Document p2MoQk9eYpqmpYbVDRy8Ngkrw

854 CHAPTER 37 1954 Guide 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 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 Table 5. Fheon-12 Liquid Lines, Tons Capacity per 100 Ft Equivalent Length Line Sue, Inches Pressure Drop per 100 Ft Equivalent Length, Psi 3 5 10 20 fOD i OD i IPS f OD I IPS f OD 1 IPS li OD 11 IPS liOD li IPS If OD 2 IPS 2i IPS 3 IPS 3i IPS 4 IPS 0.88 2.89 4.86 4.86 9.73 10.5 21.4 21.4 36.9 36.9 62.0 62.0 124. 230. 364. 539. 753. 1.14 3.64 6.81 6.81 12.6 14.1 28.2 28.2 48.1 48.1 80.2 80.2 161. 297. 469. 704. 972. 1.80 5.56 10.2 10.2 18.5 21.8 41.3 41.3 70.5 70.5 114. 114. 231. 426. 676. 1005. 1385. Note: Tonnage values above those underlined give velocities of 300 fpm or less. 2.58 8.50 15.8 15.8 27.0 33.0 60.8 60.8 101. 101. 160. 160. 328. 607. 972. 1430. 1945. 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 pa 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 Refrigeration 855 Table 6. Maximum Tons op Compressor , Capacity (Only for temperatures indicated) fob Freon-12 Lines Line Size ^NCBBS i OD 1 IPS |OD i IPS i OD 1 IPS li OD 1 IPS 'll OD li IPS If OD li IPS 2i OD 2 IPS 2f OD 2i IPS 3i OD 3 IPS 3f OD 3i IPS 4i OD 4 IPS 5 IPS 6 IPS 8 IPS 10 IPS 12 IPS Suction Lines Based on 105 F Condensing Temperature --------------------------------------Psi Pressure Drop per 100 Ft Equivalent Length at 40 F Saturation 11 234 5 Discharge Lines Condensing Temperature 115 F 90 F 0.14 o.r 0.2; 0.3 0.2( 0.24 0.35 0.45 0.21 0.34 0.51 0.65 0.3i 0.45 0.65 0.7E 0.41 0.4E 0.75 0.95 0.45 0.54 0.81 1.05 1.45 1.8' 1.15 1.50 0.55 0.68 1.26 1.43 0.76 0.94 1.80 2.01 1.1C 1.35 2.57 2.89 1.34 - 1.65 3.17 3.54 1.58 .1.92 3.76 4.17 1.75 2.15 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 6.12 ~~~8.'60 7.66 12.0 12.0 10.9 17.1 17.1 4.45 5.37 6.79 8.10 12.1 15.3 24.0 24.0 5.50 6.72 8.42 10.12 15.1 19.2 30.1 30.1 6.38 7.68 9.77 11.6 7.05 8.48 10.8 12.8 17.4 32.2 34.6 34.6 . 19.2 24.5 38.2 38.2 7.72 9.16 10.92 12.5 19.2 20.6 32.2 32.2 6.19 7.35 8.75 10.0 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 40.7 71.3 126 55.2 58.6 100 183 78.0 83.0 141 257 97.3 103 176 322 111 118 2C3 366 123 130 224 403 95.8 101.6 171.5 266 77.1 81.6 137.8 214 211 352 550 297 503 780 422 712 1106 523 887 1373 602 1024 1582 664 1130 1748 461 725 1041 370 582 836 r 'ajuu__i c__1 __ r u. wie guenon nne snouia tie 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 ARI Equipment Standards-1946, of the AirConditioning and Refrigeration Institute, and are used by permission. Table 7. Approximate Suction-line Capacity Factors for Equal Pressure Drop of Freon-12 Saturated Suction Temperature, F. factor 50 40 30 20 10 0 -10 -20 1.09 1.00 0.92 0.86 0.80 0.74 0.66 0.56