36 BULLETIN 890, U. S. DEPARTMENT OF AGRICULTURE. 
The direct-expansion system is the most economical at plants where 
it is necessary to run the machine continuously, as less refrigeration 
will be lost if it goes directly to the cooler than when it goes through 
the secondary brine medium. 
Many plants use a combination of the two systems. Direct- 
expansion coils are used in the cold room and brine is circulated from 
a tank, usually in the cold room, through the milk cooler. 
Whether direct expansion or brine is used in cooling the milk, it 
is usually more economical to use water in the first few coils of the 
cooler, as refrigeration is thus saved. In some plants, instead of 
using brine or direct expansion for cooling the milk, refrigerated 
water is used; that is, water for cooling is cooled by means of brine 
coils or direct-expansion coils. In this way the temperature of the 
cooling medium is accurately regulated and extreme temperatures are 
not required. 
Under ordinary circumstances artificial refrigeration is cheaper 
than the use of ice for medium-sized or large plants. With careful 
operation there is very little waste of refrigeration, the original 
cost of machinery and the labor and power being the chief items of 
expense. In a medium-sized or small plant, however, it is often a per- 
plexing problem to the dealer whether to install an artificial refrig- 
erating plant or to depend upon ice. In deciding this question it 
is necessary to consider such factors as the price of ice, quantity 
required each day, labor of handling, the disadvantages incident to 
its use, and the certainty of a supply of ice. Then come the ques- 
tions of size, initial cost, and the cost of operation of a refrigerating 
plant which would accomplish the same result. 
In some cases it may be necessary to increase the size of the boiler 
and of the engine, which should, of course, be large enough to run 
the compressor while the pasteurizer, bottle washer, and other ma- 
chinery are being operated. If electric power is to be used, the size 
of the boiler need not be considered. 
In comparing the cost of artificial refrigeration with that of ice it 
should be remembered that in many cases the former is of greater 
value than can be estimated, on account of the better results obtained, 
for when ice is used it is often difficult to maintain a temperature low 
enough to keep the milk in proper condition. 
Some of the disadvantages of the use of ice are the following : 
1. Cost of ice is often high. 
2. Extra work required in handling. 
3. Mold and slop incident to its use. 
4. Moist atmosphere caused by its use. 
5. Difficulty of obtaining temperature below 50° F. in storage room. 
6. Waste caused by melting in handling. 
7. Ice not always obtainable, 
