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MET 465 – Cooling Load Calculation Example Given: Single story, slab-on-grade office building located in Bozeman Montana. Floor plan as shown below. Flat roof, weight = 40 lb/ft2, color = light Infiltration rate = 0.50 air changes per hour (ACH) Roof U value = 0.112 BTU/hr-ft2-'F Wall U value = 0.128 BTU/hr-ft2-'F, heavyweight, dark color Window U value = 0.580 BTU/hr-ft2-'F Door U value = 0.470 BTU/hr-ft2-'F Room Office 1 Office 2 Office 3 Office 4 Conference Room Halls

Dimensions 22’ x 22’ 22’ x 25’ 22’ x 25’ 22’ x 25’ 22’ x 50’ 6’ x 97’

Determine the cooling load for this building

Design Occupancy # 2 2 2 2 20 0

Heating Load Calculation Process: 1.

Select outdoor design weather conditions.

Bozeman, MT.: DB = 87F, WB = 62F, (W = 0.0086 lbm/lba) 2.

Select indoor design conditions.

Comfort Level: 3.

DB = 76F, RH = 30% (W = 0.0069 lbm/lba)

Develop zoning plan for the building.

Zone 1 2 3 4

4.

Select or compute heat transfer coefficients for outside walls, roof, doors, windows, etc. (Given in problem statement) Component Walls Roof Doors Windows

5. Component Roof N. Wall E. Wall S. Wall W. Wall N. Window E. Window S. Window W. Window N. Door E. Door S. Door W. Door 6. Per site plans

Rooms 1 2,3 4 Conf. , halls

U (BTU/hr-ft2-F) 0.128 0.112 0.470 0.580

Determine corresponding areas for outside walls, roofs, doors, windows, etc. Office #1 (ft2) 484 170 170 0 0 50 50 0 0 0 0 0 0

Office #2 (ft2) 550 0 170 200 0 0 50 50 0 0 0 0 0

Office #3 (ft2) 550 0 0 200 0 0 0 50 0 0 0 0 0

Office #4 (ft2) 550 0 0 200 170 0 0 50 50 0 0 0 0

Determine building location, orientation, and external shading.

Conf. Rm. (ft2) 1100 400 0 0 170 100 0 0 50 0 0 0 0

Halls (ft2) 582 18 18 0 60 0 0 0 0 42 42 0 0

7.

Obtain schedule of lighting, occupants, internal equipment, appliances, and processes that would contribute to the internal loads.

Per owner / occupancy information 8.

Calculate peak cooling load due to conductive and solar effects (rooms 1st, zones 2nd, total last) . • Calculate conductive heat gains through walls, roof, glazing, etc. • Calculate solar gains through glazing (windows). Component Roof Walls Windows Doors

Equation Q = Uroof * Aroof * ETDt Q = Uwall * Awall * ETDt Q = Uwindow * Awindow * TD (conductive) Q = SC * Aglass * SF (solar) Q = Udoor * Adoor * TD

These loads must be calculated for each hour of occupancy in order to determine the peak load for the building. See spreadsheet (MET 465 Cool Load Example Calcs.) for summary of calculations 9. Infiltration:

Ventilation:

Compute heat gain due to air exchange (infiltration / ventilation). Qsensible = 0.91 * cfm * TD

where cfm = (Volume * ACH) / 60

Qlatent = 0.68 * cfm * GD

where GD = (Win – Wout) * 7000

Qsensible = 0.91 * cfm * TD

where cfm = (Volume * ACH) / 60

Qlatent = 0.68 * cfm * GD

where GD = (Win – Wout) * 7000

Note: Use largest of these two values (reference pg. 203 of text). See spreadsheet (MET 465 Cool Load Example Calcs.) for summary of calculations 10. Calculate internal heat gains due to people, equipment, lights, etc. Gain People Equipment Lights

Equation Qsensible = # Occupants * BTUH for activity level (p. 216) Qlatent = # Occupants * BTUH for activity level (p. 216) Per manufacturers specifications Per building plans or Estimate per table on page 216 of text

See spreadsheet (MET 465 Cool Load Example Calcs.) for summary of calculations 11. Sum all heat gains for peak zone loads. Zone

Room

1 2 3 4

1 2,3 4 Conf., hall

Peak Time 8:00 am 10:00am 4:00 pm 4:00 pm

Sensible Load (BTU/hr) 13151 26067 16280 35542

Latent Load (BTU/hr) 626 1342 671 6237

Total Load (BTU/hr) 13778 27409 16951 41779

These loads represent the peak loads for each zone. Notice that the peak time varies. See spreadsheet (MET 465 Cool Load Example Calcs.) for summary of calculations.

12. Determine the building peak load. Time Component Roof Walls Doors Windows (conductive) Windows (solar) Infiltration/Ventilation People Lights Equipment Total Sensible Load Latent Loads Total Building Load

8:00 Qsensible (BTU/hr) 1282 2765 434 3190

10:00 Qsensible (BTU/hr) 6411 2860 434 3190

12:00 Qsensible (BTU/hr) 11540 2859 434 3190

2:00 Qsensible (BTU/hr) 15386 3149 434 3190

4:00 Qsensible (BTU/hr) 15386 3021 434 3190

6:00 Qsensible (BTU/hr) 11540 3021 434 3190

8:00 Qsensible (BTU/hr) 162 2765 434 3190

25798 2948 7000 18023 1100 62540 8876 71416

25436 2948 7000 18023 1100 67402 8876 76278

21866 2948 7000 18023 1100 68960 8876 77837

25680 2948 7000 18023 1100 76912 8876 85788

24087 2948 7000 18023 1100 75190 8876 84066

16150 2948 7000 18023 1100 63407 8876 72282

0 2948 7000 18023 1100 35623 8876 44499

Peak building cooling load = 85788 BTU/hr at 2:00 pm See spreadsheet (MET 465 Cool Load Example Calcs.) for summary of calculations. 13. Adjust as necessary to account for building diversity, setback recovery, etc. Should we adjust?