In-situ experimental study of heat exchange capacity of CFG pile geothermal exchangers

• Full-scale TRT and TPT of CFG pile exchangers are performed.
• Heat exchange capacity of CFG energy piles is estimated from different power TRT.
• Effects of inlet water temperature and flow velocity on TPT are studied.
• Heat exchange of CFG energy piles varies with different operation modes.
• Temperature influence radius of a single CFG pile exchanger is over 4 m.

Pile geothermal exchangers are a popular new type of geothermal exchanger for use in ground source heat pump systems due to their technical and cost improvements over traditional borehole geothermal exchangers. An in-situ full-scale study using the thermal response and thermal performance tests (TRT and TPT) is performed to investigate the heat exchange capacity of the cement-fly ash-gravel (CFG) piles usually used in foundations for low to medium high-rise buildings in Beijing. This paper analyzes the influences of the hydration heat of cement, heating power, inlet water temperature, circulating water flow velocity, operation mode, and group-pile effects on the heat exchange capacity of CFG pile geothermal exchangers. The test results can be used for the thermal design of CFG energy piles.