Document pmwr9rZ10JMxvzg6zkXzrzqVd

100 Chapter 4 1945 Guide determining-the heat-loss through, the roof cqnstruction, attic and top floor ceiling. If the unheated attic contains windows ancTverticalwall spaces these must be taken into consideration in calculating the roof area and also its coefficient Uz. In this case an approximate value of UT may be obtained as the summation of the coefficient of each individual section such as the roof, vertical walls or windows times its percentage of total area. This coefficient may then be used with reasonable accuracy in Equation 4. If there are large vertical wall areas, the most accurate procedure is to estimate the attic temperature by means of Equation 1, Chapter 6 and to calculate the heat loss by using the ceiling coefficient only, and the attic temperature instead of the outside temperature. Information concerning basement floor and wall coefficients will be found, on Page 100. The values in Table 16 apply principally to hip and double hip roofs with unheated attics. In the case of gable and gambrel (Dutch Colonial) roofs having end wall surfaces, the values in Table 16 can be used with reasonable accuracy if the end wall area is considered as part of the roof area. Thus in arriving at the combined roof and ceiling coefficient for a pitched roof with insulating board applied to the under side of the rafters, the board must also be applied to the end wall surfaces in order for the values in Table 16 to be approximately applicable. The coefficients in Table 16 are based on % pitch roofs for which the value of n, or the ratio of the roof area to the ceiling area, is 1.2. Since these combined roof and ceiling coefficients are based on the ceiling area, small variations in the pitch do not greatly alter the coefficient. An increase in pitch above the used for calculating the values would increase the combined coefficient, and vice versa. Basement Floor and Wall Coefficients The dirt in contact with basement floors and walls below grade has an appreciable insulating value. The exact thickness or depth of the dirt which may contribute to the heat resistance of floors and vralls in contact therewith is a variable and indeterminate quantity. Tests at the A.S.H.V.E. Research Laboratory9 indicate that the rate of heat flow through basement floors, even without insulation, does not exceed 0.10 Btu per square foot per degree Fahrenheit temperature difference between the air above the floor and the soil under the floor at the point of maximum diffusion of the heat from the basement. As indicated in the footnote of Table 12, this coefficient is recommended for use whenever it is desirable to make allowance for the small basement floor heat loss, as may be the case with heated basements. Using this coefficient (0.10) the total heat loss per square foot of floor area will amount to only 2.0 Btu per square foot per hour, based on a temperature difference of 20 F between the air in the basement above the floor and the mininlum soil temperature below the basement. The same coefficient (0.10) may be used for calculating the heat loss through basement walls below grade but a somewhat higher temperature difference should be used for reasons explained in Chapter 6. Thus the total heat loss through basement walls will be greater than that through floors. According to present available data the unit wall heat loss will be V V, -V. A.S.H.V.E. Research Report No. 1213--Heat Loss Through Basement Walls and Floors, by F. C. Houghten, S. I. Taimuty, Carl Gutberlet and C. J. Brown (A.S.H.V.E. Transactions, Vol. 48, 1942, p. 369). <uSl 0.092, 0.092 1 0.12 S 0.21 0.16 y A n i.ii 10. Co e ffic ie n ts of ransm issionT U) of F rame C onstruction C e il in g s a n d F( Heat Transmission Coefficients . B,,mnN I in ii *- < cn y to wr-eo Z 1 2222' -2222 S s 1122 INSULATION BETWEEN. OR ON TOP OF. JOISTS (No Flooring Above) s Mineral Wool Insula- 5 -i III! ' fill S fill 3 "t i| 3 -- CO z 3 C 0 b. 3 Ul C4 30 1 2222 1222 llll 3222 222! 3222 III ( 3222 S3222 2222 222! 2222 s 0.072 ill 3 O 2 ;3222 ' 2222 3 X - 2 '3222 . 1222 1 < ills Isis TYPE OF CEILING nil 11 i1! isii 1. 101