1. Environmental Controls I/IG
Lecture 10
Heat Flow in Glazing
Infiltration
Ventilation

2. Window Characteristics
S: p. 1585, T.E.15

3. Super Windows
Composed of subassemblies that control conductive and radiant heat exchange.
S: p. 198, F.7.15

4. Window Characteristics
S: p. 1585, T.E.15

5. Window Characteristics
S: p. 1585, T.E.15

6. Solar Heat Gain Coefficient (SHGC)
Percentage of incident solar radiation that passes through the entire window or skylight at a normal incident angle.
High SHGC desirable for passive solar
Low SHGC desirable for where cooling is dominant issue

7. Window Characteristics
S: p. 1585, T.E.15

8. Visible Transmittance (VT)
Percentage of the incident amount of visible light transmitted through the glazing
High VT means better daylighting quantities indoor

9. Window Characteristics
S: p. 1585, T.E.15

10. Spectrally Selective Glazing
Spectrally selective coatings reduce SHGC with little reduction in VT
Low-ε coatings: reflect radiant energy back towards source
LSG: light to solar gain ratio
High LSG is better for day-lighting in hot climates

11. Window Characteristics
S: p. 1585, T.E.15

12. Air Leakage
Rate of outdoor air infiltration between the window and its frame.
Example A: 3’x5’ window at 0.65 cfm/lf.
Inf. = ( ) x 0.65= 10.4 cfm
Example B: 3’x5’ window at 0.98 cfm/sf.
Inf. = (3x5) x 0.98= 14.7 cfm
Note: use the larger value of the two results

13. Heat Flow in Glazing Conductive Heat Flow through glazing:
Q= U x A x ΔT
Q: heat flow (Btuh)
U: transmission coefficient (Btu/h-ºF-ft2)
A: area (ft2) [including frame]
ΔT: temperature difference (Ti-To)

14. Solar Heat Gain Factors
S: p. 1504, T.C.3

15. Heat Flow in Glazing Radiant Heat Flow through glazing:
Q= SHGC x A x SHGF
Q: heat flow (Btuh)
SHGC: solar heat gain coefficient for window and frame
A: area (ft2) [including frame]
SHGF: solar heat gain factor (Btu/h-ft2)

16. Infiltration
Unintentional introduction of untreated air into the occupied space(s) of the building
Heat lost or gained becomes part of the building system load

17. Infiltration Calculated by two means: Air Change per Hour (ACH)
Crack Method

18. Air Change per Hour Method
Volume of infiltration:
V= (ACH)(volume, ft3)
60 min/hr
V: total air flow volume (cfm)
ACH: Air changes per hour
volume: space volume (ft3)

19. Air Change per Hour Method
Volume of infiltration:
V= (ACH)(volume, ft3)
60 min/hr
V: total air flow volume (cfm)
ACH: Air changes per hour
volume: space volume (ft3)

20. Air Change per Hour Method
Determine Construction Type
S: p. 1601, T.E.27A

21. Air Change per Hour Method
Determine Winter & Summer Conditions
S: p. 1601, TE.27B&C

22. Crack Length Method
Calculate crack length of windows on the windward side only.
Calculate crack length of doors on the windward side only.

23. Crack Length Method Determine window and door “fit” and Find “k”
S: p. 1604, T.E.28C

24. Crack Length Method Determine wind velocity.
Find “velocity head factor.”
Determine infiltration rate
Calculate total infiltration
S: p. 1603, T.E.28A&B

25. Crack Length Method
Find winter infiltration for average fitting windows
k=2.0
S: p. 1603, T.E.28C

26. Crack Length Method Wind velocity=15 mph Velocity head factor=0.11
Infiltration rate= 0.5cfm/lf
Calculate total infiltration
Infiltration =
Rate x Crack length
S: p. 1604, T.E.28A&B

27. Ventilation
Intentional introduction of treated fresh air into the occupied space(s) of the building
Outside air is introduced via the building ventilation ductwork system
Residential buildings generally rely on infiltration
Non-residential buildings use ventilation

28. Ventilation Ventilation is determined according to:
ASHRAE Standard (S: p. 1597, T.E.25)
Estimates the number of people/1000 sf of usage type
Prescribes minimum ventilation/person for usage type

29. ASHRAE
Example:
(1) Determine the ventilation rate for 2,000 sf office space.
(2) Determine total ventilation volume.
S: p. 1598, T.E.25

30. ASHRAE
Example:
(1) Determine the ventilation rate for 2,000 sf office space.
17 cfm/person
S: p. 1598, T.E.25

31. ASHRAE 62-2001 Example: (2) Determine total ventilation volume.
=2000 sf x (5 persons/1000sf) x (17 cfm/person)
=170 cfm
S: p. 1598, T.E.25