APPLICATION" OF REFRIGERATION TO HANDLING OF MILK. 41 
METHODS OF UTILIZING REFRIGERATION. 
There are two distinct methods of utilizing refrigeration, namely, 
the direct expansion system and the brine system. 
DIRECT-EXPANSION SYSTEM. 
The coils of pipe in which the refrigerant is evaporated or 
expanded are placed directly in the room to be cooled; the heat 
necessary for the evaporation of the liquid refrigerant is, therefore, 
absorbed directly from the air, or whatever substances surround the 
tubes. The diagrammatic arrangement in figure 19 shows, in an 
elementary form, the commercial direct-expansion system. With a 
system of this kind the work of refrigeration practically ceases as 
soon as the plant is shut down; consequently it becomes necessary, in 
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Fig. 18. 
-Diagrammatic arrangement showing equipment common to both the compression and 
absorption systems of refrigeration. 
most cases, to run the plant continually or take the risk of losing the 
goods in storage. 
For economical operation the suction pressure and evaporating 
temperature should be as high as possible. The suction pressure is 
governed by the temperature desired in the refrigerator. In milk 
plants, creameries, and dairies the suction pressure with an ammonia 
system should be about 15.67 pounds gage and a consequent gas 
temperature of 0° F. 
Take, for example, a creamery cold-storage room 10 by 10 by 10 
feet inside dimensions, which is of sufficient capacity to hold a week's 
output of butter from a creamery making 2,000 pounds daily. For 
the sake of simplicity, only the storage of butter is considered. It is 
assumed that the average outside temperature of the room is 75° F. 
and the inside temperature is to be maintained at 32° F. while the 
