Ventilation Effectiveness in a Test Room: Experiments and CFD Validation

Abstract. Ventilation effectiveness is often interpreted under the assumption of fully mixed conditions, yet this assumption breaks down for localized emissions that dominate airborne-infection risk. This study presents controlled experimental and numerical evidence demonstrating how both exhaust placement and point source position strongly influence dilution performance in a mixing ventilated room. Full-scale measurements in a 5.2 m × 4.4 m × 2.85 m test space captured air velocities and CO2 tracer dynamics under different inlet-outlet layouts. These data were used to validate computational fluid dynamics (CFD) simulations, which then enabled assessment of additional source configurations. Agreement between CFD and measurements was generally satisfactory, with minor discrepancies attributable to idealized boundary conditions. The results show that changing the exhaust location fundamentally alters airflow organization, leading to pronounced differences in air-change efficiency and local air quality. While one configuration exhibited near-uniform dilution, the alternative layout promoted short-circuiting and strong sensitivity to source position, resulting in spatially nonuniform exposure conditions. These findings demonstrate that mixing ventilation does not inherently ensure homogeneous indoor air quality. The study provides a reproducible reference case for quantifying imperfect mixing under controlled conditions and establishes a foundation for future infection-risk-oriented evaluation and optimization of ventilation layouts.