Hot gas defrost using low temperature compressor discharge gas and auxiliary flash tank

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

• operating a first evaporator of a plurality of evaporators in a refrigeration mode;
• determining that operation of the first evaporator in a defrost mode is indicated;
• and
• after determining that operation of the first evaporator in the defrost mode is indicated, causing the first evaporator to operate in the defrost mode by:
• adjusting a first controllable valve positioned in a first refrigerant conduit coupling one or more low-temperature compressors of the refrigeration system to one or more medium-temperature compressors of the refrigeration system;
• adjusting a second controllable valve positioned in a second refrigerant conduit coupling an outlet of a first flash tank to the first evaporator;
• directing at least a portion of refrigerant from the first flash tank to the first evaporator;
• and
• adjusting a pressure-regulating valve disposed in a third refrigerant conduit coupling the first flash tank to a second flash tank to increase a pressure of the first flash tank relative to a pressure of the second flash tank, wherein the first flash tank is configured to receive and store refrigerant cooled by a gas cooler and the second flash tank is configured to receive and store a portion of the cooled refrigerant from the first flash tank.

A controller of a refrigeration system, the controller comprising:

• an input/output interface communicatively coupled to:
• a first controllable valve positioned downstream from one or more low-temperature compressors, the first controllable valve configured to receive compressed refrigerant from the one or more low-temperature compressors and direct flow of the received refrigerant to one or both of (i) one or more medium-temperature compressors positioned downstream from the controllable valve and (ii) one or more evaporators of a plurality of evaporators of the refrigeration system based on an operation mode of the plurality of evaporators;
• a pressure-regulating valve disposed in a first refrigerant conduit coupling a first flash tank to a second flash tank, wherein the first flash tank is configured to receive and store refrigerant cooled by a gas cooler and the second flash tank is configured to receive and store a portion of the cooled refrigerant from the first flash tank;
• and
• a second controllable valve positioned in a second refrigerant conduit coupling an outlet of a first evaporator of the plurality of evaporators to an outlet of the first flash tank;
• and
• a processor configured to:
• determine that operation of the first evaporator in a defrost mode is indicated;
• and
• after determining that operation of the first evaporator in the defrost mode is indicated, cause the first evaporator to operate in the defrost mode by opening the second controllable valve and adjusting the first controllable valve to direct a portion of the refrigerant from the first flash tank to the first evaporator and adjusting the pressure-regulating valve to increase a pressure of the first flash tank relative to a pressure of the second flash tank.