2-Year Durability Comparison of HEPA vs MERV 16 vs MERV 13 Air Filters in DIY Air Cleaners Used Daily in Elementary and Middle Schools

DEVABHAKTUNI SRIKRISHNA, Patient Knowhow, Inc.

     Abstract Number: 505
     Working Group: Indoor Air Purification Technologies, Best Practices, and their Health Impacts

Abstract
EPA recommends DIY air cleaners for temporary use during wildfires, and a recent EPA study presented at AAAR reported their inconsistent usage in homes due to excessive noise. Questions also remain about wear and tear including how long filters retain their filtration properties and need to be replaced. Herein we report real-world experience from daily usage of 47 HEPA and 60 DIY air cleaners in a California elementary school during the academic school year from spring 2021 through Winter of 2023 across 16 classrooms, a library, an auditorium, a lunchroom, and in a hallway. Three to six purifiers were needed in classrooms to meet California (CDPH) recommended 6 to 12 air changes per hour (ACH) for prevention of aerosol transmission of COVID-19 in classrooms. Teachers reported noise generated by DIY purifiers on lowest fan speed as acceptable for classroom use. Filtration efficiency at 0.3 μm (most penetrating particle size) for DIY air cleaners with an initial batch of 5” MERV 16 filters used in the classrooms averages 77% after six months, 74% after 1 year, 63% after two years. This compared to 90% for HEPA after 2.5 years, and 86% for a more recent batch of MERV 16 after 1.5 years of use. Portable air cleaners (HEPA and DIY) averaged and estimated 10 ACH (6-15 ACH) across the 16 classrooms demonstrating feasibility and unit economics of meeting CDPH targets per classroom for $200-$650 with DIY versus $600-$12,000 with the HEPA models used. In one 9000 cubic foot classroom with 7 air purifiers, air exchange rate was measured using ambient aerosols at 18 ACH from air purifiers (within 20% of ACH estimated based on CADR of purifiers) and 7 ACH from HVAC for a combined total of 25 ACH. In a nearby middle school (grades 6-8), over twenty 5" MERV 16 and twenty 5" MERV 13 (half price of MERV 16) were installed DIY air cleaners during summer of 2023 and used daily in the classrooms. Filtration efficiency at 0.3 μm (most penetrating particle size) for these DIY air cleaners with MERV 16 and MERV 13 filters were initially 96% and 91%, and dropped to 90% and 78% respectively after approximately 6 months of daily usage. The procedure using ambient aerosols to verify ACH from portable air cleaners and HVAC can be the basis for ACH certification or verification without generating aerosol contaminants (e.g. salt water, smoke, tracers) which may be unsafe or disallowed in schools.