment in different spaces. A nomenclature of electrical equipment rooms has not yet been

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determined; Rooms of similar names in different industrial plants can contain very diverse equipment. Therefore, the environmental requirements for each room have to be checked individually during the various project stages. 1.3 Application scope The environmental classification for electrical equipment and the design basis for ventilation represented here, consider all indoor spaces where electrical equipment is located. Chapters 3 (System Performance) and 2.3 (Building Layout and Structures) emphasize ventilation of electrical equipment rooms (computer-, tele-, automation and current supply rooms).

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Table 1.1.1 Operating Environments of Electrical and Electronic Equipment, Ventilated Indoor Spaces TYPICAL ENVIRONMENT

THE ENVIRONMENT CLASS OF THE EQUIPMENT ROOM according to the standard EN 60721-3-3. See 1.1 for explanation of classification

A Control- and automation rooms a1) workspaces separated from the process a2) automation rooms a3) cross-connection rooms (measuring equipment, monitors and connections) Computer rooms

3K2 / 3Z2 / 3Z4 / 3B1 / 3C1 / 3S1 /

B Electrical equipment rooms -rooms that are separated from outdoor spaces and the process b1) tele cross-connection and device rooms: b2) electrical equipment rooms of the production: (motor use, MCC) b3) electrical exchange rooms:(main distribution centres, sub-main distribution centers) b4) transformer rooms (internal)

3K3 / 3Z2 / 3Z4 / 3B1 / 3C1 / 3S1 /

C Assembling halls in the electronics industry -circuit card production, assembling of micro electronic components testing and adjustments, assembling of fine mechanisms and fibre optics

3K2 / 3B1 / 3C1 / 3S1 / 3M1 /

D Production spaces in the metal industry -engineering workshops, light metal industry, bulk assembling: (motors, robots, control devices) -cable spaces

3K4 / 3Z2 / 3Z4 / 3Z7 / 3B2 / 3C2 / 3S2 /

E Production spaces in the process industry -spaces where contaminants and corrosive gases are typical:(instrumentation with protective cover, motors, control device)

3K5 / 3Z2 / 3Z4 / 3Z7 / 3B2 / 3C2+C3 when necessary/3S2 /

F An open, dirty industrial space -dusty spaces in direct contact with outdoor air, foundries, ore mills, waste treatment plants:(equipment with protective cover, suitable for outdoor use) -outdoor transformers

3K6 / 3Z2 / 3Z4 / 3Z7 3B2 / 3C2 / 3S2 /

G Movable containers -control cabinets and electrical rooms that are movable during use (for example military purposes)

3K2 / 3Z2 / 3B1 / 3C1 3S1 /

(As above, except 3K1)

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2 DESIGN CRITERIA 2.1 Given data 2.1.1 Meteorological data Consideration of external temperature, humidity, wind forces and solar radiation are necessary in order to determine the cooling, heating and moisture loads. The design criteria shown in 2.5 have been compiled to meet the requirements of the standard EN 60721-3-3. If the maximum temperature 99% value is used i.e. (the temperature for 99% of the time below the design value). However, if a customer wishes to use higher design temperature for operational reliability the design parameters have to be agreed with the customer. 2.1.2 Air contaminants. 2.1.2.1 Chemically active substances (corrosive gases). In certain areas of the process industry (such as the pulp, chemical and petrochemical industries) and in cities, the concentrations of corrosive gases may be higher than the permissible concentrations for electrical equipment. In a corrosive environment, electrical equipment is easily damaged shortening the operating life. It is difficult to obtain information on the exact environmental air purity since: Outdoor air purity is a complex matter: the concentrations measured in the same place can vary within 1:100. This variation depends on wind direction air pressure and on process malfunctions In recent years air purity is constantly improving due to various environmental protection acts. For these reasons, details that could easily be used in defining the outside air on a design basis cannot be developed. The following approaches can be used to define the contaminant concentration of the intake air 1. Accurate concentration measurements. This however is not often practical, as: The measurements have to be carried out over a long time period (minimum 6 months) if exact initial values are required. To obtain accurate information measurements have to be obtained close to the area of concern. Attention has to be paid to the fact that a new building will create changes in airflows, which can influence standard design requirements. 2. Estimating the concentration beforehand. This can be done by the copper-strip method.

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If the measuring period is long enough, and the concentration is measured at the air intake, provided the copper-strip is in a warm location. The contaminant ratio can be 1:4 within a few meters of the air inlet. 3. General measurements of the air conditions. For example in Finland, these results can be obtained from the following sources: - The Environment Department of the company. - Measurements carried out by the county, city or town authorities. - Meteorological Institute data 4. By rough estimations. For example tables provided by the equipment manufacturers can be used. 5. Experience. This is probably the most important way knowledge is gained; it depends on experience, regarding filters life and equipment corrosion. This is accomplished by comparing practical experiences with similar plants in the organization or in other factories. While dimensioning filters the possible sudden pressure changes caused by malfunctions in the process have to be considered as these changes can cause the gas concentrations to momentarily rise up to 10-100 times the average concentrations. Measuring preconditions are described in Appendix 1. 2.1.2.2 Mechanically active substances (sand, dust) The outdoor air data, relating to dust will not normally provide a base for selecting particle filters. In 3.2.3 consideration is given on how to select a filter for electrical equipment rooms. The surrounding dust concentration can be defined by similar principles as gases. 2.2 Process description 2.2.1 Introduction Regardless of the electrical equipment installed, there are usually no other emission sources in electrical equipment rooms. In control- and automation rooms however, employees may occupy the space for long periods of time. Internal loads in electrical equipment rooms are: • the heat developed by the equipment • the emissions from humans • (control cabinets and automation rooms)

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•

In battery rooms hydrogen is liberated into the air, and care has to be taken regarding explosion hazards.

The role of the ventilation in electrical equipment rooms is to: • remove the heat developed by electrical equipment • keep the room clean of contaminants from the surroundings. 2.2.2 Typical electrical equipment room A typical electrical equipment room has equipment cabinets positioned in several rows. Many different-sized cables are fed to and from these cabinets either from below or above. In the process industry the cable space is usually separated in its own compartment. Due to fire safety reasons the cable space is confined by a raised floor forming its own fire cell (compartment). Figures 2.2.1 and 2.2.2 show two alternative typical cross-sections of electrical equipment rooms.

Figure 2.2.1. The recommended minimum dimensions of aisles for an equipment room

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Figure 2.2.2. A cable space 2.3 Building layout and structures 2.3.1 Location of electrical equipment rooms 2.3.1.1 Introduction The room shall be over-pressurised to reduce air infiltration from surrounding areas. The air tightness of electrical equipment rooms has to be sound, and the degree of overpressurization has to be sufficient to neutralize the influence of wind forces, temperature differences and surrounding process spaces, which may be operating under negative pressure. 2.3.1.2 Effect of wind forces If an electrical equipment room has external wall it can be greatly influenced by wind forces. These may, over-pressure on the wind-exposed wall resulting in polluted outdoor air entering the room. This effect has to be considered in the design process. The electrical equipment room if possible should be positioned, so that wind forces do not influence it. In spaces which rely on high air flows for cooling, the structural tightness and exhaust air openings sizes should be dimensioned so that the internal overpressure is kept to a reasonable level, e.g. not more than 20 Pa. Figure 2.3.1 shows graphically the wind pressure on the outer wall of a building with the wind velocity in the 0, 5 and 10 m.s-1 range against the wall.

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The example results have been calculated by using the formula: ∆p=K*0.5 *ρ*v2

(1)

where K= a pressure coefficient depending on building shape and the wind direction ρ= air density = 1,2,kg.m-3 v= the wind velocity [m.s-1] For air of standard density the above equation becomes ∆p = K 0.6 v2

Figure 2.3.1. The wind pressure on the outer wall of a building with wind velocities of 0, 5 and 10 m/s on the wall. 2.3.1.3 Vertical position in building A temperature difference between indoor and outdoor air causes a pressure difference on the outer wall. An internal neutral plane is formed at some height above the building floor. The actual position of the neutral plane changes due to the influence of wind forces and openings (crackage) in the structure. Above the neutral plane the inner parts of the building are over-pressurized with respect to the outdoor air and below this point it has a negative pressure when outdoor air is colder than the indoor air. This causes problems to the resulting pressure ratios, especially when the room is located on the outer wall of a high quality process space. Figure 2.3.2 shows graphically the pressure difference on the outer wall created by temperature difference, as a function of the distance from the neutral plane with different temperatures, for a room temperature of 20o C.

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Figure 2.3.2. Pressure difference created by the temperature difference between the indoor and outdoor air, on the outer wall of the building with different outdoor air temperatures. The interaction of the wind and temperature differences on the pressure difference of the outer wall is shown in figure 2.3.3. Problems of resulting pressure ratios will be created when the electrical equipment rooms are connected to both indoor and outdoor areas. If the room outlet is at a high position, the airflow will be outward from the space and if the outlet is at low level the flow will be reversed.

Figure 2.3.3. The interaction of wind and temperature on the outer wall of a building when θ = -20 C. 2.3.1.4 Surrounding rooms The external heat loads on electrical equipment rooms vary considerably. The external heat loads are due to open cable spaces, and adjacent process areas. The positioning of electrical equipment rooms close to hot process should be avoided. The pressure ratios in surrounding rooms will influence the design pressure conditions. A typical example is that a strongly negative-pressurized cable space will reduce the overpressure in an electrical equipment room. Cable spaces should be designed to have evenpressures. If located beside, under or over an electrical equipment room. Process spaces may be held at positive and negative pressure.

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2.3.2 Tightness of the structure 2.3.2.1 Introduction The air tightness of the structure is a critical factor when considering the influence the contaminant loads have on electrical equipment. It also influences the design of the ventilation system, as well as investment and operating costs. The design of the ventilation supply is related to the structural air tightness. The required over-pressure necessary to avoid infiltration will not be achieved if air leakage through the room structure is greater than that calculated. The tighter the structure, the less outdoor air flow is needed to provide the desired room over-pressure, the operating costs will also be reduced. The worst leakage areas are service holes and crackage in the structure, and it is essential that these be kept to a minimum. The structure of an electrical equipment room is usually brick, concrete or sheet metalmineral wool-sheet metal elements. Untreated tile and concrete surfaces and porous, and air flows through them. The structural leakage paths can be reduced by the use of special paints. If the electrical equipment room is built of sheet metal-mineral wool-sheet metal elements, the joints between the elements and connections to other structures have to be sealed to reduce external and internal air transfer. Partition walls also require sealing. 2.3.2.2 Estimation of the room tightness The general formula (Olander 1982) that describes the leakage air flow through walls, is following: QVL= C * (dp)0,65 [m3s-1m-2, Pa0,65]

(2)

Factor C varies according to the tightness of the wall, typical values being A tight wall An average wall A leaky wall

0,0003 0,0005 0,0007

With the above formula (2) the air tightness of electrical equipment rooms can be determined. The required air volume flow for the room pressurization depends not only on the room volume but also on the room shape and size. Therefore the correct design criteria must be based on room wall area. In normal cases the floor and ceiling can be considered as being airtight due to the coatings on them. Measurement of the make-up airflow according to new design criteria can be made using the diagram shown in Figure 2.3.4. In properly sealed rooms the required make-up airflow, to maintain a 20 Pa overpressure in the room, is 2,1 l.s –1, per m2 of wall.

