Document dYO3qa6Yj5YG4V2gYebQR6jvq

492*tJA CHAPTER 21 1954 Guide tated as much, as possible, as an air bound system will not heat readily nor properly. In designing the piping arrangement, it is desirable to maintain equivalent resistances in; the supply and return piping to and from a radiator; Arranging the piping so the total distance from the boiler to the radiator is the same as the return piping distance from the heating unit back to the boiler, tends to obtain such a result. The Table 1. Obotch Capacities fob Low Pressure Steam Systems * teste* Orifice Diameter 64TBS 07 an Inch 7 8 9 10 n 12 13 14 15 .16 17 18 19 20 21 6 in. Hg Differential 5 in. He Differential 4 in. Hg. Differential 2 m. Hg Differential 1 in. Hg Differential 18-23 23-29 29-36 36-44 44-52 52-62 62-72 72-83 83-94 94-106 106-119 119-133 133-148 148-163 163-179 In Square Feet .Exoressed KUK.-------------------------------- ---- ------------ 16-21 21-27 27-33 33-40 40-48 48-57 57-66 66-76 76-86 86-97 97-109 109-122 122-135 135-149 149-164 15-19 19-25 25-30 30-37 37-44 44-51 51-59 59-67 67-76 76-86 86-97 97-108 108-120 120-133 133-145 13-17 17-21 21-26 26-31 31-37 37-43 43-49 49-56 56-64 64-72 72-80 80-88 88-98 98-107 8-11 11-14 14-17 17-20 20-24 24-28 28-32 32-37 37-42 42-47 47-52 52-58 58-64 64-71 Capacity Expressed in Pounds per Hour JL______________ JF___.7 8 9 10 11 12 13 14 15 16 17 18 19 20 21l 4.5-5.8 5.8-7.3 7.3-9.0 9.0-11.0 11.0-13.0 13.0-15.5 15.5-18.0 18.0-20.8 20.8-23.5 23.5-26.5 26.5-29.8 29.8-33.3 33.3-37.0 37.0-40.8 I 14U0..U8-4 4A..8V 4.0-5.3 5.3-6.8 . 6.8~8.3 8.3-10.0 10.0-12.0 12.0-14.3 14.3-16.5 16.5-19.0 19.0-21.5 21.5-24.3 24.3-27.3 27.3-30.5 30.5-33.8 33.8-37.3 37.3-41.0 , 3.8-4.8 4.5-6.3 6.3-7.5 7.5-9.3 9.3-11.0 11.0-12.8 12.8-14.8 14.8-16.8 16.8-19.0 19.0-21.5 21.5-24.3 24.3-27.0 27.0-30.0 30.0-33.3 33.3 36.3 2.5-3.3 3.3-4.3 4.3-5,3 5.3-6.5 6.5-7.8 7.8-9.3 9.3-10.8 10.8-12.3 12.3-14.0 14.0-16.0 16.0-18.0 18.0-20.0 200-22.0 22.9-24.5 24.5-26.8 2.0-2.8 2.3-S.5 3.5-4J 4.3-5.0 5.0-6.0 6.0-7.0 7.0-8.0 , 8.0-9.3 9.3-10.5 10.5-11.8 11.8-13.0 13.0-14.5 14.5-16.0 16.0-17.8 Note.--The radiator orifice plates recommended in this table are made of brass stampings 0.023 in* thick cup-s'FhlaopwedoftoStbeeaminsTehrrtoeudginh OraridfiicaetosrinvtaolvReaudniaiotonrss., by S. S. Sanfordand C.B. Sprenger (A.S.H.V.E. Trans- accotinodnse,nVsoal.t3e7, 1w93h1,icp.h371o).ccurs in steam piping as well as in radiators must be drained to prevent impeding the ready flow of the steam arid air. The effect of back pressure in the returns and excessive re-vaporization, such as occurs where condensate is released from pressures considerably higher than the vacuum or pressure in the return, must be avoided. It is important that steam piping systems distribute steam not only &t full design load, but during excess and partial loads. Usually the average winter steam demand is less than half of the demand at the design outside Steam Heating Systems 493 temperature. Moreover, in rapidly warming up a system even in moder ate weather, the load on the steam main and returns may exceed the maximum operating load for severe weather, due to the necessity of raising the temperature of the metal in the system to the Steam temperature, and the building to the design indoor temperature. Investigations of the return of condensate have revealed that as high as 143 percent of the design condensation rate may exist under conditions of actual operation. The piping design of a heating system is greatly influenced by its operat ing characteristics. Heating systems do not operate under constant condi tions, as conditions change continually, due to variation in load. As the system is being filled with steam, the pressures existing in various locations may be different from those which exist for appreciable periods at other locations, although at equilibrium conditions the pressures are approximately the same. In designing piping it is of especial importance to arrange the system to preclude trouble caused by such pressure. dif ferences. The systems which readily release the air, permit uniform Fig. 18. Relation Between Elapsed Time, Steam Pressure, Condensate and Air Elimination Rates pressures to be attained in much shorter time intervals than those which are sluggish. Results are given in Fig. 18 from investigations1 to deter mine the rate of condensate and air return from a two-pipe gravity heating system. Variations in the steam pressure during the warming-up period, when the rate of air elimination and condensation is high, are clearly indicated in these curves. It is evident that the condensate flow during the initial warming-up period reaches a peak, which is greater, than the constant condensing rate eventually reached when the pressure becomes uniform. Moreover, the peak condensing rate is obtained when the system steam pressure is lower than that existing during a period of constant condensing rate. It will also be noted that the peak rate of air elimination does not coincide with the higher condensing rate. Steam Flow The rate of flow of dry steam or steam with a small amount of water flowing in the same direction, is in accordance with the general laws of gas flow, and is a function of the length and diameter of the pipe, the density f the.steam, and the pressure drop through the pipe. This relationship