Document QXYLgXDy8LL8R4Q3ZKrbQvkok

American Society of Heating and Ventilating Engineers Guide, 1932 Table 6. Mains, Capacities of Mains in Equivalent. Square Feet of Heating Surface3, and in 1000 Btu, for One-Pipe and for Two-Pipe Direct Return Gravity. Circulation Systems with a Total Friction Head of 0.6 In., a Temperature Drop of 35 Deg, and when the Mains are 4 Ft,Above the Center of the Boiler 12 Pipe Size (Inches) Equivalent Lenoth op Pipe (FEBTb) 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 Equivalent Total Length op Pipe in Feet in Longest Circuit 75 | 100 | 125 | 150 | 175 | 200 | 250 ! 300 | 350 . Unit Friction Head, in Milinches 8.0 6.0 4.8 4.0 3.4 3.0 2.4 2.0 1.7 VA 3.0 179 156 137 125 112 104 92 84 78 43.0 37.5 33.0 30.0 37.0 35.0 33.3 30.3 18.7 2 4.0 356 300 263 237 212 200 175 158 146 83.0 73,0 63.0 57.0 51.0 48.0 43.0 38.0 35.0 2K 4.5 583 480 417 375 338 314 280 254 233 140.0 115.0 100.0 90.0 81.5 75.4 67.3 61.0 56.0 3 5.0 975 850 730 667 576 555 458 446 417 334.0 304.0 175.5 160.0 143.0 133.0 110.0 107.5 100.0 m 5.5 1446 1250 1080 985 890 834 738 667 608 347.0 300.0 360.0 336.0 314-0 300.0 177.0 160.0 146.0 4 6,0 2040 1760 1540 1390 1240 1160 1040 930 853 490.0 433.0 370.0 334-0 397.0 378.0 348.0 333.0 305.0 Based on 240 Btu per square foot. ^Approximate length of pipe in feet equivalent .to one elbow in friction head. This value varies with the velocity. Table 7. Risers3, Maximum Capacities of Risers in Equivalent Square Feet of Heating Surface**, and in 1000 Btu, and Velocities of Water in Pipes in Inches Per Second for One-Pipe and for Two-Pipe Direct Return Gravity Circulation Systems with a Drop of 35 Deg Through Each Radiator Pipe Size (Inches) Flow Return Equivalent Length op Pipe (FebtcI) Sq Ft 1st Floorc 2nd Floor 1000 Btu VeL(FtperSec.)e Flow Return Sq Ft lOOO Btu 3rd and 4th Floors Sq Ft 1000 Btu AA AA H% H1 11 1 IK IK IK 1A 1A 1A 1A 1.0 21 5 26 6.3 27 6.4 33 8.0 1.5 37 9 2.3 2.3 42 10.1 58 14-0 50 13 3.2 2.0 53 13.8 71 17.1 2.0 75 18 2.5 2.5 83 30 . 108 36.0 88 31 3.0 2.0 105 35.3 142 34 3.0 109 36 3.0 3.0 179 43 229 55 142 34 4.0 2.5 3.5 200 48 3.0 3.0 This table is based on pressure heads of 450, 1800, 3150 and 4500 respectively, for the first, second, third, and fourth floor radiators, and on friction heads of 200 miiinches for the first floor radiators and con nections, and 700 miiinches for all other radiators and their connections. bBased on 240 Btu per square foot. -- cThe riser branches, the piping which connects the risers to the mains, are to be one size larger than the ^Approximate length of pipes in feet equivalent to one elbow in friction head. This value varies with the velocity. Velocities apply to the riser branches. 124 Chapter 8--Hot Water Heating Systems and Pipe Sizes Table 8. Radiator Connections, Maximum Capacities of Radiator Connections in Equivalent Square Feet of Heating Surface3, and in 1000 Btu, for One-Pipe and for Two-Pipe Direct Return Gravity Circulation Systems with a Temperature Drop of 35 Deg Through Each Radiator Pipe Size Flow Return AA AK MK K1 11 1 IK IK IK Equivalent Length op Pipe (FeETb) 1.0 1.5 2.0 3.0 1st Floor Sq Ft 17 22 29 38 52 73 97 1000 Btu 4-1 5.3 7.0 9.1 13.5 17.5 33.3 2nd, 3rd and 4th Floors Sq Ft 25 31 43 54 74 97 138 1000 Btu 5.9 7.5 10.5 13.0 17.8 33.3 33.3 Based on 240 Btu per square foot. ^Approximate length of pipe in feet equivalent to one elbow in friction head. This value varies with the velocity. To develop a rule for determining radiator sizes, assume a system similar to that of Fig. 6, in which the total temperature drop is to be 35 deg 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 deg for eatch successive radiator. If the mean temperature of the water in the first radiator is 200 F, the mean tem perature of the water in the seventh radiator will be 170 F, and, according to Table 3, Chapter 6, the heat dissipation of these two radiators will be to each other as 868 is to 617, 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. The following rule may therefore be formulated for deter mining radiator sizes for one-pipe hot water heating systems having two-pipe risers and a total temperature drop of 35 deg: Determine the radiator sizes in the usual manner. If the mean tempera ture of the water in the radiator is 215 F, select the same size radiator that would be selected for steam at this temperature. If the mean temperature of the water is to be less than 215 F, increase the amount of heating surface, above that required for steam, as explained in Chapter 6. Use the calcu lated sizes for the radiators on the first set of risers; increase the sizes of the radiators on the last set of risers Ifl per cent; those on the middle set of risers, 20 per cent, and those on the remaining risers proportionally. Applying.this rule to the five radiators of the system shown in Fig. 6, the actual sizes will be found to be 50, 55, 90, 65 and 70 sq ft of equivalent heating surface, instead of the nominal sizes of 50, 50, 75, 50 and 50 sq ft. Example 4. Design a two-pipe, direct return, gravity circulation system for the lay out shown in Fig. 7. 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 deg for the system, the pressure head caused by the difference in weight between the water in the 125