62 
BULLETIN 
U. S. DEPARTMENT OF AGRICULTURE. 
erating machines, even though the creamery is already equipped 
with a steam engine. This will depend, however, on the arrange- 
ment and efficiency of the steam plant and on the cost of electric 
power and must be determined in each individual case by those on 
the premises. The cost of power per ton of refrigeration as averaged 
from steam-driven plants in operation will compare with electric 
drive at about 3 cents per kilowatt-hour. 
There are other advantages in employing electric drive over steam, 
the value of which can not be estimated in dollars and cents, viz, 
cleanliness, less space required, and that the power required can be 
determined accurately at any time. 
Fig. 29.— Maximum and average summer temperatures in different States. 
Cleanliness in milk plants, creameries, and dairies is of special 
advantage, and with electrical drive practically all the dirt arising 
from smoke, coal dust, and ashes is ehminated. 
It is possible to install electric motors in out-of-the-way places 
where engines could not be located. This feature makes it practical 
to locate the refrigerating machine close to the cooling rooms, thereby 
eliminating long leads of refrigerating piping located outside the 
rooms to be cooled. 
The fact that the power required to operate the compressor can 
be determined accurately at any time is of great importance. This 
feature, however, may not seem of very great value at first thought, 
but it has been proved in many instances to produce higher economy. 
That the cost of production can be determined accurately is due to 
the fact that the cost of power is given in each monthly bill or, for 
that matter, can be calculated each day from the meter readings. 
With exact figures at his command the operator is able to detect 
