Improving Ventilation Performance in a Multi-Storey Solar Chimney System Using Neutral Plane Analysis: A CFD Case Study

Abstract

Multi-storey solar chimneys are often evaluated using shaft-outlet airflow, which may conceal uneven airflow distribution among floors. A shaft may provide adequate extraction while upper floors receive insufficient air or experience reverse airflow. This study examined the relationship between neutral plane (NP) position and floor-specific airflow to guide adjustments to openings in a nine-storey building with two solar chimneys. Three-dimensional unsteady computational fluid dynamics (CFD) simulations quantified airflow rate and direction on each floor, airflow at the shaft outlet, and NP height. During controlled case screening at a prescribed absorber-plate heat flux of 484.24 W/m2, each shaft’s outlet airflow exceeded the combined requirements of its connected floors, although reverse airflow occurred at 2F and 7F–9F. Reducing selected lower-floor opening areas raised the NP from 11.5 to 12.4 m in the west-shaft zone and from 29.2 to 35.9 m in the east-shaft zone, redistributing airflow upward without changing shaft geometry. Across the six evaluated transition-season months, compliance rates were 100% on 1F–7F, 79.2% on 8F, and 0% on 9F. Airflow remained inward on 8F throughout, whereas reverse airflow persisted on 9F. This study demonstrates that joint assessment of NP position alongside shaft-outlet airflow and floor-specific requirements distinguished insufficient extraction from uneven distribution and informed opening adjustments. Within the evaluated building and design space, however, the tested opening-area strategy did not resolve reverse airflow on 9F and would need to be combined with additional measures targeting the upper-floor pressure and airflow path to achieve building-wide compliance.