Turbo Power & Marine, United Technologies

The Turbo Power and Marine Division of United Technologies Corporation found that one control was as good as two. Its facility in Farmington, Connecticut, had two separate CAD rooms containing computer equipment and personnel that required independent constant temperature and humidity control. Although three contractors proposed using two separate systems with electric reheat, Gary Heck, President of H&L Mechanical Inc., proposed using a single APR Control to enhance a 5-ton Carrier air conditioning system. Heck said using a single control would reduce installation and operating costs.

His proposal recommended a single-circuit, 5-ton air cooled condensing unit with a refrigeration piping loop to separate two, 3-ton evaporators – each located in a CAD room. Each evaporator was to be controlled by a solenoid valve connected to a thermostat for independent operation. The patented APR-1.4 control by Rawal Devices was used to provide as much as 4 tons of capacity modulation to the nominal 5-ton refrigeration circuit. Capacity modulation permits the system to match changing load conditions in the two zones by responding to changes in temperature and pressure in the refrigeration suction lines.

Installed with simple piping conditions, the control forces the evaporator coils to operate in a continuously dehumidifying mode. Thus, the system provides consistent latent heat removal even when operating at partial load conditions. Electric reheat was initially included on each of the evaporators as a safety measure to supplement the load fluctuations and ensure proper system dehumidification.

The system proved effective and electric reheat was found to be unnecessary. In fact, the system has been so successful that Heck was invited to submit the only proposal for air conditioning two other CAD rooms built the following year. Turbo Power and Marine specifically requested use of the control and agreed to eliminate electric reheat coils from the system to reduce installed costs.

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