A system and humidity control method is provided for a multi-stage cooling
system having two or more refrigerant circuits that balances humidity
control and cooling demand. Each refrigerant circuit includes a
compressor, a vessel and an evaporator. A hot gas reheat circuit having a
heat exchange coil is connected to one of the refrigerant circuits and is
placed in fluid communication with the output airflow from the evaporator
of that refrigerant circuit to provide additional dehumidification to the
air when humidity control is requested. The hot gas reheat circuit
bypasses the vessel of the refrigerant circuit during humidity control.
Humidity control is performed during cooling operations and ventilation
operations. During a first stage cooling operation using only one
refrigerant circuit and having a low cooling demand, the request for
humidity control activates the hot gas reheat circuit for
dehumidification and activates a second refrigerant circuit to provide
cooling capacity. The hot gas reheat circuit is sized to match the
cooling provided by the evaporator so that air cooled by passing through
the evaporator can be reheated. Excess refrigerant is passed into the
inactive cooling circuit so that proper pressure and temperature can be
maintained in the active reheat circuit and so that high head pressure
that can damage the compressor can be avoided. During a second stage
cooling operation using two or more refrigerant circuit and having a high
cooling demand, the request for humidity control is suspended and is
initiated only upon the completion of the second stage cooling demand.