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EP-2948719-B1 - SYSTEM AND METHOD FOR CONTROL OF A TRANSCRITICAL REFRIGERATION SYSTEM

EP2948719B1EP 2948719 B1EP2948719 B1EP 2948719B1EP-2948719-B1

Inventors

  • WALLACE, JOHN
  • BELTRAN, Franklin
  • DA ROS, SAMUELE

Dates

Publication Date
20260506
Application Date
20140124

Claims (12)

  1. A CO 2 refrigeration system (10), operable in a subcritical mode and a transcritical mode, comprising: one or more compressors (13, 14, 17, 18, 19); a heat exchanger (20) configured to receive refrigerant discharged from the one or more compressors (13, 14, 17, 18, 19) and that is operable as a gas cooler when the CO 2 refrigeration system (10) is operating in the transcritical mode and as a condenser when the CO 2 refrigeration system (10) is operating in the subcritical mode; a liquid receiver (21) configured to receive refrigerant discharged from the heat exchanger (20); a first valve (30) connected between the heat exchanger (20) and the liquid receiver (21), the first valve (30) configured to control a flow of refrigerant from the heat exchanger (20) to the liquid receiver (21); a second valve (40) located in a bypass line configured to route refrigerant from the liquid receiver (21) to a suction side of the one or more compressors (13, 14, 17,18,19) configured to control a flow of refrigerant from the liquid receiver (21) to the suction side of the one or more the compressors (13, 14, 17,18,19); a valve controller (60) configured to: monitor an outdoor ambient temperature and a pressure of refrigerant exiting the heat exchanger (20), determine whether the CO 2 refrigeration system (10) is operating in the subcritical mode or in the transcritical mode, determine a pressure setpoint based on the monitored outdoor ambient temperature, and control the first valve (30) based on a comparison of the determined pressure setpoint and the monitored pressure of refrigerant exiting the heat exchanger (20) when the CO 2 refrigeration system (10) is determined to be operating in the transcritical mode; wherein the valve controller (60) is further configured to: monitor a temperature of refrigerant exiting the heat exchanger (20), calculate a subcooling temperature of the refrigerant based on the monitored temperature of refrigerant exiting the heat exchanger (20) and on the monitored pressure of refrigerant exiting the heat exchanger (20), and control the first valve (30) based on a comparison of the calculated subcooling temperature and a predetermined subcooling setpoint when the CO 2 refrigeration system (10) is determined to be operating in the subcritical mode; control the second valve (40) based on a comparison of the monitored pressure of refrigerant within the liquid receiver (21) and a predetermined pressure setpoint, and compare the monitored pressure of refrigerant within the liquid receiver (21) with a low pressure setpoint and a high pressure setpoint and control the first valve (30) and the second valve (40) in a safety mode when the monitored pressure of refrigerant within the liquid receiver (21) is above the high pressure setpoint or below the low pressure setpoint, wherein when the pressure of refrigerant within the liquid receiver (21) is below the low pressure setpoint, the valve controller (60) is configured to increase an opening of the first valve (30) and decrease an opening of the second valve (40), and when the monitored pressure of refrigerant within the liquid receiver (21) is above the high pressure setpoint, the valve controller (60) is configured to decrease the opening of the first valve (30) and increase the opening of the second valve (40).
  2. The system of claim 1, wherein the valve controller (60) is configured to determine whether the CO 2 refrigeration system (10) is operating in the subcritical mode or in the transcritical mode based on the monitored outdoor ambient temperature.
  3. The system of claim 1, wherein the valve controller (60) is configured to determine the pressure setpoint based on a lookup table that includes a plurality of ambient temperature values with corresponding pressure setpoint values.
  4. The system of claim 1, further comprising a compressor controller associated with each compressor of the one or more compressors (13, 14, 17, 18, 19) configured to store compressor identification information including at least one of a compressor model, type, size, or capacity for each compressor (13, 14, 17, 18, 19) of the one or more compressors, wherein the valve controller (60) is configured to store a lookup table selected from a plurality of lookup tables based on the compressor identification information, the lookup table including a plurality of ambient temperature values with corresponding pressure setpoint values, wherein the valve controller (60) is configured to determine the pressure setpoint based on the selected lookup table and the monitored outdoor ambient temperature.
  5. The system of claim 4, wherein the valve controller (60) is configured to select the lookup table from the plurality of lookup tables based on the compressor identification information.
  6. The system of claim 4, wherein a separate controller is configured to select the lookup table from the plurality of lookup tables based on the compressor identification information and communicate the selected lookup table to the valve controller (60).
