1. Environmental Controls I/IG
Lecture 11
Degree Days
Heating Loads
Annual Fuel Consumption
Simple Payback Analysis

2. Heating Degree Days
Balance Point Temperature (BPT): temperature above which heating is not needed
DDBPT= BPT-TA

3. Sample Calculation January TA=28ºF DD65=65-28= 37 Degree-days/day
x 31 days
= 1,147 degree-days
S: p. 1524, T.C.15

4. Heating Loads

5. Heating Loads Computed for worst case scenario: Do not include:
Pre-dawn at outdoor design dry bulb temperature
Do not include:
Insolation from sun
Heat gain from people, lights, and equipment
Infiltration in nonresidential buildings
Ventilation in residential buildings
SR-3

6. Outdoor Dry Bulb Temperature
Use Winter Conditions
S: p. 1496, T.B.1

7. Determine Temperature Difference
Indoor Dry Bulb Temperature (IDBT): 68ºF
Outdoor Dry Bulb Temperature (ODBT): 8ºF
ΔT=IDBT-ODBT=68ºF - 8ºF = 60ºF

8. Determine Envelope U-values
Calculate ΣR and then find U for walls, roofs, floors.
Obtain U values for glazing from manufacturer or other reference

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

10. Floor Slabs
For floor slabs at grade, there are two heat loss components:
slab to soil losses
edge losses
S: p. 1583, T.E.11

11. TI=Indoor Air Temperature TGW=Ground Water Temperature
Slab to Soil Losses
Q=Uslab x 0.5 x Aslab x (TI-TGW)
TI=Indoor Air Temperature
TGW=Ground Water Temperature

12. Edge Losses Method I Determine F2 based on heating degree days
S: p. 1582, T.E.11

13. Select F2 based on insulation configuration
Slab Edge Losses
Method II
Select F2 based on insulation configuration
S: 1583, T.E.12

14. TI= Indoor air temperature TO=Outdoor air temperature
Slab Edge Losses
Q=F2 x Slab Perimeter Length x (TI-TO)
where,
TI= Indoor air temperature
TO=Outdoor air temperature

15. Heating Load Example Problem
Building: Office Building
Location: Salt Lake City
ΔT=IDBT-ODBT=68-8=60ºF
Building: 200’ x 100’ (2 stories, 12’-6” each)
Uwall= Btuh/sf-ºF
Uroof= Btuh/sf-ºF
Uwindow= Btuh/sf-ºF
Uslab= Btuh/sf-ºF
Udoor= Btuh/sf-ºF

16. Heating 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, ,
Doors
Net Wall 3,980 1,980 2,950 1,980
Roof/Floor Slab 20,000

17. Heating Loads Insert roof values Insert wall values
, , ,000
N , ,895
E , ,415
S , ,558
W , , ,555
Insert roof values
Insert wall values
Insert glass values
Insert door values
Insert floor values
N , ,600
E ,300
S , ,200
W , ,400
,320 1,320
N/A N/A N/A N/A
SR-3

18. TI=Indoor Air Temperature TGW=Ground Water Temperature
Slab to Soil Losses
Q=Uslab x 0.5 x Aslab x (TI-TGW)
TI=Indoor Air Temperature
TGW=Ground Water Temperature
Ground Water= 53ºF
ΔT=68ºF-53ºF=15ºF

19. Heating Loads Insert floor values SR-3 0.025 20,000 60 30,000 30,000
, , ,000
N , ,895
E , ,415
S , ,558
W , , ,555
Insert floor values
N , ,600
E ,300
S , ,200
W , ,400
,320 1,320
N/A N/A N/A N/A
, ,000
SR-3

20. Edge Losses Method I Determine F2 based on heating degree days
S: p. 1582, T.E.11

21. Heating Degree Days
Salt Lake City
HDD65=5983
S: p. 1524, T.C.15

22. Edge Losses
Method I
Interpolate to find F2
at 5983 DD
0.50 F2? 0.56
S: p. 1582, T.E. 11

23. Interpolate to Find F2
Find difference in Degree Days: = =2083
Find difference in F2: F2?-0.50=x
=0.06
Set up proportion, solve for x: 633/2083=x/0.06
x=0.018
F2?-0.50=0.018
F2?=0.518

24. Edge Losses
Method I
Interpolate to find F2
at 5983 DD
0.50 F2= 0.56
0.518
S: p. 1582, T.E.11

25. Heating Loads Insert floor values SR-3 0.025 20,000 60 30,000 30,000
, , ,000
N , ,895
E , ,415
S , ,558
W , , ,555
Insert floor values
N , ,600
E ,300
S , ,200
W , ,400
,320 1,320
N/A N/A N/A N/A
, ,000
,648 42,648
SR-3

