Document yrOjVKZmk4dwpY6d7pdqZmw5d

HEATING VENTILATING AIR CONDITIONING GUIDE 1940 Table 3. Iron and Copper Elbow Equivalents Fitting Elbow, 90-dee..................... Elbow, 45-dee..................... Elbow, 90-dee lone turn............ Open return band...................... Open eate valve................. ' Open elobe valve. Angle radiator valve. .............. Radiator.... .............. Boiler or heater.............. Tee, per cent flowing through branch: 100...... .................... 50. ............................ 25............................... ;......... ......... Iron Pipe 07 0.5 1.0 0.5 12.0 2.0 30 3.0 4.0 Copper Tubing 1.0 and this will require f^-in. pipe. Section PQ carries 10 Mbh. and requires *4 in. pipe. To size the return start from the boiler and proceed backwards. Section IR carries 40 Mbh and from Fig. 3 a 1-in. pipe is required. Section RS carries 30 Mbh which is only slightly over the capacity of a ^-in. pipe, so use % in. Section ST carries 20 Mbh and requires a 54-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. Table 4. Piping Check Chart Load. Mbh Supply Mein Pipe Length Ft Elbows Pipe Size In. Unit Head Milinches per Ft ' Friction Milinches Total Loss Milinches AB 98 BC 58 CD 38 DE 23 EF 11 FG 4 Return Main 37 2 9 1 4 0 0 1 IX 240 9600 9.600 m 1 90 1080 10.680 155 2790 13.470 x f? 220 1980 15.450 240 2880 18.330 X 50 850 19.180 HI 98 IJ 58 JK 54 KL 47 LM 35 MN 20 Radiator Circuits 5 11 16 11 9 15 5 1 1 0 0 1 IX 240 4320 4,320 1H 90 1260 5,580 1 300 5400 10,880 1 230 2530 13.410 1 X 140 1260 14,670 170 2890 17.560 CN 20 DM 15 EL 12 FK 7 GJ 4 Supply . Return Supply ' Return Supply 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 H X X X X X 8.' X X 170 170 420 96 270 270 100 100 50 50 3910 1190 9250 2880 9180 9450 2200 2100 650 1300 5,100 12,130 18,630 4.300 1,950 318 CHAPTER 17. HOT WATER HEATING SYSTEMS AND PIPING It is desirable to check the various circuits so that if the variation from the calculated "stance is too great, it may be compensated by adding additional resistance at the nro'per point. This may be accomplished by sizing the short circuits by the procedure Previously outlined. Prepare a chart such as Table 4 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 114 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 I-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. The radiator circuits are then checked. The 20 Mbh radiator on this circuit has 3 ft of supply pipe and 13 elbow equivalents while the return is composed of 4 ft and 2 elbows. The unit loss in % in. pipe at this delivery is 170 milinches per foot. The total loss in the supply is 3910 milinches. The loss in the return is 1190. Total loss in the radiator circuit is 5100 milinches. Check each radiator circuit in a similar manner. The total calculated loss for the longest circuit was determined as 60,000 milinches. The maximum loss in the short circuit is 18,630 plus 13,410 plus 15,450 or a total of Fig. 5. A Forced Circulation Direct Return System 47,490 milinches. This difference is caused by the variation in length of the two circuits and may be corrected by using a flow control in the return main to supply the additional resistance or by introducing resistance into each separate circuit to compensate for the difference. A10 per cent variation will cause no complication as the flow from the various pipes will not exactly follow the curves of Fig. 3 any closer than this value. Example B. Design a two-pipe direct return forced circulation system with copper tubing and fittings for the piping layout as detailed in Fig. 5, based on a 20 F tempera ture drop through the radiation. The piping circuit from the boiler to the highest radiator on the farthest riser and back to the boiler is 250 ft of pipe. There are about 16 elbow equivalents having an equivalent pipe length of about 50 ft, so that the total equivalent pipe length is 300 ft. Assume that a circulator is available which will provide a pressure head of 6 ft. Solulion. Refer to Table 2, which indicates the total equivalent lengths for pressure heads from 2 to 12 ft. With a circulator having a 6 ft pressure head and a system with a total equivalent length of 300 ft, the piping system will be designed on a basis of 240 mitinch. Checking the piping diagram it will be noted that sections AB and KA, both supply 117.6 Mbh, Referring to the 240 milinch column of Table 2,1% in. is shown to be the necessary pipe size. Sections BC and JK carry 88.8 Mbh and require lj^ in. tubing. Sections CD and IJ supply 67.2 Mbh and require 1J4 in. tubing. Sections DE and HI supply 43.2 Mbh, which requires 1 in. tubing. Sections EF and GH with a load of 14.4 Mbh require % in. tubing. The risers are pipe sized in a similar manner. To secure proper distribution of hot 319