Optimizing built-in chimney ventilation: Synergetic effects of underground pipe gallery pre-cooling and PV/T post-heating

Buoyancy-driven natural ventilation is energy-efficient and stable, making it suitable for areas with limited wind or high urban density. However, its effectiveness relies on buoyancy forces driven by temperature or height differences between the air inlet and outlet. When buoyancy is weakened, ventilation efficiency decreases, and reverse airflow may occur. To address this, this study proposes an optimization strategy to enhance buoyancy-driven ventilation. Outdoor air is cooled through an underground pipe gallery to expand the effective temperature range for natural ventilation. The inner wall of a built-in chimney is heated using a rooftop photovoltaic/thermal (PV/T) system to raise exhaust temperature and enhance buoyancy forces. The results showed that supply air could be pre-cooled by up to 13.1 °C. Post-heating at 40 °C and 45 °C, the exhaust temperatures increased by 2.1 °C and 3.0 °C, respectively, and reduced reverse airflow duration by 35.9 % and 75.6 %. When the rooftop PV/T system was used as the heat source, it provided an average heat temperature of 44.3 °C, resulting in a 102.5 % increase in airflow and a 16.6 % extension in effective ventilation time. These findings demonstrate a feasible approach for integrating renewable energy into passive ventilation systems, particularly in low-wind or high-density environments.