Experimental performance evaluation and parametric study of a solar-ground source heat pump system operated in heating modes

The dual heat source coupling modes of solar-ground source heat pump system (SGSHPS) directly determine its operation characteristics. In this paper, the thermal performance of a SGSHPS operated in different dual heat source coupling modes were studied experimentally. The unit COP, solar collecting efficiency and inlet and outlet temperatures of GHE were tested for various modes. The results show that for the combination operation mode, solar and ground heat source are dynamically coupled by the water tank and plate heat exchanger, and the average unit COP and collecting efficiency are 3.61 and 51.5%, respectively. For the water tank heat storage mode, the inlet water temperature of evaporator in the daytime stop mode of GSHP is 1.85 degrees C higher than daytime operation mode of GSHP, and the average unit COP and collecting efficiency are respectively 3.43 and 34.8%, 3.91 and 34.9% for the daytime stop mode of GSHP and daytime operation mode of GSHP. For the ground heat storage mode, the ground temperature can be improved effectively for ground continuous heat storage mode and the outlet temperature of GHE can be increased significantly for ground intermittent heat storage mode. The average unit COP and collecting efficiency are 3.65 and 47.9%, 3.8 and 41.5% for the ground intermittent and continuous heat storage mode, respectively. A TRNSYS dynamical simulation model of the SGSHPS was established to explore the influences of key parameters on the system performance. The results indicate that the collector area and GHE number have evident influences on the system efficiency, but the impact of water tank volume is very small. The suitable collector area and GHE number are found to be 80 m(2) and 9, respectively, and the water tank volume should be set as small as possible with the permission of actual conditions. (C) 2018 Elsevier Ltd. All rights reserved.