Document RLLxDkpaaRG8NanezZOkxXZv

234 CHAPTER 11 1950 Guide ticularly important, as the temperature gradient from floor to breathinglevel to ceiling may depend to a large extent on whether direct radiation, unit heaters or warm air is used, and in the latter case, whether the air is moved mechanically or by gravity. It is impracticable to establish rigid rules for determining the temperature difference to use in all cases. However, for residences and structures hav ing ceiling heights under 10 ft, the comparatively small temperature differential between the breathing level and ceiling generally may be neg lected without serious error. For higher ceilings, an allowance of approxi mately 1 per cent per foot of height above the breathing level may be made for ceiling heights up to 15 ft and approximately A of 1 deg per foot of height above this level. The values in Table 3 are calculated on this Table 3. Approximate Temperature Differentials Between Breathing Level and Ceiling, Applicable to Certain Types of Heating Systems* Height (Ft) 10 11 12 13 14 15 16 17 18 19 20 25 30 35 40 45 50 Breathing Level Temperature (5 ft Above Floor) 60 65 70 72 74 76 78 80 85 .90 . 3.0 3.6 3.3 3.9 3.5 4.2 3.6 '3.7 3.8 3.9 4.0 4.3 4.5 4.3 4.4 4.6 4.7 4.8 5.1 5.4 4.2 4.6 4.9 5.0 5.2 5.3 5.5 5.6 6.0 6.3 4:8 5.2 5.6 5.8 5.9 6.1 6.2 6.4 6.8 7.2 5.4 5.9 6.3 6.5 6.7 6.8 7.0 7.2 7.7 8.1 6.0 6.5 7.0 7.2 7.4 7.6 7.8 8.0 8.5 9.0 6.1 6.2 6.6 6.7 7.1 7.2 7.3 7.5 7.7 7.9 8.1 8.6 9.1 7.4 7.6 7.8 8.0 8.2 8.7 9.2 6.3 6.4 6.8 6.9 7.3 7.4 7.5 7.7 7.9 8.1 8.3 8.8 9.3 7.6 7.8 8.0 8.2 8.4 8.9 9.4 6.5 7.0 7.6 7.7 7.9 8.1 8.3 8.5 9.0 9.5 7.0 7.5 8.0 8.2 8.4 8.6 8.8 9.0 9.5 10.0 7.5 8.0 8.0 8.5 8.5 9.0 8.7 8.9 9.1 9.3 9.5 10.0 10.5 9.2 9.4 9.6 9.8 10.0 10.5 11.0 8.5 9.0 9.0 9.5 9.7 9.9 10.1 10.3. 10.5 11.0 11.5 9.5 100 10.2 10.4 10.6 10.8 11.0 11 5 12.0 9.5 10.0 10.5 10.7 10.9 11.1 11.3 11.5 12.0 12.5 * The figures in this table are based on an increase of 1 per cent per foot of height above the breathing level (6 ft) up to 15 ft and fa of one degree for each foot above 16 ft. This table is generally applicable to forced air types of heating systems. For direct radiation or gravity warm air, increase values 60 per cent to 100 per cent. basis. For direct radiation and gravity warm air-systems, the allowance should be increased from 50 per cent to 100 per cent over those given in Table 3. These rules should, however, be used with considerable discretion. Temperature at Floor Level. According to the University of Illinois Research Residence tests,* the temperature at the floor level ranged from about 21 to 6 deg' below .that at the breathing level, or somewhat greater than the difference between the breathing level and ceiling temperatures. Tests at the University of Wisconsin4 indicated a some 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. Heating Load 235 ATTIC TEMPERATURES Frequently, it is necessary to estimate the attic temperature, and in such cases Equation 1 can be used for this purpose: AMJi, + to(ArV, + AM, + AM ** AJJ. + AtU, + AM, + AM. () K' where <, = attio temperature, Fahrenheit degrees. (i = inside temperature near top floor ceiling, Fahrenheit degrees. to -- outside temperature, Fahrenheit degrees. A. = area of ceiling, square feet. A, = area of roof, square feet. Aw = area of net vertical attic wall surface, square feet. A. = area of attic glass, square feet. U. = coefficient of transmission of ceiling, based on surface conductance of 2.20 (upper surface, see Chapter 9). 2.20 = reciprocal of one-half the air space resistance. U, ~ coefficient of. transmission of roof, based on surface conductance of 2.20 (lower surface, see Chapter 9). U, -- coefficient of transmission of vertical wall surface. V. = coefficient of transmission of glass. Example 1. Calculate the temperature in an unheated attic, assuming the follow ing conditions: ti = 70; (<> = 10; A. -- 1000; A, = 1200; A, ~ 100; A. = 10; U, -- 0.50; U. = 0.40; U. = 0.30; V. = 1.13. Solution: Substituting these values in Equation 1: (1000 X 0-40 X 70) + 101(1200 X 0.50) + (100 X 0-30) + (10 X 1-13)1 " (1000 X 0-40) + (1200 X 0.50) + (100 X 0 30) + (10 X 113) 34,413 to = = 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 teste,5 such venting of attics by means of small 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 Equation 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. When relatively large louvers are installed as is customary in the southern states, the. attic temperature is often assumed as the average between inside and outside. For a shorter, approximate method of calculating heat losses through attics, the combined ceiling and roof coefficient may be used as described in Chapter 9. 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