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Figure 2.3.4. Dimensioning diagram for pressurization airflow in electrical equipment rooms After the electrical equipment room has been completed, it should be tested to ensure that the required over-pressure in the room is achieved with the designed outdoor airflow. In normal cases it is aimed to reach the over-pressure of 20 Pa with an outdoor airflow of 2,1 l/(s m2) of wall. For checking the actual over-pressure, a pressure difference meter should be installed outside the door. The measurements recorded should logged and used for all future service checks. If the required over-pressure is not reached, or if it reduces during use, leakages may be the cause, and extra sealing is required. Fan problems also cause a pressure drop and fan airflow should be checked for design conditions. If the over-pressure is greater than the required design energy costs will increase. 2.3.2.3 Effect of openings on the room tightness DOORS: The number of doors must be kept to a minimum. Doors not in everyday use, like hauling and trap doors, should be securely sealed. It is recommended to use only one door in the room and carefully seal other exits. Doors in everyday use should have air locks to reduce uncontrollable airflow. Doors should be self-closing, essential fire doors must be fitted with tight seals. WINDOWS: These should be avoided in electrical equipment rooms. It is difficult to seal window frames. In addition solar radiation through the windows increases the external heat gain to the room. STRUCTURAL PENETRATIONS FOR CABLES AND PIPES: The holes for cables and pipes in the walls of the room should be sealed carefully with an incombustible airtight material. Gypsum can be used for sealing, but it can break down with movement.

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Leaks through penetrations must not unduly impair the air tightness of the wall. This concerns the normal use, as not all of the so-called expanding sealants are suitable for stopping penetrations. When old building stock is being rebuilt, it is essential that an asbestos study be carried out before work commences. Asbestos was in the past frequently used in structural firebreaks. ELEMENT JOINTS: All the element joints have to be carefully sealed airtight before painting the walls. The expansion joints shall not be placed on the roof of an electrical equipment room. If an expansion joint has to be located in the room, it has to be carefully tightened Figures 2.3.5 give examples of expansion joint construction. 2.3.3 Effect of the structural mass on the heat dynamics of the room Over a short time period, say, less than 10 minutes, the structural mass will not have a major influence on the decrement and the resulting thermal transmission. Obviously for a longer time period a heavy structure will balance out the room temperature changes. In the approach used, thermally lightweight structure rooms are formed when the mean surface areas are covered with timber panels or other similar materials. Structures made of light concrete are graded as medium structures. Spaces classed as heavy structures have at least a half of their surfaces of uncovered concrete. Figures 2.3.6 - 2.3.8 show calculated warming curves with the help of two time-constants model for a 1000 m3 type room during the period of time of eight hours. Figures indicate the effect of different parameters (heat load, initial temperature and weight of structure) to the warming of the room. Temperature of the environment was held at 25˚C.

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Figure 2.3.5. Tightening the expansion joint, examples.

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Figure 2.3.6. Warming curves of a middle-heavy construction room with 4 different heat loads, when the initial temperature is 25 ºC. With heat loads less than 100 W.m –2 the room temperature will not rise above 40 ºC regardless of the nature of the structure when the outdoor temperature is +25º C. With heat loads of 200 W.m –2 the temperature of the room will rapidly rise over +40 ºC when the initial temperature is 35 ºC. With an initial temperature of 30 oC warming up to 40 ºC will take 3-8 hours regardless of the nature of the structure. In rooms of heavy structure, with heat loads over 300 W.m -2 the temperature will rise above 40 ºC regardless of the initial temperature. The temperature of an electrical equipment room cannot be controlled by structural means alone. As in the case of air conditioning plant failure with high heat gains, it is impossible to maintain the design temperature. In order to control the temperature the space must be provided with back up air-conditioning.

Figure 2.3.7. Warming curves of a light construction room with 4 different heat loads, with initial temperature 25 ºC.

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Figure 2.3.8. Warming curves of a medium heavy weight construction room with four different heat loads, with initial temperature at 30ºC. 2.3.4 Materials 2.3.4.1 Construction materials Untreated tile and concrete surfaces liberate dust, causing electrical equipment problems. For this reason the walls of electrical equipment rooms have to be covered with a dustbinding coat of paint. Precoated sheet metal-mineral wool-sheet metal elements are also used Ceilings should not have mineral wool panels or other dust producing materials included in them. Alternatives for mineral wool are bag wool with a fabric top. Closed suspended ceilings, however, should be avoided in electrical equipment rooms. 2.3.4.2. Material emissions Materials that liberate gases due to aging, which are harmful to equipment, should not be used in electrical equipment rooms. After applying a surface coating, adequate time should be allowed for drying before the electrical equipment is installed. A typical drying-time for epoxy paints is 7 days and for acrylate latex 2-4 days, for wall temperatures of +20°C. 2.3.5 Insulation 2.3.5.1 Moisture insulation and gas tightness The diffusion of moisture and gases through the walls should be avoided. Holes and cracks in the structure have to be filled with an airtight material. Surfaces to be sealed by specially selected paints such as Epoxy and acrylate latex paints. Alloprene and vinyl paints are not recommended, since they emit chlorine and hydrochloric acid during a fire.

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Vapour barriers should be on the high moisture content side, usually the process side. The electrical equipment room surfaces should be painted to bind any dust. The cavity in the outer walls should be painted from inside. 2.3.5.2 Thermal insulation The heat load from the surrounding spaces into electrical equipment rooms might be high in excess of 100 W per-m2 floors. Normally the main portion of the surrounding loads comes through the roof and/or the floor from the cable spaces. In the case of a wall separating a hot process area, thermal insulating is not normally economical unless other advantages are achieved such as improved reliability of temperature control in the case of ventilation plant failure. 2.3.6 Fire protection Requirements concerning fire protection are covered in National Building Regulations and in the requirements of insurance companies. During a structural or cable insulation fire toxic gases are emitted to a room (a typical example is PVC -> HCl). Care has to be taken in the design of exits from these areas. The water used for fire fighting these toxic gases forms an aggressive liquid that destroys equipment and primary structures. Typical conditions during a fire are covered in IEC 60721-2-8. 2.4 Target level assessment 2.4.1 The effect of environmental parameters on electrical equipment 2.4.1.1 High temperature Effects of temperature on electrical equipment must consider: • The air temperature • The equipment temperature. The equipment temperature depends on its electrical loading and its ability to liberate this heat to the surroundings. The convection to the surrounding air has a major influence on the rate of heat transfer. When the equipment has a cover, the thermal conductivity of the equipment and the path to the cover is an essential factor to consider. The actual temperatures at which a fault occurs, varies with different equipment. For example semiconductor silicon components can tolerate a range of 125 to 175°C while germanium components can only tolerate 70 to 100°C. The memory in a hard disk is damaged with a temperature in the 70 ºC range. The failure frequency of plant depends on the surrounding conditions, the load and the age of the equipment. A typical failure frequency curve for electronic equipment is shown in figure 2.4.1. The service life of equipment can be divided into three stages.

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• • •

The early operating period lasting for 0,5 to 2 years, when the failure frequency is 2-10-fold compared to the actual operating period. The actual operating period that in the normal conditions lasts for 10...20 years after which the equipment is usually replaced with more efficient equipment. The ageing period when the frequency of failure increases rapidly.

Figure 2.4.1. A typical graph for the fail frequency of an electronic equipment (Z (t)=fail frequency) The temperature rise has a great influence on the failure frequency of electronic equipment. It is said that when the temperature rises by 10°C the frequency of failure doubles. It is assumed that the failure frequency of electronic components follows Arrhenius’ law: z=z0*e-E/(k*T) where

(3)

z= failure frequency z0=failure frequency in the normal conditions k=Bolzmann's constant E=the activation energy of the fault mechanism T=the component temperature K

The formula shows that temperature increase influences exponentially the failure frequency of components. If the electrical stress rate is high, the temperature effect increases the failure rate. Figure 2.4.2 indicates how temperature, affects the failure frequency of components. The figure indicates the mean time between component failures as a function of the temperature. The mean time between failures (MTBF) is the inverse value of the failure frequency. Except for MTBF, the temperature will also influence also component efficiency.

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Figure 2.4.2. The predicted mean time between failures of equipment with different component choices (A and B) as a function of the temperature (m (h)= the mean time between failures) Excessive high temperatures ages electrical equipment reducing considerably their working period. It has been claimed that a temperature rise of 14°C reduces the lifetime of electronic components by 50% Cable insulating materials age with temperature increase, the lifetime of rubber insulating materials at different operating temperatures is given in table 2.4.1: Table 2.4.1 The rubber insulation service life at different operating temperatures Temperature Insulation service life years °C 25 30 32 15 39 7,5 46 3,7 International research work has been carried out covering the environmental factors and their effects on electrical equipment. This work is published in the IEC (International Electronic Commission) standards, many of which have been adopted as European Standards. In standard EN 60068-1 the principal effects of environmental factors and typical faults caused by them are covered. The effects of high temperatures are shown in table 2.4.2:

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Table 2.4.2. The main effects of a high temperature and typical faults in electrical equipment Main effects Typical faults Thermal aging Oxidation Cracking Chemical reactions Growth of mechanical stress Softening Melting Sublimation Reduction of viscosity Evaporating Thermal expansion

Insulation faults Structural faults Impairment of greasing properties Increase in the wearing of moving parts

High temperatures also damages equipment indirectly by accelerating chemical reactions, resulting in corrosion by the air contaminants. For example when the temperature rises from 20°C to 30°C the reaction rate doubles. Evaporating of solvents and insulating materials resulting in an acceleration of gaseous contaminants, which further increase contact surfaces fouling. 2.4.1.2 Low temperature Low temperatures alone do not increase the failure frequency, provided the temperature stays above 0°C. See figure 2 where, the meantime between failures stay almost as constant between 0° and 20°C. Instability of equipment can cause a change in the parameter values, such temperature reduction, humidity, and air movement. If the intake air temperature is near to the room air dew point, moisture will condense on the surface of electrical equipment, with serious results. When the temperature falls below 0°C, the rate of failures increases rapidly. When the temperature drops to -40°C the failures of different components are about 10-fold compared to normal conditions. When the temperature is below 0°C, moisture condensing on surfaces will freeze in narrow spaces causing joint failure. The main effect of low temperatures and faults caused by them according to EN 60068-1 are shown in table 2.4.3: Table 2.4.3 The main effects of low temperatures and typical faults in electrical equipment Main effects Typical faults Increase in viscosity Ice formation Embrittlement Shrinking Impairment of mech. strength

Insulation faults Impairment of greasing properties Sealing faults Cracking Failure Structural faults Increase in wearing of moving parts

