Developing an envelope-based direct capture efficiency (EDCE) for evaluating local exhaust ventilation performance

Effective pollutant control in residential kitchens remains a major challenge due to the localized and transient nature of cooking emissions. Conventional indicators such as capture efficiency and removal efficiency fail to distinguish direct pollutant capture from recirculation, leading to overestimated performance evaluations. To address this limitation, this study proposes a novel evaluation framework, Envelope-Based Direct Capture Efficiency (EDCE), which integrates suction envelope visualization with a Virtual Purification Method. By coupling computational fluid dynamics (CFD) with a streamline-based reconstruction algorithm, the EDCE approach enables both qualitative identification of the effective suction boundary and quantitative isolation of true pollutant entrainment. Case studies examine the effects of outlet-to-wall distance and baffle installation distance under typical exhaust flow rates and pot positions. Results indicate that, unlike conventional metrics that exhibit early saturation, EDCE shows a distinct reduction from approximately 0.86 to 0.62 (about 30%), revealing a higher sensitivity to structural variations and providing physically interpretable insights into pollutant entrainment mechanisms. Outlet-to-wall distance is identified as the dominant factor, while baffles enhance lateral pollutant control when placed at optimal spacing. This methodological innovation establishes a robust, geometry-driven basis for evaluating range hood performance and offers practical guidance for the design and optimization of local ventilation systems.