  7. A method for a CO 2 refrigeration system (10) operable in a subcritical mode and a transcritical mode, the method comprising: monitoring, with a valve controller (60), an outdoor ambient temperature; monitoring, with the valve controller (60), a pressure of refrigerant exiting a heat exchanger (20) of the CO 2 refrigeration system (10), the heat exchanger (20) receiving refrigerant discharged from one or more compressors (13, 14, 17, 18, 19) and being operable as a gas cooler when the CO 2 refrigeration system (10) is operating in the transcritical mode and as a condenser when the CO 2 refrigeration system (10) is operating in the subcritical mode; determining, with the valve controller (60), whether the CO 2 refrigeration system (10) is operating in the subcritical mode or in the transcritical mode; determining, with the valve controller (60), a pressure setpoint based on the monitored outdoor ambient temperature; controlling, with the valve controller (60), a first valve (30) based on a comparison of the determined pressure setpoint and the monitored pressure of refrigerant exiting the heat exchanger (20) when the CO 2 refrigeration system (10) is determined to be operating in the transcritical mode, the first valve (30) being connected between the heat exchanger (20) and a liquid receiver (21) and controlling a flow of refrigerant from the heat exchanger (20) to the liquid receiver the method further comprising: monitoring, with the valve controller (60), a temperature of refrigerant exiting the heat exchanger (20); calculating, with the valve controller (60), a subcooling temperature of the refrigerant based on the monitored temperature of refrigerant exiting the heat exchanger (20) and on the monitored pressure of refrigerant exiting the heat exchanger (20); and controlling, with the valve controller (60), the first valve (30) based on a comparison of the calculated subcooling temperature and a predetermined subcooling setpoint when the CO 2 refrigeration system (10) is determined to be operating in the subcritical mode; the CO2 refrigeration system (10) including a second valve (40) configured to control a flow of refrigerant in a bypass line that routes refrigerant from the liquid receiver (21) to a suction side of the at least one compressor (17, 18, 19), the method further comprising: controlling, with the valve controller (60), the second valve (40) based on a comparison of the monitored pressure of refrigerant within the liquid receiver (21) and a predetermined pressure setpoint; comparing, with the valve controller (60), the monitored pressure of refrigerant within the liquid receiver (21) with a low pressure setpoint and a high pressure setpoint; and controlling, with the valve controller (60), the first valve (30) and the second valve (40) in a safety mode when the monitored pressure of the refrigerant within the liquid receiver (21) is above the high pressure setpoint or below the low pressure setpoint, wherein controlling the first valve (30) and the second valve (40) in the safety mode includes: increasing an opening of the first valve (30) and decreasing an opening of the second valve (40) when the pressure of refrigerant within the liquid receiver (21) is below the low pressure setpoint; and decreasing the opening of the first valve (30) and increasing the opening of the second valve (40) when the monitored pressure of refrigerant within the liquid receiver (21) is above the high pressure setpoint.
  8. The method of claim 7, wherein the determining whether the CO 2 refrigeration system (10) is operating in the subcritical mode or in the transcritical mode is based on the monitored outdoor ambient temperature.
  9. The method of claim 7, further comprising: determining, with the valve controller (60), the pressure setpoint based on a lookup table that includes a plurality of ambient temperature values with corresponding pressure setpoint values.
  10. The method of claim 7, the CO 2 refrigeration system (10) including a compressor controller associated with each compressor of the one or more compressors (13, 14, 17, 18, 19) that stores compressor identification information including at least one of a compressor model, type, size, or capacity for each compressor of the one or more compressors (13, 14, 17, 18, 19), the method further comprising: storing, with the valve controller (60), a lookup table selected from a plurality of lookup tables based on the compressor identification information, the lookup table including a plurality of ambient temperature values with corresponding pressure setpoint values; wherein the valve controller (60) is configured to determine the pressure setpoint based on the selected lookup table and the monitored outdoor ambient temperature.
  11. The method of claim 10 further comprising: selecting, with the valve controller (60), the lookup table from the plurality of lookup tables based on the compressor identification information.
  12. The method of claim 10 further comprising: selecting, with a separate controller, the lookup table from the plurality of lookup tables based on the compressor identification information; and communicating, with the separate controller, the selected lookup table to the valve controller (60).