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2.4.1.3 Rate of change in temperature Due to different thermal expansion coefficients, component can develop serious stresses if the component temperature varies from its design value. If the temperature changes constantly, the component will experience fatigue" and in time will fail. For example memory protection batteries will be damaged if the temperature increases too often above the permitted value. A single temperature increase above the permitted value will affect the storage capacity. In the EN 60068-1 standard the main effects of the temperature changes are thermal shocks and local temperature differences are covered. Typical faults caused by these are mechanical and insulation faults resulting in cracking and electrical leakage. Temperature changes influence the relative humidity of the surrounding air causing cause moisture to condense locally on components. 2.4.1.4 High relative humidity Changes in humidity influence the resistance of electrical insulating materials. These changes result in static electricity, particle formation and corrosion between different materials. It will also cause corrosion by: 1. Directly, by chemical reaction on metals and plastics. 2. 1. Corrosive compounds forming with other gases in the air, e.g. sulphuric acid, H2SO4 with sulphur dioxide SO2 and nitric acid HNO2 with nitrogen oxides. NOx 3. Electrochemically as an electrolyte on two different metals causing corrosion. For example: - a copper plate coated with gold, if moisture condenses on it electrolysis may result causing hairline cracks. The main problems and typical faults of high relative humidity is given in EN 60068-1 are listed in table 2.4.4. Some insulating materials adsorb moisture at high relative humidity. This results in the electrical conductivity of insulating material increasing with electrical leakage causing equipment damage. Dust particles in the air, below a 1 µm (micrometer), can adsorb moisture and gaseous contaminants. This may accelerate equipment corrosion. Corrosion due to gaseous contaminants grows exponentially with an increase in relative humidity If the air relative humidity increases above 80%,the silver used in the circuit cards may develop a "migration phenomenon” causing short circuits. The gold used to fasten chips to their beds also suffers from humidity and the chips may loosen and fail.

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Table 2.4.4. The main effects of a high relative humidity and typical faults in electrical equipment Main effects Typical faults Absorption of humidity and condensation on the surface of an article Swelling Impairment of mechanical Strength Chemical reactions such as: - corrosion and electrolysis Increasing of the conductivity of the insulation

Mechanical faults Breaking Insulation faults

When the relative humidity increases to 80 %, a water film forms on the equipment surfaces. High humidity is not an actual a problem in an automation/electrical equipment room with well-designed ventilation systems, as air movement at the correct temperature removes the moisture from the space. However if the intake air temperature is low, local moisture will condense. A failure in room over-pressurization and a poor moisture barrier will cause an increase in the local relative humidity. 2.4.1.5 Low relative humidity The main effects due to low relative humidity and the typical faults caused by them according to EN 60068-1 are given in table 2.4.5: Table 2.4.5. The main effects of low relative humidity and typical faults in electrical equipment. Main effects Typical faults Drying Embrittlement Shrinking Impairment of mechanical strength Increase in wearing of contact surfaces Developing of static charge

Mechanical faults of non-metallic parts Cracking Electrical faults

The worst threat to electrical equipment from the above-causes is that low relative humidity increases the incidence of static charges. A static charge is when similar charges build up in a substance and do not immediately become neutralized with opposite charges. A typical electrostatic phenomenon is to have high potential differences, but the appearance of small quantities of electricity. Normally an electrical charge leaks slowly along the surface of a material or through it, without causing any problems. If the potential of a charged area becomes high, a powerful discharge occurs which may cause damages to equipment wiping out memory, cause electrical shocks to employees and create fire hazards. The aim of protection is to keep the leakage rate greater than its rate of generation. By maintaining the relative humidity in the 60-70 % range will eliminate static electricity problems. As the temperature inside electrical motors is greater than that of the surrounding air, the relative humidity in the surrounding should be 65% or more. The problems of static

25

electricity are minimised when the relative humidity of the surrounding air is greater than 55%. Relative humidity influences occupant’s safety. For example cotton clothing is safe due to its good electric conductance. This is true when the relative humidity is high, but below 40% relative humidity, cotton is a good insulating material. The value of clothing electric conductance is important to neutralize the electrical charges between man and electrical equipment. Wrist and foot straps will prevent electrostatic discharge from the people to equipment; this is often a much cheaper solution than humidifying the room. If the relative humidity drops below 40% static charges will attract dust particles and cause undesirable dust forming. The formed dust causes wear of contact surfaces, breaks and corrosion depending on the dust properties. The increase in contact faults with a decrease in relative humidity is covered in figure 2.4.3

Figure 2.4.3. The effects of relative humidity on the functioning of tele-exchanges. 2.4.1.6 Rate of change of the relative humidity Rapid changes in relative humidity may cause local condensation resulting in corrosion. The corrosion rate caused by gases increases considerably when the rate of change of the relative humidity is greater than 6% in an hour. 2.4.1.7 Chemically active substances The effect of chemically active corrosive gases on electrical equipment according to EN 60068-1 is given in table 2.4.6.

26

Table 2.4.6 The main effects of chemically active gases and typical faults in electrical equipment. Main effects Typical faults Chemical reactions Corrosion Electrolysis Surface decay Increase in conductance Increase in contact resistance

Increased wearing Mechanical faults Electrical faults

2.4.1.8 Mechanically active substances The effect of mechanically active substances, such as particulate matter, on electrical equipment is given in table 2.4.7. Table 2.4.7. The main effects of mechanically active gases and typical faults in electrical equipment. Main effects Typical faults Friction, wearing Clogging Getting stuck Frictional electricity Increase in thermal insulation

Mechanical faults Increased wearing Electrical faults Over heating

2.4.2 Basis for design of electrical equipment rooms 2.4.2.1 Introduction The equipment supplier defines the environmental demands for each room, and the equipment heat loads. Initial information is given by the electrical designer. Table 1.1.1 can be used to initially define the room environmental information during the preliminary design. Other heat loads are calculated individually for each case. Condition information/ checklist: Temperature • Environment class + the requirements of air conditioning • Target value • Accuracy (range of variation) • Steadiness (rate of change) • Maximum and minimum values in the case of disturbance Humidity • As temperature Chemical contaminants • Environment class • Permitted concentration for each gas 27

Particle contaminants • Environment class Over-pressure/outdoor airflow • Electrical equipment rooms are designed in over-pressure against environment. In normal case 20 Pa over-pressure is enough. It is reached in a tight room with makeup airflow of approx. 2,1 l.s –1 per m2 wall see figure 2.3.4. The room design criteria will define the choice of the air conditioning system required. In addition to system selection the following have to be considered: - available space (foot print and height) reliability in use, and possible room future extension. 2.4.2.2 Pressurization As the requirements for electrical equipment room conditions are usually stricter than those in the surrounding areas, they require pressurising. Normally 20 Pa excess is adequate for rooms that border on outdoor air, see 2.3 and figure 2.3.4 for details. When the conditions are extreme such as exposed sites high buildings and spaces having high negative pressures, the over-pressure and the air flow rates required, have to be calculated separately. 2.4.2.3 Introduction to the environmental parameter concept When the operating conditions of electronic equipment are defined, all the condition factors have to be determined for several operating parameters. The parameters can be divided into: Base value i.e. normal conditions • Range of variation above and below the base value • Minimum and maximum values required when the equipment is in operation • Minimum and maximum values required when the equipment is not operating • The real limit values necessary to avoid equipment damage. The relationship between the parameters is shown in figure 2.4.4:

28

Figure 2.4.4. Operating parameters and reliability of electronic components. The design value relates to the constant operating conditions (temperature, humidity, particulate matter etc.) required in the area where the equipment is in use. It is necessary these parameters be met to ensure operation reliably over its lifetime. When perfect functioning of equipment is required the conditions defined by the base values must be worked to. The variation range design values define the choice of surroundings in which the equipment reliability remains constant. The reliability over this range is obviously influenced by the rate of change of conditions. The design value and its variation range define the design conditions to be selected. Equipment in normal operating situations provides the initial values for the air conditioning designer. Maximum and minimum conditions, when the equipment is operating, define the extreme environmental values surrounding the equipment in a special case. These cover the event of failure of the air conditioning plant. When conditions reach the extreme values, there is a risk of equipment failure the maximum and the equipment manufacturer provides minimum conditions for equipment, these are based on test performance under given conditions. When designing electrical equipment room ventilation systems, it should be considered that the air conditioning system must operate after a malfunction, before extreme environmental conditions are reached and the manufacturing process fails. Environmental tests for electrical equipment have been standardised. The key methods of the testing are given in EN 60068-1. The environmental standards and the tests related to 29

them are used for defining the greatest short-term environmental stresses encountered for a product. However, these classes do not provide information regarding long-term stresses that influence the equipment for its lifetime. Even remaining within the tested environmental class does not guarantee a perfect function of the product in these conditions Long-term stresses can slowly influence the product quality and result finally in failure. The classification considers that different environmental parameters (temperature, humidity of air etc.) are symmetrically divided. The extreme values of classes have been chosen so that average equipment can tolerate that the conditions do not exceed the extreme value for no more than 1% of the operating time. Maximum and minimum values for non-operating periods are used for defining the equipment storing conditions. During installation and shutdown periods the air conditioning must operate to ensure the operating conditions are achieved as soon as possible. When conditions reach the equipment critical limit immediate failure may result. 2.4.2.4 Climatic conditions (temperature and humidity) As the basis for designing air conditioning systems, a conditions curve of 75% is used. In practice the humidity can be varied over a wider range of this curve because air humidity in a space changes with the seasons, hence the risk of extreme humidity does not continue over the whole of the time. Some classes are more flexible regarding the requirements of air conditioning. Hence certain precautions can be permitted so that the temperature approaches the outdoor extreme design conditions. The extreme conditions of electrical equipment correspond to the 99% values on the conditions curve. Air-conditioning design has to ensure that the room conditions achieve average values in the middle of the permitted area. Hence care has to be taken with selection of the air terminal devices and their actual positioning. Design requirements are compiled by considering the electrical equipment in the room. Extra requirements for each room, such as workplaces, have also to be considered, see 2.4.3. Rooms with high heat loads must be prepared for a sudden temperature change due to malfunction or failure of the air conditioning. This is achieved by reducing the room temperature level with backup equipment or by natural ventilation. The conditions that correspond to individual rooms requirements should be maintained during shutdowns, as moisture condensing on electrical equipment may cause damage on plant start up. When the temperature rate of change is calculated during the design, the initial assumption is perfect mixing. The rate of change has to remain in the given range during a period of 5

30

minutes. The calculations have considered the structural damping effect on temperature change. This is achieved by the use of two time-constants models. During operation, the room conditions have to stay within given limits of the electrical equipment. This means the volume around the equipment measured from the floor level up to two meters, and at least to the 50 cm from the equipment surface. The measuring should not be carried out near an air conditioning unit (the minimum distance is 1 m) or in its airflow. Hence positioning of control sensing devices must be taken into account. The design basis given is intended for forced ventilation design. Natural ventilation can be applied by applying the design values of electrical equipment (extreme values). Table 2.4.8 and climatographs (see Appendix 1) the air conditioning design conditions for different climatic conditions have to be considered. 2.4.2.5 Special climatic conditions Most equipment permits air velocities greater than those mentioned above. This is dealt with separately in special climatic conditions categories. The permitted air velocities in the different classes are given in table 2.4.9. Table 2.4.9. Special climatic conditions; the permitted air velocity in the different condition classes Condition class 3Z4 3Z5 3Z6

Permitted air velocity m.s-1 5 m.s -1 10 m.s -1 30 m.s –1

2.4.2.6 Chemically active substances (corrosive gases) The permitted concentrations of chemically active gases in electrical equipment environments are defined in the classes C of the EN 60721-3-3, standard as are chemically active substances. In table 2.4.10 the maximum values of different gases for air conditioning design are given. Since the concentrations in the strictest classifications are extremely small, comparison at the size range level with classes (G1-G3, GX) of standard ISA-71.04-85 are used. The copper-strip method in the above standard can be used to estimate the rooms surrounding classification. The following are the two most critical classes, since concentrations of the other classes are so high, that these other classes are irrelevant for electrical equipment rooms.

