COLD STORAGE FOR APPLES AND PEARS 3l 



cult to follow, however, if one keeps in mind that heat is just as real as 

 air or water. It can be moved from one place to another, but it can- 

 not vanish completely. If heat is taken from one place, the same quan- 

 tity must show up somewhere else. For this reason it is convenient to 

 think of units of heat as quantities that have a definite meaning, just 

 as we think of gallons of water. The important thing to keep in mind 

 is that a B. t. u. is a definite quantity of heat that can be pushed around 

 or divided up but still exists somewhere. 



The capacity of the cooling system required for a given job depends 

 upon how much heat must be removed each day. In apple and pear 

 storage this heat comes from several sources, each of which can be con- 

 sidered separately. The total load is the sum of the heat from all 

 sources. 



FIELD HEAT 



When fruit is placed in storage its temperature is ordinarily higher 

 than that desired. The heat to be removed in cooling it to the storage 

 temperature is called field heat. It takes about 0.9 B. t. u. to change 

 the temperature of 1 pound of apples by 1° F. If the temperature must 

 be reduced from 65° to 32°, for example, the change is 33°, and for 

 every pound of apples 29.7 (0.9 X 33) B. t. u. must be removed. On the 

 assumption that a box of apples weighs 50 pounds, every box cooled 

 from 65° to 32° requires the removal of 1,485 (29.7X50) B. t. u. If 

 1,000 boxes are stored under these conditions, 1,485,000 B. t. u. of field 

 heat are introduced into the storage room. If the fruit is cooler or 

 warmer, the heat load will be correspondingly less or greater. 



HEAT OF RESPIRATION 



Fruit continues to live as long as it is fit for food. It is therefore 

 continually generating heat by breaking down some of its constituent 

 materials. Bartlett pears or peaches starting at 60° F. in a nonrefrig- 

 erated, well-ventilated room probably would reach a temperature of 

 85° to 90° after 4 days and might go even higher. Kieffer pears and 

 grapes produce heat more slowly and probably would not warm up 

 to above 65° or 70° under the same conditions. Storage varieties of 

 apples would very likely be intermediate between these two groups. 

 It is easily seen in the case of Bartlett pears or peaches that if not 

 refrigerated they might become worthless within a week, even if they 

 did not suffer from decay. 



The rate at which this heat is generated depends upon the fruit 

 temperature. At 32° F. a box of apples gives off about 20 B. t. u. each 

 day. At 60° the figure is seven or eight times as great. Prompt cool- 

 ing therefore reduces the total quantity of heat to be removed from 

 a storage room. It is estimated that if a packed box of apples is cooled 

 from 65° to 35° in 1 week, its heat of respiration during this period 

 would amount to about 500 B. t. u. ; for 1,000 boxes the heat load would 

 be 500,000 B. t. u., which is about a third as much as the field heat load. 

 If cooling is so slow that it takes 2 weeks to reach 35°, another 500,000 

 B. t. u. will have been generated. Even after apples are cooled to 32°, 

 they continue to give off heat. Each 1,000 boxes generates about 20,000 

 B. t. u. per day at this temperature. Thus, 1 ton of refrigeration (re- 

 moval of 288,000 B. t. u. per day) will take care of the heat from about 



