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160 CHAPTER 12 1959 Guide Table 5 .... Below Grade Heat Losses for Basement . Walls and Floors Ground Water Temperature* leoMd Floor Less* Mow Grode Wafl teas* fife/Sq ft Btu/Sq Ft widely depending on the number and size of wall vents, the amount of warm piping present and type of piping insulation. Tt is necessary, therefore, to evaluate the conditions and to select an appropriate temperature by judgment. 40 3.0 50 2.0 60 1.0 * Sm Fig. 4, Chapter 41. * Bated on h--aiaant temperature of 70 F and U of 0.10 6.0 4.6 2.0 through basement floors, the ground temperatures may be assumed to be the same as water temperatures at depths of 30 to 60 ft given in Fig. 4, Chapter 41. Test observations indicate that heat losses through basement floors frequently are over-estimated.** 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 re sult in a higher ground temperature near the surface. There fore, in localities where the ground is covered with a heavy blanket of-snow throughout the winter, the ground -tempera tures near the surface will be higher than when little or no snow is- present. Complete data on ground temperatures adjacent to build ings are not available, but since the recommended trans mission coefficient for basement 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 whether the 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 coefficients (see Chapter 9) mad the outdoor air and ground temperatures. Heat loss through win dows and walls above grade should be based on outdoor tem peratures 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 thesoil, and on the proper ground temperature. The heat loss values for below-grade basement'walls and floors given in Table 5 are sufficiently precise for general practice. If a basement is completely below grade and is not heated, the temperature in the basement .normally will range be tween that in the rooms above and the ground temperature. Basement windows will, of course, lower the basement tem perature when it is cold outdoors, 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 tran sient heat from the heating plant warms the air near the. basement ceiling sufficiently to make it unnecessary to make' an allowance for floor heat loss from rooms located over the basement. The temperature in crawl spaces below floors will vary HEAT LOSSES FROM ROOR SLABS Two types of concrete floors used in basement!ess houses are (a) the unheated floor, relying for warmth on heat de livered above floor level by the heating system, and (6) the heated floor containing heated pipes or ducts that constitute a radiant slab or portion thereof for complete or partial heating of the house. For type (a) the floor heat los, economically considered, is of minor importance since it comprises generally about 10 percent of the total,heat loss of the house. From the comfort standpoint, however, it may be most important, since houses with cold floors are not successfully heated. In this connec tion, it should be remembered that a well insulated floor does not assure comfort if downdrafts from windows or exposed walls create pools of chilly air over considerable areas of the floor. For this reason a floor of type (a) should not be used in a severe climate except with a heating system that delivers enough heat near the floor to counteract the downdrafts of the exterior walls and the heat transmission through the floor. The results of some experimentsTM-** with type (a) un heated floor slabs indicate that the heat loss from a concrete slab floor on grade is more nearly proportional to the perim eter than to the area of the floor, and that the heat loss can be estimated by means of the equation: inhere H, - FP (U - i.) (3) Hr " heat loss of the floor, Btu per hour. P = perimeter or exposed edge of the floor, linear feet. Table 6 .:.. Heat toss of Concrete Floors at or Near Grade Level per Foot of Exposed Edge Heating Load 161 F - heat loss coefficient, Btu per.(hour) (linear foot of ex posed edge) (degree difference in temperature between the indoor air and the outdoor air). (F ranges between 0.81 for a floor with no edge insulation to 0.55 for a floor with edge insulation.) U = indoor air temperature, Fahrenheit. t, * outdoor air temperature, Fahrenheit. In most instances the values given in Table 6 for edge loss are of sufficient precision for useThe insulation shown ex tending under the floor horizontally for 2 ft can also be located along the foundation wall with equal effectiveness if the insulation extends 24 in. below the floor level. Examples: Calculate the heat loss from the floor of a 12 ft x 15 ft room with two exposures. The floor, is an unheated con crete wlab which is insulated at the edge with 2 in. of insulation extending horizontally for a distance of 2 ft from the edge, and the house is located in an