Carbon dioxide refrigeration system with low temperature mode

A method of controlling a refrigeration system for a carbon dioxide based refrigerant fluid, wherein the refrigeration system comprises:

• a refrigerant circuit comprising one or more compressors a heat rejecting heat exchanger, an ejector, a receiver, an expansion valve and a heat absorbing heat exchanger;
• wherein the ejector includes a primary inlet, a secondary inlet and an outlet;
• wherein the receiver includes an inlet, a liquid outlet and a gas outlet;
• wherein the ejector primary inlet is arranged to receive fluid from an outlet of the heat rejecting heat exchanger, the ejector secondary inlet is arranged to receive fluid from an outlet of the heat absorbing heat exchanger, and the ejector outlet is arranged to direct flow to the receiver inlet;
• wherein a suction inlet of the one or more compressors is arranged to receive refrigerant fluid from the gas outlet of the receiver;
• and
• wherein the liquid outlet of the receiver is connected via the expansion valve to an inlet of the heat absorbing heat exchanger;
• wherein the refrigerant system comprises a bypass line and a bypass control valve, with the bypass line providing a fluid connection between the outlet of the heat rejecting heat exchanger and the expansion valve the method comprising:
• running the refrigeration system in either an ejector mode in which all refrigerant fluid exiting the heat rejecting heat exchanger enters the ejector primary inlet, or a bypass mode of the refrigeration system in which refrigerant fluid exiting the heat rejecting heat exchanger is permitted to flow through the bypass line to the expansion valve and then to the heat absorbing heat exchanger without first passing through the ejector;
• and
• controlling the bypass control valve to switch to running the refrigeration system in the other of the ejector mode or the bypass mode;
• wherein the bypass control valve is controlled by a controller and the method comprises either:
• (i) monitoring an ambient air temperature outside of the refrigeration system;
• and
• controlling the bypass control valve to switch from the ejector mode to the bypass mode in response to determining that the ambient air temperature is below a predetermined threshold;
• or
• (ii) monitoring a refrigerant fluid temperature or pressure at an outlet of the heat rejecting heat exchanger;
• and controlling the bypass control valve to switch from the ejector mode to the bypass mode in response to determining that the refrigerant fluid temperature or pressure is below a predetermined threshold.

A refrigeration system for a carbon dioxide based refrigerant fluid, wherein the refrigeration system comprises a refrigerant circuit, the refrigerant circuit comprising one or more compressors a heat rejecting heat exchanger, an ejector, a receiver, an expansion valve and a heat absorbing heat exchanger;

• wherein the ejector includes a primary inlet, a secondary inlet and an outlet;
• wherein the receiver includes an inlet, a liquid outlet and a gas outlet;
• wherein the ejector primary inlet is arranged to receive fluid from an outlet of the heat rejecting heat exchanger, the ejector secondary inlet is arranged to receive fluid from an outlet of the heat absorbing heat exchanger, and the ejector outlet is arranged to direct flow to the receiver inlet;
• wherein a suction inlet of the one or more compressors s arranged to receive refrigerant fluid from the gas outlet of the receiver;
• and
• wherein the liquid outlet of the receiver is connected via the expansion valve to an inlet of the heat absorbing heat exchanger;
• wherein the refrigeration system comprises a bypass line and a bypass control valve, with the bypass line providing a fluid connection between the outlet of the heat rejecting heat exchanger and the expansion valve;
• wherein, in an ejector mode of the refrigeration system, the bypass control valve prevents fluid flow through the bypass line such that all fluid exiting the heat rejecting heat exchanger enters the ejector primary inlet;
• wherein, in a bypass mode of the refrigeration system, the bypass control valve permits fluid exiting the heat rejecting heat exchanger to flow through the bypass line to the expansion valve and then to the heat absorbing heat exchanger without first passing through the ejector;
• wherein the refrigeration system comprises a controller, the controller being configured to control the bypass control valve;
• wherein the refrigeration system comprises a refrigerant fluid temperature sensor or refrigerant fluid pressure sensor located between the outlet of the heat rejecting heat exchanger and the ejector primary inlet, and wherein the controller is configured to control the bypass control valve to initiate the bypass mode based on a sensed temperature or a sensed pressure of the refrigerant at the outlet of the heat rejecting heat exchanger.