32 



CIRCULAR 7 4 0, U. S. DEPARTMENT OF AGRICULTURE 



14,000 or 15,000 boxes after they are cooled down. The approximate 

 refrigeration required for cooling and storing apples is shown in 

 table 5. 



Table 5. — Approximate refrigeration 1 required for apples if 1,000 boxes are 

 received daily and the fruit is cooled to 32° F. in 1 days 



Initial temperature (° F.) 



Tons of 

 refriger- 

 ation 



Initial temperature (° F.) 



Tons of 

 refriger- 

 ation 



55 



4.9 

 6.9 



75 



8.8 



65 



85 



10.8 









1 Allowance for open doors, workmen, motors, and other incidental sources of heat may increase this 

 requirement by 15 or 20 percent. 



INCIDENTAL HEAT SOURCES 



In addition to the fruit itself, other sources of heat are workmen, 

 motors, and lights. It may be assumed that each workman gives off 

 1,000 B. t. u. per hour. The heat from motors can be estimated at 

 3,000 B. t. u. per hour for each horsepower. Each 100-watt light 

 burning adds about 350 B. t. u. per hour. 



AIR INFILTRATION 



There are always times when it is necessary to leave outside doors or 

 conveyor ports open, and in some rooms the doors are open almost 

 continuously during the harvest season. Outside air entering the cold 

 room may carry in large quantities of heat. It is impossible under 

 ordinary conditions to estimate very accurately the heat load thus 

 added by infiltration of air. 



If it is assumed that a draft having a velocity of 200 feet per minute 

 is leaving a cold room at 35° F. through the lower half of a doorway 4 

 feet wide and 7 feet high and an equal current of dry warm air at 65° is 

 entering the upper half, an estimate of the entering heat can be made ; 

 200 feet per minute is about 2V4 miles per hour and is not a very notice- 

 able velocity. Under these conditions, however, 100,000 B. t. u. per 

 hour would enter through the open door. If the air were not very dry 

 the quantity would be even greater. It would keep an 8 -ton machine 

 busy just to remove this heat. 



At best, open doors permit a large entrance of heat, or loss of refrig- 

 eration, and prevent holding low temperatures in the room. For this 

 reason it is desirable to use small openings covered with canvas flaps 

 for loading cold-storage rooms. Such an opening, installed beside a 

 cold-storage door, is illustrated in figure 9. When it is necessary to 

 use hand trucks and keep full-size doors open, light swinging doors 

 that close after each truck has passed will reduce the loss of refrigera- 

 tion. 



HEAT PASSING THROUGH INSULATION 



Even when there is no infiltration of air through doors, windows, or 

 cracks, there is an unavoidable entrance of heat through the walls, 

 floor, and roof when the outside surfaces are warmer than the inside. 

 The quantity of heat entering through the walls may be reduced by 



