COLD STORAGE FOR APPLES AND PEARS 



27 



ATMOSPHERIC MOISTURE 





The humidity, or moisture content, of the atmosphere in a storage 

 room depends largely upon the temperature to which the air is cooled 

 in contact with the pipes or the brine. 



If doors are left open in warm weather, the warm air entering the 

 storage may be a source of moisture, but the frost on the pipes or the 

 overflow in the brine tank is largely from water vapor transpired by 

 the fruit. It is desir- 

 able to keep this 

 transpiration at a 

 minimum by main- 

 taining a relative hu- 

 midity of approxi- 

 mately 85 percent. 

 This may be done by 

 limiting the quantity 

 of water picked up on 

 the coils or in the 

 spray. Some water in 

 the form of gas or va- 

 por is contained in 

 the atmosphere. The 

 lower the tempera- 

 ture, the less the quan- 

 tity of vapor that can 

 be held. As the tem- 

 perature of the air 

 drops, a point is fi- 

 nally reached at 

 which some of the wa- 

 ter can no longer exist 

 as vapor and it con- 

 denses to form water 

 or frost. The greater 

 the temperature drop, 

 the greater the conse- 

 quent condensation. 



It is important, 

 therefore, to operate 

 without reducing the 

 air temperature 

 lower than necessary. 

 In an air-circulation 

 system, this is done 

 by using large quantities of air and plenty of cooling surface. 

 If too little air is used, its temperature must be reduced greatly and 

 excessive condensation will occur. If there is not enough coil surface 

 in a direct-expansion system the pipes will have to be extremely cold 

 and the air coming in contact with them will lose a large part of its 

 moisture. Contrary to common belief, a brine spray, when used for 

 cooling, does not add humidity to the air. On the other hand, it tends 

 to pick up moisture. For this reason some of the brine must be 



Figuee 6. — A unit cooler in which the cold air is 

 distributed from nozzles at the top of the room 

 and the warm air is returned from the floor. 

 With such installation, air is not returned from 

 the warmest areas of the room and the best 

 refrigeration efficiency is not obtained. A more 

 efficient installation is shown in figure 7. 



