Experimental study and performance evaluation of a ground heat exchanger with different intermittent ratios and soil thermal properties

Abstract

The temperature behavior as well as the heat transfer evaluation of a ground heat exchanger (GHE) are investigated under different intermittent operation strategies, different amount of water added in soil at the initial moment of heating and recovery phase. For this purpose, small-scale experiments are respectively carried out in a soil-box system and a soil-column system. The results from the soil-box experiment showed that the dimensionless temperature rise rate and recovery rate of the soli represent a downtrend with an increasing on-off ratio. The effect of heat source on its nearby soil temperature rise would fade away after the pump operation time exceeds a certain value. In addition, the larger heat transfer mainly occurs in the initial 4 h during the heating and recovery phase. Thus, the further experiment performed in the 4h-4 h mode indicates that the better temperature recovery and heat transfer performance compared with the 12h-12 h mode. Compared with soil humidification at the recovery phase, soil humidification at the heating phase has the better heat transfer of soil, and the values of the temperature rise and recovery rate at 13 cm are respectively increased by 141.9% and 63.6% when 150 ml water added in soil. Moreover, its advantage becomes more noticeable as the increasing distance of the testing position from the GHE. Additionally, it is found that there is a critical soil moisture content for the temperature recovery improvement. This research on the GHE give the idea to elevate its energy performance and may be helpful to validate the future theoretical study.