area with an outdoor design tempera ture of --15 F. Solution: From Table 6 the heat loss per foot of exposed edge is 45 Btu per hr. The length of exposed edge is 12 ft + 15 ft -- 27 ft. the total edge loss 27 x 45 = 1215 Btu per hr. Floors of type (6) containing beating pipes or ducts, are now in common use. The beat loss downward into the ground nnH outward through the edges of the floor slab is called the reverse loss. The resultsTM- of an investigation in which a warm air perimeter duct was embedded in four types of concrete floorslab and foundation constructions has .verified the indication that Equation 3 can be used to calculate the reverse loss when warm air perimeter heating ducts are. used. To make the results of this application more usable, values correspond ing to those shown in Table 6 for unheated floors" are given in Table 7 for concrete floors with a warm air perimeter duct. The desirability of edge insulation is apparent. One inch of water-resistant material is the minimum thickness of edge insulation that should be used, but a 2-in. thickness is recom-..mended.1*- " " The values of edge loss in Table 7 indicate that the reverse beat loss of heated dabs is likely to be about 20 percent of the total heat loss of many types of present day houses, ftnH may exceed 20 percent if only one inch of insula tion is used at the edge of the floor. The concrete floor dab is usually placed on a gravel fill 4 in. thick or more, both to insulate the floor from the earth and to retard the rise of ground water by capillarity. A water proof membrane should be installed over the gravel fill. Obviously, it is important that such floors be laid several inches above grade, and that effective subsoil drainage be provided to avoid slabs soaked by run or melting snow, and consequent excessive heat loss. TRANSMISSION HEAT LOSS The basic formula for the loss of heat by transmission through any surface is given in Equation 4: H, -- AU (t* -- t,)1 W where H, -- heat loss transmitted through the wall, roof, celling, floor, or glass, Btu per hour. A = area of wall, glass, roof, ceiling, floor, or other exposed surface, square feet. U -- coefficient of transmission, air-to-air, Btu per (hour) (square foot) (Fahrenheit degree temperature differ ence). Table 7.... Floor Heat Loss to be Used When Warm Air Perimeter Heating Ducts Are Embedded in Slabs* Btu per (hoar) (linear toot of hooted edge) Edge Insulation Outdoor Design l-Jn. Vertical Extend 7-in. L-Tjrpe Extend 2-in. l-Type Extend Tempcrafw*, ing Down 78 in. ing of Least 12 ing at Least 12 in. F Below Boor m. Deep and 72 ini Down and 72 to. Surface Under Under -20 105 100 85 -10 95 90 75 0 85 80 65 10 75 70 55 20 62 57 45 * Factor* include )<r downward Unouth inner are* of ateb. = indoor tepjperature near surface involved (this may not necessarily be the so-called breathing-line tem perature), Fahrenheit degrees. ( = outdoor temperature, or temperature of adjacent un heated space or of the ground, Fahrenheit degrees. Example 4: Calculate the transmission loss through an 8-in. brick wall having an area of 150 sq ft, if the indoor temperature U is 70 F and the outdoor temperature U is --10 F. Solution: The coefficient of transmission U- of a plain 8-in. brick wall is 0.41 (Chapter 9, Table 6). The area A is 150 sq ft. Substituting in Equation 4: H, * 150 X 0.41 X 170 - (-10)1 - 4,920 Btu per hour. Transmission Loss Through Ceilings and Roofs The transmission beat loss through top Boot ceilings, attics, and roofs may be estimated by either of two methods: I. By substituting in Equation 4 the ceiling area A, the in door-outdoor temperature difference (L -- ) and the proper value of U: a Flat roofs. Select the coefficient of transmission of the ceil ing and roof from Tables 11 to 14, Chapter 9, or use appro priate coefficients in Equation 1 if side walls extend.appre- ciably above the ceiling of the floor below. b. Pitched roofs. Select the combined roof and ceiling coeffi cient from Table 15, Chapter 9 or calculate the combined roof and rating coefficient by means of Equations 4 and 5, Chapter 9, where these formulas are applicable as explained in Chapter 9. 2. By the attic temperature (based on the indoor nH outdoor design temperatures) by means of Bouation 1, and substituting for t. in Equation 4, the value of t. thus obtained,' together with the ceiling area A and the ceiling coefficient V. 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 suggested in preceding paragraph la. INFILTRATION HEAT LOSS The infiltration heat loss includes (1) the sensible heat loss or the heat required to warm the outdoor air entering by infiltration, and (2) the latent heat loss or the heat equivalent of any moisture which must be added. Sensible Heat Loss The formula for the heat required to warm the outdoor air which enters a room by. infiltration to the temperature