Document vj9m1KnGzQ46Nm6LMXv6JkJb

776 CHAPTER 39 1949 Guide pressure be maintained inside the compressor during discharge than in the condenser. These losses result in a greater compression ratio and therefore greater power requirements as well as a lower volumetric efficiency and higher displacement requirements. Pressure losses in the liquid line between condenser or receiver and the expansion valve may result in some flashing of the liquid refrigerant unless the liquid is subcooled. In all cases frictional losses should be kept to a minimum, and piping should be Table 7. Maximum Tons op Compressor Capacitt fob Freon-12 Lines (Only for temperatures indicated) Lxnb See, Inches i OD f IPS i OD , i IPS i OD f IPS It OD 1 IPS 1* OD H IPS l* OD . U IPS 21 OD 2 IPS 21 OD . 21 IPS 31 OD 3 IPS 31 OD 31 IPS 41 OD 4 IPS 5 IPS 6 IPS 8 IPS 10 IPS 12 IPS Suction Lines 105 FBas^d on Condensing Teupshatube Discharge Lines Pd Pressure Drop per 100 Ft Equivalent Length at 40 F Saturation Condensing Temperature i . 2 3 4 5 115 F OOF 0.14 0.17 0.25 0.35 0.20 0.24 0.35 0.45 0.28 0.34 0.51 0.65 0.35 0.42 0.62 0.79 0.41 0.49 0.73 0.93 0.45 0.54 0.81 1.03 1.43 1.87 1.15 1.50 0.55 0.68 1.26 1.43 0.76 . 0.94 1.80 2.01 1.10 1.35 2.57 2.89 1.34 1.65 3.17 3.54 1.58 1.92 3.76 4.17 1.75 2.12 4.15 4.60 2.97 3.26 5.05 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 5.37 6.79 8.10 5.50 6.72 8.42 10.12 6.38 7.68 9.77 11.6 7.05 8.48 10.8 12.8 7.72 9.16 10.92 12.5 6.19 7.35 8.75 10.0 6.12 7.66 12.0 12.0 8.60 10.9 17.1 17.1 12.1 15.3 24.0 24.0 15.1 19.2 30.1 30.1 17.4 32.2 34.6 34.6 19.2 24.5 38.2 38.2 19.2 20.6 32.2 32.2 15.3 16.5 25.9 25.9 19.1 20.9 27.8 30.2 27.2 29.4 39.7 43.2 38.2 42.3 55.7 ' 61.0 47.8 51.8 69.8 76.1 55.0 60.0 80.3 87.0 60.7 66.2 88.7 96.0 51.5 . 54.5 72.0 78.8 39.8 43.8 57.6 63.3 38.6 55.2 78.0 97.3 111 123 95.8 77.1 40.7 58.6 83.0 103 118 130 101.6 81.6 71.3 100 141 176 203 224 171.5 137.8 126 183 257 322 366 403 266 214 211 : 297 422 523 602 664 461 352 503 712 887 1024. 1130 725 550 780 1106 1373 1582 1748 1041 370 582 836 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. Approximate values are 0.26 psi per foot for ammonia, 0.57 psi per foot for Freon-12, 0.51 psi Refrigeration 777 ' per foot for Freon-22, and 0.64 psi per foot for Freon-11. Where there is apossibility 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 powerinput 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 Fig. 14. Performance Characteristics op Compression Refrigeration Machines at Constant Speed chloiide, 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 5, 6 and 7 are published in ACRMA Equipment Standards-1946, of the "Air Con ditioning and Refrigerating Machinery Association and are used by permis-