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HEATING VENTILATING AIR CONDITIONING GUIDE 1943 11 p.m. to 7 a.m. Assume-that the price of gas is 7 cents per 100,000 Btu of fuel con sumption, and disregard the loss of heat through open windows and doors. Solution. The average hourly temperature is: ^ = (72 X 16) + (55 X 8) ^ 06 3 F The maximum hourly heat loss will be: H = 92,000 - 26'^ = 79,000 Btu. M= ~ !l6'4) = 2204.6 hundred thousand Btu. 2204.6 X *0.07 = $154.32 = estimated fuel cost per year of heating building. In the case of grayity warm air heating installations, the load is usually expressed in square inches of leader pipe. This can be converted into hourly heat loss by multiplying by the, factors in Table 1. Table 1. Heat Carrying Capacity 'of Gravity Warm Air Furnace Round Leader Pipes 180 F Register1 Temperature Leader Pips Btu per Houb at Design Conditions S I .peb q n op Leader Pipe in . i67 200 Example 4- What would be the total gas consumption over a full heating season of a gas-fired gravity warm air furnace designed according to the Code1, and with four 12 in. and two 8 in. round leaders to the first floor and six 10 in. leaders to the second floor, if the gas has a heating value of 500 Btu per cubic foot, the plant operates at a 70. per cent seasonal efficiency and is designed to maintain an average inside temperature of 65 F when it is 10 F outside in a city where the average outside temperature is 45 F and the heating season is 5088 hr long? Solution. The area of the round leaders is: 42 in.,-113 sq in.; 10 in., 79 sq in.; and. 8 in., 50 sq in. From Table 1 the total Btu transmitted is: First Floor: [(4 X 113> + (2 X.50)] X 111 = 61,272 Btu per hour. Second Floor: (6 X 79) X 167 = 79,158 Btu per hour. Total 140,430 Btu per hour. Substituting this total heat loss value as H in Equation 1 gives: 140,430 (65 - 45) 5088 0.70 (70 - 10) 500 680,483 cu ft gas! DECREE-DAY METHOD This method is based on consumption data which have been taken from buildings in operation, and the results computed on a degree-day basis. While this method may not be as theoretically correct as the Calculated Standard Code. Regulating the Installation of Gravity Warm Air Heating Systems in Residences (9th edition), and the Technical Code for the Design and Installation of .Mechanical.Warm Air Heating Systems, may be obtained from the National Warm Air Heating and Air Conditioning Association, 145 Public Square, Cleveland, Ohio. 230 CHAPTER 11. ESTIMATING.FUEL CONSUMPTION Heat Loss Method, it is considered by many to be'of more value for practical use. The amount of heat required by a building depends upon the outdoor temperature, if other variables are eliminated. Theoretically it is pro portional to the difference between the outdoor and indoor temperatures. Some years ago the American Gas Association2 determined from experi ment in the heating of residences that the gas consumption varied directly as the difference between 65 F and the outside temperature. In other words, on a day when the temperature was 20 deg below 65 F, twice as much gas was consumed as on a day when the temperature was 10 deg Table 2. Base Temperature for the Degree-Day3 Type op Building Office_____________...................................................... Office and Bank................................ ....... ................. Office and Telephone Exchange............................ Office and Stores........................................................ Stores. ........ ........................................................... Department Stores...... ............................................. Hotels:............................................ .............................. Apartments. ____ :................................... ............ Residences. ......................................................... Clubs.......... ................................................................. Lodges........................... ;.............................................. Theaters.................................................................... Churches..................................................................... Garages..................... ..................... .............................. Auto Sales and Service Newspaper and Printing Warehouse and Loft. Office and Loft ............... .............................. Manufacturing............................ ........................... No. op Buildings Analyzed 60 4 3 2 6 11 12 .7 14 8 4 5 3 2 2 4 3 3 2 8 Temperature F Cor responds to Zero Steam Consumption , 66.2 65.8 66.2 65.5 67.4 . . 64.0 64.3 66.5 68.8 66.9 65.5 64.9 67.6 65.8 64.8 61.2 67.7 67.7 65.2 65.4. Average for 163 Buildings.................... ........ . ..... 66.0 F Report of Commercial Relations.Committee, Proceedings, National District Heating Association. 1932. below 65 F. For any one day there exists as many degree-days as there are degrees Fahrenheit difference in temperature between the mean temperature for the day and 65 F when the mean temperature is less than 65 F. Studies made by the National District Heating Association of the metered steam consumption of 163 buildings located in 22 different cities and served with steam from a district heating company substantiates the fact that fhe 65 F base originally chosen by the gas industry is approxi mately correct as shown in Table 2. If the degree-days occurring each day are totaled for a reasonably long period, the fuel consumption during that period as compared with another period will be in direct proportion , to the number of degree-days in the two periods. Consequently, for a given installation, the fuel consumption can be calculated in terms of fuel used per degree-day for any sufficiently *See Industrial Gas Series, House Heating, {third edition) published by the American Gas Association. 231