Document X7XGzQZdpw9gGRbw7yjp08KDd

1938Heating Ventilating Air Conditioning Guide transmitted through a surface depends upon the nature of the exterior surface of wall or roof construction, it is necessary, in order-to determine actual amount of solar heat transmission; to apply correction factors to the values of (/). Solar radiation factors and solar absorption coefficients have'been determined3 as indicated in Fig. 2 and Table 6 respectively.. The solar heat conduction through a wall or.roof exposed to the sun may be expressed by the formula: % Hr = A F a I (2) where '' Hr = Solar heat transmission, Btu per hour. A =' Area of wall or roof, square feet. 1 F =. Percentage (expressed as a decimal) of the absorbed solar radiation which is transmitted to the inside (Fig. 2). a = Percentage (expressed as a decimal) of the incident solar radiation which is absorbed by the surface (Table 6). I -- Actual intensity of solar radiation striking surface, Btu per hour per square foot (Tables 2, 3, 4 and 5): *A Rational Heat Gain Method for the Determination of Air Conditioning Cooling Loads, by F. H. .Faust, L..Levine and.F. O. Urban-(A.S.H.V.E. -Transactions, Vol. 41, .1935, p. 327)_ . .. ...,, ....... Chapter 8. Cooling Load The total amount of heat conducted through a wall exposed to the sun is the sum of Ht and HR from Formulas 1 and 2. The calculation of heat transmission through walls and roofs does not take into consideration the heat capacity of the structure nor the con- Table 6. Solar Absorption Coefficients for Different Building Materials Surface Material Very Light Colored Surfaces White stone Very light colored cement White or light cream-colored paint Medium Dark Surfaces Asbestos shingles Unpainted wood Brown stone Brick and red tile Dark-colored cement Stucco Red, green or gray paint Very Dark Colored Surfaces Slate roofing Tar roofing materials Very dark paints Absorption Coefficient (a) 0.4 0.7 0.9 sequent time lag in the transmission of heat. In the case of massive walls the time lag may amount to several hours4. Thus in many cases the wall transmission cannot be added directly to the cooling load from other sources because the peak of the wall transmission load may not coincide Table 7. Time Lag in Transmission of Solar Radiation through Walls and Roofs Tips and Thickness of Wall oh Roof Time Lao, , .. Hours 3 . 2J4 2 2H 7M 19 . 10 : with the peak of the total cooling load and may even occur after the cooling, system has been shut down for the day. The data in Table 7. were taken from'A.S.H.V.E. research papers and whereas they result from a study of experimental slabs, they give an approximate idea of the time lag to be expected in various structures. ': 4Loc. Cit. Notes 1 and 2. 155