The Whalen Company - Four-Pipe Unit

The Four-Pipe unit employs continuous chilled water circulation through the riser heat-exchanger, intermittent warm water circulation through the heating coil, and continuous fan operation. Independent hot water risers for the heating coil are required, which can either be factory-installed or field-installed. The thermostat cycles an internal face and bypass damper which directs air either over the riser heat-exchanger when cooling is required or through the bypass section which contains the hot water coil.

A decrease in room temperature from full cooling will first cause the face dampers to close against the cold riser heat-exchanger, while simultaneously opening the bypass damper to bypass air through the inactive hot water coil. A further decrease in room temperature will open the electric valve on the hot water coil. The thermostat cycles the dampers and hot water valve as required to give each individual unit the capability of providing either heating or cooling. Heating/cooling changeover of the thermostat is automatic, and the user has manual fan speed selection of HI, LO, or OFF.