Investigation of a coupled geothermal cooling system with earth tube and solar chimney

We present a systematic study of a coupled geothermal cooling system with an earth-to-air heat exchanger and a solar collector enhanced solar chimney. Experiments were conducted with an existing test facility in summer to evaluate the performance of the system, in terms of passive cooling capability, active cooling capability, and soil thermal capability. Correspondingly, three different tests were carried out in 43 days in a sequence, from a passive cooling mode to an active cooling mode, and then back to a passive cooling mode. The results show that the coupled geothermal system is feasible to provide cooling to the facility in natural operation mode free without using any electricity. The solar collector enhanced solar chimney can provide more airflow to the system during the daytime with a stronger solar intensity. The thermal sensation analysis based on predicted mean vote and predicted percent of dissatisfied people indicates that the indoor air condition under the natural airflow stage was more acceptable in terms of thermal comfort than that of the forced airflow stage. The cooling capacity of the coupled system drops quickly after the one week forced airflow test due to the underground soil temperature increase. It takes the soil over two weeks to fully recover from the thermal saturation after the forced air test. In addition, the underground soil temperature test results indicate that the underground heat dissipation in the horizontal level was greater than that in the vertical level. The findings suggest that a minimum level of control on the system and consideration on soil saturation is needed to further improve the overall performance.