Document MGwbEb1nbLNXMNrNdq1OG4gqa

HEATINC VENTILATINC AIR CONDITIONING GUIDE 1944 Table 6. Time Lag in Transmission of Solar Radiation Through Walls and Roofs Type and Thickness of Wall or Roof Time Lag, Hours 1-in. yellow pine horizontal roof, water proofing, smooth black finish-------- 2-in. yellow pine horizontal roof, water proofing, smooth black finish-------4-in. reinforced clay tile horizontal roof, water proofing, slag finish----------2-in. gypsum horizontal roof, water proofing, stag finish---- ..------------------Slate and slaters felt on 2in. tongue and grooved yellow pine, sloped roof 4-in. gypsum horizontal roof, water proofing, slag finish---- -------------------6-in. concrete horizontal roof, water proofing, slag finish------------------------1-in. concrete, 4-in. cinders, 1 J4-in. concrete, water proofing, smooth black finish Wood siding, 1-in. sheathing, 2x4 studs, lath and plaster--------- ----------Wood siding, 1-in. sheathing, 2x4 studs (studding space filled with insula tion) lath and plaster 4-in. brick, 1-in. sheathing, 2x4 studs, lath and plaster.------------------------- 4-in. brick, 8-in. tile and plaster 13-in. brick, plastered______________________ ____________ _ 9-in. brick, 3J-in. tile, 5}-in. air space, 3%-in. tile and lj^-in. plaster-- 1 1*A 2K 2H 4M 5 8 2 5 7 10^ 12 16 to the air on each side in proportion to the difference between the gkfes and air temperatures9. The A.S.H.V.E. tests7 indicate that a single pane of double strength glass 0.127 in. thick absorbs approximately 11 pier cent of the solar radiation passing through it when the impingement is normal. For smaller angles of impingement, the glass retards percentages of the total radiant energy approximately in proportion to the sine of the angle. The amount of solar radiation delivered to an unshaded glass surface may be obtained from Tables 2,3,4 or 5. These values must be used only for the net glass area on which the. sun shines and not the entire glass area. Tests at the A.S.H.V.E. Research Laboratory8 have determined the percentage of heat from solar radiation actually delivered to a room with various types of outdoor and indoor shading. The data in Table 7 are taken from these tests. Table .7. Solar Radiation Transmitted Through Shaded Windows Ttpb op Appcbtbnancb Finish Facing - Sun Plain Aluminum Buff Inside Venetian blind, fully covering window, slats at 45 deg._ -Aluminum Outside Venetian blind, fully covering window, slats at 45 deg_ .Aluminum Peh Cent DELIVERER to Booh 28 . 22 45 68 58 22 Heat Absorbing Glass Windows, by W. W. Shaver (A.S.H.V.E. Transactions, VoI.' 41,1935, p. 287). 'A.S.H.V.E, Research Report No. 974--Radiation of Energy Through Glass, by J. L. Blaclcshaw and F. C. Houghten (A.S.H.V.E. Transactions, Vol. 40,1934, p. 93). A.S.H.V.E. Research Report No. 975 --^Studies of Solar Radiation Through Bare and Shaded Windows, by F. C. Houghten, Carl Gutberlet, and J. L. Blackshaw (A.S.H.V.E. Transactions, Vol. 40, 1934, p. 101). *A.S.H.V.E. Research Report No. 1180--Heat Gain Through Western Windows With and Without Shading, by F. C. Houghten and David Shore (A.S.H.V.E. Transactions, Vol. 47, 1941, p. 251). ' Loc. Cit. Note 7. 154 CHAPTER 7. COOLING LOAD The percentage values in this table were obtained by dividing the total amount of heat actually entering through the shaded window by the total amount of heat calculated to enter through a bare window (solar radiation plus glass transmission, based on observed outside glass tem perature). For bare windows on which the sun shines, the transmission of heat from-outside air to glass may be small or negative as the glass temperature is raised by the solar radiation absorbed. In calculating the total heat gain through windows on the sunny side of buildings, it is sufficiently accurate to proceed as outlined herewith: Consider the total heat gain as that resulting from solar radfation and neglect the heat transmission through the glass caused by the difference between the temperatures of the inside and outside air. This method should be used except at times when the calculated heat gain per square foot due to normal transmission exceeds the solar intensity. At such times, solar radiation may be neglected and the total heat gain considered as resulting from normal transmission. The solar heat transmission through windows or skylights may be expressed by the formula: He = Ac]I (2) where Ha = solar radiation transmitted through a window, Btu per hour. Ac = net area of glass exposed to sun's rays, square feet. f = percentage of solar radiation (expressed as a decimal) transmitted to the inside (Table 7). For bare windows,/= 1. >. I = intensity of solar radiation striking surface, Btu per hour per square foot (Tables 2, 3, 4 and 5). In Equation 2, / = 1 for bare windows because the tests from which Table 7 was obtained showed that approximately all of the solar radiation impinging on a bare window became a part of the heat load in the room. This was because almost all of the heat absorbed by the glass flowed into the room by conduction. Other tests9 have indicated that in the case of a building having floors of high heat capacity such as concrete floors on which the solar radiation falls, some of the heat entering a bare window is absorbed by the floor and does not immediately become a part of the cooling load, but is delivered back to the air in the building at a slow rate. The maximum solar intensity on any surface is of limited duration as shown in Fig. 1. In the case of windows the total energy impinging on the glass before and after the time of maximum intensity is further reduced by increased shading of the glass from the frame, or wall. The cooling load due to solar radiation therefore does not have to be calculated as a steady load. Another point which should be noted is that the maximum solar radiation load on the east wall occurs early in the morning when the outside temperature is low. Tests have been made which indicate that solar radiation through window glass is the most important factor to contend with in the cooling of an office building. At times it was shown to account for as much as 75 per cent of the total internal sensible cooling necessary. Because of .A.S.H.V.E. Research Report No. 1002--Cooling Requirements of Single Rooms in a Modern Office Building, by F. C. Houghten, Carl Gutberlet, and Albert J. Wahl (A.S.H.V.E. Transactions, VoL 41, . 1935. p. 53). 155