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HEATING VENTILATING AIR CONDITIONING GUIDE 1941 time lag4 in the transmission of heat through them as shown by the curves. For the types of construction covered in Figs. 2 and 3 and for the con ditions indicated, the heat flow through the inside surface at any given time can be read directly. For other types of construction, the curves may be used as a guide in estimating the heat flow. The time lag f0r other types of construction is included in Table 6 which was prepared by the A.S.H.V.E. Laboratory from data collected by it and by other authorities. Solar 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 ---------- 1 Design temperature Fig. 3. Relation Between Time and Heat Flow Through the Inside Surface of Walls of Different Construction and Orientation on a 93 F Design Day with 90 per cent of Design Solar Radiation Walls BE, BS, BW and BN--12 in, solid brick and plaster facing east, south, west and north respectively. Walls TE, TS, TW and TN--4 in. brick veneer, 8 in. tile and plaster facing east, south, west and north respectively. Walls FE, FS and FW--4 in. brick veneer, building paper, % in., matched sheathing, 2 x 4 in. studs, metal lath and plaster facing east, south and west respectively. 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 it and the sun's rays. The temperature of the glass is raised by the absorbed heat and this heat is then delivered to the air on each side in proportion to the difference between the glass and air temperatures6. The A.S.H.V.E. tests6 indicate that a single pane of double strength glass 0.127 in. thick absorbs approximately 11 per cent of the solar 4Loc. Cit. Note 2. Heat Absorbing Glass Windows, by W. W. Shaver (A.S.H.V.E. Transactions. Vol. 41, 1935, p. 287). A.S.H.V.E. Research Report No. 974--Radiation of Energy Through Glass, by J. L. Blackshaw 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 Gutberiet, and J. L. Blackshaw (A.S.H.V.E. Transactions, Vol. 40, 1934, p. 101). 132 CHAPTER 6. COOLINC LOAD 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........... in reinforced clay tile horizontal roof, water proofing, slag finish..... ......... 2-in gypsum horizontal roof, water proofing, slag finish.................................... Slate and slaters felt on 2K >n- 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, I'A-in. concrete, water proofing, smooth black Wood siding, 1-in. sheathing, 2x4 studs, lath and piaster............................... 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, 3%-in. tile, 5M_m. airspace, 3%-in. tile and 1 J-in. plaster.... 1 lM 2H 2H 2A 4H 5 8 2 5 7 10K 12 16 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 Laboratory7 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. 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: Table 7. Solar Radiation Transmitted through Shaded Windows Ttfb or Appurtenance Finish Facing Sun Canvas awning. .... Canvas awning. . Inside shade, fully drawn Inside shade, one-half drawn inside Venetian blind, fully covering window, slats at 45 deg _ Outside Venetian blind, fully covering window, slats at 45 deg.... Aluminum Buff Aluminum Aluminum Peb Cent Delivered to Room* 28 22 45 68 58 22 rLoc. Cit. Note 6. 133