Document wD1aMzorDd8gnQxRrY8410rr4

Heating Ventilating Air Conditioning Guide 1938 closets and smaller fixtures, the probability, of a given rate of flow is system. The use of this chart then-would produce results which would be on the safe side for mixed systems. For systems composed entirely of fixtures other thafi . flush valve fixtures the curve has been extended for smaller maximum possible flow Values. 786 Chapter 43. Water Supply Piping and Water Heating This chart applies to a normal building and not to installations where the inmates may all be required, for instance to bathe on certain days of the week and at certain hours of those days; or in schools for example where all the showers in the gymnasium may be used simultaneously after instruction periods. In such special cases a new factor of usage must be developed based on the maximum probable usage under the conditions involved. 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. Cold Water 50 W. C. x 45 gpm_........... .2250 gpm 50 Lavs, x 3 gpm 150 gpm 50 Sinks x 4 gpml_^_____ 200 gpm ' ' 50 Baths x 5 gpm_____ ____ 250 gpm Maximum possible flow___ 2850 gpm Fig. 1 shows a factor of usage of 9 per cent. Maximum probable flow of . cold water is 2850 X 0.09______ ____ 257 gpm Hot Water 50 Lavs, x 3 gpm................ 150 gpm 50 Sinks x 4 gpm.............. 200 gpm 50 Baths x 5 gpm_________ 250 gpm Maximum possible flow___ 600 gpm Fig. 1 shows a factor of usage of 23 per cent. Maximum probable flow of hot water is 600 X 0.23________________ 138 gpm Total for main supplying cold and hot water (2850 + ' 600) X 0.08.________ _____________ 276 gpm , It should be noted that this is a raie'of flow 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 Jby 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 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. 787