Of special interest in connection with this calorimeter laboratory are
the plans for maintaining constant temperature and humidity (fig. 6).
The room is heated by five steam radiators (each with about 47 square
feet of radiating surface) placed about the outer wall, which are
controlled by two pendant thermostats. A certain amount of indirect
ventilation is provided, as indicated by the arrows on the inner wall.
The room is cooled and the humidity regulated by a system of
refrigeration installed in an adjoining room. This apparatus is of
particular interest and will be described in detail.
In the small room shown at the south side of the laboratory is placed a
powerful electric fan which draws the air from above the floor of the
calorimeter laboratory, draws it over brine coils, and sends it out into
a large duct suspended on the ceiling of the laboratory. This duct has a
number of openings, each of which can be controlled by a valve, and an
unlimited supply of cold air can be directed to any portion of the
calorimeter room at will. To provide for more continuous operation and
for more exact temperature control, a thermostat has been placed in the
duct and is so constructed as to operate some reheater coils beneath the
brine-coils in the refrigerating room. This thermostat is set at 60° F.,
and when the temperature of the air in the duct falls below this point,
the reheater system is automatically opened or closed. The thermostat
can be set at any point desired. Up to the present time it has been
unnecessary to utilize this special appliance, as the control by hand
regulation has been most satisfactory.
Two vertical sections through the refrigerating coils are shown in fig.
6. Section A-B shows the entrance near the floor of the calorimeter
room. The air is drawn down over the coils, passes through the blower,
and is forced back again to the top of the calorimeter room into the
large duct. If outdoor air is desired, a special duct can be connected
with the system so as to furnish outdoor air to the chamber. This has
not as yet been used. Section C-D shows the fan and gives a section
through the reheater. The brine coils, 400 meters long, are in
triplicate. If one set becomes covered with moisture and is somewhat
inefficient, this can be shut off and the other two used. When the
frozen moisture melts and drops off, the single coil can be used again.
It has been found that the system so installed is most readily
controlled.
The degree of refrigeration is varied in two ways: (1) the area of brine
coils can be increased or decreased by using one, two, or all three of
the coils; or (2) the amount of air passing over the cooling pipes may
be varied by changing the speed of the blower. In practice substantially
all of the regulation is effected by varying the position of the
controlling lever on the regulating rheostat. The apparatus functionates
perfectly and the calorimeter room can be held at 20° C. day in and day
out, whether the temperature outdoors is 40° below or 100° above 0° F.
It can be seen, also, that this system provides a very satisfactory
regulation of the humidity, for as the air passes over the brine coils
the moisture is in large part frozen out. As yet, no hygrometric study
has been made of the air conditions over a long period, but the
apparatus is sufficiently efficient to insure thorough electrical
insulation and absence of leakage in the intricate electrical
connections on the calorimeters.
The calorimeters employ the thermo-electric element with its low
potential and a D'Arsonval galvanometer of high sensibility, and in
close proximity it is necessary to use the 110-volt current for heating,
consequently the highest degree of insulation is necessary to prevent
disturbing leakage of current.
The respiration calorimeter laboratory is so large, the number of
assistants in the room at any time is (relatively speaking) so small,
seldom exceeding ten, and the humidity and temperature are so very
thoroughly controlled, that as yet it has been entirely unnecessary to
utilize even the relatively small amount of indirect ventilation
provided in the original plans.
During the greater part of the winter it is necessary to use only one of
the thermostats and the radiators connected with the other can be shut
off, since each radiator can be independently closed by the valves on
the steam supply and return which go through the floor to the basement.
The temperature control of this room is therefore very satisfactory and
economical.
It is not necessary here to go into the advantages of temperature
control of the working rooms during the summer months. Every one seems
to be thoroughly convinced that it is necessary to heat rooms in the
winter, but our experience thus far has shown that it is no less
important to cool the laboratory and control the temperature and
moisture during the summer months, as by this means both the efficiency
and endurance of the assistants, to say nothing of the accuracy of the
scientific measurements, are very greatly increased. Arduous scientific
observations that would be wholly impossible in a room without
temperature control can be carried on in this room during the warmest
weather.