31

3C1:

The average air concentration in areas with no emissions of harmful gases. Near industrial plant emissions and in some city areas, chemical filtering is necessary to achieve this class. This corresponds to class ISA G1-G2, even though the concentrations are a little higher than in the ISA.

3C2:

Corresponds to class ISA G3-GX. Causes corrosion of unprotected electrical equipment.

In laboratory tests for chemical filters it is shown that the filters in the tests could not remove nitrogen oxides from the air. Therefore the customer has to specify in his equipment inquiry a wider class of filter that will deal with NOx if the concentrations of nitrogen acids rise over 0,1 mg. (nitrogen oxides alone can cause corrosion of metal surfaces, but together with other gases corrosion is accelerated) The ozone concentration range in the standard, is critical as the concentration of class 3C2 is exceeded e.g. in Finland on background levels. In practice the permitted ozone concentration should be classified to class 3C3 with the present outdoor concentrations. Ozone is not considered to be a corrosive substance, however it oxidizes plastics, rubber and textiles, and accelerates the corrosion caused by other gases.

32

Table 2.4.8. Design conditions for air conditioning in different climatic condition classes DESIGN CRITERIA FOR VENTILATION IN DIFFERENT CLASSES OF IEC 60721-3-3(CLIMATIC CONDITIONS) ENVIRONMENT CLASS

3K1

3K2

3K3

3K4

3K5

3K6

3K7

3K8

EXTREME OPERATION CONDITIONS -MIN: OF ELECTRIC -MAX: EQUIPMENT *

18°C 27°C

15°C 30°C

5°C 40°C

5°C 40°C

-5°C 45°C

-25°C 55°C

-40°C 70°C

-55°C 70°C

+19-26°C 0,5°C

+15-30°C 0,5°C

+10-30°C 0,5°C

-5-+35(45)°C 0,5°C

5-95% min 0,7g/kg max 28g/kg

5-95% min 0,7g/kg max 29g/kg

10-100% min 0,4g/kg max 29g/kg

10-100% min 0,1g/kg max 35g/kg

10-100% min 0,1g/kg max 35g/kg

DESIGN TEMPERATURE ** -RATE OF CHANGE (5 MINUTES AVERAGE)

+22-23°C±2°C 0,1°C

RELATIVE HUMIDITY ABSOLUTE HUMIDITY

40-50%±10% (in +22°C) -

INLET AIR -TEMPERATURE -RELATIVE HUMIDITY

min 16°C max 75%

min 16°C max 75%

min 10°C max 85%

min 5°C max 95%

min -5°C max 95%

-

-

-

0,5m/s

1,0m/s

1,0m/s

1,0m/s

1,0m/s

1,0m/s

5,0m/s

5,0m/s

AIR MOVEMENT (SEE ALSO SPECIAL CLIMATIC CONDITIONS) NOTE

10-65% min 1,5g/kg max:min roomTemp./65% (e.g. 19°C->9g/kg)

Change of conditions outside limits Design temperature-area is chosen for normal operation causes an alarm.inside above mentoined area. It is recommended, that room temperature is regulated in accuracy of ±2°C around chosen temperature.

EQUIPMENT REQUIREMENTS: -HEATING (Things in parentheses must be-COOLING considered case by case) -DEHUMIDIFIER -HUMIDIFIER

-HEATING -COOLING -DEHUMIDIFIER (-HUMIDIFIER)

5-70% min 0,7g/kg max:min roomTemp./70% (e.g. 19°C->9,5g/kg)

-25-+45°C(55°C)-40-+45°C(70°C)-55-+45°C(70°C) 0,5°C 1,0°C 1,0°C

Design temperature-area is chosen Design temperature-area is chosen It is recommended that temperature It is recommended that temperature inside above mentoined area. inside above mentoined area. difference between in- and outcomingdifference between in- and outcoming air During exceptionally warm season During exceptionally warm season air is 10°C in mechanical ventilation is 15°C in mechanical ventilation. may temperature rise to +35°C, if the may temperature rise to +35°C, if the and 15°C in natural ventilation. heat-load in room is under 100W/m². heat-load in room is under 100W/m². In natural ventilation extreme operation conditions can be used for bases for design.

-HEATING -COOLING(outdoor air if possible) ( -DEHUMIDIFIER)

-HEATING -COOLING(outdoor air if possible)

(-HEATING during shutdown) -COOLING(primarily outdoor air )

-COOLING(primarily outdoor air )

* CONDITIONS DURING VENTILATION BREAKDOWN ** DURING NORMAL OPERATION

33

Table 2.4.10. The permitted maximum concentrations of chemically active substances in different conditions classes, according to EN 60721-3-3. Environmental factor salts

Unit

3C1

3C2

3C3

3C4

mg/m3

no 1)

salt mist

salt mist

salt mist

0,1 0,037

0,3 0,11

5,0 1,85

13 4,8

0,01 0,0071

0,1 0,071

3,0 2,1

14 9,9

0,1 0,034

0,1 0,034

0,3 0,1

0,6 0,2

0,1 0,066

0,1 0,066

1,0 0,66

1,0 0,66

0,003 0,0036

0,01 0,012

0,1 0,12

0,1 0,12

0,3 0,42

1,0 1,4

10 14

35 49

0,01 0,005

0,05 0,025

0,1 0,05

0,2 0,1

0,1 0,052

0,5 0,26

3,0 1,56

10 5,2

cm3/m3 sulphur dioxide

mg/m3 cm3/m3

hydrogen sulphide

mg/m3 cm3/m3

chlorine

mg/m3 cm3/m3

hydrogen chloride

mg/m3 cm3/m3

hydrogen fluoride

mg/m3 cm3/m3

ammonia

mg/m3 cm3/m3

ozone

mg/m3 cm3/m3

nitrogen-oxides3)

mg/m3 cm3/m3

1) Sea salt mist can occur in weather protected spaces on the shore and in the spaces that are in costal areas. 2) Values are both calculated in cm3/m3 And mg/m3 values at 20°C temperature. The values of the table are rounded. 3) Is given as equivalent of nitrogen dioxide

2.4.2.7 Mechanically active substances (sand, dust) The permitted concentrations of particulate matter in the operation environment of electrical equipment are presented in table 2.4.11. The classification does not consider the position for measuring the dust or it’s the origin.

34

Table 2.4.11. Maximum concentrations of mechanically active substances for different classes. CONDITION CLASS

SAND

3S1 3S2 3S3

mg.m-3 no 30 300

DUST (suspended particulate) mg.m-3

DUST SEDIMENTATION

0,01 0,2 0,4

10 35 350

mg.m-3 per day

2.4.2.8 Biological conditions The classification concerns the protection of electrical equipment against mildew, fungi, organisms and small animals. Usually electrical equipment rooms are class 3B1 and these rooms have been protected against these factors. This is not normally considered in standard air conditioning design 2.4.2.9 Mechanical conditions This classification describes the influence of mechanical stress, including vibration and impact directed to the electrical equipment. This factor is normally not considered in basic air conditioning design. 2.4.2.10 Special requirements of different equipment The storage capacity of batteries decreases with a temperature decrease 2.4.3 Human occupancy. Work places should be located separately from the actual electrical equipment rooms. If they are permanent (for more than occasional work) they must be taken into account while designing the air conditioning. See 3.1.4 Ventilation.

35

Table 2.4.12. Requirements for work places LIMIT VALUES TEMPERATURE °C -Sedentary work -Light, moving work RELATIVE HUMIDITY % AIR VELOCITY (m.s-1 at 20 °C) -Sedentary work -Light, moving work NOISE dB(A)

TARGET VALUES

20-28 18-25 15-70

21-25 1) 19-23 1) 30-50 2)

0,15 0,25 55 3)

0,15 0,25 55 3)

1) There should not be any extreme thermal radiation, hot or cold, which may cause damage to the equipment 2) To reach the target value, means that the air humidity has to be controlled 3) National regulations or standards may define a lower limit value.

The air purity has to achieve values necessary for office spaces. For electrical equipment air purity of class 3C1 is usually adequate for plant and occupants 2.5 Source description 2.5.1 Introduction Waste heat generated in electrical equipment is transferred almost entirely by air convection to the room through the equipment cabinets. The surface temperature of the cabinets is normally not much higher than the surrounding temperature, so radiant heat transfer can be ignored. 2.5.2 Estimation of heat loads The maximum heat loads in electrical equipment rooms have to be calculated with accuracy. The final design should be based on the heat loads given by the electrical equipment supplier. When changes are made to existing rooms, it is essential to determine the heat loads both by measurement and calculation. Care has to be taken if rule of thumb methods are used for this purpose 2.5.2.1 Rough estimation of heat loads in electrical equipment rooms The power losses of low-voltage equipment and its associated cables in the cable space equal to the loading losses of the supplying transformer. The transformer power loss is obtained from the manufacturers technical specifications. A 1.6MVA transformer dissipates 14,6 kW at full load.

36

The power losses at low-voltage (< 500 V) in equipment rooms are about 0,3.to 0,5 % of the electrical power supplied. The dissipation power losses in low-voltage centres can be estimated on floor area of the distribution centre. A useful estimation is 800 W. m –2 of floor area of a distribution centre. The heat load generated by other equipment in the room, such as AC-inverters, lights, fans etc has to be determined separately and added to the total load. 2.5.2.2 Heat loads of different equipment The following clause, gives power losses provided by electrical equipment manufacturers. These can be used if no other information available. The values are approximate further checks are required with the chosen equipment supplier. Motor control equipment (source: ABB Strömberg, Finland, 1993) Motor control equipment having the following dissipation powers: The supply voltage of the device

Power losses (% of the nominal power)

380 V

2.0 %

500 V

1.5 %

When direct current is used, the power losses do not vary much. With alternating current the power losses depends on the rate of utilization. Automation equipment (source: Valmet Automation, Finland, 1993) The power losses of automation cabinets is 400 W.m-2). The principle of the closed air circulation is shown in figure 3.1.5.