Description

The present invention relates to a system and method for control of a transcritical refrigeration system and, more specifically, to a system and method for controlling components of a transcritical refrigeration system utilizing CO2 refrigerant and including a high pressure valve, a bypass gas valve, and a liquid receiver. This section provides background information related to the present invention which is not necessarily prior art. Refrigeration systems utilizing carbon dioxide (CO2) as a refrigerant can have many advantages over refrigeration systems utilizing non-CO2 refrigerants. Refrigeration systems utilizing CO2 refrigerant may include, for example, one or more compressors, a gas cooler, a liquid receiver, and one or more evaporators. The liquid receiver may include a bypass line to discharge refrigerant from the liquid receiver back to the compressors, thereby bypassing the evaporators. In a refrigeration system utilizing non-CO2 refrigerant, the compressors discharge high pressure gaseous refrigerant to a condenser which cools the refrigerant to below its critical point, resulting in a change in state of the refrigerant from gas to liquid. In a CO2 refrigeration system operating in a transcritical mode, on the other hand, the gaseous refrigerant is cooled in a gas cooler to a temperature that is still above the critical point of the refrigerant, resulting in a cooler gaseous refrigerant but not resulting in a change in state to liquid. The CO2 refrigerant is then discharged from the gas cooler to a liquid receiver connected to the evaporators and also connected to a bypass line. The pressure of the liquid receiver can be maintained to allow liquid refrigerant to form in the liquid receiver. Liquid refrigerant can then be supplied from the liquid receiver to the evaporators. Gaseous refrigerant in the liquid receiver can then be routed back to the compressors. Because of the higher operating temperatures and pressures associated with CO2 refrigeration systems, maintaining proper and efficient operation of the refrigeration system can be difficult. WO 2011049778 A1 discloses a vapor compression system including a compressor, a heat rejection heat exchanger, an economizer device, a secondary expansion valve and a controller. US8186171B2 discloses a CO2 refrigeration system for transcritical and subcritical operation comprising a compressor, a gascooler/condenser, a first valve downstream of the gascooler/ condenser, a liquid receiver, a second valve between the liquid receiver and an inlet of the compressor, wherein a controller is configured to control the first and the second valve; wherein the controller is configured to monitor an ambient temperature and a refrigerant pressure, to determine a pressure setpoint based on the ambient temperature and the monitored pressure in a transcritical mode, to control the first valve based on the pressure setpoint and a refrigerant pressure at the exit of the gascooler/condenser in the transcritical mode, to control the first valve to achieve a predetermined subcooling in the subcritical mode. This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. The invention is defined in the independent claims. Further preferred embodiments are defined in the dependent claims. In various embodiments of the present invention, a CO2 refrigeration system that is operable in a subcritical mode and a transcritical mode is provided. The CO2 refrigeration system includes at least one compressor and a heat exchanger that receives refrigerant discharged from the at least one compressor. The heat exchanger is operable as a gas cooler when the CO2 refrigeration system is operating in the transcritical mode and as a condenser when the CO2 refrigeration system is operating in the subcritical mode. The CO2 refrigeration system also includes a liquid receiver that receives refrigerant discharged from the heat exchanger. The CO2 refrigeration system also includes a first valve connected between the heat exchanger and the liquid receiver. The first valve controls a flow of refrigerant from the heat exchanger to the liquid receiver. The CO2 refrigeration system also includes a valve controller that monitors an outdoor ambient temperature and a pressure of refrigerant exiting the heat exchanger. The valve controller determines whether the CO2 refrigeration system is operating in the subcritical mode or in the transcritical mode and determines a pressure setpoint based on the monitored outdoor ambient temperature. The valve controller controls the first valve based on a comparison of the determined pressure setpoint and the monitored pressure of refrigerant exiting the heat exchanger when the CO2 refrigeration system is determined to be operating in the transcritical mode. In various embodiments of the present invention, a method for a CO2 refrigeration system operable in a subcritical mode and a transcritica