STORAGE 



STORAGE 



3251 



important problem of heat transference is through con- 

 vection currents. In order to offset this heat trans- 

 ference, specially constructed walls must be provided. 

 A storage chamber is a room so constructed that the 

 temperature may be maintained at or near a constant 

 point. In order to offset changes of temperature, 

 sufficient refrigerating capacity must be provided, or 

 some means to prevent the actual transmission of the 

 heat from the outside to the inside of the room. The 

 latter provision is known as the insulation of storage 

 rooms. Therefore, the rooms are constructed in such 

 a way that the walls act as barriers against the trans- 

 mission of outside heat into the room, or the loss of 

 heat of the storage room to the outside in extremely cold 

 weather. The best insulation against heat transmis- 

 sion is a vacuum. If it were possible to surround storage 

 rooms with vacuum walls, the heat leakage into the 

 room would be very slight, and after the rooms were 

 once cooled to the desired point, it would not require 

 machinery of great capacity to maintain a low tem- 

 perature. It has been found difficult, however, to main- 

 tain a vacuum under ordinary circumstances. The 

 outer air pressure is constant and 

 leakage of air into the vacuum 

 walls, although slight, gradually 

 destroys the insulating effect. 

 Attempts at vacuum construc- 

 tion on a large scale have not 

 been successful. 



Air spaces, that is, walls made 

 air-tight so that the air is closely 

 confined, have been thought to 

 be efficient insulation. Still air 

 is a necessity where this method 

 of insulating the wall is used. A 

 slight leakage into the wall is 

 sufficient to allow outer air to 

 enter and, consequently, to de- 

 stroy the insulating effects. In 

 walls constructed of free air 

 spaces, convection currents occur 

 within the spaces, which act as 

 effective transferors of heat either 

 inward or outward, as the case 



insulating material, besides non-conductivity of heat, 

 are as follows: 



1. Odorless; any strong odor would affect the goods 

 stored in the rooms. 



2. Moisture-proof or low capacity for moisture ; damp- 

 ness decreases the efficiency as an insulating material, 

 and some substances ferment or rot when damp. 



3. Vermin-proof; there should be no inducement for 

 rats or mice to nest in the walls. 



4. Non-liability to inherent disintegration or spon- 

 taneous combustion. 



5. Lightness in weight; not only on account of,.ihe re- 

 duction of the actual weight of the walls, but because light 

 materials are usually the best non-conductors of heat. 



6. Elasticity; when packed firmly in the walls the 

 material should not settle, as any settling within the 

 walls results in open spaces in the insulation. After 

 the walls are once constructed, these inequalities can- 

 not be reached for repairs without completely rebuild- 

 ing the walls. 



7. Relative cheapness and economical handling; the 

 material should not be so high in cost as to be pro- 



U 



LJ 



3701. Diagrams illustrating convection currents in walls consisting of one to four 

 dead-air spaces. 



may be. Fig. 3701 shows the action of convection cur- 

 rents within air spaces. When one air space is used, the 

 transfer of the heat is very easily accomplished, as 

 shown by the direction of the air currents shown by 

 the arrows in the diagram. Simply thickening the 

 walls, therefore, does not act as a sufficient insulation. 

 The insulating effect of air spaces is considerably 

 improved by breaking up the walls into smaller air 

 spaces. The diagram shows the convection currents 

 occurring in walls of one, two, three, or four air spaces. 

 As the number of spaces is increased, the effect of 

 convection is very greatly reduced, so that a wall 

 consisting of four air-tight spaces may be considered as 

 fairly efficiently insulated. It is, however, extremely 

 expensive to construct these air-tight divisions, and 

 some other means of insulation is desirable. 



It is preferable to use some material to fill the walls. 

 Such a filler breaks up the air spaces within the walls 

 and confines the air in the small interstices between the 

 particles. In this way, the air held within the wall 

 approaches more nearly the desirable "dead-air" con- 

 dition. Convection currents actually occur in filled 

 walls, but they are very sluggish and the effect is very 

 slight. Filled walls are effective barriers against heat 

 conduction or radiation, provided, of course, that poor 

 conductors of heat are used. 



The most effective insulating material is a substance 

 of low-heat conductivity which has many pores or 

 cells. These cells are filled with air (practically still 

 air); consequently the efficiency of the heat barrier is 

 increased. A number of substances are effective as 

 insulation for storage walls. The requirements for an 



206 



hibitive. In addition, the material must not be of such 

 a nature that its economical handling is impracticable. 



8. Must allow of practical application in general 

 work; very specialized material which would not lend 

 itself to general conditions could not be considered as 

 efficient insulating material. 



The list of materials available for insulation may be 

 divided into two classes: Those that can be considered 

 as commercial insulation that is, materials which are 

 manufactured especially for insulating purposes; and 

 common or waste materials. 



Among the most common of the first class are the 

 following: granulated cork, cork sheets or boards or 

 bricks, hairfelt, linofelt, mineral wool, and lith. 



Granulated cork is considered to be one of the best 

 and most effective insulating materials. It is prepared 

 from the trimmings of cork mills, and when used in the 

 granulated state is simply filled into the walls and 

 packed tightly. Cork sheets, bricks, or boards are 

 manufactured of the cork particles which are compressed 

 in molds at a high temperature. There is no cementing 

 material used, the heat and pressure being sufficient 

 to liquefy the natural gums and resins of the cork and 

 these hold the particles together. Cork boards or 

 sheets are also made by the addition of asphaltum 

 pitch which renders the particles water-proof but may 

 decrease the insulating efficiency. 



Hairfelt is manufactured of waste cattle hair which 

 is washed and deodorized. It is pressed or felted 

 together by special machinery into sheets from J4 to 

 1 inch in thickness. 



Linofelt is a patented material manufactured from 



