Document OXEbpQbK2Q44MJnbeVpQvEY1

HEATING VENTILATING AIR CONDITIONING GUIDE 1941 Table 5. Friction Heads (in Milinches) of Central Circular Diaphragm Orifices in Unions Du METIS or Velocity or Water in Pipe in Feet pbb Minute Orifices 15(Inches) 10 20 30 40 50 60 %-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 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 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 750 510 330 114-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 o lt: 00 850 1900 3300 600 1300 2300 400 1500 260 600 1100 180 400 760 300 540 200 380 iy^-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 50,000 14,000 30,000 10,000 21,000 7000 14,000 5000- 10,200 3000 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 3-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 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 bead 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 %~m-> 1-in., and lj-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). 302 CHAPTER 15. HOT WATER HEATINC SYSTEMS AND PIPING and which is equipped with 7 radiators, all radiators dissipating equal quantities of heat. The mean temperature of the water in the radiators will be reduced 5 F for each successive radiator. If the mean temperature of the water in the first radiator is 200 F, the mean temperature of the water in the seventh radiator will be 170 F, and, according to Table 4, Chapter 12, the heat dissipation of these two radiators will be to each other as 1.62 is to 1.15, or as 140 is to 100, and therefore if the last radiator is to dissipate as much heat as the first, its size must be 40 per cent larger. Example i. Design a two-pipe, direct return, gravity circulation system for the lay out shown in Fig. 8. Assume that the main circuit from the boiler to the farthest flow riser and from the farthest return riser back to the boiler consists of 160 ft of pipe, 6 elbows, and 1 boiler. Solution. Replacing the boiler by 3 elbow equivalents and assuming that the largest size of the main will be about 3 in., the total equivalent length of the main will be 160 plus 45, or 205 ft. Assuming that the center of the boiler will be about 4 ft lower than the . horizontal portion of the main, and that the temperature drop will be 35 F for the Fig. 8. A Two-Pipe Direct Return Gravity Circulation System system, the pressure head caused by the difference in weight between the water in the flow and return risers joining the mains to the boiler will be about 0.6 in. of water. Table 6 may be used to determine the size of the main as follows: .Refer to Column 8 and note that for Sections AB and IA, which supply 105.6 Mbh, a 3-in. pipe is too large, and a 2j^-in. pipe is too small; hence, select 2% in. rather than 3 in. as noted in Fig. 8 for Section AB and 3 in. for Section IA. For Sections BC and HI, which supply 76,8 Mbh, a 2J4-iri. pipe is almost exactly the correct size and is selected for both sections. Tables 7 and 8 are based on the assumption that the boiler pressure head must be equal to the friction head in the mains, and that the several radiator pressure heads must be equal to the respective radiator and riser friction heads. To design the radiator risers, use Table 7 and begin with the set nearest the boiler. The first floor risers must supply 28.8 Mbh. According to the table, ,lM*in. flow and return risers will supply 26.0 Mbh; if the return riser is increased to 1M in., the capacity will be increased to 34.0 Mbh. This is considerably larger than necessary, and 1 M;>n. flow and return risers are selected. However, it must be remembered that the riser branches, which are the connections from the flow and return mains to the flow and return risers, are to be one size larger than the risers. The second floor risers must supply 19.2 Mbh. According to the table, the capacity of 1 in. flow and return risers is.20.0 Mbh, and that size is selected. The third floor risers must supply 9.6 Mbh. If a M*m. flow and a J-in. return riser ' 303