I love the enthusiasm and DIY ingenuity here. That said, the post is tagged with COVID-19. The COVID virus particles are .1 to .5 microns in size, and these MERV-14 filters, while certainly better than nothing, are not going to capture a significant amount of these virus particles. A better approach is to not filter the particles, but actually rip them apart at a molecular level. This has the added benefit of destroying all sorts of other contaminents that even high grade HEPA filters will miss, such as mold mycotoxins. A system like the Molekule is a good example of this approach.https://molekule.com/technology
blagie|3 years ago
1) MERV14 will capture 75%-84% of particles in the 0.3-1μ range.
2) A filter which captures 70% of particles with an air flow of 100cfm will capture the same amount of virus as a filter which captures 100% of particles with an air flow of 70cfm. Both will clean the room just as fast. For air filters, lower filtration + higher airflow is usually a better design option. Going from 70% to 95% to 99.9% means you'll have a more expensive, power-hungry, and more noisy product over one which just has a little bit more air velocity [1].
3) The rating is for 0.3μ since that's the hardest size to capture. A filter will actually capture more particles below 0.3μ.
4) COVID19 virus particles are around 0.1-0.2μ, but that's beside the point. They're travelling on water molecules. Those are much bigger.
5) Even if there were a virus particle somehow floating around, a viral load of one virus is very unlikely to get you sick.
From an engineering standpoint, something around MERV14 is almost certainly the sweet spot for a COVID19 room air filter.
[1] High-filtrations makes sense in places like vacuums, face masks, and other places where the goal is to have clean air coming out. Vacuums shouldn't blow up dust. That's a different engineering design goal than a room air filter. If you'd like to see the impact of loading on a fan, put your hand behind one, and hear how much noise goes up. MERV14 has a much lower load than HEPA.
aarongray|3 years ago
2) It will not clean the room just as fast, it will take longer to clean the room.
4) COVID-19 particles do travel on water molecules, but they are also airborne. The CDC has admitted this and there is a growing body of research proving this to be true as well.
5) This has not been proven.
gonehome|3 years ago
Specifically about the Molekule - their claims seemed to be empirically false and the device performed worse than a standard HEPA filter (and they were resistant to allowing independent tests at all).
When the tests came out awful their responses were mostly bullshit. [1]
[0]: https://en.m.wikipedia.org/wiki/Brownian_motion
[1]: https://www.nytimes.com/wirecutter/reviews/best-air-purifier...
picture|3 years ago
gonehome|3 years ago
—
In the summer of 2019, we purchased a Molekule Air (the flagship model) and tested it. We bought an Air Mini that fall and tested it in February 2020. At the time we tested the Molekule Air, the company claimed that its “scientifically-proven nanotechnology outperforms HEPA filters in every category of pollutant.”
Our tests proved otherwise. And by mid-2020, that language had been withdrawn, after many of the company’s claims were ruled against in a case before the National Advertising Division and upheld in a later appeal before the National Advertising Review Board. The Molekule Air turned in the worst performance on particulates of any purifier, of any size, of any price, that we have tested in the eight years that we have been producing this guide. The Air Mini outperformed it, but that’s not saying much: It still produced the second-worst performance we’ve ever seen.
Guide author Tim Heffernan asked Molekule CEO Dilip Goswami why the language was removed. He answered, “The point about ‘in all categories’ is that we see a device that outperforms across all of the categories. Right? So we’re not trying to say that individually, on any particular metric, we would be number one. Right? What we’re saying is, when you look across all the categories, we outperform HEPA. Right? And that’s what we’re attempting to convey with that. And so—it’s fair to say that we needed to re-examine some of the language to make sure that it’s saying what we’re intending to say.”
https://www.nytimes.com/wirecutter/reviews/best-air-purifier...
jefftk|3 years ago
The respiratory particles that transmit covid are a range of sizes, but likely mostly a bit larger than that: https://www.jefftk.com/p/how-big-are-covid-particles