Document QJG4pw4J92oXYBDneBvy8gryv

of and 1936American Society Heating Ventilating Engineers Guide, P = 0.0000000367 ( 1 + (1) (2) where P = loss in pressure, pounds per square inch. d = inside diameter of pipe, inches. L = length of pipe, feet. D = weight of 1 cu ft of steam. W = weight of steam flowing per hour, pounds. , Example 1. How much steam will flow per hour through 100 ft of 2-in. pipe if the initial pressure is 1.3 lb per square inch and the pressure drop is 1 oz? Solution. P = A = 0.0625 lb; d = 2.067 in. (Table 1. Chapter 34); L = 100 ft; lo D = 0.04038 lb (Table 6, Chapter 1). Substituting these values in Formula 2: V:W = 5220 0.0625 X 0.04038 X 2.067 = 97.2 lb per hour. (1+'w)100 Formula 2 does not allow for entrained water in lowrpressure steam, condensation in pipe, and roughness in commercial pipe as found in practice. The latent heat of steam (htg) at atmospheric pressure (Table 6, Chapter 1) is 970.2 Btu per pound. Inasmuch as the heat emission of an equivalent square foot of heating surface (radiation) is 240 Btu, 1 lb of steam at this pressure will supply 97_0.'2 or 4.04 sq'ft of equivalent heating surface. This figure is usually taken as 4 even. In Example 1, the weight of steam flowing per hour would therefore supply 4 X 97.2 or 388.8 sq ft of equivalent heating surface:' PIPE SIZES , , The determination of pipe sizes for steam heating depends on the following*principal factors: 1. The initial pressure and the total pressure^drop which may be allowed between the source of supply and the end of the return system. 2. The maximum velocity of steam allowable for quiet and dependable operation of the system. 3. The equivalent length of the run from the boiler or source of steam supply to the farthest heating unit. ". .. 4. Unusual conditions in the building to be heated. Initial Pressure and Pressure Drop Theoretically there are several factors to be considered, such as initial pressure and pressure required at the end of the line, but it is most im portant that (1) the total pressure drop does not exceed the initial pressure of..the system;.(2) the pressure drop is not so great as to cause excessive velocities; (3) there is a constant initial pressure, except on systems 558 32--Chapter Piping for Steam Heating Systems Table 1. Maximum Allowable Capacities of Up-Feed Risers for One-Pipb Low Pressure Steam Based on A. S. 'H. V. E. Research Laboratory Tests Pips Sob Inches A i IK 1H 2 * m 3 3K 4 Velocity Feet Per Second Pressure Drop Ounces pbb 100 Ft B 14.1 17.6 20.0 23.0 26.0 29.0 31.0 32.0 C 0.68 0.66 0.66 0.57 0.54 0.48 0.44 0.39 8q Ft Radiatioa D 45 98 152 288 464 799 1144 1520 Capacity Btu per Hour E 10,961 23,765 36,860 69,840 112,520 193,600 277,000 368,000 Lb Steam per Hour F 11.3 24.5 38.0 72.0 , 116.0 199.8 286.0 380.0 INSTRUCTIONS FOR USING TABLE 1 , 1. Capacities given in Table 1 should-never be exceeded on one-pipe risers. .......................... 2. Capacities are based on K-lb condensation per square foot equivalent radiation and actual diameter of standard pipe. 3. All pipe should be well'reamed and free from constrictions. Fittings should be up to Tables 4 and 5). (See specially designed for varying initial pressures, such as the sub-atmos pheric which normally operate under controlled partial vacua, the orifice, and the vapor systems which at times operate under such partial vacua as may be obtained due to the condition of the fire; (4) there is sufficient difference in level, for gravity return systems, between the lowest point on the steam main, the heating units, and the dry return,, when considered in relation to the boiler water line. AH systems should be designed for a low initial pressure and a reason ably small pressure drop for two reasons: first, the. present tendency .in steam heating unmistakably points toward a constant lowering of pres sures even to those below atmospheric; second, a system designed in this manner will operate under higher pressures without difficulty. When-a system designed for a relatively high initial pressure and a relatively high pressure drop is operated at a lower pressure, it is likely to be noisy and have poor circulation. .. V The total pressure drop should never exceed one-half of the initial pressure when condensate is flowing-in the same direction , as the steam. Where the condensate must flow counter to the steam,'the governing factor is the velocity permissible without, interfering with the condensate flow. Laboratory experiments limit this to. the capacities given in Tables 1 and 2 for vertical risers arid in Table 3 for horizontal pipes at varying grades. ' Maximum Velocity and Reaming The capacity of a steam pipe in any part of a steam system depends upon the quantity of condensation present, the direction in which the 559