Document 2qa4Oo1XoKQdKdy2Dm8nLqpRp

198 CHAPTER 9 1951 Guide Table 14. (U)Coefficients of Transmission of Concrete Basement Floors on Ground with .Various Types of Finish Flooring U = 0.10" Btu per (hr) (sq ft) (Fahrenheit degree temperature difference between the ground and the air over the floor). " Since few data are available, a coefficient of 0.10 is frequently used for all types of basement concrete floors on the ground, with or without insulation. For basement wall below grade, use the same average coefficient (0.10). A lower ground temperature should, however, be used for walls than floors as explained in Chapter 11. For further data see A.S.H.VJ2. Research Report No. 1213--Heat Loss Through Base ment Walls and Floors, by F. C. Houghten, S.-I. Taimuty, Carl Gutberlet and C. J. Brown (A.S.H.VJ3. Transactions, Vol. 48, 1942, p. 369). will vary with local conditions, and is usually unknown. - Tests15 at the A.S.H.V.E. Research Laboratory indicate a heat flow of approximately 2.0 Btu per (hr) (sq ft) through an uninsulated concrete basement floor, with a temperature difference of 20 F between ground temperature and the air temperature 6 in. above the floor. Based on this result a coeffi cient of 0.10 Btu per (hr) (sq ft) (Fahrenheit degree difference) is recom mended for calculation where it is desirable to allow for the small base ment floor heat loss, e.g., for heated basements. For basement walls the same coefficient may be used, but due to closer proximity to the surface of the ground, the temperature difference for win ter design conditions will be greater than for the floor. The test results indicate a unit area heat loss, at mid-height of the basement wall, approxi mately twice that of the same floor area. For concrete'slab floors laid in contact with the ground at grade level, recent tests13 indicate that for small floor areas (equal to that of a house 25 feet square) the heat loss may be calculated as proportional to the length of exposed edge rather than total area. This amounts to 0.81 Btu per (hr) (lineal foot of exposed edge) (Fahrenheit degree difference between the inside air temperature and the average outside air temperature). It should be noted that this may be appreciably reduced by insulating under the ground slab, and also along the edges between the floor and the abut ting walls. See also sections on Basement Temperatures and Heat Loss, and on Floor Heat Loss in Basementless Houses, in Chapter 11. Glass-Coefficients The U values for glass sheets and hollow glass block, given in Sections A, B and C of Table 20, have been computed by methods and data given in an A.S.H.V.E. Research Paper.14 It is assumed that the surface conduct ance for convection loss to the air is 4.0 Btu per (hr) (sq ft) (F deg). It is also assumed that the glass loses heat by radiation to the ground and to the clear sky, which together have an effective radiating temperature below the air temperature. It is therefore necessary to determine, by trial and error, the temperature of the outdoor glass surface such that the sum of the radiation and convection losses equals the heat conducted through the glass section, and equals the heat delivered to the glass from the heated space. This heat flow, divided by the air-to-air temperature difference, results in a TJ value which is used in the usual manner. The equivalent surface conductance for radiation and convection combined, based on airlo-surface temperature difference, therefore varies from about 5.5 for sin gle glass to about 6.6 for double glass for exactly the same environmental design conditions. It is assumed that the room air temperature equals the average tem perature of the room surfaces seen by the glass. Special consideration should be given to those cases where the glass sees interior surfaces at temperatures differing greatly from the room air temperature, t.e., such Heat Transmission Coeflicients of Building Materials 199 - ,, Coefficients of Transmission (U) of Flat Roofs Covered with Table g^lLT up r00fing. No Ceiling--Under Side of Roof Exposed