Document G52RYvXk3OE2gdNzXVoJjMkkY

HEATING' VENTILATING AIR CONDITIONING-GUIDE 1943 110 l CHAPTER 4. HEAT TRANSMISSION COEFFICIENTS. that the under surface of the roof and the upper surface of the ceiling are more nearly equivalent to the boundary surfaces of an internal air space than they are to the external surfaces of a wall. It would be more nearly correct to use a value of 2.2 rather than the usual value of 1.65 as coef ficients for these surfaces. In most cases this would make only a minor change in U. It should be noted that the over-all coefficient should be multiplied by the ceiling and not the roof area. If the unheated attic space between the roof and ceiling has no dormers, windows or vertical wall spaces the combined coefficient may be used for Table 10. Coefficients of Transmission-(Z7) of Concrete Floors on Ground with Various Types of Finish Flooring3 Coefficients are expressed in Blu per hour per square foot per degree Fahrenheit difference in temperature between the ground and the air over the floor, and are based on stUl air (no wind) conditions. TYPICAL CONSTRUCTION . TYPE OF.FINISH FLOORING IlN/ULATlOW &TWtE.N TWO ne.tt&g.AUE. UTEF.?A0PtNG Thickness of Concrete (Inches) 2 4 6 5 10 No Flooring (Concrete , Bare) A 0.10 0.10 0.10 0.10 0.10 Wood Flooring on Sleepers on Concrete Tile or Terrazzo on Concrete K in* Battleship Liuoleunr.on' Concrete B 0.10 0.10 0.10 0.10 0.10 c 0.10 0.10 0.10 0.10 0.10 >D , 0.10 Q.10 0.10 0.10 oaa . aUntil.more complete data are available, based on tests now in progress, it is recommended that a corf-.. ficient of 0.10 be used for all types of concrete floors on the ground, with or without insulation. For base ment walls below-grade, use the same average coefficient (0.10). A lower ground temperature should^.however, be used for walls than doors as explained in Chapter 6. For further data see A.S.H.V.E. Research Paper--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. Journal Section, Heating, Piping and Air Conditioning, January 1942, p. 69). determining the heat, loss through the roof construction, attic and top floor ceiling,, If the unheated attic contains windows and vertical wall spaces these must be taken into consideration in calculating the roof area and also its coefficient- Ur. 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 4. 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 115. Ill X