Document RabBQjZgE58g0eV0bGd9V6jJB

,460 CHAPTER 24 1948 Cuidi [G3, [EH, [ED, Fig. 4. One-Pipe System ". Fig. 5. A Two-Pipe Fig. 6. A Two-Pipe Direct Return System Reversed Return System One-pipe gravity systems require very precise design owing to the small circulating head available. Also, circulation in them is slow, and tem perature drop is large-toward the end of the main, and consequently these systems are usually considered impractical. One-pipe forced systems compared with gravity systems provide more rapid circulation with consequent smaller temperature drop in mains and more uniform water temperature in all radiators, and are therefore preferred. Special flow and return fittings are available for improving the Circulation to risers. Two-pipe systems have separate flow and return mains. If the return main is direct as shown in Fig. 5 the radiator at the end of the system has the longest supply and longest return piping. The lengths of circuits to the various radiators may be.equalized by using a reversed return main, (see Fig. 6). In some cases reversed return mains require no more piping than direct return systems. ' Table 3. Heat-carrying Capacity of Type L Copper Tubing with Temperature Drop of 20 Deg3 Nominal Tube Sizes % in. to 4 *n., and Friction 60 to 720 milinches per foot. (A Capacity, Mbh. B = Velocity, inches per second') (One milinch equals 0.001 in.) i SlZB, Ilf. 720 600 A . 10 9 A B 27 24 A 20 18 B 35 30 A A B 36 30 37 34 A HB 61 46 42 88 A 104 94 1 B 48 45 A IK B 185 169 65 51 A 1M B 300 270 62 67 A 625 660 2 B 76 68 A .1130 1010 2H B 90 80 A 1840 1650 3. B 98 - 90 A 2750 ' 2480 3M B 110 100 A 3900 3505 4. B 120 108 480 8 21 16 25 26 30 40 33 82 39 149 45 235 51 495 69 890 69 1450 80 2170 89 8100 .96 Mzukcb'Fbictioii Loss pkb Foot or Tubs 360 300 240 180 6.8 6^ 18 16.5 5.4 14 4.6 13 13.5 12 10.8 21 19 17 9 15 22.1 20 17.8 15 24 21 19 17 34 31 28 23.2 27 24 21 19 70 63 56 47 34 30 25 22 125 112 ioo 84 39 35 30 . 25 200 180 160 134 43 39 .35 30 420 375 335- 280 61 47 42 .36 760 680 600 500 58 49 47 42 1210 1100 66 59 980 52 820 47 1840 1650 1450 1210 75 66 57 51 2600 2350 2090 ' 1760 83. .73 63 55 150 120 4 3.6 11 10 87 13 12 13j 11.8 15 13 20J> 18.1 17 14 42 37 19 17 75 . 66 22 19 120 105 25 22 250 200 32 27 450 395 37 33 740 650 42 36 1100 45 980 40 1580 1390 49 .44 90 75 60 3 25 . 2.4 85 8 7 : 6 5.4 4.7 10 9 8 9.9 9 7.9 11 10 9 . 15.3 135 12J .12 115 10 32 28 25 145 13 12 56 50. 44 : 17 15 13 90 81 71 19 17 15 188 22 . 335 26 650 30 170 150 20 . 18. 305 270 23 21 490 420 27 23 820 740 650 35 30 26 1180 1080 37 34 950 29.. "For other temperature drops the pipe capacities may be changed correspondingly. Forexample, with . temperature drop of 30 deg. the capacities shown in this table are to be multiplied by 1.5.' ' Hot Water Heating Systems and Piping 461 Table 4. Friction (in Milinches) of Central Circular Diaphragm Orifices in Unions {One milinch equals 0.001 in.) Duhstzb or . Obotces (Inches)-. * 3 Velocity or Water in Pips in Inches per Second 4 | 6 | 8 | 10 | 12 | IS Pipe 24: l M 0.25 0.30 0.35 0.40 0.45 0.50 0.55 1300 650 ,330 170 2900 1450 .740 380' 185 5000 11,300 2500 5700 1300 2900 660 1500 330' 740 155 350 75 170 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 0.35 0.40 0.45 0.50 0.55 0.60 0.65 900 2000 460 1000 , 270: .570 160 330 190 3500 1800 1000 580 330 200 120 1-in. Pipe 7800 4000 2300 1400 750 440 260 14,000 7200 4100 2300 .1300 800 460 22,000 32,000 12,000 17,000: 37,000 6400 9300 21,000 3700 5400 12,000 2200 3000 7000 1300, 1800 4200 720 1100 2400 65,000 37,000 22,000 50,000 13,000 28.000 7400 17,000 4300 10,000 0.45 0.50 , 0.55 0.60 0.65 0.70 ` 0.75 iobo 660 430 < 280 190 2250 .4000 1450 2600 950 1700 630 1100 420 :750 285 510 190 330 1 Yf-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 i8;ooo 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 V/rin. Pipe 7400 5400 3600 2600 1800 1200 860 13,000 21,000 8600 16,800 7200 10,400 4400 . 7000 3000 . 5000 2200 3200 1600 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 8-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 9500 5800 3700 1910 1375 37,000 20,500 12,500 7900 4200 3100 38,000 23,000 49,000 14,000 30,000 8100 16,800 4400 8850 Note.--The losses of head for the orifices in the lK-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 is a function of the ratio of the diameter of the pipe to that of the orifice. This had been found to'be practically true in the tests to determine the losses of head in orifices in H-in,, 1-in., and lK-in. pipe, con ducted by the Texas Engineering Experiment Station, and also in the tests to determine the losses of- head in orifices in 4-in., 6-in., and 12-in. pipe, conducted by the Engineering Experiment Station of the University of Illinois, (Bulletin 109. Table 6, p. 38, Davis and Jordan).