A refrigeration system including one or more first compressor(s) for compressing a carbon dioxide (CO.sub.2) refrigerant, a main heat rejection system for cooling the CO.sub.2 refrigerant, one or more high pressure expansion device(s) for reducing the pressure of the CO.sub.2 refrigerant, a receiver for storing the CO.sub.2 refrigerant, one or more high pressure expansion device(s), an evaporator and a receiver pressure regulating device. The refrigeration system further includes an auxiliary refrigeration system including an auxiliary compressor arranged to compress at least part of the CO.sub.2 refrigerant and thereafter to direct the compressed CO.sub.2 refrigerant to a heat rejection system.

A heat exchange system includes a pump or compressor 100 that pressurizes a working fluid, a first heat exchanger 200 that receives the working fluid from the pump or compressor 100 and causes the working fluid to exchange heat with a first medium to decrease a temperature of the working fluid, first adjustment means 300 for receiving the working fluid from the first heat exchanger 200 and decreasing the temperature and a pressure of the working fluid, heat absorption means 400 for receiving the working fluid from the first adjustment means 300, second adjustment means 500 for receiving the working fluid from the heat absorption means 400, and a second heat exchanger 600 that receives the working fluid from the second adjustment means 500.

A method of initiating a low-energy cooling mode using a controller of an HVAC system includes measuring a temperature of ambient air proximal to a condenser coil and determining whether the temperature of the ambient air proximal the condenser coil is less than a temperature threshold. If the temperature of the ambient air is less than the temperature threshold, the HVAC system is configured to operate in a low-energy cooling mode. In the low-energy cooling mode, the controller opens a first bypass valve to allow a refrigerant to bypass a compressor and the compressor is powered off. The HVAC system is operated until a cooling demand has been met.

A cooling system includes a heat exchanger through which a refrigerant flows, the heat exchanger having a fluid passing therethrough such that heat is rejected to the fluid, an evaporator, a refrigerant piping split point that receives the refrigerant at a given pressure from the heat exchanger and splits the refrigerant flow into a first circuit and a second circuit, the first circuit having an expansion valve that receives the refrigerant at the given pressure, and the second circuit having a first turbine coupled to a first compressor, wherein the first turbine receives the refrigerant at the given pressure, and a set of valves arranged to direct the refrigerant through the first circuit, the second circuit, or both the first and second circuits based on ambient conditions of the cooling system.

The present invention aims to alleviate the risk of leakage of refrigerant from a refrigerant circuit and particularly at the utilization side of the refrigerant circuit without the need to provide a dedicated bypass for refrigerant leakage prevention. A refrigerant system is configured such that, when a refrigerant leakage detection sensor detects refrigerant leakage, a controller is configured to adjust a opening degree of a bypass expansion valve independently of a pressure and/or temperature value detected by a sensor. A method of controlling a refrigerant system is also provided.

A multi-type air conditioner is provided that includes an outdoor unit having a liquid pipe through which a liquid refrigerant flows, and a gas pipe through which a gas refrigerant flows; a plurality of indoor units including a first indoor unit and a second indoor unit each connected to the liquid pipe and the gas pipe to circulate a refrigerant; a gas pipe connecting tube connecting the gas pipe and the plurality of indoor units so that a gas refrigerant flows therethrough; and a liquid pipe connecting tube connecting the liquid pipe and the plurality of indoor units so that a liquid refrigerant flows therethrough.

A refrigerant for a cooling device comprising a cooling circuit with at least one heat exchanger, the refrigerant undergoing a phase transition in the heat exchanger, the refrigerant being a refrigerant mixture composed of a mass fraction of carbon dioxide (CO.sub.2), a mass fraction of pentafluoroethane (C.sub.2HF.sub.5) and a mass fraction of at least one other component, wherein the mass fraction of carbon dioxide in the refrigerant mixture is up to 60 mass percent, the mass fraction of pentafluoroethane being 11 to 72 mass percent, the other component being 2,3,3,3-tetrafluoropropene (C.sub.3H.sub.2F.sub.4), the mass fraction of 2,3,3,3-tetrafluoropropene being up to 51 mass percent.

A defrost method for a heat pump system includes running the heat pump system in a heating mode to provide heat to an enclosed space and determining if an outdoor temperature is less than an outdoor threshold temperature. Responsive to a determination that the outdoor temperature is below the outdoor threshold temperature, determining if a calibration state has been previously run. Responsive to a determination that the calibration state has not been previously run, running the heat pump system in the calibration state. Responsive to a determination that the calibration state has been previously run, determining if a temperature difference between a temperature of an evaporator coil of the heat pump system and the outdoor temperature exceeds a temperature threshold value. Responsive to a determination that the temperature difference between the evaporator coil and the outdoor temperature is greater than the temperature threshold value, running the heat pump system in a defrost state.

A method for controlling a heat pump system. The heat pump system includes a compressor for compressing a working fluid of the heat pump system and an electric motor for providing an output torque for driving the compressor. The method includes the steps of recovering heat emitted from the electric motor by heating the working fluid, providing a first control mode and a second control mode for the electric motor, and controlling the electrical motor in a way creating higher heat losses of the electric motor for a given output torque of the electric motor in the second control mode than in the first control mode.

A method of initiating a low-energy cooling mode using a controller of an HVAC system includes measuring a temperature of ambient air proximal to a condenser coil and determining whether the temperature of the ambient air proximal the condenser coil is less than a temperature threshold. If the temperature of the ambient air is less than the temperature threshold, the HVAC system is configured to operate in a low-energy cooling mode. In the low-energy cooling mode, the controller opens a first bypass valve to allow a refrigerant to bypass a compressor and the compressor is powered off. The HVAC system is operated until a cooling demand has been met.