Reduction of the HVAC system size in school buildings through Earth-to-Air Heat Exchangers (EAHE)

Aligned with the sustainability objectives promoted by the European Union, increasing attention is being directed toward improving the environmental performance of non-residential buildings, particularly schools, where indoor air quality and thermal comfort must be ensured while limiting energy consumption. This study investigates the integration of an Earth-to-Air Heat Exchanger (EAHE) into the Heating, Ventilation and Air-Conditioning (HVAC) system for an existing school building located in Southern Italy, with a comparative assessment under Mediterranean (Naples, Italy) and Continental (Budapest, Hungary) climate conditions. The building is equipped with fan-coil units and an Air Handling Unit (AHU). In the proposed configuration, the EAHE is positioned upstream of the AHU to pre-condition outdoor air by exploiting the relative thermal stability of the ground, thereby reducing the thermal capacity of the AHU coils. A parametric analysis was performed by varying pipe length and diameter to identify the optimal geometric configuration. The combination of a 0.2 m diameter and a 100 m pipe length proved to be optimal, achieving the highest thermal effectiveness ( ε ≈ 88%) and the largest temperature difference between EAHE inlet and outlet air. With this configuration, the design heating coil capacity was reduced by up to 64% in Budapest and 72.9% in Naples during winter conditions. In summer conditions, the design cooling coil capacity decreased by 76.8% and 46.4%, respectively. The results demonstrate that the optimized EAHE configuration significantly reduces the thermal capacity of the AHU coils while enhancing the thermal stability of supply air, particularly in climates with pronounced seasonal variations.