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 into the room in 24 hours is 600X3 (75-32). . 77, 400 
The heat to be removed from the butter is 2,000X0.5494 l (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 2B.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. 
