Experimental study on moisture migration in soil during coupled heat storage and release processes

Abstract The soil around ground heat exchanger is the heat source or heat sink of ground source heat pump system. Most scholars had analyzed the soil heat and moisture migration in heat storage or release process, respectively. In this paper, the coupled heat storage and release experiments were conducted in saturated and unsaturated fine-grained sand under the same excess temperature. The comparison on the soil moisture migration and the temperature and humidity recovery characteristics were analyzed. Results showed that the amount of soil moisture migration is almost symmetrical for the test soil sample during heat storage and release processes under the same excess temperature, the relative difference of moisture migration is within 10%. For a certain initial moisture content, the phenomenon of moisture migration could not occur until the excess temperature reaches a certain value. Similarly, for a certain excess temperature, the phenomenon of moisture migration could not occur until the initial moisture content of soil reaches a certain value. The phenomenon of maximum moisture content exists in heat storage process, but not exists in heat release process. The time required to restore to the initial soil temperature is the same, while the time required to restore to the initial moisture content is different between soil heat storage and release processes. With the increase of the initial moisture content, the humidity recovery time increases.