Transient Simulation of a Hybrid Ground Source Heat Pump System

Abstract

In the last decades, the utilization of the ground thermal energy content represents an attractive alternative for efficient and environmentally sustainable space conditioning, following the outbreak and extensive growth of ground source heat pump systems. Nevertheless, the wider acceptance and development of this technology is largely dependent on the availability of reliable design systems and simulation models that further improve the economic feasibility and sustainable operation of such systems through the accurate design and monitoring of their long-term energy performance.

A hybrid ground source heat pump system that partially covers the heating and cooling demands of a building at National Technical University of Athens Campus in Greece was selected as a case study for the development of an analytical simulation model in the TRNSYS simulation environment. It combines both vertical ground loop heat exchangers and an open loop with flat-plate heat exchangers, utilizing respectively the thermal energy content of the rocks present in the shallow earth adjacent to the building and the thermal energy content of the groundwater.

In the framework of this study, the integrated and analytical modeling of a typical annual operation of the system is presented and the effect of critical design parameters (e.g. heat pump performance characteristics, temperature level control strategies) on its real-time operation and long-term energy performance are further analyzed and discussed. Such an analysis provides the basis for the decoding of the behavior of the system in both transient and steady-state periods of operation, unlike conventional steady-state modeling approaches, setting up dynamic modeling as an invaluable tool for the implementation of realistic ground source heat pump models that can lead to improved design, monitoring and optimization techniques for such systems.