Document JJEYnQrvky4k0pnQE4j628pYO

HEATING VENTILATING AIR*CONDITIONING GUIDE 1943 134 F ig . 1. D esig n T e m p e r a tu r e Z o ne M ap CHAPTER 6. HEATING LOAD ATTIC TEMPERATURES Frequently it is necessary to estimate the attic temperature, and in such cases Equation 4 can be used for this purpose.. __ AcUch 4~ to (ArUt 4~ AvUw 4~ AgUgl , AtUt 4" -4wt^w 4" 4~ AqUc where la -- attic temperature, degrees Fahrenheit. <i = inside temperature near top floor ceiling, degrees Fahrenheit. to -- outside temperature, degrees Fahrenheit. Ac-= area of ceiling, square feet. A r ** area of roof, square feet. Avr = area of net vertical wall surface, square feet. Ag = area of glass, square feet. Vc -- coefficient of transmission of ceiling, based on surface coefficient of 2.20 (upper surface, see Chapter 4)'. Ui = coefficient of transmission of roof, based on surface coefficient of 2.20 (lower surface, see Chapter 4). Uvt -- coefficient of transmission of vertical wall surface. . Vg =' coefficient of transmission of glass. Example 3. Calculate the temperature in an uiiheated attic, assuming the following conditions: t. = 70; to = 10; Ac =1000; Ar = 1200; Aw = 100; 4g = 10; UT = 0.50; Uc = 0.40; /w = 0.30; V% = 1.13. Solution: Substituting these values, in Equation 4: (1000 X 0.40 X 70) 4- 10 [(1200 X 0.50) 4- (100 X 0.30) 4- (10 X 1.13)] ** (1200 X 0.50) 4- (100 X 0.30) 4- (10 X 1.13) 4- (1000 X 0.40) ... 34,413 F " loir -331F- Equation 4 neglects the effect of any interchange of air such as would take place through attic vents or louvers intended to preclude, attic con densation. However, according to tests2, such venting of attics by means of louvers or other small openings does not appreciably reduce the attic temperature and may be neglected without serious error. The attic temperature may be calculated in the usual manner by means of Equa tion 4, allowing the full value, of the rpof. The error resulting from this assumption will generally be considerably less than if the roof were neglected (as is sometimes the practice) and the attic'temperature as sumed to be the same as the outside temperature. TEMPERATURES IN UNHEATED SPACES The heat loss from heated rooms into unheated rooms or spaces must be based on the estimated or assumed temperature in such unheated spaces. This temperature will'generally range between the inside and outside temperatures, depending on the `relative areas of the surfaces adjacent to the heated room and exposed to the outside. If. the respective surface areas adjacent to the heated room and exposed to the outside are ^Methods of Moisture Control and Their Application to Building Construction, by F. B. Rowley, A. B. Algren and C. E. Lund. (University of Minnesota, Engineering Experiment Station Bulletin, No. 17). 135