CO2 refrigeration system with hot gas defrost

A CO2 refrigeration system having an LT system portion and an MT system portion, and having a hot gas defrost mode, the system comprising:

• one or more compressors configured to discharge CO2 refrigerant in a high-pressure hot-gas state, the compressors operably coupled to a circuit for distribution of the CO2 refrigerant;
• one or more heat exchangers configured to cool the CO2 refrigerant, and also configured to condense the CO2 refrigerant;
• one or more evaporators operably coupled to the circuit, and configured to receive the CO2 refrigerant;
• a plurality of valves connected to the circuit and positionable to establish a refrigeration flowpath and a defrost flowpath, wherein the defrost flowpath is arranged in a first direction, and the refrigeration flowpath is arranged in a second direction;
• a flash tank operably coupled to the circuit and configured to receive a first portion of the CO2 refrigerant in a liquid state and a second portion of the CO2 refrigerant in a vapor state;
• a hot gas discharge valve disposed in the circuit downstream of the compressor and configured to establish a first CO2 refrigerant pressure at the compressor's discharge during the defrost mode;
• a flash gas bypass valve disposed in the circuit downstream of the flash tank and operable to establish a second CO2 refrigerant pressure in the flash tank during the defrost mode;
• and
• a control system configured to regulate the hot gas discharge valve and the flash gas bypass valve during the defrost mode, to maintain a differential pressure between the first and second CO2 refrigerant pressures, and to drive the flow of CO2 refrigerant in the high-pressure hot-gas state from the compressors and through the evaporators.

A CO2 refrigeration system having an LT system portion with one or more LT compressors and one or more LT evaporators, and an MT system portion with one or more MT compressors and one or more MT evaporators, and having a hot gas defrost mode of operation that uses CO2 hot gas discharge from the MT compressors to defrost the LT evaporators, the system comprising:

• a defrost circuit configured to direct the CO2 hot gas discharge from the MT compressors to the LT evaporators during the hot gas defrost mode;
• an expansion valve operably coupled to the defrost circuit, configured to open during the defrost mode, and configured to regulate the pressure of the CO2 hot gas discharge within the defrost circuit;
• a relief valve operably coupled to the defrost circuit, and configured to release at least some of the CO2 hot gas discharge from the defrost circuit;
• instrumentation operably coupled to the defrost circuit, and configured to monitor the pressure of the CO2 hot gas discharge within the defrost circuit, and configured to transmit one or more signals;
• an isolation valve operably coupled to the defrost circuit, and configured to receiving a signal from the instrumentation;
• a return line fluidly connecting the defrost circuit to a suction of the MT compressors;
• a defrost bypass valve operably coupled to the return line, and configured to receive a signal from the instrumentation;
• a control system operably communicating with the instrumentation and the isolation valve and the defrost bypass valve to prevent the CO2 hot gas discharge having a pressure above a predetermined point from reaching the LT evaporators.

A CO2 refrigeration system having an LT system portion having a low-pressure piping portion and with one or more LT compressors and one or more LT evaporators, and an MT system portion having a high-pressure piping portion and with one or more MT compressors and one or more MT evaporators, and having a hot gas defrost mode of operation that uses CO2 hot gas discharge from the MT compressors to defrost the LT evaporators, the system comprising:

• a defrost circuit configured to direct the CO2 hot gas discharge from the MT compressors to the LT evaporators during the hot gas defrost mode;
• a valve operably coupled to the defrost circuit, configured to open during the defrost mode, and configured to regulate the pressure of the CO2 hot gas discharge within the defrost circuit;
• and
• a relief valve operably coupled to the defrost circuit, and configured to release at least some of the CO2 hot gas discharge from the defrost circuit upon detection of a predetermined pressure in the defrost circuit.