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A control system for controlling a refrigeration system having an operating point, comprising: a memory configured to store a relationship of at least an evaporator efficiency, an evaporator heat load, a refrigerant amount in the evaporator, and a variable dependent on a non-volatile liquid mixed wi

A control system for controlling a refrigeration system having an operating point, comprising: a memory configured to store a relationship of at least an evaporator efficiency, an evaporator heat load, a refrigerant amount in the evaporator, and a variable dependent on a non-volatile liquid mixed with refrigerant in the evaporator an input port configured to receive a signal corresponding to at least a measured evaporator heat load during operation; an output port configured to present an output to selectively alter an operating point of the evaporator, by altering the refrigerant amount in the evaporator and thereby changing the variable; and a processor, configured to receive the signal, access the memory; and generate the output to selectively move toward an optimum operating point. A corresponding method and refrigeration system are provided.

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1. A method for controlling a phase change refrigeration system having an evaporator, employing a refrigerant and a non-volatile liquid mixed with the refrigerant in at least a portion of the refrigeration system, comprising: storing a map relating evaporator efficiency according to a predetermined

1. A method for controlling a phase change refrigeration system having an evaporator, employing a refrigerant and a non-volatile liquid mixed with the refrigerant in at least a portion of the refrigeration system, comprising: storing a map relating evaporator efficiency according to a predetermined metric, evaporator heat load, refrigerant amount in the evaporator, and a concentration or amount of the non-volatile liquid mixed with the refrigerant in the evaporator; andselectively altering an operating point of the evaporator, by partitioning refrigerant between an accumulator and the evaporator and thereby altering a concentration of non-volatile liquid mixed with the refrigerant in the evaporator, during operation of the evaporator, by retrieving the stored map with at least one automated processor and processing data corresponding to at least a measured evaporator heat load during operation and in conjunction with the stored map, to selectively transition the operating point of the refrigeration system toward an optimum operating point. 2. The method according to claim 1, wherein the optimum operating point is a feasible operating point having a highest energy efficiency. 3. The method according to claim 1, wherein the optimum operating point is a feasible operating point having a highest operating cost efficiency. 4. The method according to claim 1, wherein the optimum operating point is a feasible operating point having a highest process economic efficiency. 5. The method according to claim 1, further comprising updating the map based on at least measurements of at least one of (a) evaporator efficiency and power consumption, and (b) evaporator heat load. 6. The method according to claim 5, wherein the map is further updated based on at least a measurement of refrigerant in the evaporator. 7. The method according to claim 5, wherein the map is further updated based on at least a measurement of non-volatile liquid in the evaporator. 8. The method according to claim 1, wherein the non-volatile liquid mixed with the refrigerant in the evaporator comprises lubricating oil. 9. The method according to claim 1, wherein said selectively altering comprises controlling a flow of refrigerant into the evaporator to dynamically ensure sufficient cooling capacity to meet cooling demand, and to deviate from a steady state level of refrigerant in the evaporator to move toward a level corresponding to the optimum operating point. 10. The method according to claim 1, further comprising performing a thermodynamic analysis to determine a need to remove non-volatile liquid from the evaporator. 11. The method according to claim 1, further comprising performing a cost-benefit analysis to determine an optimal time to remove a portion of the non-volatile refrigerant from the evaporator, dependent on a cost associated with a removal of non-volatile refrigerant from the evaporator. 12. The method according to claim 1, further comprising performing a cost-benefit analysis to control removal of a portion of the non-volatile refrigerant from the evaporator, dependent on at least a cost of a removal of non-volatile refrigerant from the evaporator, a power consumption cost of operating the refrigeration system, and a benefit resulting from a process cooled by the evaporator. 13. A refrigeration system comprising: a compressor configured to compress a refrigerant;a condenser configured to condense refrigerant to a liquid, lubricated with a non-volatile liquid;an accumulator configured to store a variable portion of the condensed refrigerant;an evaporator configured to remove heat from a process by evaporation of the condensed refrigerant, having a variable amount of refrigerant gas, and subject to accretion of the non-volatile liquid which migrates from the compressor; anda controller, having a memory configured to store a relationship of at least evaporator efficiency, evaporator heat load, refrigerant amount in the evaporator, and a variable dependent on the non-volatile liquid in the evaporator, an input corresponding to at least a measured evaporator heat load during operation, and an output computed during operation of the refrigeration system, configured to selectively alter an operating point of the evaporator, by partitioning refrigerant between the accumulator and the evaporator and thereby changing the variable, and in dependence on a contents of the memory, and the input corresponding to at least a measured evaporator heat load during operation, to selectively move toward an optimum operating point. 14. The refrigeration system according to claim 13, wherein the optimum operating point is a feasible operating point selected from the group consisting of an operating point having a highest energy efficiency, a highest operating cost efficiency, and a highest process economic efficiency. 15. The refrigeration system according to claim 13, wherein the control is further configured to update the memory based on at least (a) measurements of at least one of evaporator efficiency and power consumption, and (b) evaporator heat load. 16. The refrigeration system according to claim 15, wherein the control is further configured to update the memory based on at least a measurement of refrigerant in the evaporator. 17. The refrigeration system according to claim 15, wherein the control is further configured to update the memory based on at least a measurement of non-volatile liquid in the evaporator. 18. The refrigeration system according to claim 13, wherein the control is configured to selectively alter a flow of refrigerant into the evaporator to dynamically ensure sufficient cooling capacity to meet cooling demand, and to deviate from a steady state level of refrigerant in the evaporator to move toward a level corresponding to the optimum operating point. 19. The refrigeration system according to claim 13, wherein the control is configured to perform a thermodynamic analysis to determine an optimum time to remove non-volatile liquid from the evaporator. 20. A control system for controlling a refrigeration system having an operating point, comprising: a memory configured to store a relationship of at least an evaporator efficiency, an evaporator heat load, a refrigerant amount in the evaporator, and a variable dependent on a non-volatile liquid mixed with refrigerant in the evaporator;an input port configured to receive a signal corresponding to at least a measured evaporator heat load during operation;an output port configured to present an output to selectively alter an operating point of the evaporator, by altering the refrigerant amount in the evaporator and thereby changing the variable; anda processor, configured to receive the signal, access the memory; and generate the output to selectively move toward an optimum operating point.