Document yrNE7Mv7xZYXGq424MKdo7Jar

HEATINC VENTILATING AIR CONDITIONING CUIDE 1944 Table 4. Properties op Carbon Dioxide Sat. pAaa. Volume Het Content and Enteopt Takes Feom -40 F Trap. F Lr ros Sq In Liquid Vapor Heat Content Liquk Vapor Entropy Lfqoic Vapor 50 F Superheat 100 F Superheat Hi. Ct Entropy Hi. Ct 0. 2 4 5 6 8 10 12 14 16 18 20 22 24 26 28 . 30 32 34 36 '38 39 40 41 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 . 72 74 76 78 80 82 3055 315.9 326.5 332.0 337.4 0.01570 0.01579 0.01588 001592 0.01596 . 0.29040 0.28030 0.27070 0.26610 0.26140 348.7 360.2 371.9 383.9 396.2 0.01605 0.01614 0.01623 0.01632 0.01642 0.25260 0.24370 0.23540 0.22740 0.21970 408.9 421.8 434.0 448.4 462.2 0.01652 0.01663 0.01673 0.01684 0.01695 0.21210 0.20490 0.19790 0.19120 0.18460 476.3 490.8 505.5 522.6 536.0 0.01707 0 01719 0.01731 0.01744 0.01759 0.17830 0.17220 0.16630 0.16030 0.15500 551.7 559.7 567.8 576.0 584.3 0.01773 0.01780 0.01787 0.01794 0.01801 0.14960 0.14700 0.14440 0.14185 0.13930 601.1 618.2 635.7 653.6 671.9 0.01817 0.01834 0.01851 0.01868 0.01887 0.13440 0.12970 0.12500 0.12050 0.11610 690.6 709.5 728.8 748.6 769.0 0.01906 0.01927 0.01948 0.01970 0.01995 0.11170 0.10750 0.10340 0.09940 0.09545 789.4 810.3 831.6 853.4 875.8 0.02020 0.02048 0.02079 0.02112 0.02152 0.09180 0.08800 0.03422 0.08040 0.07654 898.2 921.3 9445 968.7 993.0 0.02192 0.02242 0.02300 0.02370 0.02456 0.07269 0.06875 0.06473 0.06064 0.05648 18.8 19.8 20.8 21-3 21.8 22.9 24.0 25-0 26.1 27.2 28-3 29.4 30-5 31.7 32.9 34.1 35.4 36.7 37.9 39.1 40.4 41.0 41.7 42.3 42.9 44.3 45.6 47.0 48.4 49.8 . 51.2 52:6 54.0 55.5 57.0 58.6 60.2 61.9 63.7 65-5 67.3 69.4 71.6 73.9 76.4 138.9 138.8 138.8 138.8 138.7 0.0418 0.0440 0.0461 0.0472 0.0483 0.3024 0.3014 0.3005 0.3000 0.2994 153.7 153.7 153.7 153.7 153.7 0.3342 0.3330 0.3318 0.3312 0-3306 167.5 167.6 167.7 167.7 167.8 0.3612 0.3600 0-3588 0-3582 0.3576 138.7 138.7 138.6 138.6 138.5 138.4 138.3 138.2 138.1 138.0 0.0504 0.0526 0.0548 0.0571 0.0593 0.2982 0.2970 0.2958 0.2946 0.2933 0.0616 0.0638 0.0662 0.0686 0.0710 0.2921 0.2909 0.2897 0.2885 0.2873 153.7 153.7 153.7 153.7 153.7 153.7 153.7 153.7 153.7 153.7 0.3293 0.3281 0.3270 0.3259 0.3249 0.3238 0.3227 0.3214 0.3202 0.3189 167.9 168.0 * 168.1 168.2 168.3 0.3563 0-3550 0.3538 OJ526 0-3513 168.5 168.6 168.7 168.8 168.9 0.3501 0.3489 0.3479 0-3470 0-3460 137.9 137.8 137.7 137.4 137.2 0.0734 0.0758 0.0781 0.0804 0.0828 0.2861 0.2849 0.2834 0.2820 0.2805 153.7 153.7 153.7 153.7 153.7 0.3177 0-3164' 0.3158 0.3151 0-3145 169.0 169.1 169.2 169.3 169.4 0.3451 0.3441 0.3431 0.3421 0.3411 136.9 136.8 136.7 136.5 136.3 0.0851 0.0862 0.0874 0.0887 0.0899 0.2791 0.2783 0.2776 0.2768 0.2761 153.7 153.7 153.7 153.7 153.7 0-3138 0.3135 0.3132 0.3127 0.3122 169.5 169.5 169.6'. 169.6 169.7 0.3401 0.3396 0-3391 0.3386 0-3381 136.1 135.7 135.4 135.0 134.5 0.0924 0.0950 0.0975 0.1000 0.1027 0.2745 0.2730 0.2714 0.2699 0.2681 .153.7 153.7 153.7 15.3,7. 153.7 0-3112 0.3101 0.3091 0.3081 0.3069 169.8 169.9 170.0 170.1 170.2 0.3371 0.3362 0.3352 0-3342 0.3333 133.9 133.4 132.7 132.1 131.3 0.1054 0.1081 0.1108 0.1135 0.1164 0.2663 0.2644 0.2626 0.2608 0.2584 153.7 153.7 153.7 153.7 153.7 0.3057 0.3046 0.3034 0.3022 0.3012 170.3 170.5 170.6 170.7 170.8 0.3324 0.3315 0.3306 0-3297 0.3289 130.6 129.7 128.7 127.5 126.0 0.1194 0.1223 0.1253 0.1282 0.1321 0.2560 0.2535 0.2511 0.2487 0.2450 153.7 153.7 153.7 - 153-7._ 153.7 0.3002 0.29910.2981 0.2971 0.2962 170.9 171.0 171.1 171.2 171.3 0.3281 0.3273 0.3265 0.3257 0.3250 124.5 122.8 120.9 118.7 116.6 0.1360 0.1398 0.1437 0.1476 0.1578v 0.2414 0.2377 0.2341 0.2304 0.2195 153.7 153.7 153.7 153.7 153.7 0.29S3 0.2945 0.2936 0.2927 0.2920 171.4 171.5 171.6 171.7 173.8 0.3242 0.3235 0.3227 0.3220 0.3215 84 86 . 