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 
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. 
