A method for terminating defrosting of an evaporator (104) is disclosed. The evaporator (104) is part of a vapour compression system (100). The vapour compression system (100) further comprises a compressor unit (101), a heat rejecting heat exchanger (102), and an expansion device (103). The compressor unit (101), the heat rejecting heat exchanger (102), the expansion device (103) and the evaporator (104) are arranged in a refrigerant path, and an air flow is flowing across the evaporator (104). When ice is accumulated on the evaporator (104), the vapour compression system (100) operates in a defrosting mode. At least one temperature sensor (305) monitors a temperature T.sub.air, of air leaving the evaporator (104). A rate of change of T.sub.air is monitored and defrosting is terminated when the rate of change of the temperature, T.sub.air, approaches zero.

A refrigeration system includes evaporators, one or more medium temperature compressors, and a three-way valve positioned downstream from the one or more medium temperature compressors. The three-way valve receives the compressed refrigerant from the medium temperature compressors and directs flow of the received compressed refrigerant to (i) a gas cooler and/or (ii) one or more of the evaporators based on an operation mode of the evaporators. A controller determines that operation of a first evaporator in a defrost mode is indicated and causes the first evaporator to operate in the defrost mode by adjusting the three-way valve to direct a portion of the received compressed refrigerant to the first evaporator.

A refrigeration cycle apparatus includes: a first four-way valve having first to fourth ports; a second four-way valve and a third four-way valve each having fifth to eighth ports; a compressor; a discharge pipe connecting a discharge port of the compressor and the first port; a suction pipe connecting a suction port of the compressor and the second port; a first high pressure pipe connecting the discharge pipe and the fifth ports; a second high pressure pipe connecting the third port and the first high pressure pipe; a first valve provided at the first high pressure pipe; a second valve provided at the second high pressure pipe; a low pressure pipe connecting the suction pipe and the sixth ports; a first outdoor heat exchanger connected with the seventh port of the second four-way valve; a second outdoor heat exchanger connected with the seventh port of the third four-way valve; and an indoor heat exchanger connected with the fourth port.

An air-conditioner includes: a refrigerant circuit through which a refrigerant flows, the refrigerant circuit being formed of a compressor, a switching valve, a first heat exchanger, an expansion valve, and a second heat exchanger connected to one another by a first pipe; a heat-transfer medium circuit through which a heat-transfer medium flows, the heat-transfer medium circuit being formed of a pump, the first heat exchanger, and a third heat exchanger connected to one another by a second pipe; and control device that controls the compressor and the pump. In an operation of the air-conditioner performed before entering a defrosting operation, the control device increases a frequency of the compressor, as compared to the frequency of the compressor in a heating operation, and reduces a rotational speed of the pump, as compared to the rotational speed of the pump in the heating operation.

An apparatus includes a high side heat exchanger, a flash tank, a subcooler, an expansion valve, a load, and a compressor. The high side heat exchanger removes heat from a refrigerant. The flash tank stores the refrigerant. The subcooler heat exchanger receives the refrigerant. During a first mode of operation, the load uses the refrigerant to cool a space proximate the load and the compressor compresses the refrigerant. During a second mode of operation, the subcooler heat exchanger directs the refrigerant to the expansion valve, transfers heat from the refrigerant from the flash tank to the refrigerant from the expansion valve and directs the refrigerant from the expansion valve to the compressor. During the second mode of operation, the compressor compresses the refrigerant from the subcooler heat exchanger and directs the compressed refrigerant from the subcooler heat exchanger to the load to defrost the first load.

A system and method for controlling a refrigeration system is disclosed. The system includes a cooled compartment, at least one heat source selectively activated to provide heat, at least one sensor, and a controller. The sensor detects a temperature and a relative humidity of ambient air that surrounds the cooled compartment. The controller is in communication with the at least one heat source and the at least one sensor. The controller includes logic for calculating a dew point temperature based on the temperature and the relative humidity. The controller also includes logic for selecting a region of operation based on at least one of the dew point temperature and the relative humidity, where the region of operation is representative of ambient conditions that surround the cooled compartment. The controller further includes logic for determining if the at least one heat source is activated based on the region of operation.

Operating a vapor compression system including determining a total heat delivered by the vapor compression system, determining a total electrical energy consumed by the vapor compression system while delivering heat, maintaining a total electrical energy consumed by the vapor compression system during a defrosting cycle, determining a cumulative coefficient of performance of the vapor compression system based on the total heat delivered, the total electrical energy consumed by the vapor compression system while delivering heat, and the total electrical energy consumed by the vapor compression system during the defrosting cycle, and initiating a defrosting cycle based the cumulative coefficient of performance.

The present invention provides a system and method for an improved multistage, cascade refrigeration system using hot gas defrost to rid the evaporator of ice build-up which accumulates over time, while the air in the evaporator enclosure remains below the freezing point of water. The present invention thus provides greater defrost flexibility with increased ease of design and implementation than current refrigeration systems, which allows for more robust hot gas defrost function for multistage refrigeration systems, such that it is unaffected by temperature changes of the condensing fluid (ambient air temperature for air cooled condensers, water temperature for water cooled condensers), and can be readily adapted to any refrigerant suitable for a selected temperature range.

A refrigerant cycle apparatus is configured to suppress extension of defrost time. The refiigerant cycle apparatus includes: a refrigerant circuit including a compressor, a heat source heat exchanger having a main heat exchange unit, a sub heat exchange unit and a pressure loss portion disposed between the main heat exchange unit and the sub heat exchange unit, an expansion mechanism, a utilization heat exchanger, and a flow direction switching mechanism configured to switch a flow direction of a refrigerant; a first temperature sensor configured to measure first refrigerant temperature between the main heat exchange unit and the pressure loss portion; a second temperature sensor configured to measure second refrigerant temperature between the pressure loss portion and the expansion mechanism; and a controller configured to control the flow direction switching mechanism to switch between normal operation and defrost operation. The controller has control modes for the defrost operation, including a control mode of terminating the defrost operation based on the first refrigerant temperature and a control mode of terminating the defrost operation based on the second refrigerant temperature.

A heat pump system includes a refrigerant circuit, at least one compressor, an evaporator, and a controller programmed to defrost the evaporator in a defrost mode, wherein in the defrost mode the controller is programmed to monitor the evaporator to detect frost creation thereon, and reduce the speed of the at least one compressor and/or reduce the number of some, but not all operating compressors of the at least one compressor, if frost creation is detected on the evaporator. In some embodiments, the controller is programmed to defrost the evaporator in a second defrost mode. In the second defrost mode the controller is programmed to monitor the evaporator to detect frost creation thereon, turn off the at least one compressor when frost is detected on the evaporator, and operate a fan to force ambient air over the evaporator to defrost the evaporator.