Document yrm9a3XZ9w1rqERq7N6Lxne06

American Society of Heating and Ventilating Engineers Guide, 1925-26; and since H = H, = H, = Hc, the right hand members of equations (1), (2), (3) and (4) are all equal. The coefficient U may be determined by test, or it may be'computed for any wall provided values for Kt, K, and C are known. By proper substitution in the four equations, the unknown temperatures t, and h can be eliminated and the value of the transmission coefficient for a simple wall x inches thick is V= -L X, + .L X, + JcE. (5) and for a compound wall of several materials having thickness in inches of x,, x2, x3l etc., the coefficient is U= r + r + r + r + r+etc- (6) As in the case of the simple wall, K, and Ki are always the inside and outside surface coefficients for the two materials in contact with air. If the air is still (no wind), then for the same material Ki and K2 are the same, and X, = K2; but if the outside air is in motion then K, is always greater than K2 and will increase as the wind velocity increases. Values for Ki in still air as determined by various investigators are given in Table 3. Values for C, the conductivity of building materials, are given in Table 4, and are taken from the published values of various investiga tors. It should be noted that values of C as well as V are dependent on the temperature range, and it is therefore desirable that the investigator determine conductivity values when the wall is subjected to' an air temperature of about 70 deg. fahr. on the inside and about zero on the outside. Table 3. Surface Coefficients (X,) for Various Building Materials under Still Air (No Wind) Conditions The values in the table are in B.t.u. per sq. ft. of wall surface per hour per 1 deg. fahr. difference between the mean air temperature in the room and the inside surface tempera ture of the wall. Building Material Asbestos (sheet)....................... Brickwork (ordinary).--........ Cement Plaster (finished).... Concrete.... ................ ................ Corkboard....... .......................... Glass (window)........................ Magnesia. (blocks)................... Wood (finished surface)____ Building paper........................ Average of all values. Surface Coefficient Ki (Still Air) Harding and Willard Wood 1.40 1.40 0.93 1.30 1.25 1.50 1.45 1.40 . 1.34 1.20 1.90' 1.40 Average of both sides of glass 0.12 in. thick and for 70 deg. fahr. total temperature difference from air to air with moving air on one side. Probable value, for still air on both sides 1.60. 10 American Society of Heating and. Ventilating Engineers Guide; 192&26 Table 4. Conductivity Coefficients for Various Building Materials* Building Material Coefficient of Conductivity C IND Weight per Cu. Ft. Authority 'Harding and Willard Lb. per Cu. Ft. C Peebles** Norton U. S. Bur; Standards C CC 48.3 0.29 20.4 0.48 132.0 4.00* 140.0 8.30 6.30 6.30 9.7 0.32 13.5 0.51 5.20 0.30 33.4 1.00 1.00 1.10 1.20 1.25 8.00 1.30 1.10 1.25 1.00 0.83 1.20 0.50 0.40 0.33 0.33 0.329 0 300 0 379 0.275 3 040 0 941 Shavings (ordinary).... -................ ................. . 1 040 0.707 0 667 0.29 0.25 One course No. 2 tar felt................................. Glass (act. glass 91.4% total area)__ _____ Double Glass % in. air space (glass 69.3% total area).............................................. 2.06 4.20*** 3.00*** 2.50*** 1.382 1.50*** 6 in. Tile, ^ in. plast. both surf. ................ 2 in. Tile, plastered as above and roofing covered........................................... 1.00*** 0.60*** 0.47*** 0.84 - *For damp or wet brickwork take C = 6. . **Flat plate method using a test sample 18 in. square and up to 4 in. in thickness.***For thickness and construction stated, not per l in. of thickness. The values in the tables are in B.t.u. per square foot of wall surface per hour per inch thickness per 1 deg. fahr. difference between the two surfaces, for thoroughly dry materials. For use where air temperature difference on two sides of wall is about 70 deg. and outside air is near zero. 2See Chapter IX by Charles 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 the comprehensive collection of heat transmission data relating to building and insulating materia! wiuch is now in print. 11