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1076 Table 6. CHAPTER 49 i 1954 Guide Computation of Branch Size in Example 2 Fixtures No. and Kind Fixture Units (From Table 2 and Note c) -- Demand (From Fig. 2) Gpm Pipe Sub (From Fig. 4) In. 3x6 =18 f (2x2) = 3 1 (3 x 1) - 2.25 23.25 38 h the computed pipe sizes for the fittings. For the purposes of this example assume that the total equivalent length of the pipe fittings is 50 ft. Then the permissible pressure loss per 100 ft of equivalent pipe is 12 X 100/(100 + 50) = 8 psi. Assuming that the corrosive and caking properties of the water are such that Fig. 4 for fairly rough pipe is applicable, a 2 in. building main will be adequate. The sizing of the branches of the building main, the risers, and fixture branches follow the principles outlined. For example, assume that one of the branches of the building main carries the cold water supply for 3 water closets, 2 bath tubs, and 3 lavatories. Using the permissible pressure loss of 8 psi per 100 ft, the size of branch determined from Table 2 and Figs. 1 and 4 is found to be 1) in. Items entering the computation of pipe size are given in Table 6. COOLING WATER PIPING Water is very frequently used in refrigeration systems, cooling towers and other similar installations. In designing the piping system of such installations, the principles of hydraulics, as already outlined, are em ployed. Nevertheless, there are several practical items having particular application to cooling installations. They are outlined in the following paragraphs, and it is important that the designer be familiar with them. In choosing pipe material, the problem of corrosion should be kept in mind to prevent defects in the system. If the water does not have drastic corrosion characteristics, wrought iron or steel piping may be used; other wise, galvanized steel piping may be preferred. If sea water is used as the circulating medium, it is advisable to use alloys such as admiralty metal in pipe and tubing. In refrigeration condensers where water is the cooling medium, iron pipe is commonly employed. In regard to assembly, cast-iron flanges or welded joints are to be pre ferred to screwed joints wherever possible. Valves used in circulating systems may be of the globe, gate, or angle Table 7. Pipe Sizes for Cooling Towers* Rated Tons of Rbfriq. 3 to 5 7 to 15 20 25 35 50 75 100 150 200 250 GPM 10 to 18 20 to 45 65 86 115 170 225 300 450 600 750 Pipe Sizes (Nominal Inches) Inlet to Tower Outlet from Tower Hh 22 21 3 21 4 34 34 56 56 58 68 88 Water Services 1077 types. If water is the circulating medium, brass, valves are usually used. However, if the circulating medium is an electrolyte, such as brine, then it is preferable to use valves made of the same material as the piping itself. The friction loss in the piping may be determined from Fig. 4 for fairly rough pipe. If the coolant is brine, a correction for the proper density must be made. Experience indicates that in sizing piping for cooling sys tems, a pressure drop of the order of 2 to 3 psi per 100 ft of pipe length, and a fluid velocity of 3 to 8 fps,.yield most economical results. In the case of cooling towers, the amount of circulating water is about 3 gpm per ton of refrigeration, when based on a design wet-bulb tempera- Table 8. Maximum Daily (24-Hr) Requirements fob Hot Water in Gallons No. op Roomb Apartments and Private Homes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1 60 70 80 . 90 100 120 140 160 180 200 -- --. -- -- -- -- -- -- -- Number op Bathrooms 234 _ __ __ __ -- __ __ -- 120 -__ 140 __ 160 200 180 220 -- -- -- -- 200 240 250 220 260 ' 275 240 280 300 260 300 340 280 325 380 300 350 420 -- 375 460 __ 400 500 _ __ 540 _ -- 580 __ __ 620 __ __ -- ---- 5. , -- __ -- -- -- -- -- -- -- -- 450 500 550 600 650 700 750 800 850 Hotels Room with bath--transient....... Room with bath--resident........ 2 Rooms with bath 3 Rooms with bath Slop sink................ ........... ........... ........... ........... ........... ........... ........... ........... 10 50 60 80 100 200 160 30 Office Buildings Hospitals White collar worker (per person) Other workers (per person)....... Cleaning per 10,000 sq ft............ Jper bed................... ........... 2.0 ............. 4.0 ........... 30.0 ....... 80-100 hire of about 76 F. Table 7 gives pipe sizes frequently used for various sizes of cooling towers, assuming a hot-water temperature of 95 F and a cold-water temperature of 85 F.2 estimating heating load and storage capacity The maximum daily and the maximum hourly hot water demand form Ihe basis for the selection of the heater and the storage tank. In general, two thirds of the total daily water consumption is hot water. I or residential dwellings, a design value of about 20 to 30 gal per capita Per day may be assumed, but it should be remembered that the hot water used will depend on the number of rooms and the number of bathrooms in