Document ZJ1J3rXwxMed4DnrNN1BxyV7Z

414 CHAPTER 17 1951 Guide heat gains, such as sun effect, and many others. In order to apply this method the hourly heat loss from the building under maYimiim load, or design condition, is computed following the principles discussed in Chapters 9 and 10, and the method described and illustrated in Chapter 11. In predicting fuel consumption for heating a building by the Calculated Heat Loss Method, the general equation is: _ g(t - ON E{li - OC (1) where F quantity of fuel or energy required (in the units in which C is expressed), H calculated heat loss, Btu per hour, during the design hour, based on to and ta ^generally H )'ffi H% + Hi but may on occasion equal Ht + 2 t = average inside temperature maintained during heating period, Fahrenheit degrees. t. = average outside temperature through estimate period, Fahrenheit degrees (for cities with an Oct. 1-May 1 heating season). Id = inside design temperature, Fahrenheit degrees (usually 70 F). to = outside design temperature, Fahrenheit degrees (see Table 1 in Chapter 11). N -- number of heating hours in estimate period (for an Oct. 1-May 1 heating season, 212 days X 24 hr = 5088). E = efficiency of utilization of the fuel over the period, expressed as a decimal; not the efficiency at peak or rated load condition. C = heating value of one unit of fuel or energy. Although the assumption of an Oct. 1-May 1 heating season is reason ably accurate in the well-populated New York-Chicago zone, it is not valid as far north as Minneapolis nor farther south than Washington, D. C. and St. Louis. Consequently, it is suggested that allowance be made for this variation, especially in the far north or southern cities. Example 1. A residence building is to be heated to 70 F from 6 a.m. to 10 p.m. and 55 F from 10 p.m. to 6 a.m. The calculated hourly heat loss is 120,000 Btu per hour based on 70 F inside at --10 F outside. If the building is to be heated by metered steam, how many pounds would be required during an average heating season? Solution. The heating value of steam may be taken as 1000 Btu per lb, and since it is purchased steam, the efficiency can be assumed'as 100 percent. Assume average outside temperature as 36.4 F. The average inside temperature is: (16 X 70) + (8 X 55) Substituting in Equation 1: 120,000 (65 - 36.4) 5088 F= = 218,275 lb. 1.00170 - (-10)11000 Example . How much would the fuel cost to heat the building in Example 1 dur ing an average heating season with coal at $8 per ton and with a calorific value of 11,000 Btu per lb, assuming that the seasonal efficiency of the plant was 55 percent? Solution. Substituting in Equation 1: F = ^~ = 36,079 lb = 18 tons, which, at $8 per ton, costs $144. Estimating Fuel Consumption for Space Heating 415 BWrmZs S What will be the estimated fuel cost per year of heating a building S.xrasPassuming that the calculated hourly heat loss is 92,000 Btu based on 0 F, nnoTincludes 26,000 Btu for infiltration? The design temperatures are 0 F and 72 wmcu j heating aeason is 210 days, and the average outside temperature ? . no*arm is 36.4 F. The seasonal efficiency will be 75 percent. The Ukintalned from 11 p.m. to 7 a.m. Assume that the price of gas is 7 cents per 100,000 Bm of fuel consumption, and disregard the loss of heat through open windows and doors. Solution. The average hourly temperature is: (72 X 16) + (55 X 8) t. 66.3 F. 24 The r"T'mnm hourly heat loss will be: H = 92,000 - = 79,000 Btu. M 79,000 (66.3 - 36.4) X 24 X 210-- 2204.6 hundred thousand Btu. 100,000 X 0.75 X (72 - 0) 2204.6 X $0.07 = $154.32 = estimated fuel cost per year of heating building. Several time-saving procedures have been devised for quickly esti mating the hourly Btu loss of one and two-story residences in order that fuel estimates can be predicted more quickly from Equation 1. A graphi cal method of calculating heat losses has been developed1 which makes possible a quick solution if the gross wall, ceiling, or floor areas and respec-, tive transmission coefficients are known. The Federal Housing Administration has originated a short-cut formula for residential heat loss determinations which makes use of the floor area and three selected transmission coefficients. The formula was developed to apply to detached houses approximately rectangular in shape with total exterior door and window areas equal to about 25 percent of the floor area, and with a floor area not greater than about 1500 sq ft. Equa tion 2 is for a one-story residence, and Equation 3 is intended for two-story structures. Hi ~ A (G +V, + U. + U,) (id - to) (2) Ht = A (<? + 1.2 U, + 0.5 Uo + 0.5 Ut) (te - to) (3) where Hi = heat loss from one-story residence, Btu per hour. Ht -- heat loss from two-story residence, Btu per hour. A =* floor area, square feet, measured to the inside faces of enclosing walls and - is the sum of-the following areas: (1) all the area on each principal floor level; (2) the area of all finished habitable attic rooms, including bath rooms, toilet compartments, closets, and halls; (3) all other areas intended to be heated and not located in the basement. O = glass and infiltration factor for ordinary construction: (0.45 for no weather stripping or storm windows), (0.40 for weatherstripping), (0.30 for storm windows with or without weatherstripping). Uw = coefficient of transmission for outside wall, Uo = coefficient transmission for ceiling. Ut = coefficient of transmission for floor.