Document ba5bjnapVjpqxB4oNEkmxq1Dk

HEATINC VENTILATING AIR CONDITIONING GUIDE 1940 The variation in solar intensity is given in Fig. 1. The curves are drawn from A.S.H.V.E. Laboratory data obtained by pyrheliometer, are based on sun time, and apply for a perfectly clear day on August 1 at a north latitude of 40 deg. A study of these curves discloses the periodic relationship and wide variation in solar intensity on various surfaces. It will be observed that both the roof (horizontal surface) and south wall radiation curves are in exact phase relationship with each other and that whereas the east and west wall radiation curves overlap those for roof and south wall, they do not overlap each other. This phase relation ship has an important bearing on the cooling load. Failure to consider the periodic character of heat flow resulting from diurnal movement of the sun and the lag due to heat capacity of the structure, which determine the timing and magnitude of the heat wave flowing through the wall, may result in a large error in load calculations. Fig. 1. Curves Giving Solar Intensity Normal to Sun, on Horizontal Surface and on Walls for August 1 The values of solar intensity appearing in Fig. 1 must not be confused with the actual heat transmission through the wall for much of the solar radiation impinging against the outer surface fails to pass through the wall. Instead it is delivered to the outside air by reflection, radiation, convection and conduction. A mathematical solution for the deter mination of solar heat transmission has been developed but the equations involved are too complex for practical application.1 From results of this investigation and earlier studies,2 the Research Laboratory has prepared Tables 2, 3, 4 and 5 which give the solar intensity (/) for various hours of the day on walls of various orientations and horizontal surfaces. These values are shown for north latitudes from 30 to 45 deg. lA.S.H.V.E. Research Report No. 923--Heat Transmission as Influenced by Heat Capacity and Solar Radiation, by F. C. Houghten, J. L. Blackshaw, E. W. Pugh and Paul McDerraott(A.S.H.V.E. Transactions, Vol. 38. 1932. p. 231). *A.S.H.V.E. Research Report No. 853--Absorption of Solar Radiation in its Relation to the Tem perature. Color, Angle and Other Characteristics of the Absorbing Surface, by F. C, Houghten and Carl Gutberfet (A.S.H.V.E. Transactions. Vol. 36, 1930, p. 137). 144 CHAPTER 8. COOLING LOAD Table 2. Solar Radiation Impinging against Walls having several Orientations and a Horizontal Surface. ' For SO Deg Latitude on the twenty-first of July. Sun Time 4:59 5:00 6:00 7:00 8.00 9:00 10:00 11:00 12:00 1:00 2.-00 3:00 4:00 5.-00 6:00 7:00 7:01 Table 3. Northeast 0 1 47 136 151 127 79 21 Intensity of Sold, Baz>mt,on. Btu PEl ^ Fl pRR ^ East 0 1 51 160 205 Southeast 0 0.3 24 90 136 South Southwest West Northw 189 140 141 122 . 78 85 36 8 31 45 50 36 45 31 8 85 78 122 141 140 189 21 79 127 136 205 151 ---------------- . 90 160 24 51 0.3 1 00 136 47 1 0 - Horizontal Surface 0 0.01 9 68 147 214 265 296 305 296 265 214 147 68 9 0.01 0