Document JN1KOaobB0ya636wexaEbnNOa

Heating Ventilating Air Conditioning Guide 1939 heat transmission, to apply correction factors to the values of (7). Solar radiation factors and solar absorption coefficients have been determined1 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: where HR - A F a I . (2) Hr .= Solar heat transmission, Btu per hour. ' . A = Area of wall or roof, square feet. j F = Percentage (expressed as a decimal) of the absorbed solar radiation which is 1 transmitted to the inside (Fig. 2). o..= Percentage (expressed as aj decimal) of the incident solar radiation which is absorbed by the surface (Table 6). I = Iritensity of solar radiation striking1 surface, Btu per hour per square foot ('fables 2, 3, 4 and 5). Thd total amountjof heat conducted through a wall exposed to the sun is the sum of Ht an<| HRfrom Formulas 1 and 2. , II It I; ; >. - - ---- ! Ii j : |. : A Rational Heat Gain Method for the Determination of Air Conditioning Cdoling Loads, by F. H. Ffeustrfc. Levine;-and-F: O: UrbairTA:SvH;V7E-. TRANSACTioirorVotr?'l35rp^327)^----------- ------- 152 Chapter 8. Cooling Load * cot a Absorption Coefficients for Different Building Materials Table d- --------------- Surface Material Absorption Coefficient (o) .--------------------------- White atone i :~hr Colored Surfaces........... Very light colored cement Very Lignc White or light cream-colored paint 0.4 ------------- Asbestos shingles Unpainted wood Brown stone wMejdi-um Duaarrxk Scmurfaces......................BDraicrtk-caonldorreedd cteilement Stucco Red. green or gray paint 0.7 --------- - Slate roofing xV.e,,ry, HUaarrKk Colored Surfaces......... TVearryrodoafrinkgpmainattaerials 0.9 The calculation of heat transmission through walls and roofs does not take into consideration the heat capacity of the structure nor the con 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 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 ip 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. Radiation Transmitted Through Glass Windows present a problem somewhat different from that of opaque walls, because they permit a large percentage of the solar energy to pass through, a small amount is reflected and the balance is absorbed by the glass. The amount absorbed depends upon the character and thickness of the glass and the angle between the sun's rays and the glass. The temperature of the glass is raised by the absorbed heat and this heat is then delivered to the air on the two sides of the glass in proportion to the the difference between the glass and air temperature.6 Table 7. Time Lac in Transmission of Solar Radiation through Walls and Roofs Ttps and Thickness or Wall ob Roof Time Lao. Hours 2-in. pine___ 4-in. gypsum...............................................................!...................................................... 3-in. concrete and 1-in. cnrk 2-in. iron and cork (equivalent to %-in. concrete and 2*.15-in. cork).............. 4-in. iron and cork (equivalent to 5f$-in. concrete and 1.94-in. cork)............. 8-in. iron and cork (equivalent to 16-in. concrete and 1.53-in. cork).............. 22-in. brick and tile wall : - ih 3 2^ 2 2M 7X 19 10 `Loc. Cit. Notes 1 and 2. j `Heat Absorbing Glass Windows, by W. W. Shaver (A.S.H.V.E. Transactions. Vol. 41. 1935, p. 287).