Document RJ2JLpndJL1x4OwYRabkKoJ7

HEATING VENTILATING AIR CONDITIONING CUIDE 1942 Table 2. M"'"" fll"""cKss r,^rF" R," Based on A. S, H. V. E. Research Laboratory Tests Pips Sob Inches A i 1)4 1)4 2 2X 3 3)4 4 VeiociTr Feet Per Second Pbsssurb Drop Ounces per 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 Sq Ft Radiation 45 98 152 288 464 799 1144 1520 Capacitt Bto per Hoar 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 rv/I\ UOllVO J'AULtE 2 1. Capadties given in Table 2 should never be exceeded on one-pipe risers. of s2ta. nCdaaprdacpitiipees. are based on }-ib condensation per square foot equivalent radiation and actual diameter 3. All pipe should be well reamed and free from constrictions. Fittings should be up to sixe. Tables. R,,,, WrM Ptpb Sia . Inches . Vblocitt Feet peb Second Pressure Dbop Ounces per 100 Ft `4. 1 IX 1)4 2 2X 3; 3)4 4 ,B 20 23 27 30 ,35 38 .41 42 43 ; -C . --1.78 1.57, 1.48 . 1.33 1.16 0.95 0.81 0.71 . &Ft. Radiation D 40 74 ,151 228 438678 . 1129 1548 2042 Capacity Btu per Hoar - . 9,550 17,900 36,500 55,200 106,100 164,100 273,500 375,500 . 495,000 Lb Steam per Hour ' F 10.0 , 18.45 37.65 57.0 109.5 169.4 282.2 387.0 510.5 __________ va osmo TABLE 3 1. The capacities given in this table should never be exceeded on two-pipe risers. of s2ta. nCdaaprdacpiitpiees. arc based on condensation per square foot equivalent radiation and actual diameter 3. All pipe should be well reamed and free from constrictions. Fittings should be up to rise. 288 CHAPTER 15. PIPING FOR STEAM HEATING SYSTEMS PIPE SIZES The determination of pipe sizes for a given load in 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, taking into consideration the direction of condensate flow. 3. The equivalent length of the run from the boiler or source of steam supply to the farthest heating unit. 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 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; and (4) the equivalent head due to pressure drop does not exceed the difference in level, for gravity return systems, between the lowest point on the steam main, the heating units, or the dry return, and the boiler water line. All 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. 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. A.S.H.V.E. Research Laboratory experiments limit this to the capacities given in Tables 2 and 3 for vertical risers and in Table 4 for horizontal pipes at varying grades. Maximum Velocity 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 condensate is flowing, and the pressure drop in the pipe. Where the quantity of condensate is limited and is flowing in the same direction as the steam, only the' pressure drop need be considered. When the con densate must flow against the steam, even in limited quantity, the ve locity of the steam must not exceed limits above which the disturbance between the steam and the counter-flowing water may produce object ionable sounds, such as water hammer, or may result in the retention of 289