Document MGMrZEOEvp1DpY4dkJgj902mM

822 CHAPTER 36 1952 Guide I "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 nfthe 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 TOO 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. Freon-12 Liquid Lines, Tons Capacity per 100 Ft Equivalent Length Pressure Drop per 100 Ft Equivalent Length, Psi 3 5 1 20 - t OD i OD i IPS |OD i IPS lOD 1 IPS . li OD 11 IPS If OD 11 IPS If OD 2 IPS 21 IPS 3 IPS 31 IPS 4 IPS 0.88 2.89 , 4.88 4.88 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. 2.68 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 psi 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 pier 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 823 Table 6. `Maximum ^Tons of Compressor. Capacity for Freon-12 Lines (Only for temperatures indicated) Suction Lines Based on 105 F Condensing Temperature Discharge-Lines Line Size, Inches i OD 1I OIPDS | IPS { OD f IPS li OD 1 IPS 1| OD li IPS li OD ii ips 2i OD 2 IPS 2| OD 2i IPS 3J OD 3 IPS 3| OD 3| IPS 4J 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 2 1 .3 '4 M 5 . lift F.; (;F 0.14 0.17 0.25 0.35 ;o.55 0.68 1.26 1.43 0.20 0.24 0.35 0.45 0.76 0.94 1.80 2.01 0.28 0.34 0.51' 0.65. l.J 1.35 2.57 2.89 0.35 0.42 0.62 0.79 1.34 1.65 3.17 3.54 o:'4i 0.49 0.73 0.93 0.45 0.54 0.81 1.03 1.58 ; 1.92 3.76 4.17, 1.75 2.12 4.15 4.60 1.43 1.87 2.97 3.26 5.05 5.29 1.15 1.50 2.38 2.62 4.05 4.25 2.21 2.70 3.40 4.05 3.12 i 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 7.72 8.48 9.16 10.8 . 10.92 12.8 12.5 6.19 7.35 8.75 10.0 6.12 7.66 12.0 12.0 19.1 20.9 27.8 30.2 8.60 12.1 10.9 ! 15.3 17.1 24.0 ; ;171 24.0 27.2 38.2 29.4 42.3 39.7 , 55.7 43.2 61.0 15.1 19.2 30.1 30.1 47.8 51.8. 69.8' 76.1 17.4 32.2 34.6 34.6 55.0 60.0 80.3 87.0 19.2 24.5 38.2 : 38.2 ' 60.7 66.2 - 88.7 : 96.0 19.2 20.6 32.2 32.2 51.5 54.5 72.0 78.8 15.3 16.5 25.9 25.9 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 97.3 103 176 322 111 118 203 366 123 130 : 224 403 95.8 101.6 171.5 266 77.1 81.6 137.8 214 211 352 550 297 422 523 602 664 461 503 712 887 1024 1130 725 780 1108 1373 1582 1748 1041 370 582 836 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 tipper limit. A pressure d^op 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- Table 7. Approximate Suction-line Capacity Factors for Equal Pressure Drop of Freon-12 _io -Saturated Suction Temperature. F. 50 40 30' 20 ib 0 -20 Factor ...: . ...... 1.09, 1.00 0.92 0.86 0.80 .0:74 0.66 0.56