HEPA 13 filters can reach a 99.95% efficacy against particles larger than 300 nanometers.
An electrostatic filter has 95% of filtering capacity over 300 nanometers. A UV system of lamps is certified as killing 99 % of pahtogens, in a air flow of 4 m/s .
To what extent it is possible to make the electrostatic and UV filter in a cascade and affirm that the efficacy can be 99.95% at least as effective as the HEPA filter?
Dear Stefano,
I don´t know about such applications. I work with magnetic nanoparticles but for very different purposes.
Every good wishes,
Daniel
That is easy to test if you have access to a lab.
But combining the two will not necessarily or directly yield higher efficacy.
One point is you do not know how many passes the baseline 95% refers to, or if the 5% that it misses is because certain particles will never take an electrostatic charge and therefore will never be caught. I
F everything gets "charged", and the 95% refers to n passes, the efficiency of m passes is (.95)^(m/n).
Also, note the HEPA filter traps, but does not inherently kill pathogens.
Dear Stefano, Yes, it is possible to achieve the required effectiveness from a hybrid filter, but some research with the sources of UV radiation is necessary as we can read in the following site
https://www.healtheuropa.eu/breakthrough-ultraviolet-light-development-could-help-kill-covid-19-virus/100409/
After passing the first electrostatic stage, the flow must be directed through a system of ducts increasing the time when partially contaminated air is exposed to UV radiation. This aspect also requires some additional investigation.
For the description of the general aspects of filtration, you can consult the following document
https://www.cdc.gov/niosh/docs/2003-136/pdfs/2003-136.pdf
This material provides an invaluable summary of the techniques available to remove harmful pathogens from the air. A comparison between four different filtration principles is summarized in Figure 3.
To answer your question, there is not an affirmed way to determine if the efficacy of an electrostatic filter with UV is comparable to that of HEPA filters. We can say for sure that the HEPA can filter particles better and that the ES filter with UV light will kill the pathogens caught in the air stream. This is not a feature present in a standard HEPA filter which only traps harmful particles. It is also a bit unclear whether you mean an electrostatic filter media or an electrostatic precipitator as HEPA filters themselves can be electrostatically charged. An electrostatic precipitator has an ionizing layer that charges particles and captures them. For the best results you can opt to have a HEPA filter with UV light, some air purifiers will use both.
However, you should note that HEPA filters will have higher pressure drop which will mean they will consume more energy in a ventilation system as compared to electrostatic filters and will need to be replaced where electrostatic filters can be cleaned. Alternatively, you can consider more complex technology like nanofiber air filters, as they have longer filter life and very high filtration efficiency, comparable to that of HEPA. Modified advanced nanofiber filters can potentially have antimicrobial and viricidal functions as well.
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