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. 

 Repairs 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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Fig. 22. — Economics of insulation. 



