Document 447wpyzm1e7VO5Nxmmnevod3N

Heating Ventilating Air Conditioning Guide 1939 The radiator circuits are then checked. The 20 Mbh radiator on this circuit has 3 ft of supply pipe and 13 elbow equivalents while the return is composed of 4 ft and ? elbows. The unit loss in % in. pipe at this delivery is 170 milinches per foot. The total loss in the supply is 3910 milinches. The loss in the return is 1190. Total loss in tU radiator circuit is 5100 milinches. Check each radiator circuit in a similar manner The total calculated loss for the longest circuit was determined as 60,000 milinches The maximum loss in the short circuit is 18,630 plus 13,410 plus 15,450 or a total of 47,490 milinches. This difference is caused by the variation in length of the two circuits and may be corrected by using a flow control in the return main to supply the additional resistance or by introducing resistance into each separate circuit to compensate for the difference. A 10 per cent variation will cause no complication as the flow from the various pipes will not exactly follow the curves of Fig. 4 any closer than this value. ' Example S. Design a two-pipe direct return forced circulation system with copper tubing and fittings for the piping layout as detailed in Fig. 5, based on a 20 F tempera ture drop through the radiation. The piping circuit from the boiler to the highest radiator on the farthest riser and back to the boiler is 250 ft of pipe. There are about 16 elbow equivalents having an equivalent pipe length of about 50 ft, so that the total equivalent pipe length is 300 ft. Assume that a circulator is.available which will provide a pressure head of 6 ft. ; Fig. 5. A Forced Circulation Direct Return System Solution. Refer to Table 2, which indicates the total equivalent lengths for pressure heads from 2 to 12 ft. With a circulator having a 6 ft pressure head and a system with a total equivalent length of 300 ft, the piping system will be designed on a basis of 240 milinch. Checking the piping diagram it will be noted that sections AB and KA, both supply 117.6 Mbh. Referring to the;240 milinch column of Table 2, 1J^ in. is shown to be the necessary pipe size. Sections BC and jK carry 88.8 Mbh and require 1M in. tubing. Sections CD and 1J supply 67.2 Mbh and require 1)4 in. tubing. Sections DE and HI supply 43.2 Mbh, which requires 1 in. tubing. Sections EF and GH with a load of 14.4 Mbh require Yz in. tubing. The risers are pipe sized in a similar manner. To secure proper distribution of hot water in the direct return system among the several risers, it is necessary to introduce resistances to balance the circuit. . The first riser is 80 ft nearer the boiler than the fifth riser. In order that the two may be balanced, that is, operated under equal pressure heads, resistance must be added to the first riser equal to the friction head in the 80 ft of supply main B to F plus the 80 ft of return main G to K for a total of 160 ft of pipe. - Having designed the piping system on a 240 milinch basis, the total friction head in the supply and return mains between the first and fifth risers is therefore 160 X 240 = 38,400 milinches, or 3.2 ft which -must fje supplied by additional resistance in the first riser. r ! ; f 4 ` > Chapter 17. Hot Water Heating Systems and Piping Table 6 Friction Heads (in Milinches) of Central Circular 1A ` Diaphragm. Orifices in Unions Velocity or Water in Pipe in Inches pes Second ^4-in. Pipe 2900 1450 740 380 185 5000 2500 1300 660 330 155 75 11,300 5700 2900 1500 740 350 170 20,800 10,400 5200 2600 1300 620 300 32,000 16,000 8000 4000 2000 970 480 45.000 23,000 12,000 6800 2900 1400 700 57,000 26,000 13,000 6500 3200 1600 47,000 24,000 53,000 12,000 27,000 5700 13,000 2800 6400 1-in. Pipe 900 2000 3500 7800 14,000 22,000 32,000 460 .1000 1800 4000 7200 12,000 17,000 37,000 65,000 270 570 1000 ' 2300 4100 6400 9300 21,000 37,000 160 330 580 1400 2300 3700 5400 12,000 22,000 50,000 190 330 750 1300 2200 3000 7000 13,000 28,000 200 440 800 1300 1800 4200 7400 17,000 120 260 460 720 1100 2400 4300 10,000 0.45 0.50 0.55 o.6o 0.65 0.70 0.75 1000 660 430 280 190 2250 1450 950 630 420 285 190 4000 2600 1700 1100 750 510 330 1 /4~in- Pipe 8900 5800 3800 2500 1700 1150 750 16,000 10,400 6800 4400 3000 2000 1300 25,000 16,400 10,500 6900 4700 3100 2100 36.000 23.000 15.000 10.000 6700 4500 3000 53.000 34.000 22.000 15.000 10.000 6700 60,000 40.000 27.000 60,000 18.000 40.000 12,000 26.000 0.55 0.60 0.65 0.70 0.75 0.80 0.85 850 1900 3300 '600 1300 2300 400 850 1500 260 600 1100 180 400 760 300 540 200 380 1 yi-in. Pipe 7400 5400 ,3600 2600 1800 1200 860 13,000 8600 7200 4400 3000 2200 1600 21,000 16,800 10,400 7000 5000 3200 2300 30,000 21,000 14,000 10,000 . 7000 5000 3000 50,000 30,000 21,000 14,000 10,200 7800 53,000 39,000 28,000 19,000 45,000 13,000 30,000 0.70 0.80 0.90 1.00 1.10 1,20 1.30 890 1850 3500 470 975 1800 255 560 1000 160 340 610 214 375 195 2-in. Pipe 7400 3900 2200 1320 850 460 275 14,000 7400 4200 2520 1600 .950 525 22,300 11,700 6500 4000 2500 1360 980 33,000 17,000 37,000 9500 20,500 5800 .12,500 3700 7900 1910 4200 1375- 3100 38,000 23,000 49,000 14,000 30.000 8100 16,800 4400 8850 losses of head for the orifices in the lH-in. and 2-in. pipe were calculated from those in the smaller pipes.'the calculations being based on the assumption that, for any given velocity, the loss of head ts a function of the ratio of the diameter of the pipe to that of the orifice. This had been found to be ^.cally true in the tests to determine the losses of head in orifices in H-in*. I-in., and IH-in. pipe, con ducted by the Texas Engineering Experiment Station, and also in the tests to determine the losses of head * m *"*n" 6-in., and 12-in. pipe, conducted by the Engineering Experiment Station of the University of Il]mois,(Btt//iiB 109. Table 6. p..38. Davis and Jordan*. . 349 1