This document discusses various topics related to computing cooling loads and energy performance ratings for building architectures, including: - Calculating cooling loads based on envelope areas, U-values, glazing properties, infiltration, ventilation, occupants, lighting, and equipment. - Determining cooling degree hours to indicate relative warmth for a location. - Energy performance ratings like SEER, EER, and COP that indicate efficiency of cooling systems. - Computing annual fuel consumption and costs based on cooling load, degree hours, and system efficiency ratings. - Comparing simple payback periods of different cooling system options.

1. Technology in Architectures
Lecture 8
Cooling Loads
Cooling Degree Hours
Energy Performance Ratings
Annual Fuel Consumption

2. Cooling Loads
Computed for worst
case scenario:
 Late summer afternoon
at outdoor design dry
bulb temperature
Include:
 Insolation from sun
 Heat gain from people,
lights, and equipment
 Infiltration in residential
buildings
 Ventilation in
nonresidential buildings
SR-3

3. Summer Design Conditions
Design Dry Bulb Temperature
Mean Daily Range
S(10): T.B.1,
p. 1496

4. Determine Design Equivalent
Temperature Difference (DETD)
Construction type
Outdoor design temperature
Mean daily range
L: 0-16ºF
M: 16-25ºF
H: 25+ºF
S: p. 1653, T.F.5

5. Determine Envelope U-values
Calculate ΣR and then find U for walls
and roofs.
Note: this method ignores floors, doors,
and window U-values

6. Determine DCLF
Glazing Type
Design Temperature
Shading
Orientation
S: p. 1655, T.F.6

7. Determine Area Quantities
Perform area takeoffs for
all building envelope
surfaces on each facade:
gross wall area
window area
door area
net wall area
4’
Elevation
4’
12’
100’
8’
1200 sf
64 sf
368 sf
768 sf
-
-

8. Infiltration
S: p. 1657, T.F.7

9. Ventilation Analysis
Non-residential buildings use ventilation to provide
fresh air and to offset infiltration effects.
ASHRAE Standard 62-2001 (S: p. 1598, T.E.25)
Estimates the number of people/1000 sf of usage type
Prescribes minimum ventilation/person for usage type

10. ASHRAE 62-2001
Defines space occupancy and ventilation loads
S: p. 1639, T.E.25

11. Ventilation—Sensible CLF
S: 1657, T.F.7

12. People — Sensible Gain
Determine number of people
Activity level
S: p. 1657, T.F.8

13. Lights
Determine wattage of lighting/square foot
 ASHRAE 90.1 prescriptive levels
 Count fixture loads and add together
Note: add 15% for ballasts where applicable
(e.g., fluorescent lights)

14. Equipment
Determine operating wattage of
equipment/square foot
 ASHRAE 90.1 prescriptive levels
 Count actual loads and add together
Note: include a diversity factor (20-30%) if
specific usage patterns are unknown.

15. Equipment
Use manufacturer’s data or other
references to obtain heat gain data.
Standby mode
 Copiers
 Monitors
 Printers
 CPU
 “energy star”
S: p. 1658, T.F.9

16. Latent Load
Not calculated separately:
Apply a factor as a percentage of the total
sensible cooling load
Dry climates: 20%
Moist/Humid climates: 30%

17. Cooling Load Example Problem
Building: Office Building
Location: Salt Lake City
Building: 200’ x 100’ (2 stories, 12’-6” each)
Uwall= 0.054 Btuh/sf-ºF
Uroof= 0.025 Btuh/sf-ºF

18. Cooling Load Example Problem
Determine Building Envelope Areas (SF)
Building: 200’ x 100’ (2 stories, 12’-6” each)
N E S W
Gross Wall 5,000 2,500 5,000 2,500
Windows 1,000 500 2,000 500
Doors 20 20 50 20
Net Wall 3,980 1,980 2,950 1,980
Roof/Floor Slab 20,000

19. Determine Design Equivalent
Temperature Difference (DETD)
Roof Construction type: Light color, vented, ceiling
Design temperature: 95ºF
Mean daily range: 32ºF
L: 0-16ºF
M: 16-25ºF
H: 25+ºF
DETD=31.0ºF
S: p. 1653, T.F.5

20. Cooling Loads
Insert roof values
SR-3
0.025 20,000 31.0 15,500 15,500

21. Determine Design Equivalent
Temperature Difference (DETD)
Wall Construction type (see given)
Design temperature: 95ºF
Mean daily range: 32ºF
L: 0-16ºF
M: 16-25ºF
H: 25+ºF
DETD=11.3ºF
S: p. 1653, T.F.5

22. Cooling Loads
Insert roof values
Insert wall values
SR-3
0.025 20,000 31.0 15,500 15,500
N 0.054 3,980 11.3 2.429
E 0.054 1,980 11.3 1.208
S 0.054 2,950 11.3 1,800
W 0.054 1,980 11.3 1,208 6,645

23. Glazing Type
Design Temperature
Shading
Orientation
Determine Window DCLF
S: p.
1656,
T.F.6.B

24. Cooling Loads
Insert roof values
Insert wall values
Insert glass values
SR-3
0.025 20,000 31.0 15,500 15,500
N 0.054 3,980 11.3 2.429
E 0.054 1,980 11.3 1.208
S 0.054 2,950 11.3 1,800
W 0.054 1,980 11.3 1,208 6,645
N 1,000 14 14,000
E 500 35 17,500
S 2,000 20 40,000
W 500 35 17,500
89,000

