|
65
T
ABLE
3.29
Overall
Coef
ficients
of
Heat
T
ransmission
(
U
Factor)
of
Windows
and
Sliding
Patio
Doors
for
Use
in
Peak
Load
Determination
and
Mechanical
Equipment
Sizing
Only
,
a
B
tu/(
h
䡠
ft
2
䡠
ⴗ
F)
1
2
1
2
1
4
1
2
1
4
3
16
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66
T
ABLE
3.29
(
Continued
)
1
2
1
2
1
4
1
2
1
4
3
16
a
W
indow
manufacturers
should
be
consulted
for
specific
data
on
adjustments
for
various
windows
and
sliding
patio
doors.
b
1
⁄
8
-in.
glass
or
acrylic
as
noted,
1
to
4-in.
air
space.
c
Hemispherical
emittance
of
uncoated
glass
surface
⫽
0.84,
coated
glass
surface
as
specified.
d
Coating
on
second
surface,
i.e.,
room
side
of
glass.
e
Double
and
triple
refer
to
number
of
lights
of
glass.
f
1
⁄
8
-in.
glass.
g
1
⁄
4
-in.
glass.
h
Coating
on
either
glass
surface
2
o
r
3
for
winter
,
and
on
surface
2
for
summer
U
-factors.
i
W
indow
design
1
⁄
4
-in.
glass,
1
⁄
8
-in.
glass
and
1
⁄
4
-in.
glass.
*
1
5
mph
outdoor
air
velocity;
0
⬚
F
outdoor
air;
70
⬚
F
inside
air
temperature,
natural
convections.
**
7.5
mph
outdoor
air
velocity;
89
⬚
F
outdoor
air;
75
⬚
F
inside
air
,
natural
convection;
solar
radiation
248.3
Btu
/h
䡠
ft
2
.
S
O
URCE
:
Copyright
1985,
American
Society
of
Heating,
Refrigerating
and
Air
Conditioning
Engineers,
Inc.,
www
.ashrae.org.
Abstracted
by
permission
from
ASHRAE
Handbook,
1985
Fundamentals,
Chap.
27,
T
able
13,
P
art
A.
Design Procedures: Part 1
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Design Procedures: Part 1
67
TABLE
3.30 Overall Coefficients of Heat Transmission (
U
Factor)
of Exterior Horizontal Panels (Skylights) for Use in Peak Load
Determination and Mechanical Equipment Sizing Only,
Btu / (h
䡠
ft
2
䡠
ⴗ
F)
SOURCE
: Copyright 1985, American Society of Heating, Refrigerating
and Air Conditioning Engineers, Inc., www.ashrae.org. Reprinted by per-
mission from ASHRAE Handbook,
1985 Fundamentals,
Chap. 27, Table
13, Part B.
traffic increases air movement. Walls are porous. Airflows have been
measured even through masonry walls, and joints in metal panel walls
are never airtight. Vertical air movement in multistory buildings takes
place through elevator shafts, stairwells, utility chases, ducts, and nu-
merous construction openings.
Wind creates a positive pressure on the windward side of a building
and a negative pressure on the leeward side. These pressures vary
with changes in wind direction and velocity. Wind effects make it dif-
ficult to obtain consistent measurement of interior or exterior pres-
sures for the purposes of control.
The chimney effect in a multistory building (or even in a single-
story building) is related to variations in the air density due to tem-
perature and height and is aggravated by wind. The effect is minor
during warm weather but significant in winter. The buoyancy of the
warm air inside compared to a cold ambient condition outside the
building makes the air rise, creating a pressure gradient, as shown in
Fig. 3.7. The lower floors are negative with respect to the outside,
while the upper floors are positive. The neutral point will vary de-
pending on the building construction and height but can be observed
by a ride up the elevator that stops at every floor. The effect is to cause
infiltration on the lower floors and exfiltration on the upper floors.
This effect is also a driving force for smoke spread in a fire. Even when
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