COLD STORAGE FOR APPLES AND PEARS 21 



Where a dry climate or limited supply of cooling water makes it 

 desirable, the effect of evaporative cooling may also be obtained with 

 shell-and-tube or double-pipe condensers by using a cooling tower or 

 a cooling pond. In this type, the water from the condenser, instead 

 of being wasted, is pumped to a tower ( frequently on top of the build- 

 ing) or to a cooling pond adjacent to the building where it is forced 

 through nozzles to form a spray. After falling through the atmos- 

 phere, where it is cooled by the evaporation of a small portion, the 

 water is recirculated through the condenser. 



Another type, the atmospheric condenser, as frequently used with 

 small cooling or freezing cabinets, usually is not practical for larger 

 installations. 



COMPRESSOR 



The compressor, by pumping ammonia from the evaporator to the 

 condenser, takes the heat that has been absorbed in the coils and, by 

 raising the temperature, allows the heat to be carried away by the 

 condenser cooling water. The rate of heat removal by an ammonia 

 compressor running at a given speed depends only upon the head 

 pressure and the suction pressure at which it operates; the higher 

 the suction pressure and the lower the head pressure the more heat 

 will be removed. If the speed is increased, the rate of heat removal 

 will increase proportionately, assuming a given set of pressure con- 

 ditions. It is good practice, therefore, to operate a compressor at 

 as high a speed as its design will permit, especially during the season 

 when warm fruit is being received. 



In fruit storage the demand on the refrigerating equipment is 

 at a maximum for only a short period in fall. Much of the capacity 

 of this equipment is unnecessary during the rest of the year. To 

 get the most out of it for this critical period, while keeping the 

 investment in equipment at a minimum, it is sometimes economical 

 to operate at higher speeds than would be advisable for year-round 

 operation. Compressors, however, should be speeded up only after 

 consulting the manufacturer regarding the particular machine. 

 Greater capacity may be obtainable in some slow-speed compres- 

 sors by changing the valves and lubrication system to permit con- 

 siderably higher speeds. 



It is a mistake to judge the capacity of the refrigerating system 

 by the size either of the compressor or of the motor installed. The 

 capacity will depend upon the whole system and the conditions under 

 which it operates. For comparative purposes the refrigerating capac- 

 ity of a compressor is normally expressed as standard tons when 

 operating with a head pressure of 155 pounds and a suction pressure 

 of 20 pounds, but the actual capacity will be influenced by condi- 

 tions in the system as a whole that cause variations in these pres- 

 sures. The capacity of and power required for typical ammonia com- 

 pressors of various sizes are given in table 2. 



