A novel wall windcatcher (WWC) natural ventilation system evaluated through CFD and experimental field testing - a solution to single-sided ventilation in multi-story buildings?

As cities grow and building densities increase, maintaining indoor air quality and thermal comfort in multi-story buildings presents a significant challenge. Mechanical ventilation systems, though effective, are energy-intensive, costly to maintain, and contribute to emissions. In contrast, natural ventilation offers a more sustainable alternative but can be constrained by building design limitations, particularly in high-rise or multi-story structures where single-sided ventilation (SSV) may not be able to provide adequate airflow across multiple floors or zones, while adopting other strategies such as cross and wind tower ventilation could be challenging due to the layout of indoor spaces. This study proposes an innovative wall windcatcher (WWC) system to enhance passive ventilation in multi-story buildings. The WWC features an external rectangular ventilation duct mounted on the building façade, incorporating separate channels for supplying fresh air and exhausting stale air, utilizing wind-induced pressure differences. A combined experimental and numerical approach evaluated the WWC's performance through computational fluid dynamics (CFD) simulations and field experiment testing of a scaled model. The CFD model demonstrated good agreement with field measurements, confirming its reliability. Compared to SSV, the WWC improved airflow across all floors and wind angles. At 0° wind direction, airflow increased by 1.2 times on the ground floor, 2.2 times on the first floor, and 1.6 times on the second floor. Even at 90° and 180°, where SSV struggled, the WWC maintained improved ventilation. However, the study also identified airflow reversal in the ground-floor exhaust outlet, leading to inefficient ventilation. To resolve this, the dimensions of the exhaust duct branches were optimized by adjusting the cross-sectional areas creating transition zones, successfully redirecting airflow and preventing recirculation. Despite these enhancements, airflow remained non-uniform at certain wind angles, indicating the need for further refinements. The WWC system offers a practical and scalable solution for multi-story building ventilation, particularly in retrofit applications where internal modifications are limited. Due to its modular design, the WWC system can be installed with minimal disruption, making it well-suited for integration into both new buildings and retrofit projects.