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CIRCULAR 74 0, U. S. DEPARTMENT OF AGRICULTURE 



drained off occasionally and more salt added. If a brine-spray sys- 

 tem results in higher humidity than a direct -expansion or dry-coil 

 bunker system, it is because it removes less moisture. This is because 

 the cooling surfaces with which the air comes in contact are not so 

 cold as when brine coils are used. 



In well-designed and well-filled cold-storage plants little difficulty 

 is experienced in maintaining desirable conditions of atmospheric 

 humidity during the greater part of the storage season. If it is found 

 that the relative humidity cannot be maintained above 80 percent by 

 steps directed toward running the compressor with higher back pres- 

 sures, then a humidifying apparatus should be installed even though 



Figuke 7. — Unit cooler installed with air ducts to deliver the cold air throughout 

 the room and to pick up the return air from the warmest parts, in contrast 

 with the installation in figure 6, where the return air comes from the floor. 



the procedure throws moisture into the atmosphere only to be taken 

 out on the evaporating coils. This apparatus is constructed on two 

 principles: one is that of an atomizer; the other is vaporization of 

 water by heating. The use of the latter principle avoids the danger 

 of freezing where air temperatures are below 32° F. 



CIRCULATION OF AIR 



In all plants there is necessarily a variation of temperature in differ- 

 ent parts of the room. This variation should be kept at a minimum. 

 The equalization of temperature in all parts depends almost entirely 

 on circulation of air, either by gravity or by forced draft. Gravity 



