Urban windcatchers stabilise natural ventilation after energy modernisation

Natural ventilation is a key strategy for reducing energy demand and improving indoor air quality in residential buildings. Yet its effectiveness is often compromised following deep thermal modernisation, particularly in dense urban environments. Conventional ventilation solutions often rely on simplified aerodynamic assumptions and isolated-building analyses, limiting their applicability to real urban contexts. Here, we present a dual-scale experimental and numerical investigation comprising (i) microscale level - a controlled laboratory testing of a multidirectional eight-opening windcatcher to quantify its intrinsic aerodynamic and hydrodynamic performance, and (ii) macroscale level - atmospheric boundary layer wind-tunnel experiments on a representative five-storey residential building to resolve realistic roof-level pressure fields governing device placement. These complementary experimental campaigns, supported by computational fluid dynamics simulations, enable simultaneous characterisation of airflow capture efficiency, flow stability, and urban-induced pressure redistribution, providing a physically validated basis for assessing installation feasibility under realistic urban wind conditions. The results demonstrate relatively stable and predictable ventilation performance across a wide range of wind speeds (0.4-6.0 m s⁻¹) and angles of attack (0°-45°), with supply airflow rates reaching approximately 200 m³ h⁻¹ and limited sensitivity to wind direction. These findings indicate that multidirectional windcatchers can maintain effective wind-driven ventilation after deep residential retrofit and building adaptation interventions, providing a robust passive alternative to mechanical systems and supporting low-energy renovation strategies in compact urban areas for sustainable housing.