Performance of a Ground-Source Heat Pump System and the Heat-Moisture Migration of Surrounding Soils in Karst Areas

In recent years, ground-source heat pumps (GSHPs) have been extensively used in engineering projects because of their ability to take advantage of geothermal energy and their subsequent benefits of energy saving and environmental protection. Significant progress has been made in understanding the heat exchange between ground heat exchangers (GHEs), and surrounding soils in a GSHP system. However, relatively fewer studies have been performed to investigate the influences of the moisture variations and seepage flow in the surrounding soils on the performances of the GSHP system. Karst formations extensively exist in many areas of southern China where the subtropical climate brings frequent precipitation, rich seepage water flow, and fluctuations in the groundwater table. All these factors pose huge challenges to the implementation of GSHP systems in these areas, which makes the heat exchange between GHEs and surrounding soils a coupled heat-moisture transport problem. No previous research has been dedicated to this topic. In order to understand the coupled heat-moisture transport process and its influences on the heat exchange between GHEs and surrounding soils in karst areas of southern China, a GSHP system was constructed in Guilin, Guangxi Province to monitor its performance under the combined influences of soil temperature and moisture changes. A data-acquisition system was set up to monitor the most relevant parameters of the system, such as temperature and moisture levels of the surrounding soils, climatic factors, groundwater table, and performance of the GSHP system. Three different operation-mode tests were used to simulate possible future applications under different scenarios. The test results were analyzed, from which some conclusions were drawn regarding the influences of the coupled heat-moisture migrations in karst areas on the performance of GSHP systems. (C) 2017 American Society of Civil Engineers.