Introducing a Short-term Holistic Approach for More Efficient Ground-coupled Heat Pump Systems

Abstract

Ground-coupled heat pump systems (GHPS) become increasingly popular for providing buildings with heating and cooling, replacing existing boilers fired by fossil fuels. Focusing on the heating purpose, a heat pump uses a small amount of electrical energy to upgrade low temperature heat from the ground within a thermodynamic cycle to the target temperature of the heating network. With respect to the thermodynamic concept, the optimizing goal of such processes is a high and quasi-constant inlet temperature into the heat pump, reducing the amount of electrical energy to deliver the same amount of heat to the network. In this paper, a short-term model of a borehole heat exchanger (BHE) is presented, introducing a holistic approach to optimize the GHPS. The model is based on a large volume coaxial BHE, which, in addition, offers a favorable larger volume compared to standard (double-) U-pipes. A hybrid approach using a combined finite-volume and an analytical scheme thereby enables the continuous simulation of temperature fields within the pipe and the surrounded volume with respect to the operation of the heat pump and the characteristic parameters of the system. Thus, it becomes possible to develop a deep understanding of the impact of heat pump operation on the ground’s and working fluid’s temperature and vice versa as well as the efficiency dependencies of the overall system, which will lead to a more efficient use of GHPS.