Document 6wbZme63VXJqaDxyR9pJJm8Gm

American Society of Heating and Ventilating Engineers Guide, 1934 Example 1. Assume that in a normal building, such as a residential hotel or an apart ment house, there are 50 flush valve water-closets, 50 lavatories, 50 sinks and 50 baths, and that it is desired to determine the maximum probable flow in a line supplying all of these fixtures with both hot and cold water. Fig. 1 shows a maximum probable use for 50 water closets of about 8 per cent and for 150 ordinary fixtures, of about 31 per cent. Therefore: Cold Water 50 W. C. x 50 gpm at 8 per cent....................... 50 Lavs, x 3 gpm.................. ..................... _...... 50 Sinks x 4 gpm.......... ...................................... 50 Baths x 5 gpm.................... .................... ....... 150 Fixtures................ ........................................... ........................................ 200 gpm 150 gpm 200 gpm 250 gpm 600 gpm at 31 per cent 186 gpm Total maximum probable flow of cold water-- ................. ......... .............. 386 gpm Hot Water 50 W. C._............................................................ 50 Lavs, x 3 gpm................ ................................ 50 Sinks x 4 gpm................ ...... ......................... 50 Baths x 5 gpm.. 150 Fixtures............ ... ....... ....... .............................None 150 gpm 200 gpm 250 gpm 600 gpm at 31 per cent 186 gpm Total for main supplying cold and hot water.........................................................572 gpm It should be noted that this is a rate offlow or an instantaneous demand. KIND OF PIPE USED Before entering into the actual sizing of pipe, it is necessary to consider the kind of pipe to be used and to make suitable allowance for corrosion and fouling during the lifetime of the system. For example, if brass, copper or alloy pipe is contemplated, it is probable that the quantities indicated in Example 1 are ample; if galvanized pipe is to be used, then it is quite likely that after a period of say 15 years the area may be decreased as much as 25 per cent and the quantitities of water assumed should be increased by 35 per cent to allow for this reduction of area; if the water contains lime it is possible that 50 per cent of the area may be lost and in such cases the flow should be doubled and no branch pipe' connected to fixtures should be less than % in. In all of the following calculations, the assumption is made that the water is fairly good and that a corrosion resistant type of pipe is to be used. SIZING A DOWN-FEED RISER Down-feed systems are commonly used for tall buildings. In sizing a riser arranged for down-feed, the gravity head permits a pressure drop that is almost prohibitive in an up-feed riser. There is a gain in riser head of 0.43 X 100 or 43 lb per 100 ft of run and hence it is quite permissible to size such a riser on the basis of a pressure drop of 30 lb per 100 ft of run, as the difference between the 43 lb generated and the 30-lb drop under maximum probable demand is ample to take care of the friction caused by 550 chapter 39--Water Supply Piping the fittings. This method applied to the typical riser shown in Fig. 2 gives the schedule of sizes indicated in Table 2 for any flow from 5 to 250 gal. xxxxxxxxxxxxxxxxxxxx CS O u, . itnWx] c, ci m m c* e* & uWaQ, 2 O> Q O06 MN c73 - aDQUna a (N a gogS IN M <N < w dCOCcNNONNcJM ;*5J.!*3*3 5*S!**** * * * X X SSS!SSS*XSSSS. t-wa;oo,oS:^Kj^^a:Ufc-(aqoa)^. 06 O 82 S3 iiiiii'iiiii I 1 i. s 1 I 5 I 2 3 . utnniiniinlim^CL I< <N.<N 6 06 i! SIZING AN UP-FEED RISER When the riser is an up-feed, the opposite condition occurs, that is, there is a drop in pressure as the top of the riser is approached, due to the natural reduction in the gravity pressure, and to this must be added the 551