Document X7wvkEorod4bQe6QpqwZK1DmB

Heating Ventilating Air Conditioning Guide 1938 Table 3. Iron Elbow Equivalents3 1 90-deg elbow....... ...................................................................... ........ .......... .............. l.o 1 45-deg elbow....... .......................... 1.............................. ............................... .............. 0.7 1 90-deg long turn elbow......................................................................................... .... 0.5 1 open return bend--..................................................................................................... 1.0 1 open gate valve.... .. ........................................... ...... .......... ............ ............. ............ 0.5 1 open globe valve.............................................. ....... ................................................. 12.0 1 angle radiator valve........................................ .......................................................... 2.0 1 radiator......................................................................... ......................... ................... 3.0 1 boiler or heater.......................................... ...................................................... ......... 3.0 1 tee................................................. .......................... .............................................. (Noteb) The loss of head in one elbow can be expressed in terms of the' velocity head by the formula: where h 2g h -- the loss of head in feet, v -- the velocity of approach in feet per second, and 2g = 64.4 ft per second per second. (1) bThe loss of head in tees when water is diverted at right angles through a branch of the tee varies with the per cent diverted. When the water diverted is less than 60 per cent of that approaching the tee. the loss of head, in elbow equivalents, may be expressed as follows: where K ho -- the loss of head in elbow equivalents, vi = the velocity of approach, -- the velocity of water diverted at right angles. (2) Values in elbow equivalents for the most common percentages of water diverted in a lxlxl-in. tee are as follows: 25 per cent.......................... ............. ........... ................................... 26.0 33 per cent...... ...........................................................:...................... 9.0 50 per cent............................................................. .......................... 4.0 100 per cent.................................................................. ......... ........... 1.8 Table 4. Copper Elbow Equivalents3 1 90-deg elbow..... ...............-........................................................................................ 1.0 1 45-deg elbow................................................ ............. ............................................. . 0.7 1 90-deg long turn elbow............... !.............................................................................. 0.5 1 open return bend._....................................................................i.............................. 1.0 1 open gate valve..... .......... ... .................;............................................................. ...... 0.7 1 open globe valve......................................................................................................... 17.0 1 radiator valve............................................................................................................ 3.0 1 radiator.......... ......................................................... ......................................... *........ 4.0 1 boiler or heater.......................................................................................................... 4.0 1 tee........ ......... .................... -............1.................................................................. _.(Noteb) The loss of head in an elbow can be expressed in terms of the velocity head by the formula: where h = loss of head in milinches. v in. per second per second). r. 0.7 o* *" "2 velocity in inches per second, and g (3) acceleration of gravity (386 t>The loss of head in copper tees: where (n1 + w) N - 0.7 pj* (4) N = number of elbows that would cause the same loss as the tee when the velocity of water in the connecting pipe is vu v\ = velocity of the water in the pipe entering the tee, and p = velocity of the water in the pipe discharging from the tee at right angles to n. Values in elbow equivalents for most common percentages of water diverted in a 1 in. x 1 in. tee. 100 per cent_______________________________________________ 1.2 50 per centJ----------------------------------------- ----- ------------------- 4.0 30 per centi___________________________________ 16.0 25 per cent.20.0 340 i- i? Chapter 17. Hot Water Heating Systems and Piping The pipe sizes may be selected from Fig. 4 or from Table 1 which has been derived from Fig. 4. Size the supply main of the longest circuit first. Section AB carries 98 Mbh. From Fig. 4 it will be noted that at 240 milinches per foot, a IK in. pipe carries 98 Mbh. Therefore, use 1M in. pipe in Section AB. Section BO carries 40 Mbh. A 1 in. pipe carries 48 Mbh at 240 milinches per foot. Use a 1 in. pipe. Section OP carries 20 Mbh and this will require % in. pipe. Section PQ carries 10 Mbh and requires Yi in. pipe. To size the return start from the boiler and proceed backwards. Section IR carries 40 Mbh and from Fig. 4 a 1 in. pipe is required. Section RS carries 30 Mbh which is only slightly over the capacity of a % in. pipe, so use K in. Section ST carries 20 Mbh and requires a % in. pipe. The radiator branches are determined in the same manner. It is evident from the chart that it is impossible to maintain a constant friction loss per foot and therefore as the delivery varies there will be a change in the desired friction loss per foot of pipe. It is desirable to check the various circuits so that if the variation from the calculated resistance is too great, it may be compensated by adding additional resistance at the proper point. This may be accomplished by sizing the short circuits by the procedure previously outlined. Prepare a chart such as Table 5 to be used in calculating the resistance of each circuit. Section AB carries 98 Mbh with a unit head of 240 milinches per foot. In section AB there are 37 ft of pipe and IK in. elbow. At 240 milinches per foot this is equivalent to 9600 milinches total loss in this section. Section BC carries 58 Mbh with a length of 2 ft and 4 elbows. The unit loss in this section is 90 milinches per foot. Loss in this section is then 1080 milinches. Section CD carries 38 Mbh and has 16 ft of pipe and 1 elbow. The unit loss in 1 in. pipe is 155 milinches. The loss in this section is 2790 milinches. The balance of the supply main and the return main are handled in a similar manner. Table 5. Piping Check Chart Load, Mbh Pipe Length Ft Elbows Pipe Size In. Unit Head Milinches per Ft Friction Milinches Total Loss Milinches ` Supply Main AB 98 BC 58 CD 38 DE 23 EF 11 fg 4 37 2 16 1 4 1 IX IX 1 240 9600 9,600 90 1080 10,680 155 2790 13,470 9 0 X 220 1980 15,450 12 0 X 240 2880 18,330 16 1 X 50 850 19,180 Return Main HI 98 U 58 JK 54 KL 47 LM 35 MN 20 5 5 IX 240 4320 11 1 IX 90 1260 16 1 1 300 5400 11 0 1 230 2530 9 01 140 1260 15 1 X 170 2890 Radiator Circuits CN 20 DM 15 Supply Return Supply Return FK 7 GJ 4 Return Supply Return Supply Return 3 4 3 4 14 15 3 4 8 9 13 2 19 17 20 20 19 17 5 17 X X X X x X u X x X 170 3910 170 1190 5,100 420 9250 96 2880 12,130 270 9180 270 9450 18.630 100 2200 100 2100 4,300 50 650 50 1300 1,950 341