REFRIGERATION SI 



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 suppUed 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 ' 

 of ice which can support that meltage, gives the following 

 formula: 



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 ' 

 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 i .3 



" cotton 0.7 



" soft paper felt 0.5 



B. Insulating Structures. — In the following table by Starr,' 

 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. 



' 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. 



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

 ^Jbid.p.iSi.j 