25. ASHRAE 62-2001
Defines space occupancy and ventilation loads
S: p. 1639, T.E.25

26. Ventilation Load — Sensible
40,000 sf x 5people/1,000sf = 200 people
200 people x 17 cfm/person = 3,400 cfm

27. Ventilation Load — Sensible CLF
Design Temperature: 95ºF
Commercial Building: Ventilation
S: p. 1657, T.F.7

28. Cooling Loads
Insert roof values
Insert wall values
Insert glass values
Insert outdoor air
values
SR-3
0.025 20,000 31.0 15,500 15,500
N 0.054 3,980 11.3 2.429
E 0.054 1,980 11.3 1.208
S 0.054 2,950 11.3 1,800
W 0.054 1,980 11.3 1,208 6,645
N 1,000 14 14,000
E 500 35 17,500
S 2,000 20 40,000
W 500 35 17,500
89,000
N/A N/A N/A
3,400 22.0 74,800 74,800

29. People — Sensible Gain
Determine number of people: 280
Activity level: moderately active office work
S: p. 1657, T.F.8

30. Cooling Loads
Insert roof values
Insert wall values
Insert glass values
Insert outdoor air
values
Insert people values
SR-3
0.025 20,000 31.0 15,500 15,500
N 0.054 3,980 11.3 2.429
E 0.054 1,980 11.3 1.208
S 0.054 2,950 11.3 1,800
W 0.054 1,980 11.3 1,208 6,645
N 1,000 14 14,000
E 500 35 17,500
S 2,000 20 40,000
W 500 35 17,500
89,000
N/A N/A N/A
3,400 22.0 74,800 74,800
200 250 50,000

31. Lighting Load
Lighting load: 1.5 w/sf
Equipment load: 0.5 w/sf

32. Cooling Loads
Insert roof values
Insert wall values
Insert glass values
Insert outdoor air
values
Insert people values
Insert lighting values
Insert equipment
values SR-3
0.025 20,000 31.0 15,500 15,500
N 0.054 3,980 11.3 2.429
E 0.054 1,980 11.3 1.208
S 0.054 2,950 11.3 1,800
W 0.054 1,980 11.3 1,208 6,645
N 1,000 14 14,000
E 500 35 17,500
S 2,000 20 40,000
W 500 35 17,500
89,000
N/A N/A N/A
3,400 22.0 74,800 74,800
200 250 50,000
40,000 1.5 204,780
40,000 0.5 68,260 323,040

33. Cooling Loads
Sensible Heat Gain:
508985 Btuh
Latent Heat Gain (20%):
101,797 Btuh
Total Heat Gain:
610,782Btuh
or
50.9 Tons
Tons=Q/12,000
SR-3
0.025 20,000 31.0 15,500 15,500
N 0.054 3,980 11.3 2.429
E 0.054 1,980 11.3 1.208
S 0.054 2,950 11.3 1,800
W 0.054 1,980 11.3 1,208 6,645
N 1,000 14 14,000
E 500 35 17,500
S 2,000 20 40,000
W 500 35 17,500
89,000
N/A N/A N/A
3,400 22.0 74,800 74,800
200 250 50,000
40,000 1.5 204,780
40,000 0.5 68,260 323,040
508,985
101,797
610,782
50.9
2.5
1.1
14.6
16.7
83.3
52.8
12.3
100.0

34. Cooling Degree Hours

35. Cooling Degree Hours
Relative indicator of warmth
S(10): T.B.1,
p. 1513

36. Cooling Degree Hours
Balance Point Temperature (BPT):
temperature above which cooling is needed
CDH(BPT)= ODBT-BPT
If temperature (ODBT)=91ºF
CDH74=ODBT-74
=91-74
=17 cooling degree-hours

37. Energy Performance Ratings

38. Performance Ratings
COP: coefficient of performance
EER: energy efficiency at full load
SEER: seasonal energy efficiency ratio
Note: SEER≈COP x 3.413

39. Annual Fuel Consumption

40. Annual Fuel Usage (E)
E= UA x CDH(BPT)
SEER
where:
UA: cooling load/ºF
CDH(BPT): degree hours for balance point
SEER: seasonal energy efficiency rating

41. Calculating UA
QTotal= UA x ΔT
UA= QTotal/ΔT
From earlier example:
QTotal= 610782 Btuh
ΔT= 95-75=20ºF
UA=610782/20= 30,539 Btuh/ºF

42. Annual Fuel Usage Example
Compare two systems to determine what
is the expected annual electrical usage for
an apartment in Salt Lake City if its peak
cooling load is 12,000 Btuh?
UA=Q/ΔT
UA=12,000/20= 600 Btuh/ºF

43. Determine SEER
Obtain SEER from manufacturer’s data or
Convert COP to SEER
SEER: 5-15
For this example:
SEER1=6.8
SEER2=10.2

44. Annual Fuel Usage — Electricity
E= UA x CDH74
SEER
E1 =(600)(9,898)/(6.8)
=873,353 wh/yr
=873 kwh/yr
If electricity is $0.0735/kwh, then
annual cost = $64

45. Annual Fuel Usage — Electricity
E= UA x CDH74
SEER
E2 =(600)(9,898)/(10.2)
=582,235 wh/yr
=582 kwh/yr
If electricity is $0.0735/kwh, then
annual cost = $43

46. Simple Payback Analysis

47. Simple Payback
Cooling System Cost Comparison
First
Cost
($)
System 1 500
System 2 600

48. Simple Payback
Cooling System Cost Comparison
First Annual Incremental Incremental Simple
Cost Fuel Cost First Cost Annual Savings Payback
($) ($/yr) ($) ($/yr) (yrs)
System 1 500 64 --- --- ---
System 2 600 43 100 21 4.8
Payback exceeds 3 years, select system 1
Other factors?