Document Dj3m8kpJmNXxOo4XxvMywVbO

272 CHAPTER 12 1958 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. The temperature of the heating medium is also a faetor. 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 ceding generally may be - Table 3. Approximate Temperature Differentials Between Breathing Level .. and Ceiling, Applicable to Certain Types of Heating Systems* Breathing Level Temperature (5 ft Above Floor) (Ft) 60 65 70 72 74 76 78 80 85 90 10 11 12 13 * 14 15 16 17 18 . 19 20 25 30 35 40 45 50 3.0 3.3 3.5 3.6 3.7 3.8 3.6 3.9 4.2 4.3 4.4 4.6 4.2 4.6 4.9 5.0 5.2 5.3 4.8 5.2 5.6 5.8 5.9 6.1 5.4 5.9 6.3 6.5 6.7 6.8 6.0 6.5 7.0 7.2 7.4 7.6 6.1 6.6 7.1 7.3 7.5 7.7 6.2 6.7 7.2 7.4 7.6 7.8 6.3 6.8 7.3 7.5 7.7 7.9 6.4 6.9 7.4 7.6 7.8 8.0 6.5 7.0 7.5 7.7 7.9 8.1 7.0 7.5 8.0 8.2 8.4 8.6 7.5 8.0 8.5 8.7 8.9 9.1 8.0 8.5 9.0 9.2 9.4 9.6 8.5 9.0 9.5 9.7 9.9 10.1 9.0 9.5 10.0 10.2 10.4 10.6 9.5 10.0 10.5 10.7 10.9 11.1 3.9 3.7 5.5 6.2 7.0 7.8 7.9 8.0 8.1 8.2 8.3 8.8 9.3 9.8 10.3 10.8 11.3 4.0 4.8 5.6`6.4 7.2 8.0 8.1 8.2 8.3 8.4 8.5 9.0 9.5 10.0 10.5 11.0 11.5 4.3 5.1 6.0 6.8 7.7 8.5 8.6 8.7 8.8 8.9 9.0 9.5 10.0 10.5 11.0 11.5 12.0 4.5 5.4 6.3 7.2 8.1 9.0 9.1 9.2 9.3 .9.4 9.5 10.0 10.5 11.0 11.5 12.0 12.5 * The figures in this table are based on an increase of 1 percent per foot of height above the breathing level (5 ft) up to 15 ft and Ho of one degree for each foot above 15 ft. Tnis table is generally applicable to forced air types of hating systems. For direct radiation or gravity warm air, increase values 50 percent to 100 percent. neglected without serious error. For higher ceilings, an allowance of approximately 1 percent per foot of height above the breathing level may be made for ceiling heights up to 15 ft and approximately ^ of 1 deg per1 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 allow ance should be increased from 50 percent to 100 percent over those given in Table 3. These rules should, however, be used with considerable dis; cretion, and they do not apply to some types of heating systems such as - those using panel and baseboard radiation, where very low temperature differences between the floor and the ceding may exist. !,,1;; Temperature at Floor Level. According to tests at the University o}~. Illinois,3' 6' 6 the temperature at the floor level ranged from about 2 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 Wisconsin7 indicated a somewhat smaller differential. between the floor and breathing level temperatures. As a general rule, h;- . the breathing level to ceiling temperature differential is neglected (as with ceiling heights under 10 ft), the breathing level to floor differential may also be neglected, as the two are somewhat compensating, especially where. both floor and ceiling 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 273 ATTIC TEMPERATURES Frequently, it is necessary to estimate the attic temperature, and in such cases Equation 1 can be used for this purpose: = AJJcti + UA,U, + AWU,, + AtUt) A,,E/C + A,U, + A,,U, + A.U. (1) where i, = attic temperature, Fahrenheit. ti = indoor temperature near top floor ceiling, Fahrenheit. to = outdoor temperature, Fahrenheit degrees. Ac = area of ceiling, square feet. A, = area of roof, square feet. - A. = 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. Ur = coefficient of transmission of roof, based on surface conductance of 2.20 (lower surface, see Chapter 9). Un = coefficient of transmission of vertical wall surface. Ut = coefficient of transmission of glass. A --------vviujiwiovuiv AAA aAA uuucauou avuu, <a*aoLLAiAiilli tilt; 1U11U oKlV 1000: ^ = 1200; ^ = 100: A` = 10; U' Solution: Substituting these values in Equation 1: l = (1000 X 0.40 X 70) + 10[(1200 X 0.50) + (100 X 0.30) + (10 X 1;13)] (1000 X 0.40) + (1200 X 0.50) + (100 X 0.30) + (10 X 1.13) 34,413 * = Tom " 331 f- tat f*Uf*I0n * neglects the effect of any interchange of air such as would dent + T^ougk att*c vents or louvers intended to preclude attic conof mliil' However, according to tests,8 such venting of attics by means 1 louvrs or other small openings does not appreciably reduce the temperature and may be neglected without serious error. ellterudr this equation take into consideration such factors as heat roof R6 betwee" chimney and attic or solar radiation to and from the auentlv tbaLSe , these latter effects, actual attic temperatures are fretemDera.f Sh6r tban calculated values using Equation 1. The attic 1 allmv^Urfumry,,be ealculated in the usual manner by means of Equation ti'on will he n 7a^ue the roof. The error resulting from this assump- sometimPQtt?ray oonsiderably less than if the roof were neglected (as is as the miiovT ?rac^ce) and the attic temperature assumed to be the same as is custn 1(16 .mPerature. When relatively large louvers are installed, sumed ]?ary ln southern states, the attic temperature is often as- p the average between inside and outside. or a shorter, approximate method of calculating heat losses through