Document ppbdq9pdnw3ED20JzbrkGRRL6

American Society of Heating and Ventilating Engineers Guide, 1931 mately 15 miles per hour. The conductance of air spaces Y2 in- or more in width was taken to be 1.10`B.t.u. per hour per square foot per degree fahrenheit difference between the two sidesenclosing the air space. (See Table 3.) Problems involving the determination of the value of U from the con ductivity constants can also be solved by what is sometimes known as the resistance method which is readily derived from the basic equation No. 5 as follows: l = T + x + ir"SI*, + *0 + *1 or (9) U = ------------1------------[i + Ro + Rr\ The internal resistance of a material is equal to the reciprocal of its so-called internal conductivity (k) multiplied by its thickness and is rep- Table 5. Conductivities (k) and Conductances (C) of Building Materials and Insulations Based on Tests Conducted at the University of Illinois, By A. C. Willard, L. C. Lichty and L. A. Harding p Material Description Density (Lb. per Cu. Ft.) Mean Temp. (Deg. Fahr.) CONDUC-* TIVITY (k) OR Conduc tance (O Asbestos Board..................... .. Corrugated ................................................ 48.3 20.4 132.0 2 in. hollow clay tile, ki in. plaster both sides________ 4 in. hollow clay tile, M in. 6 in. hollow day tile, M in. Roofings...... ..... ......................... Built-up bitumen and felt, gravel or slag surfaced............................................. slag surfaced... Wood (Fir, onesurface finished___________ 140.0 9.7 120.0 127.0 124.3 13.5 --.. 33.4 110 110 100 110 110 100 105 110 -- 0.29 0.48 4.00 5.00J 8.00f 8.30 0.32 1.00b } 0.60b 0;47b 0.51 8.00 1.325d 5.30<Lb 8.001 1.00 In addition to the conductivity values for the authorities listed, considerable work of importance per-' taining to the heat transmission of various types of construction and materials has been done by the late Prof. John R. Allen and Prof. A. J. Wood of the Engineering Experiment Station of Pennsylvania State College. bFor thickness stated or used in construction, not per 1 in. thickness. ^Calculated from 2 in. tile tests. ICement mortar and stucco assumed same as cement plaster. sRoofing. 0.15 in. thick (1.34 lb. per sq. ft.), covered with gravel (0.83 lb. per sq. ft.), combined thickness assumed 0.25. The conductivity of plaster varies with the composition. Note range of values from 2.32 to 8.0. The average value for plaster is probably about 5.0. On account of the comparatively high conductivity of plaster and the fact that it is seldom-applied more than % in. thick, this material does not appreciably effect the overall transmission of a construction, excepting in the case of thin uninsulated walls. JRecommended value. See Mechanical Equipment of Buildings, by Harding and Willard. Vol. I, second edition, 1929, p. 182. pSee Chapter LX, by Chas. H. Herter of the Report of the Insulation Committee, A. S. R. E., Annual Meeting, 1922, Revised to 1924, entitled. Heat Transmission of Insulating Materials for a more compre hensive collection of .heat-transmission data relating to building and insulating materials. 32 Chapter 3--Heat Losses by Transmission Outside Inside Outside Inside Tm Still air both sides 12 Outside Inside f,= L34 fi <1.54 Clapboard: k = LOO i Riqid insulation averaqe (Board form) thickness ' V. =0.53 assumed^ I'Sheathinq kl.00 actual thickniss = || Lath i lime plaster. C- 2.00 Gvpsum plaster le =2.52. f0 . 4.02 . \ lb Airspace a=U0 \f, = I.M =o.no ` t ,_!_ + LS + kS Us , 0.262. 1.10^4.02 1.00 LOO Outside fo = 4.02 IZBncktUT- k<=5.00 V tr 3ESc Inside f, = l.-S4 w Hollow tile C*M8 J,^Gvpsum plaster, f k = 2.32. m. ^Cement mortar L = 8-0 2L fc.4.02, Tar (qnavel roofmq k a 1.525 --y averaqe thickness assumed-gy 1 "*. S" Stone concrete It 8.50 =a2ii 1.34 4.02 SOO 8.00 118 4 52. -0:610 I . I , 0-315 3.0 r54 4.02l.3I5 830 Fig. 2. Examples Showing Method of Computing Heat Transmission Coefficients of Various Types of Construction 33