48

Figure 3.1.5. Closed air circulation Designing and operating a closed air circulation is more complicated than other systems. It requires the electrical equipment supplier to designing airflows for each cabinet. In addition the cabinets have assemblies for the air conditioning. A dual ductwork system requires more space making the equipment cable- laying difficult. The closed air circulation system is more sensitive to cooling equipment malfunctions, as the air circulation capacity is less than the case of when the whole equipment room is ventilated. Half-open systems One solution is the combination of a closed air circulation and ceiling discharge. A portion of the air is discharged directly into the equipment cabinets and the remainder in to the room space. The exhaust is placed above the equipment cabinets as in open systems. This provides the best characteristics of both systems. The equipment cabinets receive controlled clean air, and the equipment space provides a buffer against the surrounding. During a malfunction all of the room air capacity can be used. Another problem in this case is how to introduce the correct air quantity into each cabinet. The principle of this arrangement is shown in figure 3.1.6.

Figure 3.1.6. A half-open system; blow into the equipment cabinets. In rooms with high heat loads (500 W.m-2) the temperature difference between intake and exhaust air can be increased, and the air flow reduced. The warm exhaust air is induced 49

directly from the equipment cabinets. In this case information regarding thermal power and airflows for each cabinet has to be obtained from the electrical equipment supplier. The principle of the system is shown in figure 3.1.7.

Figure 3.1.7. A half-open system; suction from the equipment cabinets 3.1.4.3 Workplaces. Workplaces are normally in separate control rooms near to electrical equipment rooms. The conditions in these rooms correspond to office spaces. In addition to the above methods of air distribution in control cabinets a chilled ceiling may be used, this reduces the airflow rate. Care has to be taken to ensure that condensation in or on the ceiling does not take place. This is achieved by ensuring the supply air is of the correct moisture content (See 3.1.1, system 5). In practice electrical equipment rooms, especially for automation spaces, have work places, where people may stay for long time. The draught and noise prevention in rooms with heat loads (>200 W.m-2) requires special attention. Workplaces should be separated from the other parts of the room by a movable wall, or by air conditioning solutions. Using partly or totally closed air circulation in the cabinets can reduce the heat load and airflow required in the room. See 2.4.3 for conditions of workplaces. 3.1.5 Air conditioning costs 3.1.5.1 Building costs Purchasing air conditioning equipment is carried out by tender; the actual price depending on market forces. Material quality and component also influences the price. Components used for industrial applications are usually more expensive than standard comfort-units. The cost is related to the required environmental conditions, the largest single cost is that of chemical filtering. The reliability of use of equipment has to be considered carefully, due to its effect on the initial costs.

50

The air conditioning costs can be estimated approximately see. Table 3.1.3, which shows the costs per square meter in the type room (200m2) that can be used in calculations, for different system solutions with two different values of cooling capacity. 3.1.5.2 Operating costs. The most important item in air conditioning operating costs is that of replacing the chemical filter medium. Due to the high cooling load, the use of electricity by air conditioning and cooling devices is large. Thus the economical performance and the choice of operating conditions is critical, consider absorption refrigeration

51

Table 3.1.3. Purchase costs of air conditioning plant in a type room €/m2 (price level of 1991-1992). Prices include the installation costs of the device, design costs excluded. 1

2

3

4

5

450 200

X X

X X

X X

450-570 350-480

X X

3K1/3S1/ NO CHEMICAL FILTERING

450 200

X X

X X

X X

370 280

X X

3K2/3S1/ 3C1

450 200

X X

X X

X X

380-570 300-480

300-570 250-530

3K2/3S1/ NO CHEMICAL FILTERING

450 200

X X

X X

X X

300-370 220-280

220-280 170-230

3K3-4/3S1 /3C1

450 200

X X

X X

X X

380-500 300-480

300-570 250-530

3K3-4/3S1 /NO CHEMICAL FILTERING

450 200

X X

X X

430 220

300-370 220-280

220-280 170-230

3K5/3S1/ NO CHEMICAL FILTERING

450 200

X X

X X

230 120

300-370 220-280

220-280 170-230

3K5/3S2/ NO CHEMICAL FILTERING

450 200

X X

100 50

230 120

220-300 130-220

800-220 80-170

3K5/NO FILTERING

450 200

X X

100 50

170 100

220 130

150 100

3K6/NO FILTERING

450 200

X 20

80 30

150 80

220 130

150 100

150%EXTRA COOLING COST

450 200

X X

100 -

-

130 100

130 100

REQUIREMENTS OF THE ROOM

3K1/3S1/3C1

HEAT LOAD W/m2

X=required conditions are not reached with the system

52

3.2 Selection of equipment 3.2.1 Introduction EMC-compatibility: The European EMC-directive gives requirements for equipment in industrial environments. The EMC-directive allows determination of the permitted disturbance radiation of electrical equipment to its environment, and disturbances along a flex. Standard EN 50081-1 gives general disturbance emissions experienced in light industry. Higher disturbance emissions are permitted in heavy industry according to standard EN 50081-2. It always possible that old equipment can achieve the essential requirements of the EMCdirective, covered in the above standards. This is the case with equipment having tyristor control or similar, which cause disturbances that is not allowed in the standard, unless these disturbances have been covered in the design and documentation. Equipment has to tolerate disturbances according to standard EN 50082-2 or EN 50082-1 depending on the place of use. 3.2.2 Selection of chemical filter. 3.2.2.1 Basic data for filter selection. The following covers the basic data required in the selection of a chemical filter. The customer should use this as the requirements and guarantee values in tendering. In addition to the basic data, the names of filter manufacturers should be given. The minimum following basic data should be provided: • The filtered air flow [m3.s-1] • The lifetime target of the filter medium [a] • The average concentration of the filtered gases in the air [ppb] • The maximum concentration of the filtered gases in design [ppm] • The concentration of gases [ppb] after the filtering or the required filtering efficiency The lifetime of filter medium is normally assumed to be at least one year. Often the average concentrations of filtered gases are not based on measuring information and have to be estimated. The actual replacement intervals can be considerably different from the target. The filter life for circulated air may be less than its estimated life due to pollution leakage in to the filtered space and/or ductwork. The capacity of a chemical filter has to be designed with the given maximum concentration. The concentrations of filtered gases may not exceed the planned values when the concentrations upstream the filter is below the maximum. Due to process disturbances the maximum concentrations can be high. The efficiency of the outdoor

53

filter has to be over 99% of the maximum critical gas concentration. In filtering circulated air the collection efficiency is not normally a critical factor. 3.2.2.2 Design of a chemical filter. The time for air to pass through the filter varies usually between 0,5-2,0 seconds depending on the outdoor air purity, selected lifetime of the filter and filter type. A delay under 0,5 seconds should not be allowed for filtering outdoor air Usually the delay in circulated air filters is about 0,1-0,2 seconds. The air velocity through the filter medium is designed to be less than 0,5 m.s-1. Increasing the velocity decreases the filtering efficiency and increases the pressure loss in the filter. The pressure loss of a chemical filter varies between 250-2500 Pa depending on the filter type and airflow; this has to be considered in the fan selection. Pressure loss does not usually change during use, as is the case with particle filters. The filter frame and body have to be leak tight and by-pass leakages should not exceed 1% of the nominal airflow in the outdoor air filters. Attention should be paid to corrosion problems of the material. Acid-proof material is normally used in the casing of the outdoor air filters. When the filter is selected, its space requirement and pressure loss should be designing other parts of the system. The space required for filter changing must be considered. 3.2.2.3 Guarantee values. At present no guarantee values are normally given for chemical filters. If guarantee values are given, there are difficulties in measuring them The wearing out of chemical filters is usually controlled by sending filter samples to the laboratory of the filter supplier, who analyses the samples and determines the time frequency at which the filter has to be changed. Different methods are given in 2.1.2.1. For chemical filters the defined guarantee values obtained for laboratory and field teats should be given The lifetime of a filter cannot be guaranteed or defined with accuracy. But the filter supplier should provide an estimation of the filter lifetime when the system is constructed. There are two methods of filter testing: -Testing the filter under laboratory-controlled conditions before accepting the filter for use and before the supplier accepts it. An example of laboratory test is reported in (Enbom 1994) Testing the guarantee values in the field, with a possible follow-up of the decrease of filter capacity. A problem is that there is not a suitable practical multi gas instrument on the markets to measure the small concentrations required.

54

The gas concentration after the filter, and the filter capacity to bind contaminants can be used as a guarantee value for a chemical filter. If the customer is unable to measure the gas concentrations, the method that is based on the corrosion of a copper-strip can be used as a guarantee. Figure 3.2.1 shows the documentation to define the design basis of a chemical filter, and figure 3.2.2 gives the guarantee values. The average outdoor air values used in the example are from pulp and paper industry plants in the referred research projects.

55

EXAMPLE BASIC VALUES FOR DIMENSIONING TARGET LIFETIME OF MEDIA

YEARS

MAKE-UP AIR FILTER AVERAGE (ANNUAL) GAS CONCENTRATIONS IN MILL AREA GAS

CONCENTRATION 3 µm/m ppb

LITERATURE REFERENCE NRP, E-G, T&T

b) Sulphur di(tri)oxide

SO2,3

10-20

c) Hydrogen sulphide

H 2S

10-200

d) Chlorine e) Hydrochloric acid f) Hydrogen fluoride g) Ammonia

Cl2 ClHF NH3,NH4+

10

h) Ozone i) Nitrogen oxides TRS ( incl. H2S)

O3 NOX

40 20

30 1 10-20 80 40

NRP, E-G NRP TO BE TAKEN INTO ACCOUNT BY THE SEE APPLICABLE ONLY IN SOME BRANCHES NRP HAPRO NRP, T&T Other gases in the factory area.

CIRCULAR AIR FILTER AVERAGE (ANNUAL) GAS CONCENTRATIONS IN CIRCULATING AIR GAS

CONCENTRATION 3 µm/m ppb

b) Sulphur di(tri)oxide

SO2,3

c) Hydrogen sulphide

H 2S

14

20

d) Chlorine e) Hydrochloric acid f) Hydrogen fluoride g) Ammonia

Cl2 ClHF NH3,NH4+

80

200 2 20-40

h) Ozone i) Nitrogen oxides

O3 NOX

80 40

74

200

160 80

LITERATURE REFERENCE NRP, E-G, T&T NRP, E-G E-G, NRP: 20-30 µg/m3 ? TO BE TAKEN INTO ACCOUNT BY THE SEE APPLICABLE ONLY IN SOME BRANCHES NRP HAPRO NRP, T&T

SPECIFICATION OF THE FILTER FOLLOWING TECHNICAL FIGURES SHALL BE GIVEN OF THE OFFERED FILTER - Filter media

- Delay in filter media

1. step 2. step 3. step 4. step Seconds

- If delay/step is not a constant, shall delays of different steps also be given. - Method to control workability of the filter media and the amount of unused media (%).

