Abstract: A vapor compression system having a defrost cycle is disclosed. A compressor, a condenser, an evaporator, and an expansion valve connected in a closed refrigerant loop with at least one flow control device. The at least one flow control device may control the flow of refrigerant through the closed refrigerant loop. At least one sensor monitors a predetermined parameter of the closed refrigerant loop and at least one controller receives a signal from the at least one sensor. The at least one controller controls the position of the at least one flow control device. The at least one controller initiates a defrost cycle in the closed refrigerant loop by substantially actuating at least one of the at least one flow control device to provide refrigerant flow from the compressor to the evaporator for substantially preventing formation of frost on the evaporator.

Abstract: 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 condenser and an evaporator. A hot gas reheat circuit having a hot gas reheat 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 condenser 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.