Document e71kL5rge8X5gN62956rK6XDm

490 CHAPTER 21 1950 Guide Fig. 4. One-Pipe System Fig. 5. A Two-Pipe Direct Return System Fig. 6. A Two-Pipe Reversed Return System spectively. These figures would also illustrate forced circulation if a pump or circulator were shown in the return line at the boiler. 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 Table 3. Heat-cabbting Capacity op Type L Copper Tubing with Temperature Drop op 20 Deg* Nominal Tube Sizes j in. to 4 in., and Friction 60 to 7*0 milinches per foot. (A = Capacity, Mbh. B = Velocity, inches per second) (One milinch equals 0.001 in.) Nominal Tubs SiO, In. H , B HB A HB K .B 1B .A IK B IK ,2 5K 3 SK 4 B A .B A B A B. A B A B Mojncb Friction Loss per Foot or Tub* 720 | 600 480 - 10 9 8 27 24 . 21 20 18 , 35 30 25 36 30 26 37 34 30 46 40 42 38 33 94 48 45 82 39 185 169' 149 55 51. 45 300 270 62 ' 57 235 51 625 560 76 . 68 495 59 1130 1010 90- 80 890 69 1840 1650 1450 68 90 80 2750 2480 2170 no. 100 89 3900 3505 3100 120 .103 96 360 800 ^ 240 6.8 6.2 .5.4 ' 18 16J 14- 13.5 21 12, 19 . 10.8. 17 22.1 -20 17.8 24 ' 21 19. 34 81 28 27 24 21 70 63 56 34 80 25 125 .112 39 . & 100 30 200 180 . 160 43 89- 35. 420 375 335. 51. 47 42 750 680' 600 08 .49 47 1210 1100 9S0 66 59 52 1840 1650 1450 75 66 57 2600 3350 2090 . 83. 73 . 63 ISO 150 120 4.6 4 3.6 13 .11 10 9.8 15 13 7 12- 15 13.1 1U 17 15 13 23.2 20.5 18.1 v 19 17 14 47 42 23 . 19 37 17 84 75 66 , 25 22 19 134 120 80- 25 105 22 280 250 200. 36 32 27 .600 450 42 37 895 820 740 650 47 42 86 1210 1100 51 45 980 40.. 1760 1580;- 1390 55 49 44 90 . 75 3 2.8 8.5 8 6 5.4 10 9 9.9 0 11 10 15.3 13.9 12 11.5 32 28 14.5 13 56 50 17 15 90 81 19 17. 188 170 22 20 335 305 26 550 490 30 820 740 35 1180. 10S0 27 34 60 2.4 4.7 7.9 . 12.1 10 25 71 15 150 270 420 650 950 '" * Foj other^'temperature drops the pipe capacities may be changed correspondingly. For example, with temperature drop of50 deg the capacities shown in this table are to be multiplied by 1 A. Hot Water Heating Systems and Piping - 491 Table 4. Friction (in Milinches) op Central Circular Diaphragm Orifices in Unions (One milinch equals 0.001 in.) Duketer or Orifices ------------ ;-------(Lrcsxs) 2 I 3 Velocztt or Wins ra Pin in Inches feb Second <| 6 | 5 j lo" j 12 j lT Vs-in. Pipe 0.25 .0.30 0.35 0.40 0.45 0.50 0.55 1300 650 330 170 2900 1450 740 380 185 5000 2500 1300 660 330 155 75 11,300 5700 2900 1500 740 350 170 20,800 32,000 10,400 16,000 5200' 8000 2600 4000 1300 2000 620 970 300 480 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 3500 460 1000 1800 270 570 1000 160 330 580 190 330 200 120 1-in. Pipe 7800 4000 2300 1400 750 440 260 14,000 7200 4100 2300 1300 800 460 22,000 12,000 6400 3700 2200 1300 720 32,000 17,000 9300 5400 3000 1800 1100 37,000 21,000 12,000 7000 4200 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 1000 660 430 280 190 2250 1450 950 630 420 285 190 4000 2600 1700 1100 750 510 330 lt/r-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 1 '/2-in. Pipe 850 1900 3300 7400 13,000 21,000 30,000 600 1300 -2300 5400 8600 16,800 21,000 50,000 400 "850 1500 3600 7200 10,400 14,000 30,000 53,000 260 600 1100 . 2600 4400 7000 10,000 21,000 39,000 180 400 760 1800 3000 5000 7000 14.000 28,000 300 540 1200 2200 3200 5000 10,200 19,000 45,000 200 380 860 1600 2300 3000 7800 13,000 30,000 0.70 0.80 0.90 1.00 1.10 1.20 1.30 890 470 . 255 160 1850 975 560 340 214 3500 1800 1000 610 '375 195 S-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 . The losses of head for the orifices in the IK-tn. 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 u a lunrtion of the ratio of tlm diameter of the pipe to that of the orifice. This had been found to be S!S5S?lUyAni^.in `he tests to determine the losses of head in orifices In H-io.. 1-in.. and lM-in. pipe, con- 3 hy Che Texas Engineering Experiment Station, and also in the tests to determine the losses of bead at Illinois, i(Biwullbetin 109. Tabi?le"1?6-. Bp`.I38;.c?D?adv"iscta'dnd,byJothrdeaEn)n.gineering Experiment Station of the University