■^s 
APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 59 
Suppose the ice required to cool a certain size box during the hot- 
test weather is 500 pounds per 24 hours. The refrigeration accom- 
plished by this amount of ice melting is 500X144 = 72,000 B. T. U. 
Assuming that the conditions existing in the plant will justify the 
operation of the ma- 
chine eight hours 
per day, then the 
capacity of the ma- 
chine must be suffi- 
cient to extract 
72,000 B. T. U. in 
eight hours, or in 
one-third of the 
time that it takes 
to melt the ice. 
Therefore the capac- 
ity of the refriger- 
ating machine must 
72,000X3 
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288,000 
ton. Usually lower 
temperatures than 
can be maintained 
by the use of ice are 
desired, consequent- 
ly a 1-ton machine, 
although slightly 
larger than the re- 
quirements, should 
be installed. 
In figure 29 (p. 62) are given the maximum and average tempera- 
tures for the different States. 
APPROXIMATE COST OF PRODUCING MECHANICAL REFRIGERATION IN 
SMALL PLANTS. 
Fig. 26 
U. transmitted per square foot per 24 hours per 
degree difference in temperature. 
The cost of producing a ton of refrigeration mechanically depends 
upon so many variables, especially in small plants, that it is impos- 
sible to give more than approximate costs. The average plant used 
in creameries and diaries is operated about eight hours daily during 
the summer months when the work required of the refrigeration 
machinery is at its maximum. Then the total time of operation dimin- 
ishes until the machine is shut down entirely or run very little during 
the winter months. 
