Influence of rainfall events on the energy performance of an earth-air heat exchanger embedded in a multilayered soil

Energy performance of an earth-air heat exchanger (EAHE) at a shallow depth (<2 m) is sensitive to climatic conditions and thermo-physical characteristics of the surrounding soil around the exchanger pipe. In this paper, the impact of rainfall on the energy performance of an experimental EAHE is studied. This exchanger locates on a geothermal platform equipped with a weather station. Rainfall conditions are defined using the measured rainfall. The vertical profile of moisture content is studied using an experimental full-scale setup. The experimental setup simulates rainfall of varying intensity and duration as a function of time. It is also instrumented by soil moisture sensors at different depths. A test campaign is carried out. This vertical profiles of a soil moisture content obtained with the test campaign are used to model an EAHE. Two climatic seasons, summer and winter, have been considered in the simulations. These two periods concern a rainfall period leading to significant moistening of the surrounding soil. The results of simulations show that during one single rainfall event the variation in surrounding soil moisture can reach 65%. A rainfall event of less than 3 h can increase the EAHE's energy performance by over 4% during the first 24 h and by approximately 2% during a further 24 h. This increase of energy performance is not negligible compared to the 16% increase when soil moisture content is, constantly, at its maximum. Therefore, no significant impact of the rainfall intensity is observed on the moisture variation of the soil at the exchanger's depth. A small difference is observed under different rainfall intensities. However, it can be noted that, during the first hours after rainfall, the greater the rain's cumulated precipitation, the greater the increase in performance.