Development and verification of simulation model of hybrid ground-coupled heat pump systems with inclined boreholes

This thesis proposed a new hybrid GCHP (HGCHP) system with a desuperheater and inclined ground heat exchanger (GHE) for the possibility of improving the application of the GCHP system in cooling-dominated buildings.;Firstly, an analytical inclined finite-line source model has been developed to describe the transient and steady-state heat conduction processes in GHEs with inclined and vertical boreholes for long-term operation. To compensate for the inaccuracy of the finite line source model for short-time scale, a two-dimensional numerical finite element model has been established. Comparisons between the numerical and analytical results show that the finite line-source model is capable of modeling the GHEs except for a few hours.;A simulation model of a water-to-water heat pump with a desuperheater has been developed. A comprehensive simulation program of the HGCHP system is thus developed, which is formed by the coupling of the heat pump unit and GHE models. The simulation model of the HGCHP system was extensively validated by experiments. The results show, on the whole, the simulation model is accurate to within +/-15% of the experimental data, which demonstrates that it is suitable for research study and engineering applications with an acceptable accuracy.;An exergy analysis of the HGCHP system is implemented on the basis of experimental data and the simulation model. Comparisons between the HGCHP and conventional systems show that the HGCHP system possesses the highest exergy and energy efficiencies. Finally, an annual hourly simulation of the hybrid GCHP system is performed for a small residential apartment. Compared with the conventional GCHP system, the hybrid system can effectively alleviate the imbalanced loads of the GHE on an annual basis. Besides, it can offer a significant energy saving of 67% for the DHW heating when compared with a conventional DHW heating system.;In summary, the simulation model of the HGCHP with DHW system can provide a useful and effective tool to investigate the system performance. The simulation and experimental results demonstrate that the HGCHP system can improve energy performance and occupy less ground area, as well as reduce the hot water heating capacity of boilers or electric heaters.