COOLIN-G HOT-BOTTLED PASTEURIZED MILK. 25 



B. T. U. extracted from wood, 198X0.5 (79.0-43.3) = 2,534 



B. T. U. extracted from iron, 198X0.113 (79.0-43.3) = 799 



75, 261 

 B. T. U. through walls of box, 296X4(70-58)2.47 _ -1,462 



73, 799 



The foregoing figures indicate that 12 per cent more heat was taken 

 out than the material gave up, which, of course, is impossible; hence 

 it is believed that the Pitot-tube readings were wrong, as the weight 

 and temperature of the material were carefuUy determined and are 

 beheved to be correct. On the other hand, if the anemometer read- 

 ings of air velocities are taken and calculations made with them as 

 a basis, the two sets of calculations balance withia 2 per cent. In 

 other words, 98 per cent of the heat given up in cooling the liquid, 

 glassware, and crates is accounted for in the heat balance, showing 

 that aU our observations were practically correct. With this, then, 



73 799 

 as a basis, the total amount of refrigeration performed was ^^^ q naa ^ 



Z003VOO 



0.26 ton, or at the rate of 0.106 ton an hour. The horsepower input 



98 X 20 

 to the motor = -.^ =2.6. The efficiency of the motor, how- 

 ever, was not determined, but in view of the fact that it was designed 

 for a voltage of 120 and was operated at a voltage of only 98, its 

 efficiency was necessarily low. Under the operating conditions, and 

 assuming a cost of 6 cents a kilowatt hour for electric energy, the 

 cost of power per ton of refrigeration was $1.11. When the air supply 

 is colder, the time required to cool the milk is, of course, shorter; 

 hence the cost of power is decreased. The over-all efficiency of a 

 direct-connected blower set of this size and type when operated under 

 normal service conditions should be about 40 per cent, but under our 

 conditions it was only about 22 per cent ; hence the cost of power for 

 cooling in these experiments is considerably greater than it should 

 be in a commercial plant. If the over-aU efficiency of the blower 

 set is assumed to be 40 per cent, then the total cost of electric energy, 

 under the conditions mentioned above, and at a cost of 6 cents a 

 kilowatt hour, would be only about 66 cents a ton of refrigeration. 



As the blower set used in these experiments was operated very 

 inefficiently, the cost of cooling is not typical of this method. The 

 figures obtained do serve, however, to show that the cost of cool- 

 ing by means of circulating cold outside air is very small. Of course, 

 this can not be done throughout the year, but in a great many locafi- 

 tics cooling may be accomplished by circulating cold outside air 

 through tlu; rf^frigcrating rooms during several montlis of the year. 

 In summer the air would have to be cooled artificially. This, how- 

 ever, is being done in a large number of milk plants which cool the 

 air in a separate coil room and circulate it through the milk-storage 



