Document QgdkKjNQpr01ORJGOYkpxGrok

1006 CHAPTER 48 1951 Guide Table 6. Computation of Branch She in Example 2 Fixtures No. and Kind Fixture Units (From Table 2 and Note c) Demand (From Fio. 2) Gpm Pipe Size (From Fig. 4) In. 3x6 =18 I (2 x 2) = 3 J (3 x 1) = 2.25 23.25 38 U' 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 \Yi 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 fob Cooling Towers* Rated Tons op Repbio. Cooling Water GPM (NPipe Sizes o mxnal Inches) Inlet to Tower Outlet from Tower 3 to 5 7 to 15 20 25 35 50 10 to 18 20 to 45 65 ' 86 115 170 ii 2 21 21 3 3 u 2 3 4 4 4 75 100 150 '200 250 225 - 5 300 5 460 5 . 600 ' 6 750 8 6 6 8 8 8 Water Services 1007 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-Hb) Requirements for Hot Water in Gallons Number op Bathrooms Apartment* and Private Homes 1 2 3 4 5 9 7 8 9 10 - 11 12" 13 14 15 10 . 17 18 19 20 1 2 3 4 5 60 ' __ __ 70 __ __ __ 80 -- -- -- 90 120 100 140 -- -- 120 160 200 140 180 220 _____ 160 200 240 250 180 220 260 275 __ _ __ --____ -- 200 240 280 300 -- 260 300 340 --_ -- 280 325 380 450 -- -- -- -- 300 -- -- -- 350 375 4--00 420 460 500 540 500 550 600 650 -- -- -- -- -- -- -- 580 700 -- -- 6--20 750 800 -- -- 850 Room with basin.... Room with bath--transient........ Room with bath--resident.......... 2 RooTM with bath . 3 Rooms with bath. Public shower......... Public basins.......... Slop sink............ 10 50 60 80 100 200 150 30 Office Buildings White collar worker (per person) Other workers (per person)....... Cleaning per 10,000 sq ftl............ 2.0 AO Hospitals jpcr bed........... ........................................................................................... 80-^-100 ture 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 the basis for the selection of the heater and the storage tank. In general, two thirds of the total daily water consumption is hot water. For 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