COLD STORAGE FOR APPLES AND PEARS 29 



cannot be depended upon for adequate circulation unless the whole 

 ceiling area is flooded with cold air or is provided with cooling coils. 



As the air circulates in a storage room the heat picked up raises its 

 temperature. If it is not picking up heat it is not doing any good. 

 The air returning to the brine spray or dry-coil bunker is therefore 

 warmer than that entering the room from the delivery ducts. The 

 difference in temperature between delivery and return is often referred 

 to as the "split," and this is directly related to the volume of air 

 circulated and the quantity of heat picked up in the room. If the 

 split is too large, the only way to reduce it without cutting down 

 the heat picked up is to increase the volume of air circulated. It can- 

 not be done by making adjustments of duct openings unless the 

 adjustments result in delivering a greater volume of air. 



For each ton of refrigeration used, an air volume of 1,000 c. f. m. 

 (cubic feet per minute) results in a split of about 10° F., although this 

 is modified somewhat when water transpired by the fruit is condensed 

 by the coils. This relation applies to any combination of refriger- 

 ation employed, to the volume of air, and to the resulting split. 

 For example, if 1,000 c. f. m. of air is used in picking up the heat 

 equivalent to 2 tons of refrigeration, the split will be about 20° ;, 

 or if 2,000 c. f. m. gives a split of 5°, about 1 ton of refrigeration is 

 being supplied. 



It is customary to design air-circulation systems so as to provide for 

 about 1,000 c. f. m. per ton of refrigeration capacity. For example, 

 a 25-ton plant would circulate about 25,000 c. f. m. This gives a 

 split of about 10° when the machinery is working at full capacity. 

 After the fruit has been cooled and some of the compressors are shut 

 off or slowed down, the same volume of air will result in a lower 

 split. When the refrigeration load is down to 5 tons and 25,000 

 c. f. m. is still used, a split of about 2° will result. In this case, a 

 variation of at least 2° may be expected in fruit temperatures in 

 different parts of the room. With less air volume the variation will 

 be greater. 



THERMOMETERS AND UNIFORM TEMPERATURES 



If fruit were not living and generating a small quantity of heat 

 continuously the problem of holding it at a uniform temperature 

 would be much simpler. The heat generated must be given up to 

 the air to prevent a rise in fruit temperature. To pick up this heat, 

 the air must be slightly colder than the fruit, and in picking up the 

 heat the air temperature is raised slightly. For this reason it is not 

 possible to have the same air or fruit temperature in all parts of a 

 storage room. In some rooms the variation may be kept down to 

 a fraction of a degree, while in others it may be difficult to avoid a 

 variation of several degrees even after the fruit has been cooled to 

 its final temperature. 



On account of these variations in temperature, readings from a 

 single thermometer in a room may be misleading. To operate a 

 plant to best advantage, it is desirable to know at least the highest 

 and lowest temperature in each room. It is the core temperature of the 

 fruit, however, that is most important and determines how well it 

 will keep. It is sometimes difficult to take fruit temperatures in all 



