Assessing Ventilation and Filtration Performance to Improve Indoor Air Quality in an Older Educational Building

JIANING BAO, Nigel Kaye, Ehsan Mousavi, Christopher Post, Vincent Blouin, Andrew Metcalf, Clemson University

     Abstract Number: 195
     Working Group: Aerosol Science of Infectious Diseases: Lessons and Open Questions on Models, Transmission and Mitigation

Abstract
The COVID-19 pandemic has increased awareness for the need for safer building environments regarding indoor air quality (IAQ), especially for high-occupancy environments including schools and colleges. Compared to newer buildings with modern central ventilation systems, older buildings have potentially less effective ventilation systems with respect to ventilation rate and filtration efficiency, which can increase the vulnerability of building occupants to exposure to poor IAQ. Therefore, it is important to understand how effective ventilation systems are in maintaining proper IAQ in older educational buildings.

In this study, we use low-cost sensors to evaluate IAQ by measuring the concentrations of particulate matter (PM) and carbon dioxide (CO₂) at multiple locations in a classroom that has two fan coil units (FCU) serving as its ventilation system. We conducted experiments with point sources of PM and CO₂ in the indoor space. By analyzing the exponential decay of PM and CO₂ concentrations with time, we evaluated the effectiveness of the ventilation and filtration systems in the classroom. While the PM1.0 decay rate increased by adjusting the fan speed of the FCUs from low to high and by adding HEPA filters and do-it-yourself filter box fans, the trends in CO₂ concentration were unaffected by these mitigation measures. To further understand and explore how to improve IAQ in this classroom, we used the measurements to constrain parameters in a box model of the indoor space. The box model revealed the infiltration rate to the space, which controls the trends in CO₂. By simulating real-world scenarios with the model, one can find the optimal mitigation strategies to simultaneously address both PM and CO₂ pollution in an indoor space.