32 BULLETIN 747, U. S. DEPARTMENT OF AGRICULTURE. 
Consequently, if used for heating be'low the temperature of 212° F. 
exhaust steam is practically as good as live steam. As the exhaust 
steam when not used for heating is entirely lost, it is obvious that 
by its use the efficiency of the plant will be greatly increased. 
Allowing for radiation from pipes, pasteurizers, hot-water tanks, 
etc., it is safe to assume that 800 B. t. u. are available for useful 
heating in each pound of exhaust steam. 
The exhaust steam available from the- engine, pumps, and other 
steam-driven equipment in milk plants, creameries, and dairies is, in 
general, not quite sufficient to take care of the maximum heating load 
which comes when pasteurizing is being done. But as the engine 
and pumps are operated for some time- before pasteurization com- 
mences, it is perfectly feasible to store up the heat contained in the 
exhaust steam and draw on it when needed. 
Pasteurization is now done almost entirely by the use of hot water, 
the water being heated either in the jacket space included in the 
construction of the pasteurizer or in a separate tank heater designed 
for the purpose and pumped from the heater through the pasteurizer 
and back into the heater. 
The ordinary feed-water heater found on the market is not suited 
for use in milk plants except when it is used for heating the boiler 
feed water only, as it has little or no storage capacity and the heating 
surface is entirely inadequate. As hot water in dairy plants is used 
intermittently it becomes necessary to provide a large storage ca- 
pacity in order to have a- large quantity ready without delay when 
needed. Storage heaters especially designed for creameries and milk 
plants can be obtained from a number of manufacturers. 
In designing water heating and storage tanks for use in the dairy 
industry the size should be based on the quantity and temperature 
of the water required or on the quantity of exhaust steam available 
for heating. In other words, the heat-transmitting surface should 
be proportioned so that approximately all the heat available in the 
exhaust steam will be transmitted to the water, provided, of course, 
there is use for the hot water. 
Table -L gives the capacity of water heating and storage tanks for 
different-sized creameries, with the amount of heating surface neces- 
sary to heat the water in each instance by exhaust steam at atmos- 
pheric pressure and temperature, from an initial temperature of 50° 
F. to a final temperature of 200° F. in one hour. The heating sur- 
face is supposed to be made up of steel or brass pipe. 
