Document jBeqa78NRGj4w1jDYeOLYd0kQ

262 CHARTER 14 _____________ 1946 CUide to modify the temperatures given in Table 2 so that the air temperature at the proper level will be used. By air temperature at the proper level is meant, in the case of walls, the air temperature at the mean height be tween floor and ceiling; in the case of glass, the air temperature at the mean height of the glass; in the case of roof or ceiling, the air temperature at the mean height of the roof or ceiling above the floor of the heated room; and in the case of floors, the air temperature at the floor level. _ Temperature at Ceiling: The air temperature at the ceiling is generally higher than at the breathing level due to stratification of air resulting from the tendency of the warmer or less dense air to rise. An allowance for this fact should be .made in calculating ceiling heat losses, particularly in the case of high ceilings. However, the exact allowance to be,made may be Table 3. Approximate Temperature Differentials Between Breathing Level and Ceiling, Applicable to Certain Types of Heating Systems Ceiling Height (Ft) 60 Breathing Level Temperature .(5 ft Above Floor) 65 70 72 74 76 78 80 85 90 10 3.0 3.3 3.5 3.6 3.7 3.8 3.9 4:0 4.3 4.5 11 3.6 3.9 4.2 4.3 4.4 4.6 '4.7 4.8 5.1 5:4 12 4.2 4.6 4.9 5.0 5.2 5.3 5.5 5.6 6.0 6:3 13 4.8 5.2 5.6 5.8 5.9 6.1 6.2 6.4 6.8 7:2 14 5.4- 5.9 6.3 6.5 6.7 6.8 7.0 7.2 7.7 8.1 15 6.0 6.5 7.0 7.2 .7.4 7.6 7.8 8.0 8.5 910 16 6.1 6.6 7.1 7.3 7.5 7.7 7.9 8.1 8:6 9.1 17 6.2 6.7 7.2 7.4 . 7.6 7.8 8.0 8.2 8.7 9.2 18 6.3 6.8 7.3 7.5 7.7 7.9 8:1 8.3 8.8 93 19 6.4 6.9 7.4 7.6 7.8 8.0 8.2 8.4 8.9 9.4 20 6.5 7.0 7.5 7.7 7.9 8.1 8.3 8.5 9.0 9.5 25 30 35 40 . 45 . 50 , 7.0 7.5 8.0 8.2 8.4 8.6 8.8 9.0 9.5 10.0 7.5 8.0 8.5- 8.7 8.9 9.1 9.3 9.5 10.0 10:5 8.0 8.5 9.0 9.2 9.4 9.6 9.8 10.0 10.5 1110 8.5 9.0 9.5 .9.7 9.9 10.1 10.3 10.5 11.0 11.5 9.0 9.5 10.0 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 wd (5.ft) up to 15ft 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 SO per cent to 100 per cent. ' . ., t somewhat difficult to determine as it depends,on many factors, including (1-) the. type of heating system, (2) ceiling height, and (3) . the insideoutside temperature differential. The type of heating system is par ticularly important as the temperature gradient from floor to breathinglevel to-ceding,may depend to a large extent on'whether direct radiation; unit heaters or warm air is used, and in the latter case, whether the circu lation is by gravity, auxiliary fan or forced air. Although with properly, adjusted air flow, the temperature differential with unit heaters can be reduced to a minimum, it is possible with improper adjustment that it ' may - be increased over that which, would- normally result without me: chanical circulation of the-air if the air flow is not properly, adjusted. . It would `be difficult from- present available information' to establish rules for determining the temperature difference-'to-use in all cases; However,-.f6r residences and other structures having ceiling.heights under 10 ft, the i comparatively small temperature - differential between . the j HRatine-Load 263 breathing level and ceiling, may generally be neglected without serious error.: For higher ceilings.where spedfic:test data are not-available; an allowance of approximately 1 per cent per foot of height above the breathing level may be made for ceiling heights up to 15 ft and approxi mately 1/10 of 1 deg per foot of height above this level. The values in Table 3 are calculated on this 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 2J4 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 Wisconsin* 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. . ATTIC TEMPERATURES Frequently it is necessary to estimate the: attic, temperature, and in such cases Equation 1 can be used for'this purpose. (a " AcTJf\ 4* to (A4* AwUyr 4* AfUr + AnUw + AgU% 4* AcUc' (1) where /a = attic temperature, Fahrenheit degrees:ti = inside temperature near top, floor ceiling, Fahrenheit .degrees. a. i0 : outside temperature, Fahrenheit degrees. Ac, area of .ceiling,.square feet. ` At . area.of roof, square feet. Aw 1 area of net vertical attic wali surface, square feet. , As = area of attic glass, square feet. *' * . ' ...Uc- coefficient of transmission of ceiling, based, on. surface conductance of. 2.20 (upper surface, see Chapter.6). 2.20 = reciprocal of oneVhalf the.air sp^ce resistance... V.-VV. *. 'tv = coefficient of - transmission of roof, based on- surface, conductance of;-2.20- . (lower surface, see Chapter 6). Uw coefficient ,of transmission of vertical wall surface, U* coefficient of transmission of glass. ............. Example 1. Calculate the temperature in.an unheated .attic, assuming the following conditions: t\ = 70; to -- 10;Ac * 1000; Uc * 0.40; iV*= n0:a3n0?; ttfig~ *1.i1i3a. ' a12d0; .. . 100; Aj 10; l/r s 0.50; ` 1 ' Solution: Substituting these values in Equation 1: . . (1000 X 0.40 X 70) + IQ [(1200 X 0.50) + (100 X 0.30) + (10 1.13)1 Jm; h (1200 X 0.50) + .(100 X 0.30) + (10. X 1.13) +. (1000 X 0.40) " 34,413 ' 33.i F. 1041 .S