Document qdzbGL7j6Dk84gedpVzenbYmq

American Society of Heating and Ventilating Engineers Guide, 1929 Material Thickness Inches Brickwork. ...................... Cement Mortar..................... Plaster (gypsum)._............... 13 2 Yi Internal Conductottt (C or Cui Surface CoErncENts (K\ or it*) 5.0 (C) 8.0 (C) 1.14 fCu) 2.32 (C) 4.02 (K2) 1.34 (K,) Internal Resistance 2.600 0.063 0.877 0.215 3.755 Total resistance (R)...... Surface Resistance 0_._24_9 0.746 0.995 3:755 4.750 U=^ =0.210 B.t.u. per hour per square foot per 1 deg. fahr. difference in temperature between the air on the two sides of the wall. Table 6. Factors to be Used in Determining Values of Outside Surface Coefficients (K,) under Moving Air Conditions In bach case, the moving air factor is based on still air coefficient (iCi) for same material. For conditions where wind velocity is not known use the factor (3) or TAKE Ki AS 3Kl FOR SAME MATERIAL. Wind Velocity in Miles per Hour 5 10 15 20 Brickwork 2.38 .< 3.20 3.76 4.22 Multipliers of Ki* Wood 2.19 2.71. r- 2.95 3.02 Average 2.28. 2.96: 3.36** 3.62 10 20 Above 20 Additional Values--Smooth Surface ........ 2.20 2,60 3.00 ___^ . Taken from Engineering Experiment Station Bulletin No. 102. of the University of Illinois. Addi tional values from Engineering Experiment Station. Pennsylvania State College, reported by Professor Wood. Tests at Pennsylvania State College indicate character of surface, rough or smooth, more important than material of surface. This is usually taken as 3 even. The thicknesses upon which the coefficients in Tables 7 to 13, inclusive, are based, are as follows: Brick veneer.................................................................................. 4 in. Plaster and metal !ath._...................................... ...................... % in. Plaster [on wood lath, plasterboard, fiber insulation (board form), or corkboard]__I.............. .................... ..... . in. Slate (Roofing)......... :.......................... ........ ,......... .................... Yl in. Stucco on wire mesh reinforcing......................................... . 1 in. Tar and gravel or slag surfaced built-up roofing.... ......... . % in. Wood shingles (average thickness)................ ........................ % in. Wood siding or clapboard (average thickness).................... Yu in. 1-in. Lumber (S-2-S)...... .......... ......................... , ;...............f| in. l>6-in. Lumber (S-2-S)...................................... ! ................ 1& in. 2-in. Lumber (S-2-S)................................................... ............... 1% in. 23'6-in. Lumber (S-2-S)........................... ......... ..................... '2}/g in. ,. 3-in. Lumber (S-2-S)............................... ........... ....................... 2Ys in. 4-in. Lumber (S-2-S)........................................................... ____ 0% in. Finish flooring (Maple or Oak):.._________________________ in. ; Note that actual thicknesses of lumber are used in the computations rather than nominal thicknesses. On account of the fact that the internal resistances of metal and single 20 Chapter I--Heat Losses from Buildings thicknesses of building paper4 and roofing felt are very small, these resistances were neglected in the calculations, in accordance with standard practice. The computations for wood shingle roofs applied over wood stripping are based on 1 by 4 in. wood strips, spaced 2 in. apart. Since no reliable figures are available concerning the conductivity of Spanish and French clay roofing tile, of which there are many varieties, the figures for such types of roofs were taken the same as for slate roofs, as it is probable that the values of U for these two types of roofs will compare favorably. The coefficients of transmission of the pitched roofs in Table 12-A apply where the roof is over a heated'attic or top floor, such that the heat passes directly through the roof structure including whatever finish, if any, is applied to the underside of the roof rafters. By a heated attic is meant an attic to which heat is supplied directly from the furnace or boiler by means of radiators, hot-air registers, or other means. If the attic is unheated, the roof structure and ceiling of the top floor must both be taken into consideration and the combined coefficient of transmission determined. The formula for calculating the combined coefficient of transmission of a top-floor ceiling, unheated attic space and pitched roof, per square foot of roof area, is as follows: where XJ -- E^r.X Uce n X Ur -|- Uce UT = coefficient of transmission of the roof. (From Table 12-A, Pitched Roofs), Uce = coefficient of transmission of the ceiling. (From Table 10). n -- the ratio of the area of the roof to the area of the ceiling. The following example will illustrate the use of this formula: Determine the combined coefficient of transmission of a roof constructed of wood shingles applied over wood strips on rafters, an unheated attic, and a wood lath and plaster ceiling, based on a roof having a Vi pitch, for which the value of n is 1.2 (Roof No. 251a). Ur = 0.483 (Roof No. 238-a, Table 12-A) Uce = 0.502 (Ceiling.No. 167-a, Table 10-A) Substituting these values in the preceding formula: r 0.483 X 0.502 U 1.2 X 0.483 + 0.502 = 0.224 B.t.u. per hour, per square foot of roof area per 1 deg. fahr. difference in temperature between the air near the underside of the ceiling and the outside air. Combined coefficients for many common types of pitched roofs and top-floor ceilings for unheated attics are given in Table 12-B. 4 Building paper is used because of its value as a wind stop only. 21