20 



BULLETIN 



U. S. DEPARTMENT OF AGRICULTURE. 



be admitted into the storage room at a low level, as indicated in 

 figures 6 and 7. The cold air will then pass over the goods in storage, 

 and as it becomes warmer will gradually rise to the bunker, where it 

 is recooled. As natural circulation is brought about by the difference 

 in temperature between the warm air and cold air, which is only a 

 degree or two, advantage must be taken of the difference in height 

 of the respective columns. The simplest and most effective way to 

 accomplish this is to extend the cold-air duct to within about 2 feet 

 of the floor. The inner side of this duct should be insulated to pre- 

 vent condensation. The uptake duct should be similarly insulated 



and should extend 

 /\ from the bunker floor 



/ "x. to near the ceiling of 



the room, leaving an 

 area equal to the 

 cross-sectional area 

 of the warm-air duct. 

 The warm-air duct 

 should be located on 

 the warmest wall of 

 the room in order to 

 take advantage of the 

 natural air circula- 

 tion, and for the same 

 reason the cold-air 

 duct should be on the 

 coldest wall. 



SIDE BUNKERS. 



Ice bunkers are 

 often constructed as 

 shown in figure 7, and 

 the same care in con- 

 struction and insulation should be observed as in the overhead type 

 of bunker. 



GRAVITY BRINE SYSTEM. 



The system illustrated in figure 8 has made it possible to obtain 

 temperatures considerably lower than can be obtained with the 

 bunker system. It consists of a tank filled with ice and salt, in the 

 proportions required to produce the desired temperatures, and an 

 endless-pipe circuit. 



The pipe is completely filled with a brine solution of the proper 

 density to insure against freezing. It is customary to use a solution 

 of calcium chlorid, as lower temperatures are obtained without 

 danger of freezing and the corrosive action is less than that of com- 



Fig. 7. — Side ice bunker. 



