Document qZLZorBDKp1p3mpygpkX156q

American Society of Heating and Ventilating Engineers Guide, 1936 branch BC and 57 in BJ. It will be noted that 28 Mbh is slightly over the capacity of a % in. pipe, therefore use a V in. pipe in BC and a 1 in. in Section HR. Section CD should have a capacity for 23 Mbh, therefore use a V in. pipe in CD and GH. A capacity of 20 Mbh is not sufficiently under the capacity of a V in. pipe to warrant the use of a V in. pipe, so use V in. in Sections DE and FG. The radiator branches are sized ac cordingly,with Vi in. up to 11,000 Btu (11 Mbh) and V in. up to 25,000 Btu (25 Mbh). Due to the difference in the equivalent lengths of each circuit, a static head of 6 in. on the pump would produce a greater velocity in the shortest branch than in the longer branch and consequently a higher friction loss per ft. This variation is usually a negligi ble factor in most installations and can usually be overlooked. Should the variation in friction head be sufficient to allow the use of smaller pipes, this factor should be taken into consideration. For purposes of illustration in this example, assume that Section AB is 4 ft, and then 4 X 240 = 960 milinches. 71,800 -- 960 = 70,840 milinches. 70,840 divided by 231 (total equivalent length of short branch) = 306 milinches per ft which is ' 66 milinches per ft more than is available in the longer circuit. Therefore approximately 12 per cent more capacity is available in the pipes which will change the pipe size only a slight amount. If it is necessary to correct this variation, generally a stop cock may be placed in the return line of the short branch and adjusted after complete installation. However, if the variation be of sufficient magnitude, the pipes in the shorter branch should be sized accordingly. In this case the pipe size should be selected according to a frictional loss of 240 milinches per ft. Due to the fact that Section BJ requires a capacity of 57 Mbh, which is slightly over 1 in., use a 1 in. pipe in BJ and QR. Section JK has a Table 2. Capacities of Pipes in Mbh (1000 Btu per Hour) and Velocities of Water, in Pipes in Inches, per Second for Forced Circulation Systems with a Total Friction Head of 2 ft and for a Maximum Temperature Drop of 10 Fa 1 Pipe Size (Inches) 2 Equivalent Length op Pipe (FEBTb) 63 4 5 7 89 Equivalent Total Length op Pipe in Feet in Longest Circuit 100 . 150 200 250 300- 350 400' Unit Friction Head, in Milinches 240 160 120 96 80 69 60 V1 6.2 15 4.8 12 4.1. 10 .3.4 9 2.9 2.6 8. 7.5 2.4 7 V 2' 13.2 10.3 8.6 ' - 7.3 6.2 6.0 6.5 18 14 12 11 10 9 8.5 i 2.3 26.0 19.2 16.3 - U:4 12.5 12.0 11.1 22 17 ... 15 1? 12 11 10,5 IV 3.0 52.8 40.8 34.8 . 31 .2 27.8 26.4 24.0 27 21 v18- 16 15 14 13 i.H 3.5 79:2 60.7 51.2 46.6 40.8 40.0 36.0 30 23 20 18 16 15 14 2 4.0 158.8 120:0 104.0 93.5 86.4 81.6 73.8 36 28 24 22 20 18 17 m '6:0 250.0 192.0 164.5 149.0 139.2 135.8 122.5 41 32 28 25 22 21 19 3 6.5 444-0 348.0 294.0 270.0 254.0 240.0 223.0 48 37 32 29 26 24 22 For other temperature drops the capacities of pipes are to be changed correspondingly. For example, for a temperature drop'of 30 F, the capacities shown in this table are to be multiplied by 3. The velocitiesremain unchanged.. . bApproximate length of pipe in feet equivalent to one elbow in friction head. This value varies with the velocity. 592 Chapter 33--Hot Water Heating Systems and Piping load of 47 Mbh which is approximately 1 in. Therefore use 1 in. in JK and PQ. KL carries 35 Mbh which is approximately half-way between V and 1 in. Use % in. in KL and 1 in. in OP. Section LM requires a capacity of 20 Mbh, therefore use V in. in LM and NO. Size radiator branches as previously described. Many times a Vi in. pipe will prove to be too large, but at the present time there seems to be a slight aversion in practice against the use of pipes of smaller sizes, especially for hot water installations. If a number of heating systems are to be designed for similar conditions, i.e., for a total friction head of 6 ft and a temperature drop through the radiators of 20 F when the maximum quantity of heat is being delivered to the building, a table such as Table 3 may be prepared from the data of Fig. 4. Having this table, the pipe sizes for the system of Example 1 can be easily selected; For example, for Sections AB and i?/, each supplying 85 Mbh, the equivalent pipe length of the system is 299 ft. In the table the length shown nearest to this length is 300 ft,. In the 300-ft column, a 1-in, pipe is too small and a lj^-in. pipe is too large. The lj^-in. pipe will therefore be selected. For other systems, it will be economical to operate with different friction heads, and tables may be prepared similar to Tables 2 and 4, which are based on total friction heads of 2 and 18 ft, respectively. ... Table 3. capacities of riPEs in Mbh (100U Btu per Hour), and Velocities of Water in Pipes in Inches per. Second for Forced Circulation Systems with a Total Friction Head of 6 ft and for a Maximum Temperature Drop, of 10 Fa 1 2 3: 4 5- | 6 r 18 Pipe Size (Inches) Equivalent Length op Pipe (Feet*>) Equivalent Total Length op Pipe in Feet in Longest Circuit 200 | 300 | 400 | 000 800 |...1000 360 . .Unit Friction Head, in Milinches 240 . iso 120 90 72 V' 1 7.4 18 6.0. 15 5.0 13 3.8 : 10 3.4 3.1 9 7.5 V2 15.8 22 12.7 j 18 10,8 8-4 16 \ 12 7.7 11 6.7 9 1 2.5 80.0 24.0- 20.4 15.8 13.9 12.5 27 22 19 , 15 13 11 IV' 3.3 64.8 33 52.51 26 44-4 23 33.6 18 30.0 . 26.8 16 14 iv 4.0 96.0 76.8 64.8 50.1 44-7 40.8 37 31 26 20 18 15 2 5.0 192.0 153.0: 130:0 .100.1 90.0 78.0 44 36 30 24 21 18 IV 6.0 300.0 244.0 206.0 161.0 144-0 . 130.0 50 41 35 26 24 21 3 7.5 550.0 436.0 368.0 287.0 249.0 228.0 *8 42 .. 32 27 24 iemPerauire; arops tne capacities of pipes are to be changed correspondingly. For example, reirmin^ncl^n^d^^^ * ^ ^ capacities shown in this table are tp.be multiplied by 3. The velodties the'ireiority"1*3^ pipe in ^eet equivalent to one elbow fa friction head. This value varies with 593 'i"-'