87.8 1017.7 1043.0 1069.9 0.02553 0.02686 0.03454 0.05223 0.04789 0.03454 79.4 83.3 97.0 113.9 110.4 , 97.0 0.1679 0.1781 0.1880 0.2087 0.1978 0.1880 153.7 153.7 153.7 0.2914 0.2907 0.2901 176.0 178.2 180.1 0.3209 0.3204 0.3199 Types of Compressors There are many different types of compressors, using various refrig erants. Each type has its advantages for its particular application, and those generally used for air conditioning are of the following types: . 1. Reciprocating compressors (commonly referred to as piston type). 2. Centrifugal compressors. 3. Steam jet. Reciprocating compressors are available in a wide range of sizes and types. Any of a number of refrigerants, including dichlorodifluoromethane 470 CHAPTER 25. REFRIGERATION (Fu), methyl chloride, ammonia, carbon dioxide, and sulphur dioxide may be used in reciprocating machines. The first of these is used exten sively in direct expansion systems of comfort air conditioning. Compressors may be classified into two general types, (a) open type, (6) enclosed type. If the driving mechanism is external to the compressor, then the shaft must be brought out through the crankcase and a shaft seal or stuffing box must be used to prevent escape of the refrigerant. This type of compressor is known as an open-type compressor. When the driving mechanism is located within the crankcase of the compressor in such a way as to avoid the necessity of a shaft seal, the compressor is known as the completely enclosed or hermetically sealed type. Open type compressors may be further classified as belt driven and directly conhected. A great number of direct-driven units are now being used which generally operate at' higher rotational speeds than the beltdriven type. The present tendency is toward forced lubrication of the bearings of . compressors by means of an oil pump driven from the crankshaft, although there are many splash lubricated compressors on the market. The chief advantages of the forced lubricated compressor are that the lubrication system requires less energy for its operation than the splash type, the oil can be easily filtered before it enters the bearings, and less oil is usually required. The compressor, capacity must be selected for and matched to the maximum load for the installation on which it is to be used. Air-con ditioning loads, however, vary over a wide range, and a wide fluctuation in air conditions may result during periods of light load if on-and-off control of full compressor capacity is used. To prevent such undesirable fluctuation, several methods are employed to vary the capacity of reciprocating compressors, such as: 1. By-passing one or more cylinders, of a multi-cylinder compressor, from discharge to suction. 2. Rendering the suction valves of one or more cylinders of a multi-cylinder compressor inoperative. This is usually accomplished by depressing the suction valves. 3. Varying the speed of the compressor, usually by using variable speed or two-speed electric motors. 4. Using clearance pockets to control the quantity of refrigerant pumped. 5. Restricting the suction inlet to one or more of the cylinders of a multi-cylinder compressor either by an automatic modulating valve or by an on arid off valve. All of these methods, with the exception of variable speed, result in a slightly lowered overall compressor efficiency when in use, since the mechanical losses remain constant whereas the quantity of refrigerant pumped is lowered. Centrifugal compressors are used with very low pressure refrigerants; usually both evaporator and condenser work below atmospheric pressure. Water and monofluorotrichloromethane (Fu) are the refrigerants com monly used in centrifugal machines. Compression of the refrigerant is accomplished by means of centrifugal force; therefore, this type of compressor is inherently suitable for large volumes of refrigerant at low pressure differentials. Two or more stages are usually required and high speeds are necessary to obtain good efficiency. 471