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A TRNSYS model of ground source heat pump (GSHP) system is constructed and validated according to the measured running data of the studied GSHP system. It has been found that there exists a serious thermal accumulation problem under the ground, and the cooling tower is introduced to the GSHP system for auxiliary heat dissipating. By the simulation of the improved GSHP system in TRNSYS software, the input time of cooling tower, the auxiliary cooling ratio (ACR), and also two control strategies of cooling tower are studied, and the following conclusions are derived: the cooling tower should be put into operation in the third year for the energy saving purpose of the studied GSHP system at the optimal auxiliary cooling ratio of ACR = 30%. For the further study of control strategy, the optimal control parameter is ΔT = 6 °C if the temperature difference control strategy is adopted; while it is Tu / Tl=30 °C /28 oC if the fixed temperature control strategy is adopted.

A ground-source heat pump (GSHP) system located in Chongqing, a cooling dominated region in China, was taken as an experimental system. In order to explore the operating characteristics of the GSHP system, the GSHP system was monitored with a data acquisition system. The measured data were analyzed, including the inlet/outlet water temperatures, power consumptions, EER / COP and also the ground temperature variations. The measured system EER of 2013 and 2014 are 3.01 and 2.91, respectively, while the system COP of 2013 is 2.59. A TRNSYS model was established based on the studied GSHP system. The accuracy of the model was validated by the comparison between the measured and the simulated outlet water temperatures, and also the ground temperatures. The model was then used to predict the long-term performance of the GSHP system. It has been found that after 20-years running of the system, the heat accumulation under the ground and the deterioration of system efficiency aggravate: the ground temperature would rise up to 30.5 °C from the initial value of 20 °C, while the ASPF value would descend to 2.72 from the initial value of 3.12. As a remedy for the problem, the domestic hot water (DHW) system was supposed to be operated in the following years, and the simulation showed that the operation of DHW system could effectively reduce the ground temperature and improve the system performance.