Air purifiers fighting infectious aerosols
Researchers at the renowned German Fraunhofer Institute for Building Physics IBP published new results on air purifiers in March 2021. In a paper titled "Reducing the risk of infection in premises with people contact: requirements for indoor air purification for hygiene concepts", the researchers offer findings for reducing infectious aerosols in indoor spaces. For this purpose, they investigated various air purification technologies - including possible by-products - based on ISO 16000-36 test conditions with surrogate viruses. Incidentally, the AiroDoctor® air purifier was also developed according to this test standard and was finally certified in March of this year in accordance with ISO 16000-36:2018.
So what requirements must an air purifier meet? We briefly summarize the most important results below:
1. Capabilities: person-related volume flow
- Based on DIN standards on ventilation rates, the Fraunhofer Institute researchers calculated a volume flow of uncontaminated air of 39.6 m³/h for rooms that can be ventilated in parallel, which an air purifier should be able to provide per person. This then results in the maximum number of people per device or, conversely, the necessary number of devices for the people in the room. (In total - together with other ventilation - a requirement of 54m³/h of uncontaminated room air per person is assumed). The volumetric flow rate of a device is clearly more meaningful than the Clean Air Delivery Rate (CADR) in this context, according to the researchers.
- Depending on the cleaning performance of the device, the minimum room occupancy or the number of air cleaners required can be calculated.
- It is best to install the units so that the supply and exhaust air can flow freely.
2. Efficiency: Separation vs Disinfection
- The researchers emphasize that when stating efficiency, a clear distinction must be made between "only" separating particles (e.g. HEPA filters) or actually reducing infectivity (e.g. UV-C, in the case of the AiroDoctor this would be photocatalysis).
- In contrast to pure filter technology (e.g. HEPA), there is currently no uniform standardization for the efficiency of devices with a disinfecting effect (e.g. UV-C or photocatalysis). Here, the manufacturer would have to be able to demonstrate efficacy, explicitly for infectious aerosols (not just for surface disinfection).
- The study emphasizes that especially in the case of technologies with a disinfecting or inactivating effect (e.g. UV-C irradiation or ionization), attention must be paid to harmful by-products such as ozone.
3. Operation: Noise level, safety and maintenance
- The noise emissions of the air purifier should not exceed 38dB for small rooms under 50m³, 45dB for medium rooms under 200m³, and 55dB for large rooms over 200m³ for one unit and 50dB for multiple units.
- The manufacturer would have to provide a declaration of conformity on the tested safety of its device. Air purifiers with UV sources must not emit radiation under any circumstances, either during operation or maintenance.
- Information and instructions on maintenance and operation would have to be transparent and comprehensible.
What do these results say about the AiroDoctor?
"We have read the study with great interest," says Carsten Hermann, co-developer of the AiroDoctor. "We can see that we largely meet the criteria that the Fraunhofer Institute has worked out. Thanks to its unique filter technology, the AiroDoctor is able to perform not only powerfully, but also very effectively." As mentioned earlier, the AiroDoctor was recently certified in the ISO 16000-36:2018 test chamber process, and AiroDoctor production also received ISO 13485:2016 certification for quality benchmarks in medical device manufacturing.