Experimental comparison of earth-air and earth-water-air heat exchangers in bioclimatic comfort

Abstract

Bioclimatic comfort involves harnessing geothermal energy to cool or preheat ambient air before it is introduced into indoor spaces. The system used for this heat transfer is commonly referred to as an Earth-Air Heat Exchanger (EAHE). According to the literature, the main limitation of such systems is the soil saturation effect, which reduces their performance over time. Studies have also shown that the Earth-Water Heat Exchanger (EWHE), which uses water instead of air, improves heat transfer with the soil. However, its main drawback is the additional energy consumption due to pumps and the risk of corrosion. This paper proposes a novel system, the Earth-Water-Air Heat Exchanger (EWAHE), as a solution to the thermal saturation problem encountered in conventional Earth-Air Heat Exchangers. The EWAHE model integrates a water layer between the air duct and the soil, enhancing thermal exchange and maintaining system performance over time. Experimental comparisons between EAHE and EWAHE systems demonstrated that the EWAHE model provides improved cooling performance. Specifically, it achieved a higher heat transfer rate of 0.15 W more than the EAHE model. Most importantly, the progressive performance degradation of 5.8% per minute observed in the EAHE model due to soil saturation was completely mitigated in the EWAHE model. In light of these findings, the EWAHE model offers a promising and energy-efficient alternative for bioclimatic thermal regulation in buildings, particularly in hot climates where passive cooling is essential.