Can 10× cheaper, lower-efficiency particulate air filters and box fans complement High-Efficiency Particulate Air (HEPA) purifiers to help control the COVID-19 pandemic?

• Published in: The Science of the total environment Vol. 838; no. Pt 1; p. 155884
• Main Author: Srikrishna, Devabhaktuni
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 10.09.2022; The Author. Published by Elsevier B.V
• Subjects: ACH; Aerosol; Aerosols; Air Filters; Air filtration; Air Pollution, Indoor - analysis; Air Pollution, Indoor - prevention & control; Airborne bacteria; Airborne virus; Box fan-filter; COVID-19 - prevention & control; DIY air cleaner; Dust; HEPA purifier; Humans; Pandemic; Pandemics - prevention & control; SARS-CoV-2; SARS-CoV-2; DIY air cleaner; ACH; Airborne virus; Aerosol; Airborne bacteria; Pandemic; Box fan-filter; HEPA purifier; Air filtration
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.155884

Public health departments such as CDC and California Department of Public Health (CA-DPH) advise HEPA-purifiers to limit transmission of SARS-CoV-2 indoor spaces. CA-DPH recommends air exchanges per hour (ACH) of 4–6 air for rooms with marginal ventilation and 6–12 in classrooms often necessitating multiple HEPA-purifiers per room, unaffordable in under-resourced community settings. Pressure to seek cheap, rapid air filtration resulted in proliferation of lower-cost, Do-It-Yourself (DIY) air purifiers whose performance is not well characterized compared to HEPA-purifiers. Primary metrics are clean air delivery rate (CADR), noise generated (dBA), and affordability ($$). CADR measurement often requires hard-to-replicate laboratory experiments with generated aerosols. We use simplified, low-cost measurement tools of ambient aerosols enabling scalable evaluation of aerosol filtration efficiencies (0.3 to 10 μm), estimated CADR, and noise generation to compare 3 HEPA-purifiers and 9 DIY purifier designs. DIY purifiers consist of one or two box fans coupled to single MERV 13–16 filters (1″–5″ thick) or quad filters in a cube. Accounting for reduced filtration efficiency of MERV 13–16 filters (versus HEPA) at the most penetrating particle size of 0.3 μm, estimated CADR of DIY purifiers using 2″ (67%), 4″ (66%), and 5″ (85%) filters at lowest fan speed was 293 cfm ($35), 322 cfm ($58), and 405 cfm ($120) comparable to best-in-class, low-noise generating HEPA-purifier running at maximum speed with at 282 cfm ($549). Quad filter designs, popularly known Corsi-Rosenthal boxes, achieved gains in estimated CADR below 80% over single filter designs, less than the 100% gain by adding a second DIY purifier. Replacing one of the four filters with a second fan resulted in gains of 125%–150% in estimated CADR. Tested DIY alternatives using lower-efficiency, single filters compare favorably to tested HEPA-purifiers in estimated CADR, noise generated at five to ten times lower cost, enabling cheap, rapid aerosol removal indoors. [Display omitted] •Performance of DIY air purifiers is not well characterized versus HEPA-purifiers.•Tested DIY configurations consisted of 1 to 2 box fans and 1 to 4 filters.•9 DIY compared favorably to 3 HEPA in est. CADR, noise, at 5×–10× lower cost.•4-Filter designs (e.g. Corsi-Rosenthal boxes) had est. CADR up to 70% over 1-filter.•4-Filter gains were below 100% gains of adding a second 1-filter DIY purifier.