COLD STORAGE FOR APPLES AND PEARS 



41 



because they permit delivery of the required volume of air without 

 excessive velocities. Ducts that are too small in cross section or cause 

 abrupt turns in the air streams build up a resistance that results in 

 high power consumption and inefficient circulation. 



Increased resistance is also caused by attempting to deliver the air 

 through many small openings in the ceiling of a cold-storage room. 

 This system of delivery has the added disadvantage of short-circuiting 

 the air flow from delivery to return openings. Unless the air passes 

 through the body of the stacked fruit the maximum quantity of heat 

 is not being removed. 



Figuee 13. — Air duct passing beneath a girder. Unless the interior is streamlined 

 to give smooth walls, rounded curves, and small changes in area, the resistance 

 from turbulence will greatly interfere with air flow. 



SPACING AIR DUCTS 



The distance between the delivery and the return openings is de- 

 pendent upon several conditions. The temperature of the air leaving 

 a storage room is necessarily warmer than that entering it from the 

 delivery ducts. The larger the volume of air circulated, the less this 

 temperature difference will be. In fact, in a given room from which 

 a certain quantity of heat is being removed, the temperature difference 

 is determined almost entirely by the rate of air circulation, in cubic 

 feet per minute or in air changes per hour. 



The method of distributing the circulation has no direct effect on 

 the temperature rise in the air unless it affects the volume circulated 

 or the quantity of heat picked up. Since the temperature of the air 

 leaving the room is dependent upon the volume circulated, the dis- 

 tribution within the room or the relation between discharge and return 

 openings can be adjusted to the requirements of the specific room, 

 bearing in mind the necessity for having the warmest air in the room 

 enter the returns and the desirability of having relatively high veloci- 

 ties to keep the fruit temperature down as nearly as possible to that of 

 the air. 



