Control of a refrigeration circuit

Abstract

There is disclosed a controller for a refrigeration circuit, configured to monitor a set of prevailing conditions relating to the refrigeration circuit including a space temperature of a temperature-controlled space associated with the refrigeration circuit. The controller has a simulation module configured to determine a limit setting of a control variable for the refrigeration circuit by an iterative optimisation procedure based on a model corresponding to the refrigeration circuit. The objective function for the optimisation relates to an operating efficiency. The controller further comprises a dynamic control module configured to: adjust an operating setting of the control variable within an operating range to target a performance threshold for a monitored performance parameter, based on monitoring of the performance parameter during operation of the refrigeration circuit; and apply the limit setting received from the simulation module as a limit to the operating range.

1 . A controller for a refrigeration circuit;
 wherein the controller is configured to monitor a set of prevailing conditions relating to the refrigeration circuit including a space temperature of a temperature-controlled space associated with the refrigeration circuit;   wherein the controller has a simulation module configured to determine a limit setting of a control variable for the refrigeration circuit by an iterative optimisation procedure based on a model corresponding to the refrigeration circuit;
 wherein the iterative optimisation procedure is defined based on an objective function which relates to an operating efficiency of the refrigeration circuit and is determined based on evaluating the model for a respective simulated operating point; 
 wherein the simulated operating point is defined by the monitored set of prevailing conditions, and by a simulated setting for the control variable which is iteratively varied in the optimisation procedure, and 
   wherein the controller further comprises a dynamic control module configured to:
 adjust an operating setting of the control variable within an operating range to target a performance threshold for a monitored performance parameter, based on monitoring of the performance parameter during operation of the refrigeration circuit; 
 apply the limit setting received from the simulation module as a limit to the operating range. 
   
     
     
         2 . The controller according to  claim 1 , wherein the dynamic control module is configured to adjust the operating setting of the control variable during operation of the refrigeration circuit, based on concurrent monitoring of the performance parameter during operation of the refrigeration circuit. 
     
     
         3 . The controller according to  claim 1 , wherein the model does not determine the performance parameter. 
     
     
         4 . The controller according to  claim 1 , wherein the objective function is a coefficient of performance. 
     
     
         5 . The controller according to  claim 4 , wherein the coefficient of performance is determined based on a simulated heat transfer capacity and a corresponding simulated power consumption, each determined based on the model. 
     
     
         6 . The controller according to  claim 1 , wherein the monitored performance parameter is a rate of change of a monitored condition relating to the refrigeration circuit. 
     
     
         7 . The controller according to  claim 1 , wherein the targeted performance threshold for the monitored performance parameter is selected from the group consisting of:
 a heat transfer parameter relating to a heat transfer capacity of the refrigeration circuit; and   a predetermined minimum refrigerant superheat at a superheat monitoring location along a suction line of the refrigeration circuit.   
     
     
         8 . The controller according to  claim 7 , wherein the heat transfer parameter is:
 a predetermined minimum heat transfer capacity of the refrigeration circuit; or   a predetermined minimum magnitude of a monitored rate of change of a space temperature of the temperature-controlled space.   
     
     
         9 . The controller according to  claim 1 , wherein the dynamic control module comprises a PI or PID control module configured to control the control variable of the refrigeration circuit during operation of the refrigeration circuit;
 wherein the PI or PID control module is configured to vary the control variable based on an error signal relating to a difference between the performance threshold and the monitored performance parameter; and   wherein the limit setting for the control variable is applied as saturation limit of the PI or PID controller.   
     
     
         10 . The controller according to  claim 9 , wherein the targeted performance threshold for the monitored performance parameter is a predetermined minimum magnitude of a monitored rate of change of the space temperature; and
 wherein the PI or PID control module:
 is configured to control an operating parameter of the compressor as the control variable; 
 is configured to determine the error signal as the difference between the predetermined minimum magnitude of the rate of change of the space temperature and a monitored rate of change of the space temperature. 
   
