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. 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 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. 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.