Long-Term Size Dependent Filtration Efficiency Test (ASHRAE 52.2) of 5" MERV 16 Air Filters Used in DIY Air Cleaners Operated in K-12 Schools

DEVABHAKTUNI SRIKRISHNA, Christopher Barnes, PatientKnowhow.com

     Abstract Number: 576
     Working Group: Reducing Aerosol Exposure with Control Technologies and Interventions

Abstract
Do-it-yourself (DIY) air cleaners can be a temporary, low-cost, ventilation strategy to help meet Centers for Disease Control and Prevention (CDC) and California Department of Public Health (CDPH) recommendations of ≥5 air changes per hour (ACH) in buildings, which can help reduce airborne contaminants to improve indoor air quality. However, the long-term performance of DIY air cleaners remains unclear. Furthermore, there is no guidance on when to replace filters used in DIY air cleaners. In this study, we report the long-term filtration performance of two DIY air cleaners constructed with a 20” box fan and a 5" MERV 16 filter deployed in an elementary school in California from February 2022 to Dec 2023. An additional three DIY air cleaners constructed in the same manner were deployed in a middle school in the same locale from August 2023 to Dec 2023. The DIY air cleaners were operated daily during school hours as reported by the teachers. It is also important to note that a wildfire smoke event was recorded for one week while the DIY air cleaners were deployed. At the end of the study, the size-dependent filtration efficiencies, for particles between 0.3 to 10 µm in diameter, were evaluated per an initial ASHRAE 52.2 test for each filter. The filtration efficiencies of the filters deployed in the elementary school degraded to <50% for particles in the 0.3 – 0.4 μm size range, which includes the most penetrating particle size (0.3 μm), over the 16-month period. Filtration efficiencies were retained (>85%), in the same size range, for filters deployed in the middle school over the four-month period. Overall, this study found the size-dependent filtration efficiency varied for the MERV 16 filters used to build the DIY air cleaners deployed in the schools. The three filters deployed in the middle school retained filtration efficiencies equivalent to MERV 15 or higher, while the two filters deployed in the elementary school degraded to MERV 12 or lower. We suspect the filtration performance varied due to changing ambient particulate concentrations (i.e., wildfire smoke event), and the operating time. More research could help inform filter replacement intervals to maintain 5 ACH in the participating classrooms in this study.

Disclaimer: The findings and conclusions in this report are those of the author(s) and do not necessarily represent the official position of the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention. Mention of any company or product does not constitute endorsement by the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention.