Document KJQ3o7k1oJmbg7D3v5ao7eBvo

American Society of Heating and Ventilating Engineers Guide, 1934 a 2-in. pipe for Section KA. The pipe sires for the remaining eight sections and for the radiator connections can be selected in the same manner and recorded on the pipe diagram as shown. The circulating pump for the system should be one which has its highest efficiency when it is delivering 13.8 gpm against a head of 2 ft. If a number of heating systems are to be designed for similar conditions, i.e., for a total friction head of 2 ft and a temperature drop through the radiators of 10 deg when the maximum quantity of heat is being delivered to the building, a table such as Table 2 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 BC and JK, each supplying 54 Mbh, the equivalent pipe length of the system is 227 ft. In the table the length shown nearest to this length is 200 ft. In the 200-ft column, a l]/2-in. pipe is slightly too small and a 2-in. pipe is too large. The lj^-in. pipe will therefore be selected. For Sections CZ) and IJ, supplying 42 Mbh,'a 134'in pipe is too small and a 134-in- P'Pe is too large, so 134 in. will be selected for the flow and 134 in. for the return line. For larger 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 deg* i Pipe - Size (Inches) 2 Equivalent Length op Pipe (Fserb) 63 * 5 8'1 Equivalent Total Length op Pipe in Feet in Longest Circuit 9 350 | too 150 200 250 500 400 Unit Friction Head, in Muinches 240 160 ,120 96 80 69 60 Ai 6.2 15 4.8 12 4-1 10 3.4 2.9 98 2.6 2.4 7.5 7 %2 13.2 10.3 8.6 7.3 6.2 6.0 5.5 18 14 12 11 10 9 8.5 l . 2.3 25.0 22 19.2 17 16.3 15 14-4 13 12.5 12 12.0 11 u.i 10.5 f'A 3.0 52.8 40.8 34.8 31.2 27.k 26.4 24.0 27 21 18 16 15 14 13 ia 3.5 79.2 60.7 51.2 45.6 40.8 40.0 36.0 30 23 20 18 16 15 14 2 4.0 153.8 120.0 104.0 93.5 86.4 81.5 73.8 36 28 24 22 20 18 17 2A 6.0 250.0 192.0 164-5 149.0 139.2 185.8 122.5 41 32 28 25 22 21 19 3 6.5 444-0 348.0 294.0 270.0 254.0 24O.O 223.0 48 37 32 29 26 24 22 por oiner lempeiamie uiups vuc capaviuca u< pipca **>_ vv ----------------------------------------for a temperature drop of 30 deg, the capacities shown in this table are to be multiplied by 3. The velocities remain unchanged. ^Approximate length of pipe in feet equivalent to one elbow in friction head. This value varies with the velocity. 476 Chapter 33--Hot Water Heating Systems systems, it will be economical to operate with higher friction heads, and tables may be prepared similar to Tables 3 and 4, which are based on total friction heads of 6 and 18 ft, respectively. Example 2. Design a direct return two-pipe forced circulation system for the layout shown in Fig. 5. For this system the length of the pipe line from the boiler to the highest radiator on the farthest riser and back to the boiler is about 250 ft. There are about 16 elbow equivalents having an equivalent pipe length of about 50 ft, so the total equivalent pipe length is about 300 ft. Solution. The same pipe size tables may be used as those developed lor the reversed return system of Fig. 3. Since this system is somewhat larger than that shown in Fig. 3, Table 3 which provides for a friction head of 6 ft may be used instead of Table 2 which provides for a friction head of only 2 ft. Referring to the column for an equivalent total length of 300 ft for Sections A B and KA, each supplying 117.6 Mbh, it will be found that a 1 J4-in. pipe is too small and a 2-in. pipe is too large. Consequently, a lJ4-in. pipe is selected for the flow line AB, and a 2-in. pipe for the return line KA. For Sections BC and JK, each supplying 88 Mbh, a lj^-in. pipe is only slightly too small and it is selected. The remaining pipe sizes are selected in a similar manner and recorded in Fig. 5. For a temperature drop of 10 deg, 24.5 gpm of water must be circulated. The pump to select is one which has its highest efficiency when it is delivering 24.5 gpm against a 6-ft head. i able <s. capacities of fipes in Mbh (1000 Btu per Hour) and Velocities 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 deg* 1|2 Pips Size (Inches) Equivalent Length op Pipe (FEETb) 3 4 5| 61 7 8 CirEquivalent Total Lenqth op Pipe in Feet in Lonqbst 2UIT 200 | 300 | 400 | 600 | 800 | 1000 360 Unit Friction Head, in Muinches 240 180 120 90 / 72 A1 7-4 18 6.0 15 5.0 13 3.8 10 3.4 3.1 9 7.5 2 15.8 12.7 10.8 8.4 7.7 6.7 22 18 16 12 11 9 1 2.5 30.0 24.0 20.4 15.8 13.9 12.5 27 22 19 15 13 11 1M 3.3 64.8 52.5 . 44-4 33.6 30.0 26.8 33 26 23 18 16 14 1A 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 "4A 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 58 48 42 32 27 24 "For other temperature drops the capacities of pipes are to be changed correspondingly. For example, for a temperature drop of 3Q..deg, the capacities shown in this table are to be multiplied by 3. The velocities remain unchanged. ^Approximate length of pipe in feet equivalent to one elbow in friction head. This value varies with the velocity. 477 NI