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Ceiling Air Purifier

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Re: Ceiling Air Purifier

#71

Post by alexpw »

kolencherry wrote: post #55
sha256sum wrote: post #6

Great idea. What's worked for me is simply taking a 20"x20"x1" filter and sliding it into the back cover of a standard $25 Lasko box fan. Cheap, easy option for air filtration in the home.

Yes! This is the basis for the Corsi-Rosenthal Box [1]. Five 20"x20"x1" filters and a box fan, with duct tape to seal the edges. Not the prettiest, but it's effective. [1] https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box

> An updated design, also known as a Comparetto Cube, [1] uses four filters and a cardboard base that can sit directly on the floor.

I never understood the purpose of the bottom filter in the Corsi-Rosenthal Box, so it felt like a waste of a filter, but I'm a big fan of the Comparetto Cube (no put intended). And 4 packs of filters are readily available -- 20x20x2 is suggested for the Comparetto Cube.

[edit] Also, thank you. I couldn't recall the Corsi-Rosenthal name/link, but thought of the wiki immediately.

[1] https://www.thisoldhouse.com/green-home/22231148/diy-air-fil...

Re: Ceiling Air Purifier

#72

Post by [deleted] »

discreditable wrote: post #10
bombcar wrote: post #5

If you have a whole-home furnace you can often make it run the fan even if cool/heat is off - and install a high power filter and change it regularly and it’ll filter the air reasonably well. The ecobee has a “minimum fan time per hour” setting - it can also help to balance the air temperature.

I've had HVAC techs tell me not to use those thick filters unless your system is designed for it. They make the fan work harder to pull less air. This reduces how much air it can move.

[deleted]

Re: Ceiling Air Purifier

#73

Post by [deleted] »

malfist wrote: post #56
foobarian wrote: post #38

Earlier quoted context omitted.

>Plus, your "motor" isn't an engine, it's not variable speed, it only has one "hardness" that it works at. This is incorrect - electric motors draw more current when under load. I would suggest researching this or playing with some toy electric motors run from a battery through a current meter.

I have a degree in electrical engineering, thank you for telling me to do my research, I spent four years doing that. Sure, some motors have characteristics that can be tweaked to run at different work loads either with PWM, or allowing them to pull more amps to drive higher loads. Hell, you can even overvolt them and make them actually work harder. That's not how HVACs work though. Have you ever opened one up and di…

[deleted]

Re: Ceiling Air Purifier

#74

Post by picture »

aarongray wrote: post #69

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 destroy…

Is this legit? Their website feels kinda sketchy to me, with the huge and somewhat tacky CG pictures, sweeping claims, apparent SEM photography that just looks too good to be true (could there really be zero residue? and the background never change, presumably over time span of at least minutes!) This really reminds me of vaporware like WaterSeer, or one of the recent "turn kitchen garbage into dry dust" appliances that I've seen ads for

Re: Ceiling Air Purifier

#75

Post by turtlebits »

blagie wrote: post #52

I think people are missing the point. YES this is bad engineering for a finished product: - The fan is not designed for high static pressure. It won't do well pulling air through filters. - It's ugly. It will get uglier as filters get dirty. - It's expensive to replace filters. - Etc. But it's not a finished, industrial project. It's a prototype. Those sorts of issues are universal for prototypes. They're easy to add…

This is just an air filter with more filters, the installation location is part of the prototype, which is not practical at all.

Re: Ceiling Air Purifier

#76

Post by gonehome »

aarongray wrote: post #69

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 destroy…

Brownian motion affects how small particles move around at small scales [0]. This is why HEPA filters can be effective even against smaller particles (which bounce around and get caught).

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...

Re: Ceiling Air Purifier

#77

Post by anarticle »

bombcar wrote: post #62
malfist wrote: post #56

Earlier quoted context omitted.

I have a degree in electrical engineering, thank you for telling me to do my research, I spent four years doing that. Sure, some motors have characteristics that can be tweaked to run at different work loads either with PWM, or allowing them to pull more amps to drive higher loads. Hell, you can even overvolt them and make them actually work harder. That's not how HVACs work though. Have you ever opened one up and di…

Modern furnaces have variable-speed fans - Blower Motor Variable-speed constant airflow full-featured ECM https://www.bryant.com/en/us/products/gas-furnaces/987m/

The vast VAST majority of hvac systems are still bang bang systems.

Re: Ceiling Air Purifier

#78

Post by devenson »

malfist wrote: post #56
foobarian wrote: post #38

Earlier quoted context omitted.

>Plus, your "motor" isn't an engine, it's not variable speed, it only has one "hardness" that it works at. This is incorrect - electric motors draw more current when under load. I would suggest researching this or playing with some toy electric motors run from a battery through a current meter.

I have a degree in electrical engineering, thank you for telling me to do my research, I spent four years doing that. Sure, some motors have characteristics that can be tweaked to run at different work loads either with PWM, or allowing them to pull more amps to drive higher loads. Hell, you can even overvolt them and make them actually work harder. That's not how HVACs work though. Have you ever opened one up and di…

Even a motor without a fancy control system will consume more power under load. See:

https://en.m.wikipedia.org/wiki/Counter-electromotive_force

Re: Ceiling Air Purifier

#79

Post by blagie »

aarongray wrote: post #69

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 destroy…

Erm, this isn't quite correct:

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.

Re: Ceiling Air Purifier

#80

Post by gonehome »

picture wrote: post #74
aarongray wrote: post #69

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 destroy…

Is this legit? Their website feels kinda sketchy to me, with the huge and somewhat tacky CG pictures, sweeping claims, apparent SEM photography that just looks too good to be true (could there really be zero residue? and the background never change, presumably over time span of at least minutes!) This really reminds me of vaporware like WaterSeer, or one of the recent "turn kitchen garbage into dry dust" appliances t…

Your intuition is correct - it’s bullshit.

—

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...

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