and a Bourdon tube thermostat to hold the tank 
temperature to within 2° of any desired value. The 
water is drawn from the center of the bottom of this 
tank to the circulating pump and returns from the 
calibration tank to the top, thereby maintaining a 
constant circulation as long as the solenoid value 
between the tank and the pump is open. The meter- 
ing valve is mounted in the pipeline between the 
pump and the calibration tank, as near the latter as 
feasible. The two heating elements are connected in 
series to enable the use of 220 volts for this 3000- 
watt heating system. 
Cold Tank 
The cold tank is also of brazed sheet brass con- 
struction, measuring 282 by 9'2 by 22 inches (fig. 3). 
The dimensions were dictated by the size requirements 
of a bank of three refrigerating coils known as 
THERMOMETER 
RETURN FLOW 
HOT TANK 
HEATING 
ELEMENTS 
HOT INFLOW 
COLD INFLOW 
THERMOSTAT 
METERING 
VALVE 
DRAIN VALVE 
Figure 3. 
needle coils, mounted in parallel to the expansion 
valves for speed of heat transfer. This tank is in- 
sulated in the same manner as the hot tank and 
mounted a few inches to the right of it, sharing the 
common circulation return with the hot tank. The 
cold liquid is drawn off the bottom of the tank, which 
is in the shape of a shallow pyramid. Circulation is 
controlled by the thermostat-operated solenoid valve 
and the manually controlled metering valve, both 
arranged as for the hot tank. 
All external piping, pumps, and valves are insu- 
lated with Prestite insulation which can be molded 
to fit any irregularities of form. A thermometer is 
mounted at the base of this tank and the compressor 
is controlled by a thermostat that can be set to hold 
the temperature of the liquid to within 2° from that 
of the room to —3°C. The compressor used is rated 
at 1.2 tons, and is mounted outside the building to 
provide sufficient air circulation for cooling. 
THERMOSTAT 
HOT TANK 
CONTROL 
COLD TANK 
THERMOMETER 
PUMP 
Thermal system. 
