A novel wall windcatcher (WWC) natural ventilation system evaluated through CFD, wind tunnel, and field testing: a solution to single-sided ventilation in multi-storey buildings

The ongoing trend of rapid urbanisation and the resultant densification of urban environments have led to an increased reliance on multi-storey buildings, where achieving effective natural ventilation remains a significant challenge. As cities grow and building densities increase, maintaining indoor air quality in such structures becomes increasingly complex. While mechanical ventilation systems offer reliable performance, they are energy-intensive, costly to maintain, and contribute to greenhouse gas emissions, raising concerns about long-term sustainability and the risk of indoor air quality issues such as Sick Building Syndrome. Conventional passive strategies, such as single-sided ventilation (SSV), often fall short in delivering sufficient airflow, particularly in buildings with multiple floors or complex internal zoning. Their dependence on single-facade openings frequently results in stagnant zones and limited cross-floor ventilation, especially under oblique or perpendicular wind conditions. Addressing these limitations, this study introduces a novel Wall Windcatcher (WWC) system—a façade-mounted, modular ventilation solution incorporating separate ducts for fresh air intake and stale air exhaust. The WWC design utilises wind-induced pressure differentials to drive consistent bidirectional airflow, regardless of wind orientation. Despite the WWC’s promising performance, some operational challenges emerged during testing. Notably, airflow reversal was observed at the ground-floor exhaust outlet, leading to inefficient ventilation and localised recirculation. To mitigate this, the exhaust duct design was refined by adjusting the cross-sectional areas of individual branches, introducing aerodynamic transition zones that redirected the airflow and reduced the occurrence of backflow. Although some non-uniform airflow distribution persisted at certain oblique wind angles, overall system efficiency improved markedly following these design optimisations. Due to its externally mounted and modular structure, the WWC offers a flexible, low-impact solution particularly well-suited to retrofit applications where internal reconfiguration is impractical. Its minimal disruption during installation and adaptability across varying building types make it a viable strategy for enhancing natural ventilation in both new and existing multi-storey buildings. To comprehensively evaluate the WWC’s performance, a hybrid methodology was employed, combining atmospheric boundary layer wind tunnel experiments, computational fluid dynamics (CFD) simulations, and field testing of scaled physical models. Results demonstrated that the WWC significantly outperformed SSV across all evaluated wind directions and speeds. At a 0° wind angle and reference wind speed (Uref = 3.82 m/s), the system achieved up to a 430% increase in average indoor airflow velocity, with sustained improvements observed even at higher wind speeds (Uref = 7.59 m/s). In wind conditions where SSV typically fails—such as at 90° and 180°—the WWC maintained reliable ventilation, preventing stagnation and ensuring effective air movement. Floor-by-floor analysis indicated enhanced performance across all levels, with airflow increases of 1.2 times on the ground floor, 2.2 times on the first floor, and 1.6 times on the second floor. Among the various turbulence models tested, the k-epsilon RNG model yielded the most accurate pressure coefficient predictions, especially under perpendicular wind flow scenarios. Overall, the findings of this study demonstrate the Wall Windcatcher (WWC) system’s potential to address long-standing limitations in passive ventilation for multi-storey buildings. By combining aerodynamic innovation with practical adaptability, the WWC offers a viable alternative to energy-intensive mechanical systems and a significant improvement over conventional single-sided ventilation. Its ability to enhance airflow distribution across multiple floors under diverse wind conditions, along with its suitability for both new construction and retrofit applications, underscores its relevance in the context of sustainable urban development.