     
     
         11 . The controller according to  claim 1 , wherein:
 the monitored performance parameter is a rate of change of a monitored condition relating to the refrigeration circuit;   the model is configured to determine the simulated power consumption based on one or more of:
 an operating parameter of the compressor, as the control variable or derived from the set of prevailing conditions; 
 an operating parameter of a first fan associated with the first heat exchanger, as the control variable or derived from the set of prevailing conditions; and/or 
 an operating parameter of a second fan associated with the second heat exchanger, as the control variable or derived from the set of prevailing conditions. 
   
     
     
         12 . The controller according to  claim 1 , configured to repeatedly conduct the optimisation procedure and update the limit setting. 
     
     
         13 . The controller according to  claim 12 , wherein the controller is configured to:
 repeat the optimisation procedure at predetermined intervals; and/or   repeat the optimisation procedure based on determining a threshold change or rate of change of a prevailing condition of the set of prevailing conditions.   
     
     
         14 . The controller according to  claim 1 , wherein the simulation module is configured to determine a limit setting of a plurality of control variables for the refrigeration circuit by the iterative optimisation procedure;
 wherein the simulated operating point is defined by the monitored set of prevailing conditions and by respective simulation settings for the plurality of control variables;   wherein for each control variable, the simulation control module is configured to determine a respective limit setting by the optimisation procedure;   wherein the dynamic control module is configured to adjust each respective operating setting of the control variables within respective operating ranges to target the performance threshold for the monitored performance parameter, and to apply each respective limit setting received from the simulation module as a limit to the respective operating ranges.   
     
     
         15 . A refrigeration circuit comprising:
 a compressor,   a first heat exchanger,   an expansion device,   a second heat exchanger, and   a controller;   wherein the controller is configured to monitor a set of prevailing conditions relating to the refrigeration circuit including a space temperature of a temperature-controlled space associated with the refrigeration circuit;   wherein the controller has a simulation module configured to determine a limit setting of a control variable for the refrigeration circuit by an iterative optimisation procedure based on a model corresponding to the refrigeration circuit;
 wherein the iterative optimisation procedure is defined based on an objective function which relates to an operating efficiency of the refrigeration circuit and is determined based on evaluating the model for a respective simulated operating point; 
 wherein the simulated operating point is defined by the monitored set of prevailing conditions, and by a simulated setting for the control variable which is iteratively varied in the optimisation procedure, and 
 wherein the controller further comprises a dynamic control module configured to:
 adjust an operating setting of the control variable within an operating range to target a performance threshold for a monitored performance parameter, based on monitoring of the performance parameter during operation of the refrigeration circuit; 
 
 apply the limit setting received from the simulation module as a limit to the operating range. 
   
     
     
         16 . A method of controlling a refrigeration circuit using a controller, wherein a control variable of the refrigeration circuit is variable during operation of the refrigeration circuit,
 the method comprising:
 monitoring a set of prevailing conditions relating to the refrigeration circuit, including a space temperature of a temperature-controlled space associated with the refrigeration circuit; 
 the controller, in a simulation module, conducting an iterative optimisation procedure to determine a limit setting of a control variable for the refrigeration circuit based on a model corresponding to the refrigeration circuit; 
 wherein the iterative optimisation procedure is defined based on an objective function which relates to an operating efficiency of the refrigeration circuit and is determined based on evaluating the model for a respective simulated operating point; 
 wherein the simulated operating point is defined by the monitored set of prevailing conditions, and by a simulated setting for the control variable which is iteratively varied in the optimisation procedure; 
   wherein the method further comprises:
 a dynamic control module of the controller applying the limit setting as a limit to an operating range for the control variable; 
 monitoring a performance parameter for the refrigeration circuit during operation of the refrigeration circuit; 
 the dynamic control module adjusting an operating setting of the control variable within the operating range to target a performance threshold for the monitored performance parameter; 
 whereby the dynamic control module biases operation of the refrigeration circuit to the limit setting of the control variable determined by the optimisation procedure when the limit setting corresponds to compliance with the performance threshold during operation of the refrigeration circuit; and 
 whereby the dynamic control module biases operation of the refrigeration circuit to depart from the limit setting of the control variable to achieve the target performance threshold when the limit setting corresponds to non-compliance with the performance threshold during operation of the refrigeration circuit.