58 



BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. 



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supply curve is based on the monthly percentage of the average 

 supply. The temperature curve is the average of the mean 24-hour 

 temperatures. Referring to the curve showing the variation in the 

 supply of milk from month to month, it will be noted that there is 

 practically a fixed relation between the temperature of the air and the 

 supply of milk. The average of the milk supply, which is taken as 

 100 per cent, is available during April and September, while the 

 maximum occurs during June. The highest summer temperature 

 occurs the latter part of July and the first of August, and the maxi- 

 mum amount of work to be done by the refrigerating plant is during 



July. Therefore the condi- 

 tions existing at this time 

 should be taken as a basis for 

 determining the size of the re- 

 frigerating plant required. If 

 the capacity of the refrigerat- 

 ing plant is sufficient to han- 

 dle the maximum load run- 

 ning eight hours a day, it will 

 handle the average load run- 

 ning four hours a day. The 

 time of running the machine 

 will decrease from a maximum 

 of eight hours during July until 

 it can be shut down entirely 

 in the Northern States during 

 December, January, and Feb- 

 ruarj^. In the South it will 

 be necessary to operate the 

 refrigerating plant to some 

 extent during the entire year. 

 The curve marked "compres- 

 sor curve" shows the approx- 

 imate daily hours the compres- 

 sor will have to be operated to produce sufficient refrigeration to 

 take care of the milk during the different months of the year. This 

 curve, however, is based on the milk supply and weather conditions 

 existing in the Northern States, where the dairying industry is prin- 

 cipally located at the present time. In the Southern States the daily 

 hours of operation will have to be increased. However, the flush 

 period is not so marked as in the North, as the seasons are longer; 

 consequently the refrigerating load is more uniform and the peak 

 load is not so great. 



A simple and fairly accurate estimate on the size of refrigerating 

 machine required to do the work of a given amount of ice may be 

 made as follows: 



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Fig. 25.— B. T. U. transmitted per square foot per 24 

 hours per degree difference in temperature. 



