Document 85b2m632Lj6wv4y3qzRjOk6kB

250 CHAPTER 12 1953 Guide as the outside temperature. When relatively large louvers are installed, as. is customary in the southern states, the attic temperature is often as sumed as the average between inside and outside. For a shorter, approximate method of calculating heat losses through attics, the combined ceiling and rtfof 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 spaces. This temperature will lie in the 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. ^ _ t(.AiUi 4- AtUi -1- A,U% 4- etc.) -b lj(Aat/a -b Ab(/b -b AcUe -b etc.) AiUi -b AsUt -b A,Ut + etc. -b Aat/a -b AbUb -b A0t/0 -b etc. where t,, = temperature in unheated space, Fahrenheit degrees. t = inside design temperature of heated room, Fahrenheit degrees. = outside design temperature, Fahrenheit degrees. Al( At, Aa, etc. = areas of surface of.unheated space adjacent to heated space, square feet. A,, Ab, Ac, etc. = areas of surface of unheated space exposed to outside, square feet. Ui, Ut, Ui, etc. = coefficients of transmission of surfaces of A, A,, A,, etc. U., Ub, U', etc. = coefficients of transmission of surfaces A,, Ab, Ac, etc. Example 2: Calculate the temperature in an unheated space adjacent to a heated room having surface areas (A,, A,, and A,) in contact therewith of 100, 120, and 140 sq ft and coefficients (Ui, U,, and Uj) 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 ground and is neglected in this example. Assume t = 70 and t,, = -- 10. Solution: Substituting in Equation 2: 70[(100 X 0.15) + (120 x 0.20) + (140 X 0.25)1 + -101(100 X 0.10) -b (140 X 0.30)] (100 X 0.15) + (120 X 0.20) + (140 X 0.25) + (100 X 0.10) + (140 X 0.30) 4660 tn 126 37 F. . The temperatures in unheated spaces having large glass areas and having two or.more surfaces exposed to the outside (such as sleeping porches and sun parlors), generally are assumed to be the same as outside. GROUND TEMPERATURES Ground temperatures to be assumed for estimating basement heat losses usually will differ in the case of basement walls and floors, the tem peratures under the floors generally being higher than, those adjacent to walls. Factors affecting these temperatures will be discussed. Heating Load 251 Temperatures Under Basement Floors ! The temperature of the ground under basement floors9 is affected by heat sources within the basement and .is not influenced by atmospheric conditions. In computing losses through basement floors, the ground tem peratures may be assumed to be the same as water temperatures at depths of 30 to 60 ft given in Fig. 3, Chapter 35. Test observations indicate that heat losses through basement floors frequently are over-estimated.10 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 will be the ground temperature. 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. Therefore, in localities where the ground is covered with a heavy blanket of snow throughout the Table 4. Below Grade Heat Losses fob Basement Walls and Floors Temperature* R a rem ent Floor Loss1* Btu/Sq Ft Below Grade Wall Loss*3, ; Btu/Sq Ft 40 3.0 6.0 50 2.0 4.0 60 1.0 2.0 * See Fig. 3, Chapter 35. b Based on basement temperature of 70 F and U of 0.10. winter, the ground temperatures near the surface will be higher than when little or no snow is present. Complete data on ground temperatures adjacent to buildings are not available, but since the recommended transmission coefficient for base ment walls in contact with the soil is only 0.10, any reasonable, assumed ground temperature will not materially affect the calculated heat loss. BASEMENT TEMPERATURES AND HEAT LOSS The allowance to be made for basement heat loss depends on whetherthe basement is to be heated or not. If the basement is heated to a specified temperature, the heat loss should be calculated in the usual manner, based on the proper wall and floor co efficients (see Chapter 9) and the outside air and ground temperatures. Heat loss through windows and walls above grade should be based on out side temperatures and the proper air-to-air coefficients. Heat loss through basement walls below grade should be based on the floor and wall coeffi cients for surfaces in contact with the soil, and on the proper ground temperature. The heat loss values for below grade basement walls and floors given in Table 4 are sufficiently precise for general practice. If a basement is completely below grade and is not heated, the tem perature in the basement normally will range between that in the rooms above and the ground temperature. Basement windows will, of course, lower the basement temperature when it is cold outside, and heat given off by the heating plant will increase the basement temperature. In any case, the exact basement temperature is indeterminate if the basement , is not heated. In general, it is found that the transient heat from the heating