8o MANAGEMENT OF DAIRY PLANTS 



Size of Machinery Required. — In determining the size of 

 machinery needed, an estimate should be made of the heat 

 units to be removed during a period of 24 hours. To this result 

 should be added at least 20 per cent for clearance ' and other 

 losses. The size of a compressor is usually designated in tons of 

 refrigeration per 24 hours, basing it on the heat units required 

 for melting one ton of ice from 32° F. to water of the same tem- 

 perature. A 4-ton compressor has, therefore, the capacity of 

 removing 2,000 X 142 X 4 = 1,136,000 B. T. U. of heat in 24 

 hours. If this amount of work is to be accomplished in one- 

 fourth the time, a machine of four times that capacity will be 

 required. 



Cost of Producing Refrigeration by Compression. — The 

 relative amount of power required for operating an ammonia 

 compressor differs inversely with the size of the compressor. 

 Thus, a compressor of 10 tons capacity or less usually requires 

 two horse power or more per ton of refrigeration. A larger 

 machine will require proportionately less; while for large com- 

 pressors, the power required may be reduced to about one 

 horse power per ton of refrigeration. It is safe, however, to 

 figure on the size of the engine being one and a fourth times as 

 great as the theoretical power required to propel the compressor. 

 Bowen ^ estimates the amount of steam consumed b}' the com- 

 mon creamery engine as 40 pounds per horse power per hour. 

 If a 6-ton compressor is operated for 24 hours, and if it requires 

 a is-H. P. engine for operating, and if each pound of coal pro- 

 duces 6 pounds of steam, then 



Amount of coal consumed in operating compressor 24 hours 



40 X 24 X 15 , 



= = 2,400 pounds. 



6 



Figuring coal at $5 per ton, the cost for coal per ton of refriger- 

 ation will amount to one dollar. In addition, there should be 

 added the cost of water used for boiler and for the ammonia 

 condenser, the cost of labor, of oil, waste, etc. The amount of 

 water required for the ammonia condenser will amount to about 



^ Clearance is the dead space between the piston and the cylinder head. 

 - U. S. Bureau Animal Industry, Circular 20Q, IQ13. 



