The present invention is directed to a humidity control method 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 condenser and an evaporator. A hot gas re-heat circuit having a hot gas re-heat 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 re-heat circuit bypasses the condenser of the refrigerant circuit during humidity control. Humidity control is only 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 re-heat circuit for dehumidification and activates a second refrigerant circuit to provide cooling capacity. During a second stage cooling operation using two or more refrigerant circuits 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.
One embodiment of the present invention is directed to a method of providing humidity control to air for an interior space. The method includes the steps of providing a first refrigerant circuit having a first compressor, a first condenser and a first evaporator, providing a second refrigerant circuit having a second compressor, a second condenser and a second evaporator and providing a hot gas re-heat circuit connected to the first refrigerant circuit. The hot gas re-heat circuit has a re-heat coil positioned adjacent to the first evaporator and is configured, when enabled, to bypass the first condenser and to permit refrigerant to flow from the first compressor through the re-heat coil to the first evaporator. The method also includes the steps of enabling the first refrigerant circuit and the second refrigerant circuit in response to a demand for humidity control and a demand for cooling, wherein the demand for cooling is one of a demand for stage one cooling and a demand for stage two cooling, and enabling the hot gas re-heat circuit in response to a demand for humidity control and a demand for stage one cooling.
Another embodiment of the present invention is directed to a heating, ventilation and air conditioning (HVAC) system for an interior space. The HVAC system includes a first refrigerant circuit having a first compressor, a first condenser and a first evaporator, a second refrigerant circuit having a second compressor, a second condenser and a second evaporator, and a hot gas re-heat circuit connected to the first refrigerant circuit. The hot gas re-heat circuit has a re-heat coil positioned adjacent to the first evaporator and is configured, when enabled, to bypass the first condenser and to permit refrigerant to flow from the first compressor through the reheat coil to the first evaporator. The HVAC system also includes a control system to control operation of the first refrigerant circuit, the second refrigerant circuit and the hot gas re-heat circuit. The control system enables the first refrigerant circuit, the second refrigerant circuit and the hot gas re-heat circuit in response to demands for humidity control and stage one cooling. The control system also enables the first refrigerant circuit and the second refrigerant circuit and disables the hot gas re-heat circuit in response to demands for humidity control and stage two cooling.
One advantage of the present invention is that comfort cooling in the interior space is not completely sacrificed when there is a demand for humidity control.
Another advantage of the present invention is that the use of the re-heat coil for additional dehumidification provides greater energy efficiency.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.