Document jpr3rg86JOdDw5zZoG9694O9

126 Chapter 6________ ,_____ ______ 1945 Guide . Solution. Substituting in Equation 2: 70[(100 X0.15)+(120 X 0.20)+(140 X0.25)] +-10[(100 X0.10)+(140 X0.30)] u (100 X 0.15) + (120 X 0.20) + (140 X 0.25) +(100 X 0.10) +(140 X 0.30) , 4660 *" " W 37 F. The temperature in unheated spaces having large glass areas and with two or more'surfaces exposed to the outside (such as sleeping porches and sun parlors), are generally assumed to be the same as the outside tem perature. GROUND TEMPERATURES 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 climates 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 floors5 is influenced by the heat from the. basement or protected from the influence of atmospheric conditions by the basement.. In computing losses through basement floors the ground temperatures may be assumed the same as the approximate water temperature at depths of 30 to 60 ft given in Fig. 3, Chapter 26. 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 a basement is completely below grade and is not heated, the tem perature in the basement will normally range between that in the rooms above and the ground temperature. Basement windows will of course A.S.H.V.E. Research Repost No. 1213--Heat Loss Through Basement Walls and Floors, by F. C. Houghten! S. I. Taimuty, Carl Gutberlet and C. J. Brown (A.S.H.V.E. Transactions, Vol. 48, 1942, p. 369). Heating Load 127 lower the basement temperature when it is colder outside and any heat given off by the heating plant will increase the basement temperature. In any case, the exact basement temperature is likely to be a somewhat indeterminate quantity, if the basement is not heated. Since the base-' ment temperature will generally be lower than that of the rooms above, an allowance.should theoretically be made for the loss from the rooms above through the floor over the basement. If the basement is heated 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 4) and the outside air and the ground temperatures. Heat loss through windows and walls above grade should be based on outside temperatures and the proper airto-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. TRANSMISSION HEAT LOSS The basic formula for the-loss of heat by transmission through any surface is given in Equation 3. where Ht = AU(t - (3) Hi = heat loss transmitted through the wall, roof, ceiling, floor or glass, Btu per hour. + = area'of wall, glass, roof, ceiling, floor or other exposed surfaces, square feet. U = coefficient of transmission, air to air, Btu per hour per square foot per degreeFahrenheit temperature difference (Chapter 4). t = inside temperature near surface involved which may not necessarily be the so-called breathing line temperature, degrees Fahrenheit. to = outside temperature, or temperature of adjacent unheated space or of the ground, degrees Fahrenheit. Example S. Calculate the transmission loss through an 8 in, brick wall having an area of 150 sq ft if the inside temperature (1) is 70 F and the outside temperature (!<>) is -10 F. ' Solution. The coefficient of transmission ( U) of a plain 8 in. brick wall is 0.50 (Chapter' 4, Table 6). The area (+) is 150 sq ft. Substituting in Equation 3: Ht -- 150 X 0.50 X [70 -- ( -- 10)] = 6000 Btu per hour. Transmission Loss Through Ceilings and Roofs The transmission heat loss through top floor ceilings, attics and roofs may be estimated by either of two methods: 1. By substituting in Equation 3 the ceiling area {A), the inside-outside temperature difference (t -- to) and the proper value of (U): a. Flat roofs. Select the coefficient of transmission of the ceiling and roof from Table 14, Chapter 4. b. Pitched roofs. Select the combined roof and ceiling coefficient from Table 16, Chapter 4 or calculate the combined roof and ceiling coefficient by means of Equation 4, Chapter.4, where this formula is applicable as explained in Chapter 4. 2. By estimating the attic temperature (based on the inside and outside design tem perature) by means of Equation 1, and substituting for to in Equation 3, the value of *a thus obtained, together with the ceiling area (A) and the ceiling coefficient (/). This applies to pitched roofs. In the case of flat roofs it is not necessary to calculate the attic' temperatures as the ceiling-roof heat loss can be determined as per paragraph la.