Document nkBybYz4Yz84d8BZEDgrmMk32

264 CHAPTER 14 1946 Guide Equation 1 neglects-the effect of any interchange of air such as would take place through attic vents or louvers intended to preclude attic com densation. However, according to tests *, such venting of attics by means of 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 Equa tion 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. 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 adjacent to the heated room and exposed to the outside. If the respective 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(A,U, -|- AjUt + AtU, + etc.) + to (AoU* + AbUb 4- AcUc + etc.) AiUi + AtUx + AiUi + etc. + AaVa + AbUb + ACUC + etc. . . , where .. . = temperature in unheated space, Fahrenheit degrees. / -- inside design temperature of heated room, Fahrenheit degrees.' . to = outside design temperature, Fahrenheit degrees. Ai, At, At, etc. = areas of surface of unheated' space adjacent to heated space, square feet. Aa, A b, Ac, etc. = areas of surface of unheated space exposed to outside, square feet. Ui, U,, Ui, etc. = coefficients of transmission of surfaces of A,, At, Ai, etc. Vo, Ub. Uc, etc. = coefficients of transmission of surfaces Aa, Ab, Ac, etc. Example S. Calculate the temperature in an unheated space adjacent to a heated room having surface areas (j4r. At, and A,) in contact therewith of 100, 120 and 140 sq ft and coefficients (Vi, XJt, and Ui) of 0.15, 0.20 and 0.25 respectively. The surface areas of the unheated space exposed to the outside (A,, and ,4b) 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 ! = 70 and to = --10. : Solution. Substituting in Equation 2: = 70[(i00X0.15)+(l20 X0.20) +(140 X0.25)]+ --10[(lb0XQ.i0)+(140 X0.30)] " (100 X 0.15) + (120X 0.20) + (140 X 0:25) +(100 X 0.10) + (140 X 0.30) 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. Heating Load 265 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 die 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 floors6 is influenced by the.heat from the basement or protected from die 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 37.. Test results indicate that the heat losses through basement flobrs are frequently over estimated 6. 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 lower the basement temperature when it is colder outside arid 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 basernent. If the basement is heated and a specified temperature is id Be main tained, the heat, loss, should be estimated in the usual manner, basedfon' the proper wall and floor, coefficierits (see Chapter 6) and the outside air. and the ground temperatures. Heat loss through windows and Walls