REFRIGERATION 5 1 



maintained inside. R represents the number of units of re- 

 frigeration lost through these walls every 24 hours, and hence 

 of refrigeration that must be supplied every 24 hours to offset 

 that loss. 



In other words, R is the measure of ice meltage in 24 hours, 

 expressed in British thermal units. This, translated into tons l 

 of ice which can support that meltage, gives the following 

 formula: 



fn(t-f)' 



R = -^ - tons 

 284,000 



Factors Governing Insulation of Storage Rooms. The 



selection and use of insulating materials are to be guided by the 

 following factors: 



i. Insulating Powers of Materials, Structures, and Walls. 

 The insulating power of any material, structure, or wall is really 

 the same as its heat-conducting power applied inversely, and 

 is measured by the value of n as given in the formulas above. 



A. Insulating Materials. For different materials, Siebel 2 

 gives the following values for n: 



For pine wood 2.0 B. T. U. 



" mineral wool 1.6 



" granulated cork 1.3 



:< wood ashes i.o 



" sawdust i.i 



" charcoal, powdered 1.3 



" cotton 0.7 



" soft paper felt 0.5 



B. Insulating Structures. In the following table by Starr, 3 

 the value of n for different structures is shown in column I. 

 Column II shows the meltage of ice in pounds per 24 hours, 

 where the difference in temperatures is 40 F. and the trans- 

 mitting surface is 100 square feet. 



1 To convert i pound of ice at 32 F. into water at 32 F. requires an amount of 

 heat equal to 142 B. T. U. known as the "latent heat of fusion'' for ice. 



2 Siebel's Compend. of Mechanical Refrigeration and Engineering, 1911, p. 117. 

 3 1 bid, p. 381. j 



