Earth-Air Heat Exchangers: Impact of Surrounding Conditions on Long-term Performance

Earth-Air Heat Exchanger (EAHE) is a shallow geothermal tube exchanger buried under the ground to exchange heat with the upper soil layers at low temperatures. As an abundant renewable energy source, EAHE can efficiently pre-heat and cool the air supplied to buildings saving and reducing the use of non-renewable energy. The performance of an EAHE is affected by the climatic zone in which it installed as well as many other parameters in its surrounding environment. The work in progress here aims at studying these parameters that affect the energy performance of the buried pipe near the building. The study uses database measurements (temperature, humidity, precipitation, etc.) of flowing air and surrounding soil in a full-scale experimental EAHE site at University of Strasbourg. Previous research work on this site found that there is an effect of the buildings near the EAHE, so a numerical model will be updated to consider the underground heat exchange with these buildings. This model will then be verified using experimental data available. In addition, the convective heat transfer coefficient in the pipe is significantly affected by condensation on the internal pipe wall. This condensation plays an important role in determining heat exchange between the air and the surrounding soil, and as the literature poorly addresses the effect of water condensation in EAHEs, experimental setup allowing the visualization and study of this phenomenon will be built complete the numerical analysis. This will allow the identification of different mechanisms inducing the condensation in a geothermal heat exchanger and the effect of this phenomenon on the energy performance of the EAHE. Also, usually the EAHE extracts heat from the ground during winter, but if there was lack or insufficient heat reinjection in the summer, the performance of the exchanger decreases. Thus, the study aims at finding an optimized inter-seasonal operation mode between heating in winter and cooling in summer. Therefore, this research work is carried out to investigate the impact of several parameters on the long-term performance of the EAHE and it contributes to improve this technology.

Work In Progress