Figure 3.2.1. The basic design data and dimensioning of chemical filters

56

GUARANTEE VALUES OF THE FILTER The concentration of the chemical gases after the chemical filter shall remain in every situation below the limit values stated here, when the incoming concentration is same or lower than maximum concentration. Concentrations after filter shall be fulfilled for each of defined gases alone and together with other gases. MAKE-UP AIR FILTER GAS

MAX. CONCENTR. ppb

µg/m3

CONCENTRATION AFTER FILTER ppb µg/m3

REMARK

b) Sulphur di(tri)oxide

SO2,3

1000

2700

37

c) Hydrogen sulphide

H2S

1000

1500

7,1

10

d) Chlorine e) Hydrochloric acid f) Hydrogen fluoride g) Ammonia

Cl2 ClHF NH3, NH4+

1000

3000 3

100 100 3 300

Do electrical equipment supplier guarantee

300

34 66 3,6 420

h) Ozone

O3

150

50

100

Demand 3C3.

i) Nitrogen oxides

NOX

150

52

100

Medias normally used don't filter NOX.

420

100

operation. ISA GX: 10 ppb.

Usually it is not noticed.

Analogues guarantee values, when tested with indirect method are following: Thickness of a corrosion film on a copper strip; - Before filter - After filter

10000 300

A A

or less or less

CIRCULATION AIR FILTER GAS

MAX. CONCENTR.

b) Sulphur di(tri)oxide

SO2,3

c) Hydrogen sulphide

H2S

d) Chlorine e) Hydrochloric acid f) Hydrogen fluoride g) Ammonia

Cl2 ClHF NH3, NH4+

h) Ozone

O3

i) Nitrogen oxides

NOX

ppb

µg/m3

CONCENTRATION AFTER FILTER ppb µg/m3

REMARK

74

200

19

14,2

20

3,5

50 5

68

200 3

420

300

17 33 1,6 210

50 50 1,5 150

150

50

100

Demand 3C3.

150

52

100

Medias normally used don't filter NOX.

Analogues guarantee values, when tested with indirect method are following: Thickness of a corrosion film on a copper strip; - Before filter - After filter

2000 300

A A

or less or less

METHODS TO CONTROL FULFILLMENT OF TARGET VALUES Shall be controlled by measurements. There are two methods possible: - DIRECT METHOD - Using gas-analyzer - INDIRECT METHOD - Corrosion coupon test - Gas concentrations before filter can be found out with gas-analyzer also in this case. REFERENCES NRP E-G HAPRO T&T

Nordic Research Project: Corrosion of electronics. Enso-Gutzeit Ltd. measurements. Finnish Environmental Ministry, Acidification in Finland, Final-raport (in Finnish). Tekniikka & Talous-magazine,

Figure 3.2.2. Guaranteed values of chemical filters

57

3.2.3 Selection of mechanical filter The recommendation for filtering classes used to provide the required conditions in an electrical equipment room is given in table 3.2.1. Table 3.2.1. Recommendation for the filtering classes used in electrical equipment rooms. Filter classes according to EN 779: CONDITION CLASS FILTERING CLASS 3S1 F 7(F 8) 3S2 G 3(G 4) 3S3 -* *Near an emission source G3 is recommended. A filter for circulated air should be at least to class F6. Upstream of a chemical filter it is recommended that a F7 (or F8) filter is installed, as small particles in the air reduce the capacity of a chemical filter. Downstream of a chemical filter another mechanical filter should be installed, with a similar capacity, to filter any dust leaving the chemical filter. Special attention has to be paid to the filter air tightness and its frames, to avoid dust penetration into the supply air. The allowed by-pass leakage depends on the filtering class according to table 3.2.2. Table 3.2.2. The permitted by-pass leakage of a particle filter in different filtering classes (EN 1886:1998). G 1-4 F5 F6 F7 F8 F9 6% 6% 4% 2% 1% 0,5%

3.2.4 Cooling. 3.2.4.1 Selection of cooling medium. There are three reasons why water should be used in the first place as a cooling medium: 1) ENVIRONMENTAL ISSUES: The amount of refrigerants used should be minimized for environmental reasons. Cooling water can be produced from a centralised plant with a water chiller, and in some cases without the use of refrigerants. 2) CONTROLLING THE COOLING: The step less control approach is simple similar to a water radiator. When cooling media is used a continuous control, leads to more difficult solutions and periodic control causes changes in the conditions.

58

3) FREE COOLING: With the free cooling water, outdoor air is readily cooled during the winter. Refrigerant systems have to be used when cooling equipment is placed in electrical equipment rooms, as water may presents electrical problems in the case of leakage. Cooling a single space with a compressor set is usually more economical, if cold water is not available. 3.2.4.2 Control of a cooling coil. OUTDOOR APPLIANCE: The purpose of a cooling coil in an outdoor appliance is to cool the supply air and to remove outdoor air moisture. The control of a cooling coil can be achieved in two ways: Keeping either the dew point or the temperature of the intake air constant. In a supply air unit, the cooling coil is placed before the fan and the chemical filter. Placing the coil directly after the chemical filter makes coil control more difficult. Also the temperature measuring of the supply air should be carried out before the chemical filter, since the filter causes delay, influencing the control In addition the temperature varies after the filter. Dew point method: Supply air is cooled in the coil to the desired dew point temperature (for example +8°C). The cooling coil sensor is located directly after the cooling coil. A separate reheat coil controls the air supply temperature, its sensor is positioned after the fan and before the chemical filter. The air supply temperature is kept constant 16°C. The principle of this control method is shown in figure 3.2.3.

Figure 3.2.3. Dew point control method Inlet air temperature method: The inlet air is kept at a constant temperature of 16 ºC, during the winter by heating, and cooling the outdoor air in the summer. To avoid concurrent heating and cooling with the associated energy loss, the heating is isolated when the outdoor air temperature is 14°C. The cooling coil keeps the supply air temperature constant, say at 16 ºC. The sensor is placed after the fan and before the chemical filter. In the design of the cooling coil it is essential to consider the fan gains For example if a 2 ºC gain takes place in the fan, the leaving design temperature for the coil must be 14°C for a discharge temperature into the room of 16°C. As the relative 59

humidity of the supply air may be high, it has to be ensured that the supply air mixes effectively with the room air; otherwise unsatisfactory moisture levels may enter the electrical equipment. The dew point method is more expensive and consumes more energy than the constant inlet air temperature method. The last-method is unable to keep the humidity of the inlet air constant and cannot be maintained as low as with the dew point method.

Figure 3.2.4. Control of intake air temperature CIRCULATED AIR COOLING: The aim is to remove the heat generated by equipment. The room temperature exhaust air is kept at its set point by controlling the supply air temperature (see figure 3.2.5). In addition there is a minimum value for the supply air. A continuous control method is essential as periodic control causes undesired temperature variations in the room. If periodic control for is used, care must be taken that the capacity step is small enough, as the temperature has a requirement for the rate of change and has to be met. Problems are given in detail in clause 3.3.2.

Figure 3.2.5. Constant room/exhaust air temperature control method.

60

The air is dried in the supply air unit where condensation will not occur or the circulated air coils during normal conditions of use. However, the cooling coils should be equipped with drip pans with adequate drain lines and drop separators if necessary. The controlling detector is located in the exhaust air duct, or if no ductwork exists for circulated air, or when it is follow up the conditions in the room (for example work places). The detectors in the room must be placed according to the instructions given in 2.4.1.2, and ensure that the average room conditions are met. 3.2.5 Selection of other equipment. When equipment is selected, attention should be paid to the ductwork and equipment tightness. The system must meet the tightness class B of prEN 1507. The ductwork should meet class C, and the air-handling units class B (in low-pressured and small systems ductwork they may meet class B and the units class A). The reason for this is, that leakages increase the handling costs of the air, cooling costs and the depletion of the chemical filtering medium. They also make air control more difficult, and depending on pressure ratios may allow contaminants to enter the room. Fire dampers should be as tight fitting as possible, and be of good quality to ensure they operate in fire conditions It is wise to consider connecting fire dampers with the automation system allowing the a damper to be tested automatically at set intervals. The hygiene aspects of humidifiers must be considered, according to EN 13053, to reduce the possibility of growth of microorganisms. It is recommended that steam humidifiers be used. A humidifier requires to be fitted with a drop separator to ensure droplets do not come into contact with electrical equipment. In the selection and placing of the control device the special requirements placed by the environment have to be taken into account (the environment tolerance of the equipment). Cooling and heating coils and heat recovery units are heat exchangers. When these are selected, the normal requirements (tightness, materials, de-icing, control, removing condensate etc.) have to be considered. Electrical equipment rooms are provided with electrical radiators to ensure they are warmed up during down time. As a set point, the radiator thermostat is +15°C to control concurrent heating and cooling. Installing sewers and water pipes that pass through electrical equipment rooms should be avoided. If this is not possible the pipes have to have a waterproof cover. The walls floors and ceilings where these pipes pass through have to be carefully sealed It is recommended that electrical equipment rooms be provided with a central vacuum cleaning system, or provided with a vacuum cleaner with high-quality filters. The use of

61

an ordinary vacuum cleaner increases the particle concentration in the space being cleaned 3.2.6 Selection of materials. While selecting materials, attention has to be paid that on the dirty side the corrosion conditions on some fields of industry (pulp & paper, chemical, petrochemical industry) may present many problems. Issues to consider are: -acid-proof or aluminium outdoor grilles, acid-proof or stainless steel for the first part of the ductwork, Al-HSt-structure for the gate valves and stainless steel for the coils. 3.3 Implementation design 3.3.1 Location of ventilation equipment 3.3.1.1 Air conditioning units The air conditioning units serving electrical equipment rooms will be positioned in a separate space close to the room for maintenance reasons. This will minimise the unnecessary occupancy in the electrical room for maintenance. If the air conditioning equipment is located inside the electrical equipment room, the equipment must be provided with safe access for the maintenance personnel. It must be ensured that maintenance will not cause damage to the electrical equipment. Special attention has to be paid to removing the condensate from the coils from the room. If the air of the room is filtered chemically, the filter has to be positioned with the following issues in mind 1. The chemical filter mounted upstream the fan: The intake air of the ventilation equipment plant room should be chemically filtered, to reduce the risk the fan inducing dirty air from the room in to the electrical equipment room. 2. Chemical filter downstream of the fan: A recommended position as all the air entering the electrical equipment room will flow through the chemical filter. The filter for circulated air is designed on the concentration level in the electrical equipment room. Leakages from the ventilation plant room will reduce the filter capacity considerably. The two solutions for this problem are: • The supply air to the plant room is to be filtered • Leakages will be considered in filter designing for the circulated air, which increases the particulate contact time in the filter. 3. No chemical filter in the circulated air unit. If the circulated air unit is in the ventilation equipment room a chemically filtered air supply is required for the room, due to leakages (clause 1.)

