Document M4OmXyO18KpgEnKw9Qmb3GwQ9

360 CHAPTER 38 1959 Guide Table 7.... Approximate Suction-tine Capacity Factors for Equal Pressure Drop of COsFi (Refrigerant 12) SoKnltJ ftBfwretot, F. SO 40' 30 20 10 0 -10 -20 Factor.. 1.09 1.00 0.92 0.86 0.80 0.74 0.66 0.56 and discharge CCLF* lines. Table 7 presents suction-line capacity factors for equal pressure drop. ACCESSORIES Dehydrators, oil separators, strainers, vibration elimi nators, sight and various types of valves are ac cessories 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, activated 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 com pressor crankcase and its passage into the condenser and evaporator. The oil is separated from the gaseous refrig erant by gravity during its passage through a chamber of sufficient size to reduce the velocity. A float-operated valve imunfauna a minimum oil level in the separator, and ad ditional oil is forced by pressure difference through, a line back to the crankcase. / X *> / /A 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 that permit visual inspec tion of the condition of the refrigerant are sometimes in stalled on factory-assembled commercial unit systems. It is particularly advisable to place such a fitting before the expansion valve, if the evaporator is located above the condenser. Flexible vibration eliminators, usually consisting of a bellows design covered with woven copper wire, are some times installed in copper lines where units such as com pressors are installed on flexible mountings, or where vi bration is otherwise a problem. Packed or packless shut-off valves are necessary where it may be required to isolate portions of a system. EQUIPMENT CHARACTERISTICS AND SELECTION The various types of compression systems have quite different characteristics of capacity and power with varying evaporator and condenser temperatures, as may be noted from curves in Figs. 16 and 17. From Fig. 16 it may be observed that power require ments for the centrifugal compressor increase much more rapidly than for the reciprocating compressor, with in crease in evaporator temperature. Similarly, the capacities of the steam ejector and centrifugal compressors increase more rapidly than those of the reciprocating compressor with increase in evaporator temperature. Thus, both the steam-jet and centrifugal machines tend to be more seifregulating than the reciprocating. It is also evident from Fig. 16. that the steam-jet equipment is best suited for operation at high evaporator temperatures. The effect of condenser temperature upon the power and capacity of the different types of compressors is shown in Fig. 17. It may be noted that the power required by the . X '/ f/ / * L* R y cstln / L- iiii Fig. 16 .... Performance Characteristics of Compression Refrigeration Machines at Constant Speed Fig. \7 .... Performance Characteristics of Compression Refrigeration Machines at. Constant Speed Refrigeration 561 Capacity Tons Table 8 .. .. Basis ef Equipment Selection Majority Died Sam Umd Few (M 0 to 10 Unit systems in conditioned space. Unit central systems using duct Built-up central systems. distribution. 10 to 25 Unit- central systems using duct distribution. Unit systems in conditioned apace. Built-up central systems using re ciprocating compressors, adsorp tion, and absorption systems. 25 to 100 Built-up central systems using re ciprocating compressors. Unit central systems using duet distribution. Central systems using adsorption systems or centrifugal refrigera tion. 100 to 200 Built-up central systems using re ciprocating compressors. Built-up central systems using ab sorption and centrifugal com pressors. Built-up centra] systems using steam jet. 200 and Over Built-up central systems using cen Built-up central systems using Built-up central systems using re trifugal compressors- steam jet or absorption systems. ciprocating compressors. reciprocating compressor increases rapidly with increase in condenser temperature, while the power curve for the centrifugal compressor is relatively flat. It is also evident that the capacity of the steam-jet compressor is independent of condenser temperature untU a certain point is reached, where-it drops to zero. As previously stated, steam-jet equipment requires more condensing water than other types of compression systems. Consequently, steam-jet systems are well suited to those applications where condensing water is cheap, or where condensing water is rather high in temperature. The selection of proper refrigeration equipment for any' air-conditioning job is of utmost importance for satisfactory " results. The most important factors in the selection of the equipment are: 1. Loads (as determined by the conditions of the space to be cooled). 2. Economics (both initial and operating costs). 3. Codes (local safety codes must be adhered to and in fluence the type of system to be used). A broad division of equipment to be used for a particular installation or application may be made on the basis of the magnitude of the load. Current general practice is outlined in Table 8. Unit or' packaged systems, consisting of .a reciprocating compressor, condenser, evaporator, and fans, are generally used in the smaller sized jobs where electric power is avail able, as they are manufactured complete, ready to install, and are the most economical (See Chapter 16). The reciprocating compressor in the built-up central sys tem (see Chapter 29) covers the widest range of application since it is applicable to either the direct-expansion or in direct systems, and can be driven by steam or gas engines, or by electric motors. The quantity of condensing cooling medium required is also less than for any other system, with the exception of the centrifugal compressor, which uses the same amount. Table 9 .... Typical Operating Conditions for Two Types of Load Air Entering Coif Operating SeJcace Point Typo of 6idoiw Lood Bfu Sera&fo par Hr. to Total Heat Tmp. RoL H%' Evapo rator Condertjer Pri~ Pti klT Hoot % Restaurant Sensible Latent Total 103.000 45,000 148.000 0.695 82 45 34.4 123 69.9 Office............ Sensible 121,000 Latent 27,000 Total 148,000 0.820 82 45 42.2 100 82.1