Physics:Corsi-Rosenthal Box

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Short description: Air purifier design
The Corsi-Rosenthal Box air filtration unit is an inexpensive air purifier constructed from a box fan, furnace filters and duct tape
An example of a homemade Corsi-Rosenthal Box air filtration unit

The Corsi-Rosenthal Box, also called a Corsi-Rosenthal Cube, is a design for a do-it-yourself air purifier that can be built inexpensively. It was designed during the COVID-19 pandemic with the goal of reducing the levels of airborne viral particles in indoor settings.

Background and history

Since COVID-19 was declared a pandemic by the World Health Organization on 11 March 2020,[1] evidence, including increasing amounts of peer-reviewed research, has been accumulating that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus causing COVID-19, is airborne.[2][3][4] Superspreading events are generally associated with indoor gatherings.[5][6] In response to the emerging evidence and recommendations of infectious disease researchers,[7][8] engineers have turned their attention to considering how improved ventilation may reduce indoor viral loads.[9]

Air purification units with HEPA filtration can be expensive, often costing considerably more than US$500.[10] In August 2020, the incoming Dean of Engineering at the University of California, Davis, Richard Corsi,[11] challenged STEM Twitter to devise a citizen science solution. HVAC specialist, Jim Rosenthal, responded with a design that came to be known as a Corsi-Rosenthal Box.[12]

Design

The Corsi-Rosenthal Box is made of four furnace filters, preferably of MERV13 or higher, which form the sides of a cube. A 20-inch box fan is placed on top and duct taped to the filters, sealing the system so that air is drawn through the filters, up and out of the box.[12][10] Some implementations also use shrouds made of cardboard or similar material to cover the corners of the box fan to improve efficiency and reduce backflow.[13]

The filtration units can be assembled in around fifteen minutes, last for months, and materials cost between US$50 and $150.[12][10][9]

Efficacy

Airborne virus particulates range in size from 1 to 50 microns (μm). Rosenthal used his HVAC company's testing equipment to run an informal test of the design, in which he found that around 60% of 1μm particles were removed by the system, and almost 90% of 10μm particles were removed.[9] Clean air delivery rates (CADR) of a US$75 design were estimated at between 165 and 239 (depending on fan speed) in an August 2021 case study by UC Davis researchers.[13] Corsi told WGBH in October 2021 that "People are now reporting 600 cubic feet per minute in clean air delivery rates. That’s phenomenal. That’s actually better than a lot of the more expensive HEPA-based portable air cleaners".[10]

A study of a home-built air purifier to remove wildfire smoke, using a box fan and filter mounted in a window, showed that particulate matter between 1 and 10μm in size was reduced by about 75%. Wired wrote that this study may be suggestive of the efficacy of Corsi-Rosenthal Boxes, which use similar filters, and which aim to filter virus particles similar in size to the particles studied.[9][14]

