Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTS 



47.93 



Figure 19-5.— Evaporator tubing. 



is subcooled slightly below its boiling point at 

 this pressure to ensure that it will not flash 

 into vapor. 



A water-cooled condenser for an R-12 re- 

 frigeration system is shown in figure 19-7. 

 Circulating water is obtained through a branch 

 connection from the firemain or by means of an 

 individual pump taking suction from the sea. 

 A water regulating valve (not shown) is usually 

 installed to control the flow of cooling water 

 through the condenser. The purge connection 

 shown in figure 19-6 is on the refrigerant side; 

 it is used to remove air and other noncondens- 

 able gases that are lighter than the R-12 vapor. 



Most condensers used in naval refrigeration 

 plants are water cooled. However, some small 

 units have air-cooled condensers. These consist 

 of tubing with external fins to increase the heat 

 transfer surface. Most air-cooled condensers 

 have fans to ensure positive circulation of air 

 around the condenser tubes. 



RECEIVER.— The receiver, shown in figure 

 19-8, acts as a temporary storage space and 

 surge tank for the liquid refrigerant which flows 

 from the condenser. The receiver also serves 

 as a vapor seal to prevent the entrance of vapor 

 into the liquid line to the thermostatic expansion 

 valve. 



ACCESSORIES AND CONTROLS .-In addition 

 to the five major components just described, a 

 refrigeration system requires a number of con- 

 trols and accessories. The most important of 

 these are discussed briefly in the following 

 paragraphs. 



in the liquid 

 Figure 19-10 

 thermostatic 

 The thermo- 



A dehydrator (or dryer ) is placed in the 

 liquid refrigerant line between the receiver 

 and the thermostatic expansion valve. In older 

 installations, such as the one shown in figure 

 19-2, bypass valves allow the dehydrator to be 

 cut in or out of the system. In newer instal- 

 lations, the dehydrator is installed in the liquid 

 refrigerant line without any bypass arrange- 

 ment. A refrigerant dehydrator is shown in 

 figure 19-9. 



A solenoid valve is installed 

 line leading to each evaporator, 

 shows a solenoid valve and the 

 control switch that operates it. 

 static control switch is connected by long flex- 

 ible capillary tubing to a thermal bulb which 

 is located in the refrigerated space. When 

 the temperature in the refrigerated space drops 

 to the desired point, the thermal bulb causes 

 the thermostatic control switch to open, thereby 

 closing the solenoid valve and shutting off all 

 flow of liquid refrigerant to the thermostatic 

 expansion valve. When the temperature in the 

 refrigerated space rises above the desired point, 

 the thermostatic control switch closes, the 

 solenoid valve opens, and liquid refrigerant 

 once again flows to the thermostatic expansion 

 valve. 



The solenoid valve and its related thermo- 

 static control switch serve to maintain the 

 proper temperature in the refrigerated space. 

 However, we may wonder why the solenoid 

 valve is necessary, since the thermostatic 

 expansion valve controls the amount of refrig- 

 erant admitted to the evaporator. Actually, the 

 solenoid valve is not necessary in systems 

 having only one evaporator. In systems having 

 more than one evaporator, where there is wide 

 variation in load, the solenoid valve provides 

 the additional control required to prevent spaces 

 from becoming too cold at light loads. 



In addition to the solenoid valve installed 

 in the line to each evaporator, a large refrig- 

 eration plant usually has a main liquid line 

 solenoid valve installed just after the receiver. 

 If the compressor stops for any reason except 

 normal suction pressure control, the main liquid 

 line solenoid valve closes and prevents liquid 

 refrigerant from flooding the evaporator and 

 flowing to the compressor suction. Great dam- 

 age to the compressor can result if liquid is 

 allowed to enter the compressor suction. 



Whenever several refrigerated spaces of 

 varying temperatures are to be maintained 

 by one compressor, an evaporator pressure 



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