62

If the cooling system is inside the electrical equipment room, and the chemical filter is placed after the fan, the air in the ventilation plant room does require filtering 3.3.1.2 Outdoor air inlets Air inlets should be located so that the entering outside air is as clean as possible and for summer operation as cool as possible. An air inlet should not be located close to process emissions. The introduction of moisture through air inlets should be eliminated In some branches of industry, e.g. pulp & paper, the humidity in the factory environment is high resulting in condensation problems on air inlets, these will freeze in the winter. Defrosting coils are required in this instance for deicing. 3.3.1.3 Ductwork The supply air ductwork to electrical equipment rooms must be as short as possible. Care being taken so that the ductwork does not pass through dirty process spaces. When the ductwork is manufactured consideration must be made that the electrical equipment room will form its own fire compartment. Insulation, fire dampers etc. should be cleared in advance with regards to suitability with the local fire authorities and insurers. 3.3.2 Control and monitoring. 3.3.2.1 Introduction. This clause deals with control at a basic level, so that the design room conditions are maintained. The principles of different air conditioning systems are given in clause 3.1.1. The control of each method covered in clause 3.2.4. At the commencement of a project it is essential to determine if the air conditioning is controlled locally, or if the control is connected with the factory automation system, or with a separate building automation system. Alarms warning of plant malfunction should be connected to areas of regular occupancy. 3.3.2.2 Control Control of temperature and relative humidity are important factors in electrical equipment rooms. Humidity control is based on the requirement that the maximum relative humidity is a fixed point If the room humidity constantly adjusted (class 3K1), it will be controlled by the measurement of room or exhaust air. The maximum humidity of the intake air must be limited.

63

The requirements for thermal conditions and control are given in clause 2.5. The room temperature is maintained within the required range and rate of change by the controls. The temperature control should be continuous as periodic control causes adverse temperature variations. When periodic control is used, the design should ensure that the cooling capacity is divided to several capacity steps to achieve the rate of change requirements. The size of the capacity steps can be evaluated during the designing process with the help of a twotime constants model. Example: A space has a volume of 1000m3 with a temperature change of 2,5°C in five minutes (average 0,5°C/min). This change is caused by a power input of 18 kW (90 W.m-2) If the total cooling capacity is 400 W.m-2 the cooling should be divided into steps of 20% (400/90). In clause 2.5.1.2 it is shown in which cases the room design conditions have to be maintained. The method of air distribution selected will have a considerable influence on the actual conditions. The following deals with the methods of temperature control of the air conditioning with different system. NATURAL VENTILATION: Gravity ventilation is designed with a temperature difference of 15°C. It will be appreciated that this system provides no direct control of the cooling. If necessary, a separate heating system can be used to ensure that the temperature is maintained above the lower limit in the winter. FORCED EXTRACT VENTILATION: The space temperature is kept at the set point by starting and stopping the fan (On-Off control). Control for example is achieved in the following manner (3K5): A thermostat starts the fan when the room temperature reaches 35°C and stops the fan when it reaches 30°C. In the winter the requirements of warming the air in the classes 3K3-5 must be considered OVER PRESSURE VENTILATION: The supply air unit works continuously keeping the room at a positive pressure to the surroundings the room temperature is maintained at the set point (for example 20°C), by adjusting the supply air temperature. Supply air can be warmed either by a heating coil or with re circulated air. The room temperature may increase above the set point in the summer depending on the room heat loads Air conditioning is more effective with a summertime fan, if there is no need for chemical filtering. This fan will start when the temperature of the room rises to the upper

64

set point (e.g. 30°C) and stops when the temperature drops below the lower set point (e.g.25 °C). COOLING WITH CIRCULATED AIR: The supply air unit operates continuously ensuring over pressurisation of the room. The temperature and humidity of the supply air is kept constant. The exhaust air or room temperature is maintained at the set point by controlling the cooling of the circulated air. The temperature and humidity of the intake air is maintained at a maximum and minimum value. If periodic control is used the next capacity step will depend on if the temperature rises or falls above the upper and lower set points. SEPARATE COOLING PLACED IN THE ROOM: The control is achieved in the same manner as in the circulated air-cooling. 3.3.2.3 Monitoring. The alarms fitted to air conditioning equipment are divided into different categories on the grounds of importance. Urgent alarms are those that immediately influence the working capacity and require service persons' immediate attention. Urgent alarms should always be directed to the manned control room. These alarms are: • • • • •

Increase of room/exhaust air temperature to a limit that results in an alarm sounding. If a fan or duct air flow stops. If the temperature of the intake air falls below the permitted minimum. Failure of thermostat resulting in the freezing of a heating coil. (If the air humidity exceeds the control range).

Less urgent alarms are e.g.: • Pressure difference alarms on mechanical filters Issues that have to be monitored regularly: • When chemical filters wear out • Maintaining the room over pressure In the use and service plan, the frequency of regular servicing and checks belonging to normal maintenance of the equipment should be listed. The aim is to ensure the reliability of use and should be directed to eliminating plant failure the most important components are fans and cooling equipment. Controlling detectors should not be placed after a chemical filter.

65

4 COMMISSIONING 4.1 The construction schedule In figure 4.1.1 a construction schedule for an electrical equipment room is shown which indicates the dependences between different measures. If an old electrical equipment room is to be renovated, the schedule will be different and will depend on the quality and extent of the work. Figure 4.1.1 Construction Schedule for an Electrical Equipment Room DESIGN

CONSTRUCTION

GUARANTEE PERIOD

OPERATION TIME

ACCEPTANCE OF SYSTEM & EQUIPMENT SELECTION CONSTRUCTION OF THE ELECTRICAL EQUIPMENT ROOM SEALING AND SURFACE FINISHING OF THE CONSTRUCTION HVAC & ELECTRICITY INSTALLATIONS SEALING OF THE HVAC-PENETRATIONS PERFORMANCE TESTS FOR MAKE-UP AIR UNIT ADJUSTMENT OF THE CONTROL SYSTEM FOR MAKE-UP AIR UNIT OPERATION TESTS FOR THE MAKE-UP AIR UNIT OVERPRESSURIZING OF THE EL. ROOM

>

INSTALLATION OF ELECTRICAL EQUIPMENT SEALING OF CABLE PENETRATIONS PERFORMANCE TESTS FOR AIR CONDITIONING SYSTEM ADJUSTMENT OF THE CONTROL SYSTEM OF AIR CONDITIONING OPERATION TESTS AND CHECKINGS FOR AIR CONDITIONING SYSTEM CHECKING OF THE ROOM TIGHTNESS AND MAKE-UP AIR FLOW RECEPTION OF HVAC & AC SYSTEM ADDITIONAL SEALING, IF NEEDED CHECKING THE ROOM TIGHTNESS AGAIN, IF NECESSARY INTRODUCTION OF THE ELECTRICAL EQUIPMENT CHECKINGS OF THE HVAC-CONTROL SYSTEM DURING OPERATION - FOLLOW-UP OF TEMPERATURE CONDITIONS (SUMMER/WINTER) CHECKINGS OF CONTAMINANT CONCENTRATIONS OF THE EL. ROOM CHECKING THE ROOM TIGHTNESS GUARANTEE CHECKINGS REGULAR MAINTENANCE AND CHECKINGS - CHECKING OF THE CONTAMINANT CONTROL - OVERPRESSURE OF THE ROOM - TEMPERATURE CONDITIONS - CONDITION OF THE HVAC-EQUIPMENT

66

4.2 Checks For the acceptance of the electrical equipment room air conditioning, a group of checks over and above those normally carried out on an ordinary HVAC-project are necessary. The following are recommended extra checks during different stages in the project: Structural, device and installation checks: • Tightness test for the air conditioning units (in the factory) • By-pass leakage of the filter package (a factory-made package) • Filling of the chemical filter. • Air Tightness test of the ductwork. • Guarantee values of the chemical filter medium (tests in advance?) Performance tests: • Timing the test of over pressure equipment. Test run: • Test run for the whole air conditioning system. • Measuring the over pressure in the electrical equipment room during the test run. • Comprehensive check measurements of the air and water flow rates. Guarantee period: • Operating the air conditioning control during different situations in the summer and winter (Thermal conditions/ balanced operation of equipment). • The contaminant concentration of the room; at the start and end of the guarantee period. • Operating of the chemical filtering, if necessary. • Checking the over pressure in the end of the guarantee period. Operation: • Thermal conditions. • The contaminant concentration in the room. • Operating of the chemical filtering, if necessary. • The over pressure measurement in the room. 4.3 Spare parts To secure reliability of use, spare parts must be stored for the most important components. They should be purchased at the same time as the main equipment. To minimize the amount of spare parts and for reliability in use, spare parts should be evaluated as soon as possible in the project. The best results for the whole factory will be achieved if the reliability of use and spare parts planning are part of the main design

67

4.4 Documentation During different stages of design, the basic data and the system solutions with their reasons should be well documented, and all participants in the project should be informed consider the documentation examples in figures 4.1.2-4.1.4. Changes made during the construction, in connection with the acceptance tests and during the guarantee period should be updated in the design and maintenance documents. Updated documentation is an essential part of plant reliability.

68

Figure 4.1.2 Check List for the Project (Ventilation of Electrical Equipment Rooms) PHASE/TASK

REPORT

REFERENCE

SCHEDULE

2.1

EGO XXX

13.11.1993

1.2, 1.1 3.1.2

EXPLANATIONS: REPORT: Refers to applicable clause in text REFERENCE: E.g. Standard or guideline that is to be followed in task

PROGRAM PHASE (Preliminary plan) GIVEN DATA - Location of building - Outdoor air dimensioning criteria (preliminary) - Summer/Winter - Dimensioning criteria for electrical equipment's - Level of reliability (generally) SYSTEMS, ALTERNATIVE SYSTEMS - Going through all solutions

3.1.1 Fig 4.1.3

- Factory level - Cooling solutions water/refrigerant/? - Production of cooling water centralized/dissipated - Connections of HVAC-systems to other networks - Premise level (types) - Cooling water/refrigerant/? - Need of chemical filtration - Air conditioning system options - Equipment loads in different types of premises

PLACEMENT OF HVAC SYSTEMS AND REQUIRED SPACE (prelim.) - Placement - Required space

READY #######

APPR.

e-b/nnn

APPENDIX CL.NO 11972-001

3.2.4.1 3.2.4.2

3.2.4.2 2.1.2.1 3.1.1 2.5.2

2.3.1

69

Figure 4.1.2 Check List for the Project (Ventilation of Electrical Equipment Rooms) PHASE/TASK

REPORT

REFERENCE

SCHEDULE

READY

APPR.

