60 



BULLETIN 98, 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 fire 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- 

 <^^^^^^^^ 1 awe si ze f° r 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- 

 frigeration in creameries 

 with belted, steam-driven 

 equip ment, has been aver- 

 aged from reports on adarge 

 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, 



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Fig. 27. — B. T. U. transmitted per square foot per 24 hours 

 per degree difference in temperature. 



