Technology in Architecture
Lecture 6
Heat Flow in Glazing
Infiltration
Ventilation
Window Characteristics
S: p. 1627, T.E.15
Super Windows
Composed of
subassemblies
that control
conductive and
radiant heat
exchange.
S: p. 202, F.7.15
Window Characteristics
S: p. 1627, T.E.15
Window Characteristics
S: p. 1627, T.E.15
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
Window Characteristics
S: p. 1627, T.E.15
Visible Transmittance (VT)
Percentage of the incident amount
of visible light transmitted
through the glazing
High VT means better daylighting
quantities indoor
Window Characteristics
S: p. 1627, T.E.15
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
Window Characteristics
S: p. 1627, T.E.15
Air Leakage
Rate of outdoor air infiltration between the
window and its frame.
Example A: 3’x5’ window at 0.65 cfm/lf.
Inf. = (3+5+3+5) 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
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)
Solar Heat Gain Factors
S: p. 1534, T.C.3
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)
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
Infiltration
Calculated by two means:
1.
2.
Air Change per Hour (ACH)
Crack Method
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)
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)
Air Change per Hour Method
Determine Construction Type
S: p. 1642, T.E.27A
Air Change per Hour Method
Determine Winter & Summer Conditions
S: p. 1642, TE.27B&C
Crack Length Method
Calculate crack length of windows on the
windward side only.
Calculate crack length of doors on the
windward side only.
Crack Length Method
Determine
window and
door “fit” and
Find “k”
S: p. 1644, T.E.28C
Crack Length Method
1.
2.
3.
4.
Determine wind
velocity.
Find “velocity head
factor.”
Determine infiltration
rate
Calculate total
infiltration
S: p. 1643, T.E.28A&B
Crack Length Method
Find winter
infiltration for
average
fitting
windows
k=2.0
S: p. 1644, T.E.28C
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. 1643, T.E.28A&B
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
Ventilation
Ventilation is determined according to:
ASHRAE Standard 62-2001
(S: p. 1597, T.E.25)
Estimates the number of people/1000 sf of
usage type
Prescribes minimum ventilation/person for
usage type
ASHRAE 62-2001
Example:
(1) Determine the ventilation rate for 2,000 sf
office space.
(2) Determine total ventilation volume.
S: p. 1639, T.E.25
ASHRAE 62-2001
Example:
(1) Determine the ventilation rate for 2,000 sf
office space.
17 cfm/person
S: p. 1639, T.E.25
ASHRAE 62-2001
Example:
(2) Determine total ventilation volume.
=2000 sf x (5 persons/1000sf) x (17 cfm/person)
=170 cfm
S: p. 1639, T.E.25