Document ng7Y3KEkdb6LJpKY0L0nmNe6

260 CHAPTER 14 1949 Guide* densation. However, according to tests6, 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 temperatures. For a shorter, approximate method of calculating heat losses through attics, the combined ceiling and roof coefficient may be used as described in :Chapter 6. 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 ad jacent to the heated room and those exposed to the. outside. If the re spective 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 __ KAit/j -j- AiUi + AtUt + etc.) + <0(AmUm AbE/b 4- AcUc + etc.) ' AtUt 4- AtUt + AiUn + .etc. 4- A.U, 4- Abf/b 4- AeUa 4- etc. where tu = temperature in unheated space, Fahrenheit degrees. t = inside design temperature of heated room, Fahrenheit degrees. to = outside design temperature, Fahrenheit degrees.. ... At, Ai, At, etc. = areas of surface of unheated space adjacent to heated space, square feet. Am, Ab, Ac, etc. = areas of surface of unheated space exposed to outside, square .. . feet. Ui, Uj, U1, etc. = coefficients of transmission of surfaces of Alt At, Aa, etc. Um, Ub, Uc, etc. = coefficients of transmission of surfaces Am, At, Ac, etc. Example S. Calculate the temperature in an unheated space adjacent to a heated room having surface areas (At, At, and A,) in contact therewith of 100,120j and 140 sq ft and coefficients (Ut,Ut, and /,) of 0.15,0.20, and 0.25 respectively. The surface areas of the unheated space exposed to the outside (A, and Ab) are respectively 100 and 140 sq ft and the corresponding coefficients are 0.10 and 0.30. The sixth surface is on the groundand is neglected in this example. Assume 1 = 70 and f0= -- 10. Solution. Substituting in Equation 2: ... , 701(100 X 015) 4- (120 X 0 20) 4- (140 X 0.25)] 4- -101(100 X 010) 4- (140 X 0-30)1 (100 X 0.15) 4- (120 X 0.20) 4- (140 X 0 25) 4- (100 X 0.10) 4- (140 X 0.30) Heating Load 261 The temperatures in Unheated spaces having large glass areas and with two or more surfaces exposed to the outside (such as sleeping porches and gun parlors), are generally assumed to be the same as outside. GROUND TEMPERATURES . 1 Ground temperatures to be assumed for estimating , basement heat losses will usually differ in the case of basement walls and. floors, the temperatures under the floors being generally higher than those adjacent to walls. Temperatures Adjacent to Basement Walls Ground temperatures near the surface and under, open spaces vary with the climate, the season of the year and the depth below the surface. The nearer the surface (during the cold weather), the lower the tem perature. Frost will penetrate to a depth of over 4 ft in some localities if not protected by snow. A thick blanket of snow will result in a higher ground temperature near the surface. Consequently ground tempera tures near the surface may be higher in cold climates where the snow remains on the ground for a greater length of time'than in more moderate climates where the snow melts away periodically during the winter. Complete data for various localities are- not as yet available but in estimating heat losses through. vertical walls below grade, it is advisable not to assume average ground temperatures above. 32 F in northern cli mates when estimating heat losses from heated basements. This is for the mean height of the basement wall. Since the recommended wall coefficient for basement: walls in contact with the soil is only 0:10, any small variation in the assumed ground temperature will not materially affect the calculated heat loss. . Temperatures Under Basement Floors The temperature under basement floors6 is influenced by the heat from the basement or protected from the influence .of atmospheric conditions by the basement. In computing losses through.baseinent floors the ground temperatures may be assumed the same as the approximate water tem peratures at depths of 30 to 60 ft given inFig. 3, Chapter 37. rr Test results indicate that the heat losses through basement floors are frequently over-estimated7. BASEMENT TEMPERATURES AND HEAT LOSS The allowance to be made for basement heat loss depends on whether the basement is to be heated or not; " *. If the basement is healed and a specified temperature is to be main tained, the heat'loss should be estimated in the usual manner, based on the proper wall and floor coefficients (see Chapter 6) and. the outside air and ground temperatures. Heat loss through Windows and walls above grade should be based on outside temperatures and the proper air-to-air coefficients. Heat loss through basement walls below grade should be based on the floor and wall coefficients for surfaces in contact with the soil and on the proper ground temperature. If a basement is completely below grade- apd is not heated, the tem perature irr the basement'will normally range bctween'that in the rooms above and the ground temperature.' Basement windows will of course lower the basement temperature when it is colder outside and any heat