Holistic optimization of the operation of a GCHP system: A case study on the ADREAM building in Toulouse, France

Abstract

Ground-source heat pumps are more energy-efficient, especially when compared to their water and air source counterparts. However, when operating and design conditions are vastly different, the expected gains in efficiency could be easily negated. Under such scenarios, measures to improve energy performance are explored through performing mathematical optimization on the appropriate model of the system.Components of a heat pump system are often operated at pre-defined setpoints or independently optimized, disregarding the overall performance. Formulation of a holistic optimization problem which expresses the system in its tuneable variables, while capturing the tight-coupling between its components results in a complex mixed-integer non-linear program. Our paper concerns itself with the mathematical modeling and optimization of the hourly operation of a ground-coupled heat pump system for improving energy and operating cost. We judiciously abstracted and decoupled the component models of the system, so that the problem could be formulated as a mixed-integer linear program. This vastly benefited the solvability of the optimization problem.For illustration, we implemented this methodology on a system in the ADREAM building of the LAAS-CNRS laboratory in Toulouse, France. Four case studies are defined in the lead up to holistic optimization, allowing the results to be easily understood. The results reveal significant limitations, which prompted the hybridization of the system with a hypothetical water-to-air heat exchanger. Results indicated electricity and cost savings of up to 35.0% and 12.7% respectively, depending on the objective function. Our findings postulate that the additional investment is recoverable within five years.