APPENDIX

DESIGN PHASE 1 (scetch plan) GIVEN DATA - Documentation and approval - Outdoor-air conditions for dimensioning - Conditions of surrounding premises - Structures - Dimensioning conditions of single premises - Loads of premises (preliminary) - If loads for premises will be approximated in the first phase of scetch, then it has to be reserved enough time in last phase that plans can be updated to the real level of loads. - Requirement for reliability, premise by premise

SELECTION OF SYSTEM (FACTORY/PREMISES) - Documentation and approval - Selection criteria PREDESIGN PLAN (based on the selected system) - System schemes and equipment lists - Selection of equipments, requirements for components - Drawings - Placement of HVAC-equipment in the building - Duct routes and placement of main ducts - Control and automation - Air conditioning process - Connection to the automation system COMMENT OF OPERATIONAL AND MAINTENANCE PERSONNEL

70

Figure 4.1.2 Check List for the Project (Ventilation of Electrical Equipment Rooms) PHASE/TASK DESIGN PHASE 2 (Detailed design) GIVEN DATA (in detail, look scetch plan) - Evaluation, documentation and approval - Electrical equipment supplier: Heat loads of single cabins (air-flows), if not available on the scetch phase.

DESIGN - Precision of dimensioning calculations and documentation (approval?) - Precise placement of HVAC-systems in the building - Connection of HVAC-equipments to other systems - Control and automation - detailed - Holes in structures - Explanation (pictures of holes) - Tightening - Spare parts/Reliability

REPORT

REFERENCE

SCHEDULE

READY

APPR.

APPENDIX

2.1 2.5.2

3.3.1 3.3.2 2.3.2

3.1.2

COMMENTS of OPERATIONAL AND MAINTENANCE PERSONNEL

71

Figure 4.1.2 Check List for the Project (Ventilation of Electrical Equipment Rooms) PHASE/TASK

REPORT

TASKS DURING CONSTRUCTION PHASE ADDITIONAL AND MODIFICATION TASKS - Design - Same principles and procedures as during design phase is followed

4.1

REFERENCE

SCHEDULE

READY

APPR.

APPENDIX

SUPERVISION - Supervisors tasks - Agreement of supervision CHECKINGS - Construction, equipment and installation checks - Performance tests - Functional tests - Check measurement - ACCEPTANCE TESTS

4.2

POSTACCEPTANCE TESTS

4.2

AS BUILT DRAWINGS - Documentation if changes made during construction - Documentation of accomplished system

4.4

MAINTENANCE - Operation and maintenance plan - Training of operation and maintenance personnel - Spare part plan

4.4

72

Figure 4.1.2 Check List for the Project (Ventilation of Electrical Equipment Rooms) PHASE/TASK

REPORT

INTRODUCTION (Guarantee period) MAINTENANCE - Obtaining of spare parts (if not included in the initial delivery)

4.4

CHECKINGS DURING GUARANTEE PERIOD

4.2

REFERENCE

SCHEDULE

READY

APPR.

APPENDIX

GUARANTEE TESTS

POSTACCEPTANCE TESTS

DOCUMENT UPDATE - Documentation of changes made during guarantee period OPERATION CHECKINGS - According to operation and maintenance plan

4.2

MAINTENANCE - According to operation and maintenance plan

MODIFICATIONS AND EXTENSIONS - Documentation of changes

73

Figure 4.1.3. System selection, example SYSTEM SELECTION ROOMTYPE

ELECTRICAL ROOM

CONDITION CLASS: 3K3/3Z2/3Z4/EB1/3C1/3S1 (EN 60721-3-3) ALTERNATIVE AIR CONDITIONING SYSTEMS 1. 2. 3.

OVER-PRESSURE VENTILATION COOLING WITH CIRCULATED AIR SEPARATE COOLING PLACED TO THE ROOM

PROPERTIES OF ALTERNATIVE AIR CONDITIONING SYSTEMS (Clause 3.1.1) ENCLOSURES:

1-3

SELECTED SYSTEMS

2. COOLING WITH CIRCULATED AIR

GROUNDS FOR SELECTION

1. Centralized cold supply and cold water pipeline

in the building. 2. It is prohibited to bring waterpipes into el. room. 3. The temperature conditions can be hold uniform,

which improve the reliability of operation. 3. SEPARATE COOLING PLACED TO THE ROOM

1. Cheaper solution to single rooms far away of the

main building, where extending of the cold air pipeline is to expensive. 2. The ventilation equipment room size can be

minimized in a separate building.

REJECTED SYSTEMS 1. OVER-PRESSURE VENTILATION

REASON FOR REJECTION 1. System is not suitable for rooms that have heavy heatloads and need for chemical filtering.

74

Figure 4.1.4 Table of Start Values for Design, Example ELECTRICAL EQUIPMENT ROOMS; START VALUES AND DESIGN CRITERIA FOR VENTILATION DESIGN SUBJECT: Pulp & Paper Mill, Moodyriver, Woodland PROGRAM PHASE PRE DESIGN PHASE DESIGN PHASE OUTDOOR AIR - Temperature winter/summer - Air Humidity summer/winter - Corrosive gases* DESIGN CRITERIA 1. ELECTRICAL ROOMS - Condition classification - Dimensioning temperature** - Relative Humidity** - Heat loads from el. equipment - Reliability demand 2. AUTOMATION ROOMS - Condition classification - Dimensioning temperature** - Relative Humidity** - Heat loads from el. equipment - Reliability demand 3. CONTROL ROOMS - Condition classification - Dimensioning temperature** - Relative Humidity** - Heat loads from el. equipment - Reliability demand

30°C/-15°C*** 15g/kg / 1,5g/kg Filtering needed

32°C/-10°C**** 17g/kg / 1g/kg Filter for circulation system only in boiler house

REMARKS

No changes

Table 1.1.1, Class B

300 W/m

2

Max 25°C**** Max 50%**** Loads in different rooms, see Appendix N

Appendix N, Rev. B****

150 %

Table 1.1.1, Class A

250 W/m

2

Max 25°C**** Max 50%**** Loads in different rooms, see Appendix N

Appendix N, Rev. B****

200 %

Table 1.1.1, Class A

150 W/m

2

Workers; see Table 2.4.12 Max 28°C**** Loads in different rooms, see Appendix N

Appendix N, Rev. B****

100 %

* Dimensioning of gas filter, see separate Appendix. ** Shall be announced only if is wanted more strict conditions than is stated for condition class. *** Source: Ashrae-weather data (HVAC-Designer). **** Binding Criteria (by Client)

75

APPENDIX 1 - BASIS FOR DESIGN FOR VENTILATION IN ELECTRICAL EQUIPMENT ROOMS, CLIMATIC CONDITIONS CLIMATOGRAMMES FOR CLASSES 3K1-3K4 (EN 60721-3-3) GUIDE FOR THE READER AREA 1:

Design conditions for ventilation. During normal operation of ventilation system shall conditions stay inside the borders. Conditions shall be on an average in the center of the area.

AREA 2:

Area, that is expanded from area 1 with dash line, classes 3K3 and 3K4. Conditions may slide to this area during extremely heavy outdoor conditions during summer, if the heat load of the room is under 100 W/wallm2.

AREA 3:

Border of the environment class of the electrical equipment. Conditions shall not exceed the border in any conditions, when electrical equipment is in operation, including the breakdown in ventilation equipment.

* Relative humidity and minimum temperature define together the allowed absolute humidity

76

APPENDIX 2 - THE MEASURING PRECONDITIONS OF GASES Environmental measurements • Instruments suitable for emission and environment measurements can be purchased at reasonable prices. With most gases an accuracy of tenths of ppm can be achieved. To obtain reliable results a long-term follow-up (6 months) is necessary. •

Measuring methods available: 1. Direct measurements. • Gas analysers 2. Indirect measurement based on the aggressiveness of the contaminants in the environment • Copper-strips (ISA-S71.04-1985) • Metal spirals (ISO 9223)

Electrical equipment rooms The required concentrations are very low, and acceptable measurements can be only be determined with accurate instruments. With the indirect measurement the aggressive nature of contaminants in the air can be observed. •

•

Measuring methods available: 1. Direct measurement. • an expensive and unsuitable option for continuous follow-up. 2. Indirect measurement. • Copper-strips, different options (30 days follow-up and analysis; comparing with the reference-strips). With copper-strips the seriousness of the corrosion can be determined however different gas concentrations cannot be determined. "Purafil"-instrument (on-line, Cu-Ag-corrosion measurement, temperature, humidity and the rate of change; this can be connected with the building control system. The price is in the 6.000 € or USD.range.

Efficiency measurements of the filter medium in a laboratory • direct measurement, high quality instruments requirements for high-class results. • a SO2-converter is required to measure hydrogen sulphide H2S. • chlorine measurement by means of a sampling collector method. • The filtering ability in a steady-state (storage capacity) is easily tested in a laboratory. Determining filter efficiency and the time when filter medium replacement is necessary in the field •

The following methods are in common use: 1. Taking a sample of the filter medium. 77

2. A change in colour of indicator paper. •

Other possible methods: 3. Concentration measurement from inside the filter medium. 4. The copper-strip in the duct after the filter - filter medium is changed too late.

When acceptance tests are made, it is possible to measure the filtering capacity of the gases with indicating instruments (a Research Institute services would be required), the cost of this service is high, about 2.000 € or USD/room, gas. The test would have to be repeated in order to obtain a meaningful answer.

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APPENDIX 3 - REFERENCES Enbom, S., Hagström,K. and Railio, J., Laboratory tests of chemical filters. In: Anders Jansson and Lars Olander (Eds): Proceedings of Ventilation 94, Vol.2, p. 441-446. Arbete och Hälsa 1994:18, Part 2. Arbetsmiljöinstitutet, Sweden Olander,L., Beräkningsamband för luft och luftföroreningar. En litteratursammanställning. Arbetarskyddstyrelsen. Undersökningsrapport 1982:14, Sweden.

International standards ISO 9223

Corrosion of metals and alloys -- Corrosivity of atmospheres – Classification

IEC 60721-2-8 Classification of environmental conditions - Part2: Environmental conditions appearing in nature. Section 8: Fire exposure.

European standards EN 779

Particulate air filters for general ventilation - requirements, testing, marking

EN 1886

Ventilation for buildings - Air handling units - mechanical performance

EN 13053

Ventilation for buildings - Air handling units - ratings and performance of units, components and sections

EN 61000-6-1 Electromagnetic compatibility (EMC) - Part 6-1: Generic standards. Immunity for residential, commercial and light-industrial environments EN 61000-6-2 Electromagnetic compatibility (EMC) - Part 6-2: Generic standards. Immunity for industrial environments EN 61000-6-3 Electromagnetic compatibility (EMC) - Part 6-3: Generic standards. Emission standard for residential, commercial and light-industrial environments EN 61000-6-4 Electromagnetic compatibility (EMC) - Part 6-4: Generic standards. Emission standard for industrial environments EN 60068-1

Basic environmental testing procedures. Part 1: General and guidance

EN 60721-3-0 Classification of groups of environmental parameters and their severities. Introduction EN 60721-3-3 Classification of environmental conditions. Part 3: Classification of groups of environmental parameters and their severities. Section 3: Stationary use at weatherprotected locations prEN 1507

Ventilation of buildings - Ductwork - Rectangular sheet metal air ducts, requirements for testing strength and leakage

Other standards ISA 571.04-85 Environmental conditions for process measurements and control systems: Airborne contaminants.

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