26. Infiltration
Residential buildings use infiltration to provide fresh air
“Air change/hour (ACH) method” (see S: p.1601, T. E.27) or
“Crack length method” (see S: p. 1603, T. E.28)
Prone to subjective interpretation
Vulnerable to construction defects
Provides a relatively approximate result

27. ASHRAE Standard 62-2001 (S: p. 1597-99, T.E.25)
Ventilation Analysis
Non-residential buildings use ventilation to provide fresh air and to offset infiltration effects.
ASHRAE Standard (S: p , T.E.25)
Estimates the number of people/1000 sf of usage type
Prescribes minimum ventilation/person for usage type

28. ASHRAE 62-2001 Defines space occupancy and ventilation loads
S: p. 1598, T.E.25

29. ASHRAE 62-2001 Defines space occupancy and ventilation loads
S: p. 1598, T.E.25

30. Ventilation Load — Sensible
40,000 sf x 5people/1,000sf = 200 people
200 people x 17 cfm/person = 3,400 cfm
3,400 cfm x 60min/hr = 204,000cfh

31. Heating Loads Input Ventilation Load—Sensible SR-3
, , ,000
N , ,895
E , ,415
S , ,558
W , , ,555
Input Ventilation Load—Sensible
N , ,600
E ,300
S , ,200
W , ,400
,320 1,320
N/A N/A N/A N/A
, ,000
,648 42,648
204, ,320
SR-3

32. Ventilation Load — Latent
Determine ΔW
WI= #H2O/#dry air
-WO= #H2O/#dry air
ΔW= #H2O/#dry air

33. Heating Loads Input Ventilation Load — Latent SR-3
, , ,000
N , ,895
E , ,415
S , ,558
W , , ,555
Input Ventilation Load — Latent
N , ,600
E ,300
S , ,200
W , ,400
,320 1,320
N/A N/A N/A N/A
, ,000
,648 42,648
204, ,320
204,
SR-3

34. Heating Load Total Load 504551 Btuh or 505 MBH 5.9 7.6 8.4 SR-3 14.7
, , ,000
5.9
N , ,895
E , ,415
S , ,558
W , , ,555
Total Load
Btuh or
505 MBH
7.6
N , ,600
E ,300
S , ,200
W , ,400
14.7
,320 1,320
0.3
N/A N/A N/A N/A
, ,000
,648 42,648
8.4
204,
204, ,
63.1
SR-3
504551

35. Annual Fuel Consumption

36. Annual Fuel Usage (E) E= UA x DDBPT x 24 AFUE x V where:
UA: heating load/ºF
DDBPT: degree days for given balance point
AFUE: annual fuel utilization efficiency
V: fuel heating value

37. Calculating UA QTotal= UA x ΔT UA= QTotal/ΔT From earlier example:
QTotal=504,551 Btuh
ΔT= 60ºF
UA=504,551/60=8,409 Btuh/ºF

38. Determine AFUE
Annual Fuel Utilization Efficiency of an electric heating system is 100%
S: p. 258, T.8.7

39. Determine Heat Content (V)
Heat content is the quantity of Btu/unit
Note: Natural Gas is sold in therms (100 cf)
S: p. 255, T.8.5

40. Annual Fuel Usage Example
What is the expected annual fuel usage for a house in Salt Lake City if its peak heating load is 39,000 Btuh?
UA=Q/ΔT
UA=39,000/60= 650 Btuh/ºF

41. Determine AFUE
Annual Fuel Utilization Efficiency of an electric heating system is 100%
S: p.258, T.8.7

42. Determine Heat Content (V)
Heat content is the quantity of Btu/unit
S: p. 255, T.8.5

43. Annual Fuel Usage — Electricity
E= UA x DDBPT x 24
AFUE x V
EELEC =(650)(5,983)(24)/(1.0)(3,413)
=27,347 kwh/yr
If electricity is $0.0735/kwh, then
annual cost = $2,010

44. Annual Fuel Usage — Gas E= UA x DDBPT x 24 AFUE x V
=1,111 therms/yr
If gas is $0.41/therm, then
annual cost = $456

45. Simple Payback Analysis

46. Simple Payback Heating System Cost Comparison First Electricity 6,000
($)
Electricity 6,000
Oil 8,000
Gas 8,900

47. Simple Payback Heating System Cost Comparison
First Annual Incremental Incremental Simple
Cost Fuel Cost First Cost Annual Savings Payback
($) ($/yr) ($) ($/yr) (yrs)
Electricity 6,000 2,
Oil 8,000 1,152 2,
Gas 8, ,900 1,
If money is available, select gas furnace system