Thermo-aerodynamic response of a multilayer ventilated façade under high solar radiation: A full-scale, full-height experimental analysis of a 0.6-m-wide instrumented test channel on a nine-storey residential building

Codes and analytical/CFD models characterise the ventilated air cavity of double-skin façades through a single, height-averaged velocity and temperature. An assumption that was not previously tested at full building scale under real solar exposure, and a gap that became consequential for tall façades in hot climates, where solar loading and buoyancy-driven flow can vary with height. To address this gap, a full-height, 0.6-m-wide instrumented test channel replicating a multilayer ventilated façade was installed on a nine-storey residential building in southern Kazakhstan and monitored over three consecutive days under three inlet/outlet configurations, using temperature sensors, anemometers, thermal camera and pyranometer distributed along the full cavity height. The evidence-based finding was that, contrary to the assumption embedded in design equations, both air velocity and temperature non-uniformly vary with height: velocity follows a U-shaped profile, while cavity and surface temperatures increase monotonically with height. Moreover, airflow drops to near-zero after sunset, contradicting the steady-state convection assumption of current models. An order-of-magnitude analysis indicates that wind-induced pressure is comparable in magnitude to the buoyancy-driven stack pressure. Thus, the observed airflow cannot be attributed to the solar-driven convection alone. These findings should be read as follows: a single east-facing building, a non-replicated three-day sequence, and point-sensor measurements without cross-sectional velocity mapping or heat-flux instrumentation, all of which limit the statistical and metrological certainty of the reported magnitudes. This study provided a full-scale, height-resolved dataset and a set of quantified relationships that can inform future CFD and code-development efforts for tall ventilated façades in hot climates.