54 
BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. 
As before stated, in order to obtain the maximum economy from a 
cold-storage plant, it is necessary that the investment and operating 
expenses should be so balanced that their sum is a minimum. The 
refrigerators or cold rooms may be constructed with a small amount 
or poor quality of insulation, requiring only a comparatively small 
investment, but on the other hand this saving must be offset by 
machinery of greater capacity and consequently more expensive both 
in initial cost and in the cost of operation. There is, however, a 
possibility of investing too much money in insulation, so that the 
fixed charges on same may be greater than the corresponding saving 
in investment in machinery and in operating expenses. Generally 
speaking, the cheaper the insulation the more should be used, and 
also the more expen- 
sive the refrigeration 
the more insulation 
should be installed. 
In order to deter- 
mine the relative 
amount of refrigera- 
tion and insulation 
to be used to obtain 
the greatest saving, 
it is necessary to con- 
sider the cost per ton 
of refrigeration; the 
cost per square foot 
of insulating mate- 
rial; the repairs and 
depreciation on insu- 
lating material; the 
insulating value of 
the material; the temperature maintained inside of room; and the 
average outside temperature. 
The curve in figure 22 is based on the above-mentioned variables, 
which are assumed to be as follows: 
Cost per ton of refrigeration. 
Cost per square foot of insulation, 1 inch thick, installed, $0.10. 
Kepairs and depreciation of insulation material, 15 per cent. 
Insulating value of material per board foot per 24 hours for each 
degree difference between the inside and outside temperature of 
room, 8 B. T. U. 
Inside temperature of room, 30° F. 
Average outside temperature of room, 70° F. 
There is also shown a curve calculated from an inside room tem- 
perature of 0° and an average outside temperature of 70° F. . 
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THICKMESS OF INSUi-AT/Of* /IS l/SCHES. 
Fig. 22. — Economics of insulation. 
