60 
BULLETIN 93, U. S. DEPARTMENT OF AGRICULTURE. 
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In most small creameries the engine is ordinarily run for only two 
or three hours while the churning, working the butter, and pasteuriz- 
ing is being done. The balance of the day the foe in the boiler is 
banked and only 10 to 15 pounds' pressure is kept on the boiler. If, 
in order to operate a refrigerating plant, it is necessary to keep a 
greater pressure on the boiler and to operate an engine which is a 
great deal larger than is required for the compressor, the cost per ton 
of refrigeration will, of course, be greatly in excess of what it would 
be if the engine was of suit- 
able size for operating the 
compressor only. Again, the 
refrigerating machines are 
often operated intermit- 
tently, thereby increasing 
the cost per ton of refriger- 
ation above what it would 
be if run continuously. In 
view of the above, it is im- 
practical to arrive very 
closely at the actual cost 
per ton of refrigeration 
when the compressor is 
operated by a steam engine 
which is also used for 
driving other machinery. 
The curves in figure 30 
(p. 63), showing the approx- 
imate cost of producing re- 
m 
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Fig. 2 
B. T. U. transmitted per square foot per 24 hours 
per degree difference in temperature. 
frigeration in creameries 
with belted, steam-driven 
equip ment, has been aver- 
aged from reports on a-large 
number of creameries, and 
in view of the fact that the 
engines were used for pur- 
poses other than driving the 
refrigerating machines, it should be borne in mind that the results 
are only approximate and should not be considered as positive. 
The cooling water supplied to the condenser and the wages of an 
attendant have not been taken into consideration in averaging 
the cost of producing the refrigeration. The water in most cases 
costs little or nothing, and it can be used for feeding the boiler, wash- 
ing utensils, and for other purposes after it has passed through the 
condenser, as it is only raised a few degrees in temperature. In op- 
erating small-machines of the size commonly used in milk plants, 
