Document bBDM7JE5w8M43Zjg4j64oz92k

788 CHAPTER 36 1950Guide Table 5. Maximum Tons op Compressor Cafacty"fob Fseon-12 Lines ' (Only for temperatures indicated) , - - SoCCION Lutes ' Based on 105 F Condensing Temperature Dxschabod Lines Line Sizb, Inches *OD I IPS I OD i IPS { OD i IPS HOD 1 IPS '" 11on iJ_jps n od IPS 2} OD 2 IPS 2| OD 2* IPS 3* OD 3 IPS 3J OD 31 EPS 4} OD 4 IPS 5 IPS 6. IPS 8 IPS 10 IPS 12 IPS Psi Pressure Drop per 100 Ft Equivalent Length at 40 F Saturation Condensing Temperature 1 0.14 0.20 - 0.17 0.24 0.25 ' 0.35 0.35 0.45 2 0.28 0.34 0.51 0.65 g. 4 ` : 5 0.35 0.41 0.42 0.49 0.62 0.73 : - 0.79 0.93 0.45 0.54 0.81 1.03 115 F 1.43 1.87 90 F 1.15 1.50 0.55 0.68 1.26 1.43 0.76 . 1.10 . 0.94 1.35 1.80 2.57 2.01 2.89 1.34 1.65 3.17 3.54 1:58 L92 3.76 4.17 1:75 2.97 2.12 . -3.26 4.15 5.05 4.60 5.29 2.38 2.62 4.05 4.25 2.21 2.70 3.40 4.05 3.12 3.82 4.78 5.75 4.45 6.37 6.79 8,10 5.50 6.72 8.42 10.12 6.38 . 7:05 7.68 8.48 9.77 10.8 11.6 ' 12.8 .7.72 - 6.19 9.16 7.35 10.92 8.75 12.5 10.0 6.12 7.66 12.0 12.0 8.60 10.9 17.1 17.1 12:1 15.1 15.3 ' 19.2 24.0 30.1 24.0 - 30.1 19.1 27.2 20.9 29.4 27.8 . 39.7 30.2 43.2 38.2 42.3 55.7 61.0 47.8 51.8 69.8 76.1 38.6 40.7 71.3 126 55.2 58.6 100 183 78.0 83.0 141 1 257 97.3 103 176 322 211 297 422 352 503 712 550 . 780 . 1106 523 887 1373 17.4 32.2 34.6 34.6 55.0 60.0 80.3 87.0 111 118 203 366 602 1024 1582 19.2 24.5 38.2 38.2 60.7 66.2 88.7 96.0 123 130 224 403 664 1130 1748 19.2 20.6 32.2 32.2 51.5 54.5 72.0 78.8 95.8 101.6 171.5 266 461 725 1041 15.3 16.5 25.9 25.9 39.8 43.8 57.6 63.3 77.1 81.6 137.8 .214 370 582 836. t selected which will give the smallest loss consistent with overall economy in the system. Refrigerant liquid lines from the receiver to the expansion valve should be preferably designed with a pressure drop of less than 5 psi, and with 10 psi as the maximum. A velocity of 100 to 250 'fpm is recommended to prevent a pressure drop great enough to cause vaporization of the refriger ant ahead of the expansion valve. If the evaporator is' to be located at a higher elevation than the condenser or receiver, account should be taken of the pressure drop for each foot of static liquid lift'.1 Approximate values are 0.26.psi per foot for ammonia, 0.57 psi per foot for Freon-12, 0.51 psi Table 6. Approximate Suction-line Capacity Factors fob Equal Pressure Hdop m? 1?iraoTf-12 ... Saturated Suction . .. Temperature, F. 50 Factor.... . --: 1:09 40 1.00 30 0.92 20 0.86 10 0:80 0- 0.74 -10 0.66 -20 - 0.56 Refrigeration '7 per foot for Freon-22, and 0.64 psi per foot for Freon-11. Where there is a possibility of vaporization of some of the liquid before reaching the ex pansion Valves; means for subcooling-should be provided. Since a reduction of suction pressure at the compressor results in an appreciable reduction in capacity and more power input per ton of refrigera tion, great care should be given to the proper sizing of suction lines between the evaporator and the compressor. Although comparatively high veloci ties, 500 to 5000 fpm, may be used, the optimum value will depend upon the refrigerant and the operating pressure, range. Since return of the oil to the compressor must be considered in the case of Freon and methyl chloride, for these refrigerants, the minimum velocity should be 500 fpm for horizontal runs and 1000 fpm for vertical runs. For the Freons, the usual design velocities range between 1000 and 2000 fpm. Too high velocities create noise problems and excessive pressure drops. The total pressure drop in the suction line should be between one and two psi, if the velocity can be kept to within the specified limits. . Compressor discharge or hot gas lines may be designed with velocities from 1000 to 5000 fpm, except for dense gases such as carbon dioxide, where noise considerations will reduce the upper limit. A pressure drop of 2 to 4 psi is recommended for the discharge lines. Extensive tables are available in the literature for the determination of pressure drops through refrigerant lines with various refrigerants. The capacities listed in Tables 4, 5 and 6 are published in ACRMA Equipment Standards-1946, of the Air Con ditioning and Refrigerating Machinery Association, and are used by permis sion. Table 4 shows the tonnage capacity normally allowed for Freon-12 liquid lines per foot equivalent length of pipe, and Table 5 the maximum tonnage for suction and discharge Freon-12 linles. Table 6 presents suc tion-line capacity factors for; equal pressure drop. ACCESSORIES Dehydrators, oil separators, strainers, vibration eliminators, sight glasses, and various types of valves are accessories frequently needed for the proper installation and operation of refrigeration systems. Refrigerant-line de hydrators or dryers usually consist of copper containers fitted with tubing connections at either end, and contain a desiccant such as silica gel, acti vated alumina; or calcium chloride. The liquid refrigerant is circulated through the dryer during operation of the system, and the moisture content of the refrigerant charge is thus.kept to a minimum. Oil separators are installed between the compressor and condenser to prevent excessive oil removal from the compressor crankcase and its passage into the condenser and evaporator. The oil is separated from the gaseous refrigerant by gravity during its passage through a chamber, of sufficient size to reduce the velocity. A float-operated valve, maintains a maximum .oil level in the separator, and additional oil .is forced by pressure difference through a line back to the crankcase. Screen strainers are frequently installed in the liquid line piping before solenoid Valves and expansion valves, as well as before regulating valves in water lines leading to water cooled condensers.' Sight glasses which permit visual inspection of the condition of the refrigerant are sometimes installed on factory assembled commercial unit systems. It is particularly advisable to place such a fittingbefore the expansion valve, if the evaporator is located above the condenser. v- .