A carbon dioxide/co-fluid mixture is provided for use in a refrigeration cycle in which the carbon dioxide is alternately absorbed and desorbed from the co-fluid. Suitable co-fluids are selected from the class of alkoxylated carboxylic amides, wherein the amides are cyclic or non-cyclic. It has been discovered that N-2,5,8,11-tetraoxadodecyl-2-pyrrolidinone and its homologs exhibit an advantageous property of a high rate of desorption at lower temperatures.

An integrated CO.sub.2 refrigeration and air conditioning (AC) system for use in a facility includes one or more CO.sub.2 compressors configured to discharge a CO.sub.2 refrigerant at a higher pressure for circulation through a circuit to provide cooling to one or more refrigeration loads in the facility and a receiver configured to receive the CO.sub.2 refrigerant at a lower pressure through a high pressure valve. The integrated system further includes an AC module configured to deliver a chilled AC coolant to AC loads in the facility. The AC module includes an AC evaporator and an AC compressor. The AC evaporator has an inlet configured to receive CO.sub.2 liquid and an outlet configured to discharge a CO.sub.2 vapor. The AC compressor is arranged in parallel with the one or more CO.sub.2 compressors and is configured to receive CO.sub.2 vapor from both the AC evaporator and the receiver.

A vapor compression system comprising a centrifugal compressor (22) having: an inlet (24); an outlet (26); a first impeller stage (28); a second impeller stage (30); and a motor (34) coupled to the first impeller stage and second impeller stage. A first heat exchanger (38) is downstream of the outlet along a refrigerant flowpath. An expansion device (56) and a second heat exchanger (64) are upstream of the inlet along the refrigerant flowpath. A bypass flowpath (120; 320) is positioned to deliver refrigerant from the compressor bypassing the first heat exchanger. A valve (128) is positioned to control flow through the bypass flowpath, wherein: the bypass flowpath extends from a first location (140) intermediate the inlet and outlet to a second location (142; 342) downstream of the first heat exchanger along the refrigerant flowpath.

A refrigeration cycle device includes a refrigeration cycle formed by connecting a compressor, a condenser, an expansion valve and an evaporator to each other. As a refrigerant in the refrigeration cycle, a working fluid containing 1,1,2-trifluoroethylene (R1123) and difluoromethane (R32) is used. A degree of opening of the expansion valve is controlled such that the refrigerant has two phases at a suction portion of the compressor. With such a configuration, it is possible to provide highly reliable refrigeration cycle device by suppressing occurrence of a disproportionation reaction of R1123.

In various implementations, an air conditioner may include one or more compressors, more than one expansion device, and/or a microchannel condenser. High pressure events may occur during operation of the air conditioner and may be identified. When a high pressure event is identified a bypass operation may be allowed.

There is disclosed a refrigeration device in which a cooling capability and efficiency can be improved by controlling a high pressure side pressure of a low stage side refrigerant circuit into an optimum value. A refrigeration device 1 includes a high stage side refrigerant circuit 4, first and second low stage side refrigerant circuits 6A and 6B, and cascade heat exchangers 43A and 43B to evaporate a refrigerant of the high stage side refrigerant circuit 4, thereby cooling high pressure side refrigerants of the low stage side refrigerant circuits 6A and 6B, and carbon dioxide is charged as the refrigerant in each of the refrigerant circuits 4, 6A and 6B, and in the device, there are disposed pressure adjusting expansion valves 31 to adjust high pressure side pressures of the low stage side refrigerant circuits 6A and 6B.

Methods and systems for operating a refrigeration system for refrigerating a product are provided. A first temperature of the refrigerant downstream of a condenser and upstream of an evaporator may be obtained. A first pressure of the refrigerant downstream of the condenser and upstream of the evaporator may be obtained. A second pressure of the refrigerant downstream of the evaporator and upstream of a compressor and/or a temperature of the product being refrigerated may be obtained. A first valve, disposed between the condenser and the evaporator, may be controlled based on the first temperature and the first pressure to maintain a pre-determined cooling set-point for the refrigeration system. A second valve of the refrigeration system, coupled to the compressor, may be controlled based on the second pressure or the temperature of the product to optimize a capacity of a compressor of the refrigeration system.

A method of and system for heating and/or cooling a fluid, the method comprising moving the fluid through a secondary side of a heat exchanger and controlling the temperature of a primary side of the heat exchanger such that the temperature of the primary side of the heat exchanger is maintained substantially at a determined temperature interval from a reference temperature which is a function of at least one of: a temperature of an inlet to the secondary side and a temperature of an outlet of the secondary side.

In various implementations, an air conditioner may include one or more compressors, more than one expansion device, and/or a microchannel condenser. High pressure events may occur during operation of the air conditioner and may be identified. When a high pressure event is identified a bypass operation may be allowed.

A refrigeration system comprises a compressor, a condenser, a receiver tank, an evaporator and a heat exchanger. The heat exchanger comprises an inlet positioned downstream of the receiver tank and an inlet positioned downstream of the compressor. The heat exchanger is configured to transfer heat between refrigerant received from the compressor and refrigerant received from the receiver tank, wherein a transfer of heat causes at least a portion of the refrigerant received from the receiver tank to transition from liquid to vapor. This process propels the head pressure of the compressor to increase to compensate for low ambient conditions. The heat exchanger comprises a first outlet in fluid communication with the first inlet, the first outlet configured to dispense the vapor refrigerant toward the receiver tank, and a second outlet in fluid communication with the second inlet and configured to dispense the refrigerant received from the compressor toward the condenser.