A numerical framework to evaluate the impact of HEPA filtration on classroom air quality

This paper presents a CFD-based framework to assess classroom air quality with portable HEPA filtration, explicitly resolving the interaction between filter-induced airflow and realistic human exhalation of CO 2 and aerosols. Unlike existing approaches, the framework captures spatially resolved contaminant transport and removal under occupied conditions and is complemented by a statistical method to quantify contaminant dispersion dynamics and local airflow mixing intensity. The model is validated against in situ measurements of CO 2 and aerosol concentrations (0.7–1 μ m ) in a classroom under matched scenarios with one and three HEPA units, alongside a stale-air baseline, showing good agreement. Results demonstrate that HEPA filtration significantly alters airflow by enhancing mixing and suppressing occupant thermal plumes, leading to a more spatially uniform CO 2 distribution despite largely unchanged mean concentrations. In situ measurements indicate aerosol reductions of approximately 21% for a single HEPA unit and up to 90% for a three-HEPA configuration. While, the CFD results and statistical analysis reveal that, although increasing the number of units improves aerosol removal through higher CADR, the removal performance remains strongly dependent on filter placement relative to the emission source. This is evident as single-HEPA configurations are highly sensitive to placement and may promote contaminant dispersion through discharge airflow, whereas multi-unit configurations provide more robust control when the filter intake is aligned with the emission source. These findings highlight the critical role of filter number and placement and demonstrate the limitations of CO 2 as a proxy for aerosol exposure in HEPA-filtered classrooms.