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CHAPTER 15
1948 Guide
Table 15. Instantaneous Rates of Heat Gain Due to Solar and Sky Radiation for Single Sheets of Unshaded Common Window Glass a* b (Concluded)
Sun Time
Instantaneous Rate,of Heat Gain, Btu per Hour for Each Square Foot of Unshaded Glass
N' NE
E
SE
s.. sw w NW Horizontal
6 7 8 .9 10 11 12
2 3 4 5 6 7
45 Deg North Latitude
2.0 9 23
12.5 22
111
23.0
13 135
33.5
14 116
44.0
15 63
53.0 Ifi 22
60.0
16 16
63.0
16' 16
60.0
16 16
63.0
16 16
44.0
15 15
33.5
14 14
23.0
13 11
12.5 22 6
2.0 9 1
23
129 182 192
168
123 ` 56
16 16 16 15 14 11
6.
1
8
68 121
153 166
154 127
76 . 30
16 15
14 11 .6
1
1 .6
11 24 55
88' : 113
119 113
88 55 24 11
6 1
1 6.
11 14
15 16 30
76 127
154 166
153 121
68 8
1 6
11 14
15 16 16 16 56
123 168. 192 182
129 23
1 6
11 14
` 15 16
16 16
16 22 63
116 135
111 23
2
28 82 141 189 225 249 256 249 225 189 141 82
28 2
50 Deg North Latitude
X
4.5 18 48 48 17 2 2 2 2
5
6
13.5 22 119 139 . 75 6 6 . 6 , 6
32
7
23.5 :
11 131 183 127 : 11
11 11
11
S4 '
8
33.0
13 103 190 161 30 13 13 13
138
9
42.0
14 51 165 173 69 14 14 14
179
10
50.0
16 19 122 166 109- 16 16 16
214
11
56.0
16 16 55 138 133 41 16 * 16
235
12
58.0
16 16 16 92 140 92 16 16
242
56.0
16 16 16 41 133 138 55 . 16
235
2
.50.0
16 16 16 16 109 166 122 19
214
3
42.0
14- 14
14 14
69 173 165
51
179
4
33.0
13 13 13 13 30 161 190 103
138
5
23.5
11 11 11 11 11 127 183 131
84
6
13.5
22
6
6
6
6 75 139 119
'32
7
4.5 18 2 2 2 2 17 48 48
5
Table compiled from solar radiation transmission data developed by A.S.H.V.E. Research Labora tory* and direct intensity values developed by Moon1, recently enlarged and revised by the A.S.H.V.E.
Research Laboratory.
bFor relatively clear atmosphere at sea level. For hazy atmosphere values may be reduced 10 per cent.
Above sea level add one per cent per 1000 ft elevation.
,
inclusive, and for all exposures from 10:00 a.m. to 2:00 p.m. inclusive. For Southern exposures at .8:00 a.m. or at 4:00 p.m. the error may be *15 per cent. At noon this method gives accurate results; the error becomes progressively larger as the time differs from noon.
In regard to glass blocks, data on the over-all unit conductances for heat transfer by convection and conduction are given in Table 18, Chapter 6; these will serve also for cooling load calculations for shaded or northexposure walls. (Steady-state calculations as suggested there take no account of the time lag present with periodic cycles of air temperature.)
The results of experimental observations 12 on heat gains through glassblock sections are given in Table 18. Tabulated heat-gain rates are based upon a constant indoor-air temperature of 78 F and a maximum outdoor-air temperature of 95 F for the design day chosen. The values given are approximate, and intended for estimates only; they are averages for four representative glass block designs, two with smooth exterior faces and two with ribbed exterior faces.
Cooling Load
279
Table 16.
Ratio of Instantaneous Rate of Heat Gain Through Single Thickness
of Heat Absorbing Sunlit Glass to Heat Gain for Common Glass as Given in Table 15
Trans missivity*
0.90 0.87 0.80
Approximate Ratio
1.02 1.0 0.93
Trans missivity*
.0.70 0.60 0.50
Approximate Ratio
0.85 0.76 0.68
Trans missivity*
0.40 0.30 0.20
Approximate ' Ratio
0.60 0.52 0.45
For direct solar radiation at normal incidence.
Table 17. Approximate Solar Declinations in Degrees
Date
April 1 April 15 May 1 May 15
Declination
4.5 10.0 15.0 19.0
Date
June 1 June 15 July 1 July 15
Declination
22.0 23.5 23.0 21.5
Date
Aug. 1 Aug. 15 Sept. 1 Sept. 15
Declination
18.0 14.0 8.5 3.0
Table 18. Total Instantaneous Rates of Heat Gain for Glass Blocks u on Design Day of August 1
( Values tabulated include solar and sky radiation, convection, and conduction averaged for four types of blocks)
Mean Sun Time
North Latitude, Deg
7 a.m.
11 12 noon
1 p.m. 2
5
Total Instantaneous Rate of Heat Gain, Btu per Hour for Each Square Foot of Sunlit Glass Block
Vertical Surface Facing
East
West
South
30 to 45
61 78 74 58 45 37 30 24 20 16 . 13 11 8
30 to 45
--v---
5.0 6.5 7.5 11 22 35 55 77 86 55 19
30
-4.5 0.0 5.0
11 17 22 25 26 24 20 15 9.5 3.5
35
-2.0 2.0 7.0
15 22 -28 32 32 30 26 20 14
7.0
40
-0.5 4.0 10 18
26 34 39 39 37 32 25 18 11
45 1.0
26 18
Shading of Glass Areas--Design Tables
The effects and possibilities of shading should be carefully investigated whenever the heat gain from glass is a large portion of the cooling load.
Vertical glass which is not mounted in the plane of the building surface is partially shaded by the setback. If a vertical window of height l and width w be set back from the plane of the building a distance s, the fraction of the total area of the window which receives direct solar radia tion is:
Gf = 1 -- D tan p -- r, tan y + rj r, tan p tan y
(13)
where
r} = //{> r ~ s!w, p = solar altitude, and y is the difference between the azimuth
angles of the wall in question and of the horizontal projection of the sun's rays (r is always equal to or less than 90 deg.)