52 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. 



in 24 hours per square foot per degree difference of outside and inside 

 temperatures of the room. The total surface of the room is 600 

 square feet. Then; 



B. T. U. 

 The heat that will leak through mto the room in 24 hours is 600X3 (75-32). . 77, 400 

 The heat to be removed from the butter is 2,000X0.5494 1 (58-32) 28, 574 



Total heat that will have to be removed 105, 974 



From the above figures it will be noted that practically three- 

 fourths of the refrigeration required in the average cooling room is 

 done to remove the heat that leaks in through the insulation. Hence 

 the necessity for good insulation. 



It would seem from the foregoing that the more insulation put into 

 the walls, floor, and ceiling the better, which is true when viewed 

 from the standpoint of the refrigerating machine, as the more and 

 better insulation used the less work the machine will have to do. 

 But as insulation is expensive, a point is soon reached where the 

 interest on the money invested, repairs, and depreciation on the insu- 

 lating material balances the saving in reduced machine capacity and 

 operating expenses. By installing more and better insulation, the 

 saving in the capacity of the refrigerating machine is an item of 

 considerable importance and one that has not been given the atten- 

 tion that it justifies. 



From the data at hand, it appears that the most economical point 

 to insulate for is a transmission in 24 hours of 2 B. T. U. per square 

 foot per degree difference of outside and inside temperature of room, 

 when the average outside temperature is 70° F. and the inside tem- 

 perature of the room is 32° F. With an average outside temperature 

 of 70° F. and an inside temperature of 0° F., the economical point is 

 about 1 \ B. T. U. In view of the fact that dairy products are extremely 

 perishable when held at a temperature of 60° F. or above, the added 

 security which the lowest heat transmission affords in order to hold 

 over temperatures in case of the machinery breaking down, or where 

 the plant is operated during the day only, makes the increased invest- 

 ment in insulation desirable. Good insulation not only permits 

 operating the plant with the least refrigeration, power, time, and 

 cost, but also helps to reduce fluctuations in room temperature. 

 After shutting down the refrigerating plant the inflow of heat con- 

 tinues, but at a constantly decreasing rate. With a properly insu- 

 lated room it will be several days before the inner air temperature 

 will be near that of the outside temperature. 



As an example of the saving effected by good insulation, take two 

 cold-storage rooms of the same size and construction, say 10 by 10 

 by 10 feet. The walls are assumed to be built of brick 13 inches 



1 0. 5494 specific heat of butter. 



