Air purification — Luchtreiniging — Purificaton d’air — HEPA
In this document you will find an overview of studies on the effectiveness of air cleaning to remove SARS-COV-2 from the air in different settings (schools, gym, hospitals, …) and thus greatly reduce the chance of infection.
A consumer model that purifies 600 m3/hour will cost approximately €500 to €600. For a unit that cleans 300m3/hour you will pay approximately €300. These are recommended prices on which (quantity) discounts can certainly be obtained.
Installation is no more difficult than installing a coffee machine. Maintenance costs are negligible. It is limited to cleaning the pre-filter approximately every month. This requires 2 minutes of work.
Depending on the model, the filters need to be replaced every 1 to 2 years and will cost between €50 and €100 for a consumer model.
The energy consumption is also negligible. For a model that cleans 600m3/h, you should count on 60Wh. Negligable compared to the heating costs caused by continuously having to fully open the windows.
One should also be attentive to the noise production, especially for consumer models. At the highest setting, most appliances produce too many decibels to operate at the most powerful setting all day. A lower setting is therefore recommended. And of course this has an impact on the number of devices needed. If, for example, you need a CADR of 800m3/h in a room, you will need 3 units with a CADR of 600m3/h working at e.g. half speed (3x300=900). Professional devices (with a cost of €3000-€5000) have a quieter operation.
The combination ventilation and air cleaning should change the air 6 times per hour (6 Air Changes per Hour, ACH) according to e.g. The Harvard T. Chan School of Public Health and the Deutsche Aerosolgesellschaft. Another approach is to change/clean at least 50 (preferably 80) m3/hour per person, see Supreme Health Council (HGR NR 9616, February 2021).
It is recommended to do both calculations and to apply the most stringent result. Consider oversizing the unit so that it does not have to operate at its highest setting to avoid noise pollution.
“The addition of two HEPA air cleaners that met the Environmental Protection Agency (EPA)–recommended clean air delivery rate (CADR) reduced overall exposure to simulated exhaled aerosol particles by up to 65% without universal masking. Without the HEPA air cleaners, universal masking reduced the combined mean aerosol concentration by 72%. The combination of the two HEPA air cleaners and universal masking reduced overall exposure by up to 90%”
2. California Department of Public Health
3. Univ. Stuttgart
4. Testing mobile air purifiers in a school classroom: Reducing the airborne transmission risk for SARS-CoV-2
“the aerosol concentration was reduced by more than 90% within less than 30 min when running the purifiers (air exchange rate 5.5 h−1). The reduction was homogeneous throughout the room and for all particle sizes.”
5. The removal of airborne SARS-CoV-2 and other microbial bioaerosols by air filtration on COVID-19 surge units
6. Real-world data show that filters clean COVID-causing virus from air
“Research at a hospital swamped by people with COVID-19 has confirmed that portable air filters effectively remove SARS-CoV-2 particles from the air — the first such evidence in a real-world setting1. The results suggest that air filters could be used to reduce the risk of patients and medical staff contracting SARS-CoV-2 in hospitals” https://www.nature.com/articles/d41586-021-02669-2
7. Use of portable air cleaners to reduce aerosol transmission on a hospital coronavirus disease 2019 (COVID-19) ward
“Aerosols rapidly travelled from the patient room into other parts of the ward. Air cleaners were effective in increasing the clearance of aerosols from the air in clinical spaces and reducing their spread to other areas. With 2 small domestic air cleaners in a single patient room of a hospital ward, 99% of aerosols could be cleared within 5.5 minutes.”
Use of portable air cleaners to reduce aerosol transmission on a hospital coronavirus disease 2019…
Air cleaners may be useful in clinical spaces to help reduce the risk of acquisition of respiratory viruses that are…
8. Ventilation and air cleaning to limit aerosol particle concentrations in a gym during the COVID-19 pandemic
Ventilation and air cleaning to limit aerosol particle concentrations in a gym during the COVID-19…
Aerosol particle concentration measurements in a gym with 35 exercising persons. * Assessment of deposition…
“The gym test showed that ventilation with air-change rate ACH = 2.2 h−1, i.e. 4.5 times the minimum of the Dutch Building Code, was insufficient to stop the significant aerosol concentration rise over 30 min. Air cleaning alone with ACH = 1.39 h−1 had a similar effect as ventilation alone. Simplified mathematical models were engaged to provide further insight into ventilation, air cleaning and deposition. It was shown that combining the above-mentioned ventilation and air cleaning can reduce aerosol particle concentrations with 80 to 90% , depending on aerosol size. This combination of existing ventilation supplemented with air cleaning is energy efficient and can also be applied for other indoor environments.”
