Energy and exergy analysis of an energy system based on an earth-air heat exchanger

Institut de Recherche, ESTP, 94230 Cachan, France

^* Corresponding author: alapertot@estp.fr

Abstract

In the battle against global warming, the European Union has placed significant emphasis on reducing energy consumption within buildings. Recent regulations require well-insulated structures equipped with renewable energy-based systems to support these initiatives. One promising method to support efficiency involves integrating an Earth-Air Heat Exchanger (EAHE). This system harnesses geothermal energy to preheat buildings during winter and offer cooling during summer via ventilation. It involves an underground pipe that draws in external air to capture geothermal energy of the ground in order to transfer it into the building. This study introduces an innovative methodology by applying energy and exergy balances to a dynamic EAHE model. Findings reveal that, under certain conditions, the air introduced into the building can reach saturation levels, highlighting deficiencies in the system’s air quality. Furthermore, the system is efficient, since coefficient of performance values of 5.7, that indicating energy recovered surpassing the electrical consumption of the fan. Nevertheless, significant exergy destruction occurs within the system, resulting in irreversible losses at the fan level and heat transfers within the exchanger. Additionally, the system harnesses only 5.6 % of its potential for energy recovery over the year. A sensitivity analysis was carried out to see the influence of the parameters on the energy and exergy criteria. Tube length and radius have the greatest influence on system performance, because reducing these parameters leads to a reduction in flow rate and therefore in the fan’s power consumption. Finally, the economic analysis showed a CER of 0.169 €/kWh, making the system profitable.