Document 6B17pboZOZb9QgxQxrN5DKR8m

438 CHAPTER 17 1952 Guide -The year under consideration may then be compared, month by month, with the previous year. Column 3, Consumption for Heating, would be used if the same fuel is used for heating and process steam. Some reason able figure must be assumed for the process requirement and should be deducted from the amount shown in column 2.. This would leave in column 3 only the fuel chargeable to heating. The degree-day values in column 5 are. obtainable from the local Weather Bureau. . Values in column 6 are obtained by dividing-corresponding values.in column 3 by the degree-days in column 5. The heating index in column 6 is, then, a figure of heat' con sumption, corrected for outdoor temperature, and should be relatively con stant, month by month. . Column 7 in Table 8 may be used if the heat consumption is to be compared on a building volume basis with average values shown in Table 7. MAXIMUM DEMANDS AND LOAD FACTORS In one form of district heating rates,,.a portion of the charge is based upon the maximum demand of the building. The maximum demand may be measured in several'different ways. It. may be. taken as the instantane ous peak or as the rate of use during any specified interval. One method is to take,the average of the three highest hours during the winter. These figures are shown for a number of buildings- in Detroit in Table 9." These maximum demands were measured by an attachment on the con densation meter, and therefore represent the amounts of condensation passed through the meter in the highest hours, rather than the true rate.at which steam is supplied. There might be slight differences in these two quantities due to time lag and to storage of condensate in the system, but wherever this has been investigated it has been found to be-negligible, ? 'The . load factor of a building is the ratio of the average 'ioad to the maximum load and is an index .of the utilization. Thus, in Table 9, the theaters, operating for short hours, have a load factor of 0.126 as compared with the figure of 0.318 for clubs and lodges. REFERENCES . 1 Comfort Heating {American GasAssocialion, 1938). ' Are Automatic Air Shutters Justified on a Gas-Fired Conversion Burner? by W, M. Myler, Jr. and H, W. Nelson (A.S.H.V.E. Joohnal, Section, Healing, Piping arid Air Conditioning,Oct. 1948, p. 111). * Efficiency of Bituminous-Goal-Burning Space Heater, by J.'W. Tieman and F. L. Bagby (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning: Journal Section, Fefi. 1951, p. -117). . .. . 4 Heat Losses and Efficiencies of Fuels in Residential Heating, by R. A. Sherman and R. C. Cross (A.S.H.V.E. Transactions, Vol. 43, 1937, p. 185). 'The Stoker-Fired Warm-Air Furnace in the Research Residence, by S. Konzo {University of Illinois, Engineering Experiment Station, Circular 39, 1939, p. 98). * Performance of a Hot Water Heating System in the I = B = R ResearchHome at the University, of Illinois {University of Illinois, Engineering Experiment Station, Bulletin No. 349, Jan. 4, 1944). . .1 Fuels and Burners (Univesrity of Illinois, Small Homes Council, Circular G3.5, July 1949),. , 8 Investigation of Oil-Fired Forced-Air Furnace Systems in the Research Resi dence, by A. P. Kratz and S. Konzo {University of Illinois, Engineering Experiment Station, Bulletin No. 318, Nov. 7, 1939). 9 Graphical Method of Calculating Heat Losses, by Paul D. Close (A.S.H.V.E. Transactions, Vol. 49, 1943, p. 345). 10 House Heating (Industrial Gas Series, American Gas Association, Third Edition). n Report of Commercial Relations Committee {Proceedings, National District Heating Association, 1932). 18 The Heat Requirements of Buildings, by J. H. Walker and G. H. Tuttle (A.S.H.V.E. Transactions, Vol. 41, 1935, p. 171). v, v. CHAPTER 18 GRAVITY WARM AIR SYSTEMS Warm Air Leaders, Stacks, and Registers; Return Air Grilles, Ducts, and Connections;.Outline of Design Procedure WARM air heatihg systems of the gravity type are described in this chapter.1 In these systems the motive head producing flow depends upon the difference in weight between the heated air leaving the top of the casing and the cooled air entering, the bottom of the casing, while in the; forced air type a fan may supply all or part of the motive head. A gravity warm-air furnace heating plant consists , of a fuel-burning furnace or heater, enclosed in a casing of sheet metal, which is placed in the basement of the building. The Heated air, taken from the top or sides near the top of the furnace casing, is distributed to the various rooms of the building through sheet metal warm-air pipes. The warm-air pipes in the basement are known as leaders, and the vertical warm-air pipes which ., are installed in the inside partitions of the building are called stacks. The heated air is discharged into the rooms through registers which are' set in register boxes placed either in the floor or in the side wall, usually ator near the baseboard. A sectional view .of a typical plant showing good installation practice is given in Fig. 1. The air. supply to the furnace is usually, taken entirely from inside the building through one or more recirculating ducts,.although in some cases an outside air supply duct is provided; WARM AIR LEADERS, STACKS, AND REGISTERS In a gravity circulating warm-air furnace system, the size of the leader pipe to a given room depends upon the length of tHe leader and the tem perature of the warm air entering the room .at the register. For most successful operation, the furnace should be centrally located with respect to register and stack positions so that the leaders will be of uniform-length and as short as possible, in which case the frictional resistance to'air flow and the temperature loss from the ducts will be. about the same for all. leaders and stacks. Originally, the design was based on the heat carrying capacities per. square inch of leader, pipe area with register air temperatures of J.75 F. Later, in the revision of the entire design procedure, as shown in the section entitled Outline of Design Procedure, the carrying capacities of leader pipes have been expressed directly in terms of Btu per hour. In general, it is advisable to use .two or more leader pipes to rooms requiring more than the capacity of a 12 in. round pipe. The tops of allsizes of leader pipes should be cut into the furnace bonnet at the same elevation, and from this point there should be a uniform upgrade of at least 1 in. per foot Of run. Leaders over 12 ft in lehgth, or having a large num ber of elbow fittings should be avoided if possible. In cases where such leaders are necessary, it is fecommebded that smooth transition .fittings be used, and that duct insulation be applied.' Asbestos paper, unless of the corrugated type, should not be considered as insulation. To assist 439