Document V334OX89JDpJoG9px9YxoMkz4

124 Chapter 6 1945 Guide Table 3. --Approximate-Temperature_Differentials_Between_Breathing Level and Ceiling, Applicable to Certain Types of Heating Systems2------------- Ceiling Height (FT) 10 . 11 12 13 14 15 16 17 18 19 20 25 30 35 40 45' 50 60 3.0 3.6 4.2 4.8 5.4 6.0 6.1 6.2 6.3 6.4 6.5' 7.0 7.5 . 8.0 8.5 9.0 9.5 Breathing Level Temperature (5 ft Above Floor) 65 3.3 3.9 4.6 5.2 5.9 6.5 6.6 6.7 6.8 6.9 7.0 7.5 8.0 8.5 9.0 9.5 10.0 70 3.5 4.2 4.9 5.6 6.3 7.0 7.1 7.2 7.3 7.4 7.5 8.0 8.5 9.0 9.5 10.0 10.5 72 3.6 4.3 5.0 5.8 6.5 7.2 7.3 7.4 7.5 7.6 7.7 8.2 S.7 9.2 9.7 10.2 10.7 74 76 78 80 85 90 3.7 3.8 3.9 4.0 4.3 4.5 4.4 4.6 4.7 4.8' 5.1 5.4 5.2 5.3 5.5 5.6 6.0 6.3 5.9 6.1 6.2 6.4 6.8 7.2 6.7 6.8 7.0 7.2 7.7 8.1 7.4 7.6 7.8 8.0 8.5 9.0 7.5 7.7 7.9 8.1 8.6 9.1; 7.6 7.8 8.0 8.2 8.7 9.2 7.7 7.9 8.1 8.3 8.8 9.3. 7.8 8.0 8.2 8.4 8.9 9.4 7.9 84 8.3 8.5 9.0 9.5 8.4 8.9 9.4 9.9 10.4 10.9 8.6 9.1 9.6 10.1 10.6 11.1 8.8 9.3 9.8 10.3 10.8 11.3 9.0 9.5 10.0 10.5 11.0 11.5 .9.5 10.0 10.5 11.0 11.5 12.0 10.0 10.5 11.0 11.5 12.0 12.5 *The figures m this table are based-on an increase of 1 per cent per foot of height above the breathing level (5 ft) up to 15 ft and 1/10 of one degree for each foot above 15 ft. This table is generally applicable to forced air types of heating systems. For direct radiation or gravity warm air, increase values 50 per cent to 100 per cent. what smaller differential between the floor and breathing level tempera tures. As a general rule, if the breathing level to ceiling temperature differential is neglected (as with ceiling heights under 10 ft), the breathing level-floor "differential may also be neglected as the two are somewhat compensating, especially where both floor and ceiling heat losses are calculated for the same space. In other cases, the 10 ft temperature differentials in Table 3 may be used in arriving at the floor heat loss, these differentials to be subtracted from the breathing level temperature! ATTIC TEMPERATURES Frequently it is necessary to. estimate the attic temperature, and in such cases Equation 1 can be used tor this purpose. where 't = Ip (ArUT -{- AyrUyr ~f" AgUy) .' ArUr -b AVUW 4- AgUs + AcUc ' fa = attic temperature, degrees Fahrenheit. <1 = inside temperature near top floor ceiling, degrees Fahrenheit. to = outside temperature, degrees Fahrenheit. Ac -- area of ceiling, square feet. Ar = area of roof, square feet. Aw = area of net vertical wall surface, square feet.. Ag = area of glass, square fret. Uc = coefficient of transmission of ceiling, based on surface coefficient of 2.20 (upper surface, see Chapter 4). Ur = coefficient of transmission of roof, based on surface coefficient of 2.20 (lower surface, see. Chapter 4). Uy, = coefficient of transmission of vertical wall surface.' ; v Us = .coefficient:of transmission of glass. , Heating Load 125 Example 1. Calculate the temperature in an unheated attic, assuming the following -conditions:_/i_=i_70; <ojf 10, ^4c = 1000; A, = 1200; A= 100; Ag = 10. 1/, -- 0.50: Uc = 0.40; Vw = 6.30; Us = 143. ^----------------------------------- Solution: Substituting these values in Equation 1: (1000 X 6.40 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 /a --- = 33.1 F. 1041 Equation 1 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 tests4, 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 1, allowing the full value of the roof. 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 approximately the same, and if the coefficients of transmission are approximately equal, the temperature in the unheated space may be assumed to be the mean of the inside and outside design temperatures. If, however, the surface areas and coefficients are unequal, the tempera ture in the unheated space should be estimated by means of Equation 2. J t(AJJt 4- A,u, + A,u, + etc.) 4- to (AyUy + AbUb + ACUC +. etc.) u . A,U, 4- A,U, 4- A,U, 4- etc. 4- Ay.Ua + -4bf/b 4- AcUt 4- etc. 1 ' where fa = temperature in unheated space, degrees Fahrenheit, f = inside design temperature of heated room, degrees Fahrenheit. to = outside design temperature, degrees Fahrenheit. Ai, At, Ai, etc. = areas of surface of unheated space adjacent to heated space; square fret. Ay, 4b, Ac, etc. = areas of surface of unheated space exposed to outside, square feet. Ui, Ut, Ut, etc. = coefficients of transmission of surfaces of At, At, At, etc. ' Uy, Ub, Uc, etc. = coefficients of transmission of surfaces Ay, 4b, Ac, etc. Example 2. Calculate the temperature, in an unheated space adjacent to a heated room having surface areas (4i, 4j, and 4,) in contact therewith of 100, 120 and 140 sq ft and coefficients (Ui, Ut, and Ut) of 0.15, 0.20 and 0.25 respectively. The surface areas of the unheated space exposed to the outside (Ay and 4b) are respectively 100 and 140 sq ft and the corresponding coefficients are 0.10 and 0.30. The sixth surface is on the ground and is neglected in this example. Assume t = 70 and tQ = --10. A. Methods of Moisture'Control and Their Application to-Building Construction', by F. B. B. Algren and C. E. Lund. (University of Minnesota, Engineering Experiment Station Bulletin, Rowley. Noi 17). *