Multi-year exergy analysis and irreversibility mapping of a hybrid EAHE–PVT ventilation system with optimal design and real-time control in hot–dry climates

In this paper, a combined ventilation system consisting of an earth–air heat exchanger (EAHE) and a photovoltaic/thermal (PVT) solar collector was investigated under the climatic conditions of Kermanshah using energy, exergy, and thermal comfort criteria. The system geometry, along with two hourly control variables—fresh-air ratio and air mass flow rate—was simultaneously optimized. The results showed that the optimization reduced annual energy consumption by more than 65%, while causing only a modest ≈8% increase in the AHU exergy. The optimized γ–m˙ behavior significantly decreased the thermodynamic distance between the inlet air and the comfort state, resulting in a 70–95% improvement in annual thermal-comfort performance. Moreover, the discomfort risk index (CVaR95%) dropped from 2.6 to 2.8 in the baseline to 0.5 in the optimal scenario, representing an 80% reduction in critical discomfort conditions. Additionally, the exergy efficiency index more than doubled, demonstrating a substantial improvement in the thermodynamic quality of the ventilation process. The results suggest that using exergy-based control improves the thermal comfort conditions of the building, while the required increase in the system's exergy consumption is very limited. Therefore, the combination of EAHE and PVT can be a suitable option for designing low-energy ventilation systems for office buildings.