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Ceiling Air Purifier

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Re: Ceiling Air Purifier

#101

Post by jefftk »

hinkley wrote: post #96
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…

One way to reduce static pressure is to increase the number of filters. I saw one design last year, during the fires, that was a cube. Lasco fan on one side, and five filters tied into a box shape. A couple problems. One, space - this thing was bigger than a dorm fridge. Two, availability - no way you were finding five filters during a wildfire. Three, etiquette - if you found five filters that meant two other people…

> Two, availability - no way you were finding five filters during a wildfire. Three, etiquette - if you found five filters that meant two other people weren’t getting any at all.

Filters last a long time unopened: buy them in advance and store them until you need them, rotating stock.

Re: Ceiling Air Purifier

#102

Post by hinkley »

_ea1k wrote: post #82
Brajeshwar wrote: post #60

Can we also please add a wi-fi access point to the ceiling fans? I always thought that would be awesome.

That's kind of brilliant, tbh. The biggest downside that I can think of is that they tend to be electrically noisy and fairly space constrained. It'd have to be really small, but probably possible.

Might be easier to do on a fan with a light fixture. The part that sticks down below the fan is a lot of dead space, and farther from the motor.

Re: Ceiling Air Purifier

#103

Post by hinkley »

jefftk wrote: post #101
hinkley wrote: post #96

Earlier quoted context omitted.

One way to reduce static pressure is to increase the number of filters. I saw one design last year, during the fires, that was a cube. Lasco fan on one side, and five filters tied into a box shape. A couple problems. One, space - this thing was bigger than a dorm fridge. Two, availability - no way you were finding five filters during a wildfire. Three, etiquette - if you found five filters that meant two other people…

> Two, availability - no way you were finding five filters during a wildfire. Three, etiquette - if you found five filters that meant two other people weren’t getting any at all. Filters last a long time unopened: buy them in advance and store them until you need them, rotating stock.

Sure, but that’s hard to do when reading a tutorial that was posted after the sky turned orange.

Edit: To your point though, help out the distribution networks by buying yourself an extra filter or two now, and put it on the shopping list every time you use one.

Re: Ceiling Air Purifier

#104

Post by jefftk »

aarongray wrote: post #90
blagie wrote: post #79

Earlier quoted context omitted.

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…

1) You're correct. 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.

> > 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.

> It will not clean the room just as fast, it will take longer to clean the room.

Here are two different models:

A. Air moves sequentially. First you filter all of the air once, then you filter all of it another time etc. In this model, a filter with 100% efficacy will get everything in a single pass, and the CFM determines how long that pass takes, while a filter with lower efficacy will never get it all, but will get pretty close after a few passes. In this model you want high filtration.

B. Air moves randomly. At each minute, the purifier selects air from the room at random, filters it, and spits it back out. In this model, a filter with 100% efficacy at 70 CFM is exactly equivalent to a filter with 70% efficacy at 100 CFM, and you will often want to trade off efficacy for flow.

I think real rooms are generally much closer to (B) than (A), though of course somewhere in the middle?

Re: Ceiling Air Purifier

#105

Post by aarongray »

aarongray wrote: post #89
gonehome wrote: post #80

Earlier quoted context omitted.

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…

Thanks for sharing some background on Molekule, I did not know about this.

That said though, the Molekule team themselves have said that their device is not optimized for filtering particulate matter, but rather for denaturing mold, viruses, and bacteria. See: https://www.reddit.com/r/molekule/comments/6u7d5y/putting_mo...

This is reflected as well in the testing on Molekule's own website: https://molekule.cdn.prismic.io/molekule/4ec92005-d806-4991-...

And, I will say that they have numerous tests by independent labs. They did do some testing with their own lab and with a lab affiliated with them, but this is far from all the testing they have done. So to say that all their tests were tainted or affiliated with them is simply not true. See: https://molekule.com/papers

Re: Ceiling Air Purifier

#106

Post by Johnny555 »

post_break wrote: post #42
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.

My dad worked in AC his whole life. Do not put a constrictive filter on your ac. He even recommends the cheap ugly ones as they are the least restrictive. The AC is not meant to filter air. The only reason it has filters is to keep large particles out of the evaporator coils.

