Quick co2 warm liquid defrost with additional heat

A method of operating a refrigeration system, the method comprising:

• operating a first low-temperature evaporator and a second low-temperature evaporator in a refrigeration mode;
• determining that the first low-temperature evaporator should be operated in a defrost mode;
• and
• causing the first low-temperature evaporator to operate in the defrost mode, after determining the first low-temperature evaporator should be operated in the defrost mode by:
• opening a first valve to allow defrost refrigerant to pass from a heat exchanger to the first low-temperature evaporator;
• closing a second valve to prohibit output refrigerant from the first low-temperature evaporator from passing to one or more compressors;
• closing a third valve to prohibit defrost refrigerant from passing to the second low-temperature evaporator;
• opening a fourth valve to allow output refrigerant from the second low-temperature evaporator to flow to the one or more compressors;
• and
• causing defrost refrigerant from the first low-temperature evaporator to flow to the second low-temperature evaporator;
• wherein:
• the heat exchanger is configured to receive warm liquid from a flash tank and a portion of compressed refrigerant from the one or more compressors, and
• the heat exchanger is configured to extract heat from the portion of the compressed refrigerant and add it to the warm liquid to produce the defrost refrigerant.

A controller of a refrigeration system, the controller comprising:

• an input/output interface communicatively coupled to:
• a first valve positioned between a heat exchanger and a first low-temperature evaporator and configured to pass, when open, defrost refrigerant to the first low-temperature evaporator;
• a second valve positioned between the first low-temperature evaporator and one or more compressors and configured to pass, when open, output refrigerant from the first low-temperature evaporator to the one or more compressors;
• a third valve positioned between the heat exchanger and a second low-temperature evaporator and configured to pass, when open, defrost refrigerant to the second low-temperature evaporator;
• a fourth valve positioned between the second low-temperature evaporator and the one or more compressors configured to pass, when open, output refrigerant from the second low-temperature evaporator to the one or more compressors;
• and
• a processor configured to:
• determine that the first low-temperature evaporator should be operated in a defrost mode;
• and
• after determining the first low-temperature evaporator should be operated in the defrost mode, cause the first low-temperature evaporator to operate in the defrost mode by:
• opening the first valve to allow defrost refrigerant to pass to the first low-temperature evaporator;
• closing the second valve to prohibit output refrigerant from the first low-temperature evaporator from passing to the one or more compressors;
• closing the third valve to prohibit defrost refrigerant passing to the second low-temperature evaporator;
• opening the fourth valve to allow output refrigerant from the second low-temperature evaporator to flow to the one or more compressors;
• and
• causing defrost refrigerant from the first low-temperature evaporator to flow to the second low-temperature evaporator.