Document 5D93zORnzE44nm8z3ewOeEMwV

752 CHAPTER 56 1959 Guide Table 3.... Performance Requirements of Water Meters* Site, In. Normal Test-Flow liailt, Gpm Minimum Test-Flaw, Gpm feed systems are the same. The principal difference in pro cedure is that in the down-feed system, the difference in elevation between the house tank and the fixtures provides the pressure required to overcome pipe friction. Procedure for Sizing Cold Water Systems The recommended procedure for sizing piping systems is outlined in following paragraphs 1 to 6, inclusive. 1. Draw a sketch of the main lines, risers, and branches, and indicate the fixtures to be served. Indicate the rate of flow of each fixture. 2. Using Table 2, compute the demand weights of the fixtures in fixture units. 3. Determine the total demand in fixture units and, using Fig. 1 or Fig. 2, find the expected demand in gallons per minute. X............................................ X............................................ l................................................ IK............................................ 2................................................ 3................................................ 4......... ................................... 6................................................ 1 to 2 to 3 to 5 to 20 34 53 100 8 to 160 16 to 315 28 to 500 48 to 1,000 K X ik 2 4 7 12 * American Water Works Association Standards; BeatntioB. The rapstniioo on the meter dial ehaU indicate the quantity recorded to be not lees than 98 percent nor more than (08 percent at the water .rfwtiiy passed through the meter while it b being tested at rates of flow within tt. specified limit# nnihr normal test flow Limits; There shall be not leee tUn w percent of the aetual Sow recorded when a test h made at the rate of flow set forth under minimum test flow. 4. Determine the equivalent length of pipe in the main lines, risers, and branches. Since the sizes of the pipes are not known, the exact equivalent length for various fittings, etc., cannot be made. Add the equivalent lengths, starting at the street main and proceeding along the service line, the main line in the building, and up the riser to the top fixture of the group served. 5. Determine the average minimum pressure in' the street main and the rpirumnm pressure required for the operation of the topmost fixture. This latter pressure should be 8 to 15 psi. 6. Calculate, by means of Equation 1, the approximate de sign value of the average pressure drop per 100 ft of pipe in the equivalent length determined in paragraph 4. p - IF -- 0.43H - 101 ^ 0) where p ** average pressure loss per 100 ft of equivalent length of pipe, psi. P = pressure in street main, psig. H =* height of highest fixture, above street main, feet. L = equivalent length determined in paragraph 4, feet. If the system is of the down-feed supply from a gravity tank, the height of water in the tank, converted to pounds per square Table 4.... Allowance in Equivalent Length of Pipe for Friction Loss in Valves and Threaded fittings Equivalent Length of Pipe for Various Fittings Oiatnefer of Fitting, in. 90-Dog Stand ard Bl, Ft 45-Dog Stand ard Bl, Ft Coupling 90-Dog or Straight Side Too ft Run of Too, Ft Goto Valve, Ft Globe Anglo ft ftValve, Valve, B. Laundry compression faucet, C-l. H-fa- compcutaco safe foueet (Mfr. I). C-2. compression cmk faucet (Mfr. 2). 0. CoabihoMon compression baffifub faucets (both open). E. Combination compression smfc faucet. F. Basin faucet. G. Spring self-closing faucet. H. Slow raff-dotmg faucet. (Dashed line* indicate recommended extrapolation) fig. 7.... Variation of Pressure loss with Rate of Row for Various Faucets and Cocks - X.......... x.......... X.......... l............... IX.......... 1 2 2.5 3 4 IX.......... 2............... 2X.......... 3............... 3H.......... 5 7 8 10 12 4............ 5............ 6............... 14 17 20 0.6 1.2 1.5 1.8 2.4 3 4 5 6 7 8 10 12 1.5 3 4 5 6 7 10 12 15 18 21 25 30 0.3 0.6 0.8 0.9 1.2 1.5 2 2.5 3 3.6 4.0 5 6 0.2 0.4 O'. 5 0.6 0.8 1.0 1.3 1.6 2 2.4 2.7 3.3 4 8 15 20 25 35 4555 65 80 100 125 140 165 4 8 12 15 18 22 28 34 40 50 55 70 80 Water Services Table 5___ Equivalent Lengths of Iron Pipe to Give Some Loss os Special fittings and Apparatus Fitting Apparatus Nominal Diagnotor of Pipe-- Inches X Vs iK 30-gal Vertical hot water tank, K-in. pipe.................................................. 4 17 56 30-gal Horizontal hot water tank, H-in. pipe....................... ....................... 