Exhaust positioning and stagnation risk in mixing ventilation

This thesis introduces a novel evaluation metric for ventilation effectiveness, stagnation risk, which quantifies the likelihood of contaminant accumulation in poorly ventilated zones. Such stagnation areas lead to locally elevated pollutant concentrations that are insufficiently diluted or removed, posing potential health and comfort risks. The primary objective is to systematically assess the influence of exhaust air positioning on the formation and extent of stagnation zones. For this purpose, a numerical parameter study was conducted, varying supply air strategies and flow conditioning. The simulation results were validated against experimental measurements and literature data to ensure robustness. Building on the simulation data, correlation and sensitivity analyses were performed to identify key influencing parameters. These investigations led to the formulation of generalized recommendations for optimizing ventilation design. In addition to the numerical approach, an analytical model was developed that enables prediction of stagnation risk based primarily on air change efficiency. Which is again mainly dependent on the supply and exhaust opening configuration for a room-encompassing airflow. The results demonstrate that exhaust position significantly affects ventilation performance. The proposed stagnation risk metric allows for a concise yet informative evaluation of system effectiveness and supports the design of ventilation systems that minimize the formation of stagnant regions. This approach provides a practical tool for engineers and researchers seeking to improve indoor air quality through more effective and energy-efficient ventilation strategies.