9. VITO (Vlaamse Instelling voor Technologisch Onderzoek) — Flemish Institute for Technological Research
10. Harvard T. Chan School of Public Health
Keeping Schools Open Needs to be Prioritized
Keeping schools closed comes with massive, long-term individual and societal costs. Many children cannot effectively…
11. THE LANCET COVID-19 COMMISSION
12. SARS-CoV-2 aerosol transmission in schools: the effectiveness of different interventions
“One HEPA filter was as effective as two windows partly open all day during the winter (2.5-fold decrease) while two filters were more effective (4-fold decrease). Combined interventions (i.e., natural ventilation, masks, and HEPA filtration) were the most effective (≥ 30-fold decrease). Combined interventions remained highly effective in the presence of a super-spreader. Natural ventilation, face masks, and HEPA filtration are effective interventions to reduce SARS-CoV-2 aerosol transmission. These measures should be combined and complemented by additional interventions (e.g., physical distancing, hygiene, testing, contact tracing, and vaccination) to maximize benefit.” SARS-CoV-2 aerosol transmission in schools: the effectiveness of different interventions (medrxiv.org)
13. Air filters on Addenbrooke’s wards removed nearly all traces of airborne Covid-19 virus, Cambridge University Hospitals study shows
14. Are the Portable Air Cleaners (PAC) really effective to terminate airborne SARS-CoV-2?
“All the air samples collected before using PAC and 75% of swab samples were positive for SARS-CoV-2. After the PAC usage, all samples except one were negative, displaying a 80% device effectiveness. Portable HEPA cleaners usage allowed the removal of SARS CoV-2 and, therefore, they could be recommended for places with inadequate ventilation”
15. Aanbevelingen voor de praktische implementatie en bewaking van ventilatie en binnenluchtkwaliteit in het kader van COVID-19 Taskforce Ventilatie Version 2.O — 12 juli 2O21
“Het toepassen van luchtzuivering leidt tot een verlaging van de aerosol- of fijnstofconcentraties” https://werk.belgie.be/sites/default/files/content/documents/Coronavirus/Implementatieplan_ventilatie.pdf
16. Performance analysis of portable HEPA filters and temporary plastic anterooms on the spread of surrogate coronavirus
“Results suggested that the temporary anteroom alone could prevent the migration of nearly 98% of the surrogate aerosols into the adjacent corridor.”
“the best location of a single portable air purifier unit is inside the isolation room and near the patient’s bed”.
Performance analysis of portable HEPA filters and temporary plastic anterooms on the spread of…
The outbreak of COVID-19, and its current resurgence in the United States has resulted in a shortage of isolation rooms…
17. Hidden hazards of SARS-CoV-2 transmission in hospitals: A systematic review
“In addition, when HEPA filters were utilized, regardless of the type of ventilation, number of ACH or hospital area, minimal surface-borne & no airborne SARS-CoV-2 RNA was detected.”
“When HEPA filters were present, infrequent SARS-CoV-2 contamination was observed on surfaces (2/90 = 2.22%; p < 0.001; Appendix Table 1) and none found in the air (0/148=0.00%)”
“when HEPA filters were utilized, regardless off the type of ventilation, number of ACH or hospital area, minimal surface-borne and no airborne SARS-CoV-2 RNA was detected”
“Very low detection rates were observed in the presence of laminar flow ventilation in combination with and without negative pressure or HEPA filters. An alternative to such sophisticated ventilation systems with similar effects on airborne SARS-CoV-2 contamination proved to be mechanical ventilation with either HEPA filters, air purifiers, or strict fresh-air supply, which could be more readily utilized throughout the hospital. “ https://onlinelibrary.wiley.com/doi/10.1111/ina.12968
18. Efficacy of Ventilation, HEPA Air Cleaners, Universal Masking, and Physical Distancing for Reducing Exposure to Simulated Exhaled Aerosols in a Meeting Room
“The use of multiple HEPA air cleaners spread out around the room provides a faster and better mixing and cleaning of the room air, thereby reducing the overall concentrations for participants in the room and reducing the probability of SARS-CoV-2 transmission.” https://www.mdpi.com/1999-4915/13/12/2536/htm
19. Transmission and reduction of aerosols in classrooms using air purifier systems
“different scenarios with infected persons in the room have been analyzed, showing that the air purifier system leads to a significant reduction of airborne particles in the room dependent on the location of the infected person. The system can support additional ventilation strategies with fresh air, especially in cold seasons.” https://aip.scitation.org/doi/10.1063/5.0044046#_i33
20. Quebec: Number of cases in schools with air purifiers is three to four times lower.
This is not really a scientific research like the other ones in this document , but the following data are from a comparison of infections in schools with vs. schools without air purification. Unfortunately, as far as I know, there is no calculation of the number of cases per 100 pupils to be able to compare schools with air purification and schools without.
“In a sample of 677 schools with confirmed COVID-19 cases since the beginning of January, 4,223 cases found in total, an average of 6.8 cases per school. But in the 62 schools with purifiers, only 110 cases found or an average of 1.8 cases per school”
21. Effectiveness of In-Room Air Filtration and Dilution ventilation for Tuberculosis Infection control. (1996)
22. Air purifiers for schools: study results pave the way for long-term Corona strategy
“The use of the AiroDoctor with closed windows also reduced the risk by a good 50%. The device performed best when it was placed in the middle of the room. The use of the air purifier in combination with window ventilation was interesting: here the risk of infection dropped by a full 73%”
Air purifiers for schools: study results pave the way for long-term Corona strategy
Infectious aerosols: Latest real-life study in South Korean school confirms results of laboratory tests AiroDoctor air…
23. Quantifying environmental mitigation of aerosol viral load in a controlled chamber with participants diagnosed with COVID-19
“Ventilation, filtration, and humidification substantially reduce the environmental aerosol viral load, and therefore inhalation dose, and should be prioritized to improve building health and safety.” https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciac006/6498295?searchresult=1
Warning concerning ionisation— plasma — UV
As a consumer, the safest thing to do is to simply opt for appliances that are limited to the use of a HEPA filter (and possibly a carbon filter). Avoid appliances with ionisation, plasma, UV-C, unless you have reliable test reports from reputable institutes that show that the appliance in question is safe and does its job properly.