References

  1. ↑ Cucinotta, Domenico; Vanelli, Maurizio (19 March 2020). "WHO Declares COVID-19 a Pandemic". Acta Bio Medica Atenei Parmensis 91 (1): 157–160. doi:10.23750/abm.v91i1.9397. PMID 32191675. PMC 7569573. https://doi.org/10.23750/abm.v91i1.9397. 
  2. ↑ Morawska, Lidia; Cao, Junji (June 2020). "Airborne transmission of SARS-CoV-2: The world should face the reality" (in en). Environment International 139: 105730. doi:10.1016/j.envint.2020.105730. PMID 32294574. PMC 7151430. https://linkinghub.elsevier.com/retrieve/pii/S016041202031254X. 
  3. ↑ Morawska, Lidia; Milton, Donald K (6 July 2020). "It Is Time to Address Airborne Transmission of Coronavirus Disease 2019 (COVID-19)". Clinical Infectious Diseases. doi:10.1093/cid/ciaa939. ISSN 1058-4838. PMID 32628269. PMC 7454469. https://doi.org/10.1093/cid/ciaa939. 
  4. ↑ Zhang, Renyi; Li, Yixin; Zhang, Annie L.; Wang, Yuan; Molina, Mario J. (30 June 2020). "Identifying airborne transmission as the dominant route for the spread of COVID-19" (in en). Proceedings of the National Academy of Sciences 117 (26): 14857–14863. doi:10.1073/pnas.2009637117. ISSN 0027-8424. PMID 32527856. PMC 7334447. https://www.pnas.org/content/117/26/14857. 
  5. ↑ Wainer, Gabriel. "How to prevent COVID-19 ‘superspreader’ events indoors this winter" (in en). http://theconversation.com/how-to-prevent-covid-19-superspreader-events-indoors-this-winter-147439. 
  6. ↑ Lewis, Dyani (23 February 2021). "Superspreading drives the COVID pandemic — and could help to tame it" (in en). Nature 590 (7847): 544–546. doi:10.1038/d41586-021-00460-x. https://www.nature.com/articles/d41586-021-00460-x. 
  7. ↑ Noorimotlagh, Zahra; Jaafarzadeh, Neemat; Martínez, Susana Silva; Mirzaee, Seyyed Abbas (February 2021). "A systematic review of possible airborne transmission of the COVID-19 virus (SARS-CoV-2) in the indoor air environment" (in en). Environmental Research 193: 110612. doi:10.1016/j.envres.2020.110612. PMID 33309820. PMC 7726526. https://linkinghub.elsevier.com/retrieve/pii/S0013935120315097. 
  8. ↑ Greenhalgh, Trisha; Jimenez, Jose L; Prather, Kimberly A; Tufekci, Zeynep; Fisman, David; Schooley, Robert (May 2021). "Ten scientific reasons in support of airborne transmission of SARS-CoV-2". The Lancet 397 (10285): 1603–1605. doi:10.1016/s0140-6736(21)00869-2. ISSN 0140-6736. PMID 33865497. PMC 8049599. https://doi.org/10.1016/S0140-6736(21)00869-2. 
  9. ↑ 9.0 9.1 9.2 9.3 Rogers, Adam (6 August 2020). "Could a Janky, Jury-Rigged Air Purifier Help Fight Covid-19?" (in en-US). Wired. ISSN 1059-1028. https://www.wired.com/story/could-a-janky-jury-rigged-air-purifier-help-fight-covid-19/. 
  10. ↑ 10.0 10.1 10.2 10.3 Emanuel, Gabrielle (17 August 2021). "DIY: How To Build A Cheap, Effective Classroom Air Filter" (in en). https://www.wgbh.org/news/local-news/2021/08/17/diy-air-filters-for-classrooms-experts-are-enthusiastic-and-a-citizen-scientist-makes-it-easy. 
  11. ↑ Bartl, Aditi Risbud (2 July 2021). "Richard Corsi Appointed College of Engineering Dean" (in en). https://engineering.ucdavis.edu/news/richard-corsi-appointed-college-engineering-dean. 
  12. ↑ 12.0 12.1 12.2 Lapook, Jon (7 October 2021). "New air purifiers filter at least 90% of COVID-carrying particles, researchers say" (in en-US). https://www.cbsnews.com/news/covid-air-purifiers-particles/. 
  13. ↑ 13.0 13.1 Pistochini, Theresa; McMurry, Robert (August 2021). Testing Different Configurations of Do-it-yourself Portable Air Cleaners (Report). https://energy.ucdavis.edu/wp-content/uploads/Case-Study_DIY-Portable-Air-Cleaners-083121.pdf. Retrieved 9 October 2021. 
  14. ↑ Tham, K.W.; Parshetti, G.K.; Balasubramanian, R.; Sekhar, C.; Cheong, D.K.W. (2018). "Mitigating particulate matter exposure in naturally ventilated buildings during haze episodes" (in en). Building and Environment 128: 96–106. doi:10.1016/j.buildenv.2017.11.036. https://linkinghub.elsevier.com/retrieve/pii/S0360132317305498. 




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