Transient assessment of an earth air heat exchanger in warm climatic conditions

Abstract

The Earth Air Heat Exchanger (EAHE) is a promising passive technique that utilises shallow geothermal energy to improve the thermal comfort in buildings. EAHE has the potential to minimize the amount of electrical energy used by traditional air conditioning systems. The aim of this research is to examine the thermal performance of the EAHE under continuous operation. A transient numerical model was developed using the implicit finite difference method. Afterwards, the thermal performance was evaluated by using the means of derating factor. In addition, an experimental setup is realised in Biskra University (Algeria) to take measurements during cooling period. According to numerical calculations, the high thermal performance of EAHE is dependant on high thermal conductivity of soil and low air velocity. The values of the derating factor in the studied cases ranged from 0% to 35% that can mislead the design of the EAHE if ignored. The experimental findings revealed that for 3.5 m/s of air velocity, the maximum air temperature drop can reach up 19 °C. It is noticed that the initial 33 m of the pipe can provide 91% of the whole reduction in air temperature. In extreme real cases, the maximum air temperature increasing does not exceed 0.85 °C during all 95 h. Consequently, ambient temperature decreases during night operation and then cools the heated subsoil and assists the soil to recover its cooling capacity.