Document 3ekEZZgDazoJmVm1m2nLz7Z7O

American Society of Heating and Ventilating Engineers Guide, 1930 The one-pipe system would not be suitable for this installation because the sizes, of tjie radiators, in the buildings receiving the cooler water, would be excessive. Either of the two-pipe systems shown in Figs. 11 and 12 could be used. To determine the pipe sizes it is necessary to assume some unit.velocity or some unit friction head for the system. The higher the velocity, for Fig. 11. Two-Pipe, with Reversed Return, Forced Circulation System for Six Buildings which the system is designed, the smaller will be the pipe and its cost, and the larger will be the cost of the pump and of its operation. For every case there will be an optimum velocity for which the total cost is a minimum. This velocity must be calculated for every case. For the system of Fig. 11, assume that the temperature drop through each building is to be 20 deg., and that the velocity of the water in the 382 Chapter 21--Piping for Hot Water Heating Systems largest pipe of the main is to be approximately 5 ft. per second and in the smaller generally less, but adjusted so that the friction will be prac tically the same throughout the system for any one of the six possible paths. Divide the system into seven sections as shown in Fig. 11 and in Table 4. Table 4. Tabulation of Friction Head Calculations for the Forced Circulation System Shown in Fig. 11 Section Heat 1,000 B.t.u. % Pipe Length, Feet Elbows A-B 3,000 B-C 2,500 C-D 2,000 200 100 100 10 D-E 1,500 200 2 E-F 1,000 100 F-G 500 G-H 3,000 100 200 iQ Pipe Diameter Veloctit . 5 in. 5 in. 35 ft. 5 in. 65 ft. 4J in. 35 ft. 4H in. 165 ft. 5 in. 15 ft. 4 in. 85 ft. 3 in. 71.5 ft. 3 in. 28.5 ft. 254 in. 5 in. 58 48 .40 45 36 29 32 39 27 41 58 Unit Friction, Mil-Inches Pipe Elbows Total Friction, Mil-Inches 180 2,700 63,000 130 13,000 84 155 13,015 85 50 1,100. 690 13,015 75 140 13,025 82 250 12,988 180 2,700. 63,000 Total Friction Head :.Mi!-Inches 191,043 It is evident from Fig. 11 and Table 4 that.the water may flow from the central plant through any one of the six buildings and back to . the central plant with a loss of head of 15.9 ft. of water, plus the losses of head in the building, and in the central plant. If the six buildings are piped so that the loss of head is the same in each of the six buildings, the water will flow uniformly through the buildings. If the buildings are piped so that the loss of head is not the same in all, the losses can be made equal by adjusting the valves at the several buildings. For this purpose every building must be supplied with gate valves in the flow and return lines at the building connections and with thermometers in the pipe lines near the valves which should be adjusted so that the calculated temperature drop (20 deg. in this particular problem).is obtained in each building. Using the prices shown in Table 5, the cost of the 1,600 ft. of mains Table 5. - Approximate Cost of Covered Pipe Installed in Tunnel Sizes--Inches 2 2H 3 4 4K 5 6 8 10 Cost per Foot.... $0.75 81.00 $1.25 $1.50 $1.75 $2.00 $2.25 $2.75 $4.50 $6.25 383