Model-based Optimizing Control of a Water-to-Water Heat Pump Unit

Abstract

This paper outlines the basic principles of on-line model-based steady-state optimizing control of continuous processes, and illustrates how this control approach can be used to optimize the operating conditions of heat pumps. The multilayer approach of hierarchical control theory is used to synthesise the control structure, and the control objectives are decomposed into regulatory and optimizing control tasks. The optimization problem in the optimizing control system is solved within an infeasible path nonlinear programming approach, where the performance criterion, the adaptive steady-state process model, and the operational feasibility constraints are solved simultaneously using a sequential quadratic programming (SQP) algorithm. An on-line model-based optimizing control algorithm is implemented on a personal computer and used to minimize the energy consumption of an experimental water-to-water electric-motor driven heat pump unit. During a period of steady process operation, process data is gathered and used to update parameters in the steady-state heat pump model. The updated process model is then used to calculate new set-points for the regulatory control system that minimize the total electric power input to the heat pump unit while not violating the operational feasibility constraints. The various energy losses in the heat pump unit are shown to verify the ability of the optimizing control system to conserve energy.