Document wg5JEkZ3B1Zx7yqzJ4Y40m6q3

American Society of Heating and Ventilating Engineers Guide, 1926-27 produced by the pump. It may be neglected in the design if it is less than 20 per cent of that produced by the pump. To illustrate, let it be required to determine the pipe size for the central hot-water heating system shown in Fig. 37. The system is to supply 12,500,000 B.t.u. per hour to a group of eleven buildings with a temperature drop of 40 deg. The system is provided with a reversed return. The pipe sizes are selected so that the friction heads in the eleven circuits are practically equal. The Fig. 38. Layout for Sizing Hot Water Mains velocity of the water varies from 3to ft. per second. The theo retical horsepower required to circulate the water through the main is 11.9. The table in Fig. 37 shows the calculations for one* of the eleven circuits. ' If the circulation within the buildings is maintained by the pump, the power required therefor must be added to that already calculated. Each flow and return pipe, connecting a building and the mains, should be provided with a gate valve and a thermometer and the gate valves should be adjusted so that the temperature drop in each of the eleven buildings is 40 deg. 86 American Society of Heating and Ventilating Engineers Guide, 1926-27 SIMPLE RULE FOR SMALL GRAVITY SYSTEMS In designing a hot-water system for a residence or other small buildings the following simplified method by N. S. Thompson and C. A. Fuller gives good results for the usual two-pipe basement main system. Determine the size of radiator tapping and connection from Table 49 and the size of riser and main from Table 50. To illustrate assume the layout in Fig. 38. The radiator connections determined from Table 49 are as follows: A -- 1 in. B = 1 in. C = VAin. D = 1 in. E = 1M in. F = 1J^ in. G = 1 in. H = IH in. Where one radiator only is supplied the riser and mains are sized the same as the radiator connection. Where more than one radiator is supplied the pipe size is determined from Tables 49 and 50 as follows: A = 1 in. = 10 Equivalent carrying capacity S = 1 in. =10 " "" C= 20 = in. pipe between D and C in. = 20 Equivalent carrying capacity 40 = 2 in. pipe between D and C D = 1 in. = 10 50 = 2 in. pipe between J and D Proceeding in like manner the other sections of pipe are found to be as follows: E to F = 1in. F to G = 2 in. G to H -- 2 in. H to Mains = 2% in. J to K = 3 in. Table 49. Hot Water System Pipe Sizes and Connections Pipe Size First Floor Second Floor Third Floor Fourth Floor w i" 'V/i" m" 2" 40 70 110 180 300 50 60 70 80 90 100 120 135 150 195 210 230" 350 400 500 In connection with Table 49, the following equalizing Table 50, should be used to determine the size of risers and basement mains. 87