1.2 5 16 -- Water meters (No valves included) X in. with K~in. connections -- 6.7 28 90 -- X in. with %-in. connections------ 4.8 20 64 -- X in. with %-in. connections------ 3.4 14 45 -- 1 in. with 1-in. connections............ -- 9 30 115 IX in. with 1-in. connections.... -- Water softener............................................. -- 4.4 14 --50-200 54 -- 753 Table 7.... Pipe Sizes for Cooling Towers* Bated Tons of Befrig. Cooling Wafer Gpm Pipe Sixes (Nominal Inches) Inlot to Tower Outlet from Tower 3 to 5 . 7 to 15 20 25 35 50 75 100 150 200 250 10 to 18 20 to 45 65 86 115 170 225 300 450 GOO 750 IK .2 2K 2K 3 3 5 5 5 6 8 IK 2 3 4 4 4 6 6 8 8 8 inch by multiplying by 0.43, replaces the street main pressure, n<( the term 0.43 H in Equation 1 is added instead of sub tracted in calculating the term p. In this case, H will be the vertical distance of tee fixture below the bottom of the tank. 7. From the expected rate of flow, determined as in paragraph 3, and the value of p, calculated as in paragraph 6, choose the of pipe from Figs. 3, 4, or 5. Example t: Assume a minimum street main pressure, of 55 psig; a height of topmost fixture above street main of 50 ft; a developed pipe length from water main to highest fixture of 100 ft; a total load on the system of 50 fixture unite; and that the water closets are flush-valve operated. Find the required size of supply main. Solution: From Fig. 2 the estimated peak demand is found to be 51 gpra. From Table 3 it is evident that several sizes of meters would adequately measure this flow. For a trial computa tion choose the lyi-in. meter. From Fig. 6 the pressure drop through a lVi-in. disc-type meter for a flow of 51 gpm is found to be 6.5 psi. Then the pressure drop available for overcoming friction in pipes and fittings is 55 -- (15 + 50 X 0.43 + 6.5) = 12 psi. At i-hia point it is necessary to make some estimate of the equivalent pipe length of the fittings on the direct line from the street main to the highest fixture. The exact equivalent length of the various fittings cannot now be determined since the pipe sizes of the building main, riser, and branch leading to the highest fixture are not known as yet, but a first approxima tion is necessary in order to make a tentative selection of pipe sizes. If the computed pipe sizes differ from those used in deter mining the equivalent length of"'pipe fittings, a recalculation will be necessary, using the computed pipe sizes for the fittings. For the purposes of this example assume that the total equiva lent length of the pipe fittings is 50 ft. Then the permimible pressure loss per TOO 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. Table 6.... Computation of Branch Size tn Example 2 Fixture* No. and Kind Fixture Units (From Table 2 and Note c) Demand Fig. 2) Gpm Pipe Size (From Fig. 4) to. 3 flush valves.......... 3x6 - 18 X (2 X 2) - 3 X (3 x 1) - 2.25 23.25 38 IX The sizing of the branches of the building main, the risers, and fixture branches follows the principles outlined. For exam ple, assume that one of the branches of the building-main car ries the cold water supply for 3 waterclosets, 2 bathtubs, 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 Vi 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 hy draulics, as already outlined, are employed. Nevertheless, there are several practical items having particular applica tion to cooling installations which are outlined in the fol lowing paragraphs. 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 failure of the system. If the water is not severely corrosive, wrought-iron or steel piping may be used; otherwise, galvanized-eteel 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 preferred to screwed joints wherever possible. Valves used in circulating systems may be of the globe, gate, or angle 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 correc tion for the proper density must be made. Experience indi cates that in sizing piping for cooling systems, 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 temperature of about 76 F. Table 7 gives pipe sizes frequently used for various rizes of cooling towers, assuming a hot water temperature of 95 F and a cold water temperature of 85F*