52 



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



OVERHEAD SPACE 



In most storage rooms air circulation is planned so as to have the 

 primary movement over the tops of the boxes and through aisle spaces. 

 The cooling in the interior of the stacks is accomplished partly by 

 secondary, or convection, currents up and down the spaces between 

 boxes. This cooling is effective only insofar as the warm air that rises 

 to the ceiling is moved away and replaced by colder air. Leaving rea- 

 sonable space overhead permits sufficient circulation for carrying off 

 the heated air (fig. 21) . If the space is limited there is a tendency for 

 the air to move along aisles or unfilled channels in preference to the 



ceiling space ; when 

 fruit is stacked too 

 close to the ceiling, air 

 m o v e m e n t is re- 

 stricted, cooling is re- 

 tarded, and it cannot 

 be accomplished even- 

 ly (fig. 22). No rule 

 has been established 

 on the minimum space 

 required over the 

 boxes to permit good 

 circulation, but it is 

 good practice to leave 

 a space of several 

 inches even if the ceil- 

 ing is free from gird- 

 ers or other obstruc- 

 tions. 



If the primary air 

 circulation can be 

 forced to move 

 through the spaces be- 

 tween stacks, more 

 rapid cooling can be 

 accomplished. Keduc- 

 ing the space over the 

 boxes will tend to 

 move more of the pri- 

 mary circulation through the spaces, but it will also divert more of it 

 through aisles or other open channels. Unless such channels are 

 avoided, loading close to the ceiling or putting baffles across the ceil- 

 ing to force more air into the box spaces may result in moving most of 

 the air through the aisles, where it is least effective for cooling. 



For storage rooms in which relatively slow cooling is not objec- 

 tionable the type of circulation that provides for flooding the ceiling 

 space with moving air and depends upon natural convection to cool 

 the interior of the stacks will provide fairly uniform temperatures 

 throughout the room, with a minimum of care in laying out the 

 loading arrangement. Sometimes in order to hasten cooling, the pri- 



FlGUEE 21. 



-Packages properly separated and with 

 adequate space overhead. 



