Document 4vQ7pnM2Qo1D2MKoExYmg1yNQ

American Society of Heating and Ventilating Engineers Guide, 1932 use. The assumed percentage of simultaneous use varies greatly among designers of water supply systems. Even a precise mathematical calcu lation as to its value must be based on an assumption of the probable number of times the fixture is used per unit of time. To arrive at a safe practical value of the probability an analysis of the composite layout was made which shows the flow following closely along the curve shown in Fig. 1, the probability being, almost 100 per cent at the last floor supplied and diminishing to a minimum of 10 per cent. The following equation may be written to fit the curve of Fig. 1: Ph;; - 110 (1): where P -- per cent of simultaneous use (expressed as a whole number). F = the number of floors being supplied. : Example l. For a riser supplying two bath rooms on each floor, each batlj room fitted with one lM-in. flushometer connection,' one %-in. bath and one Mi-in. lavatory con nection, the rate of flow for each room if all fixtures were opened simultaneously as taken from, Table 1 would be 68 gpm, and for each floor, 136 gpfn. For the fifth floor the amount will be 5 X 136 = 680 gpm. The probable simultaneous use at the fifth floor, however, is only: ; : 224 . -z--;--= + 10 = 42 per cent 5 H- Z and the riser must therefore be designed to carry 0.42 X 680 gpm = 286 gpm ; at whatever friction loss the conditions will allow. (See Example 2). ; At.the 10th floor supplied, the amount flowing at some one time may be expected to reach: 10 X 136 X percent ?= 394gpm In a 10-story building with 22 similar risers the main would be required to supply: ... - - 224 "6 + 10 = 11 per cent of the total fixture supply. . (lu, X ) -h * Formula 1 is based on the number of floors in the building and therefore Only applies when the distribution of fixtures on each floor is equal, or nearly equal. Where the fixtures are unequally distributed a percentage of Imaximum simultaneous use must .be estimated for the fixtures on each level and on each portion of the riser, this percentage grading from 100 per cent for. the first two fixtures on the end of each branch down to a mini mum of about 25 per cent where 500 Or more fixtures are installed/ The number of . gallons per minute used, by all the fixtures supplied' by a branch or riser at any particular point multiplied by this estimated per centage, of, miximum use will then give the maximum probable number of gallons per minute passing through the pipe at this point, and: the pipe may then. be sized on the basis of the friction drop allowable for the conditions involved. Special percentages of maximum simultaneous use must be developed for gang showers, batteries of lavatories for industrial work,, and. other groups of fixtures where an /unusual, maximum: demand may exist during certain specified hours. ....... : . :.- 208 Chapter 13--Domestic Water Requirements and Pipe Sizes Table 3. Number of V-in. Pipes Accommodated by a Single Pipe in the Average Type Building with Allowance for Simultaneous Use Pipe Diameter (In.) i i% i'A 2 m 3 Number op In. Pipes 3 to 5 6 to 11 12 to 44 45 to 100 101 to 220 221 to 430 Pipe Diameter (In.) Z'A 4 5 6 8 Number op >6 In. Pipes 431 to 700 701 to 1200 1201 to 2400 2401 to 5000 5000 up Due to a lack of variety in commercial sizes it is not possible to change the size of the riser at each floor. When an increased size is first used the friction loss per unit of length must of necessity be less than the pre determined amount but will increase as the floors are added until it is approximately an equal amount in excess of the loss desired when the size must again be increased. The average loss through the section will be near that desired. To facilitate the design, the equivalent number of smaller pipe supplied by each large pipe at its location in the composite layout was determined as shown in Table 3. For convenience these values are all referred to the equivalent in in. pipes as specified in Table 2. It should be noted that Table 3 allows for the diversity factor or per cent Of simultaneous use. Example 2. Fig. 2 shows the piping layout of the upper half of a 22-story structure which is typical of office, hotel, club and apartment risers. Taking riser No. 1, the out lets on each floor consist of two flushometer valve connections, two %-in. con nections for bath, and two J4-in. connections for the lavatories. The total factor value for the cold water riser as taken from Table 2 is: 2 X 9.7 = 19.4 for flushometers 2 X 2.7 = 5.4 for baths 2X1 = 2.0 for lavatories Total for each floor 26.8 pipe equivalents Thus with the first floor supplied (the 12th story in this case) the riser must supply Table 4. Amount of Water in Gallons per Minute Which Will Flow Through Various Sized Pipes for Various Pressure Drops Friction Pressure Drop per 100-pt. Run U l 'A 5 5.4 11 19 7 6.4 13 23 10 7.6 15 27 20 10.8 22 38 30 13.2 27 47 40 15.0 31 54 50 17.0 35 60 75 21.0 43 74 100 24.0 49 85 125 27.0 55 96 150 30.0 60 105 Pipe Sizes in Inches i'A 2 2A 3 30 62 109 171 36 74 129 203 43 88 154 242 61 125 218 343 76 153 267 420 86 176 308 485 96 197 345 542 117 242 423 665 136 278 485 769 152 311 544 858 166 341 598 939 4 252 353 298 . 418 357 499 504 706 618 864 714 998 800 1115 978 1365 1130 1578 1260 1765 1380 1930 5 610 720 862 1221 1500 1725 1930 2370 209