When I upgraded my HVAC system, the installer recommended an AprilAire filter box, I uses a 4" high pleated filter, each MERV-13 filter has around 16 pleats, so if you unfolded it, it'd be around 10 feet long.

Comes with full warranty from the manufacturer, so I don't think it's going to shorten the lifetype of the system.

I wouldn't put a regular flat MERV-13 in an existing HVAC system, but the pleated ones have so much more surface area that they seem safer.

Re: Ceiling Air Purifier

#108

Post by Kadin »

UI_at_80x24 wrote: post #87
jaggederest wrote: post #7

Very cool, if I was going to build something like this de novo I would start with a squirrel cage fan. When you oversize them and run them at low RPM they can produce a startling amount of airflow with virtually no sound at all. You could also bump it up to a MERV 16 with enough intake filter area.

I too am a fan of the squirrel cage fan, and have collected a lot over the years. One excellent location to source them for 'reuse' are photocopiers. Old analog copiers can have as many as 4 fans while newer digital ones seem to have 2-3 depending on size/capacity. Mostly DC too, but I have also come across some big A/C fans. They almost always are designed for higher voltages (i.e. 20+VDC) so when combined with a co…

Old furnaces nearly always have big-ish squirrel cage blowers in them, and many are replaced before the fan motors fail for various reasons. In my area they are a reasonably frequent sight by the side of the road on bulk garbage day. If you get there before the scrap metal guys do, you could easily nab a blower.

They're typically 120V single-speed devices, although some newer ones may have variable-speed fans. Not 100% sure how most of them vary the speed; my bet is that they just have some capacitors switched inline with the fan motor to add reactance to the circuit and slow it down. (That would probably be how I would slow down a single-speed one to make it quieter, at any rate.)

There are a lot of projects online that you can find, showing how to build fairly big workshop air cleaners with a furnace blower and some cheap plywood/MDF/whatever. Basically you just build a 5-sided box around the blower with a hole for the outgoing air, and then mount a furnace filter on the open face of the box.

Re: Ceiling Air Purifier

#109

Post by Kadin »

russnewcomer wrote: post #28

I wonder if there is going to be an issue with the structural integrity of the filters, since they are designed to rest on an object rather than hang? Wouldn't think it would be a big issue, but possibly? If you were wanting to do this long term, feels like a series of light wood frames to support would not be too expensive/difficult to construct or possibly 3d print, and have advantage of reduced adhesive smell.

Most filters (especially the 1" and thicker ones) are surprisingly sturdy across most dimensions except for torsion.

Thinking about 3D printing, you could probably print a nice corner bit, that would hold the corner of 3 filters together and square to each other. That would make the whole assembly easier to put together and seal up with tape.

Re: Ceiling Air Purifier

#110

Post by blagie »

aarongray wrote: post #90
blagie wrote: post #79

Earlier quoted context omitted.

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…

1) You're correct. 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.

You're making statements with no backing, logic, or argument behind them.

2) The percent of material removed by a filter per unit time is the product of (1) filter efficiency with (2) what percentage of a room's air passes per unit time.

4) "Airborne" is generally via microscopic droplets. The CDC's guidance changed from large droplet transmission (which is relatively short-distance and short-time) to airborne. This doesn't mean individual viruses are floating around without any H20.

5) No one credible believes 1 virus particle is likely to infect you, except by very bad luck. Most citations give claims in the 100-1000 particle range. Low initial infectious dose also /appears/ to correspond to less aggressive infections. This has not been rigorously proven (and it's hard to do), but has a strong theoretical basis:

- One virus particle is unlikely to make it past the mucous layer, unless you're super-unlucky.

- If it does, your innate immune system can usually handle minor infections before they escalate.

- If it can't, your adaptive immune system has more time to respond. You're looking at a few days before it kicks in. With a lower initial infectious dose, you'll still have that much less virus when it kicks in.

If you'd like to contradict any of this, please provide citations. I'll read them. I'm glad to be proven wrong. Perhaps I'll learn something.

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