Document 9KDDwVbeDw5RNV9ZddwznG5p

T a b l e 2. S c h e d u l e o f S iz e s f o r D o w n - F e e d R is e r (S e e F ig . 2) HEATINC VENTILATING AIR CONDITIONING GUIDE 1941 closets and smaller fixtures, the probability of a given rate of flow is greater for the system composed of water-closets than for the mixed 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 than flush valve fixtures the curve has been extended for smaller maximum possible flow values. 772 CHAPTER 45. WATER SUPPLY PIPING AND WATER HEATINC This chart applies to a normal building arid 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. CoW Water, 50 W. C. x 45 gpm----__ ..2250 gpm 50 Lava., x 3 gpm_______ -- 160 gpm , 50 Sinks. x 4 gpm__ : 200 gpm 50 Baths x 5 gpm-------------- 250 gpm Maximum possible flow__2850 gpm Fig. 1 shows a factor of usage of 0 per cent. Maximum probable flow of cold water is 2S50 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_f_o_r__m__a_in suppl_y_i_n_g_ co__ld ISS) x _____ - 276 gpm It should be noted that this is a rate 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 I 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 increa'sed by"35 per cent tb'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 >< 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. " o. 773