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Ceiling Air Purifier

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Re: Ceiling Air Purifier

#81

Post by sampo »

SOLAR_FIELDS wrote: post #32
havblue wrote: post #29

An ac filter is pretty gray after just a few months. Granted this will take longer to get dirty but I suspect it will look ugly before you know it.

A good reminder to change it at least. If this were a purchasable product, I envision making the filters replaceable and the frame compatible with some standard furnace filter size, so that you can just run to the store and grab new filters when you can visually see the filter needing replacement. Contrast this with the furnace filter, which needs some other mechanism (often, a schedule) to determine when to change t…

I read on the internet, that HEPA filters actually just filter better when they start getting clogged. But clogging increases air resistance, so you need higher power level in the fan to get the same throughput. So the economics calculation is, the cost of new filters vs. the cost of electricity of running the fan and eventually the cost of a new fan. And the comfort factor is more noise when the fan is running at higher power level.

So running the filters a long time before replacing, might be the cost-saving option.

Re: Ceiling Air Purifier

#82

Post by _ea1k »

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.

Re: Ceiling Air Purifier

#83

Post by foobarian »

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…

> I have a degree in electrical engineering, thank you for telling me to do my research, I spent four years doing that.

Apologies for the tone!

> Have you ever opened one up and did a repair?

Well funny you should ask, but yes! Two times. One time, a power relay on the control module shorted and blew a hole in the circuit board. Had to replace the control module there. Another time, the start capacitor needed to be replaced on the giant 2KW squirrel cage motor. I removed the blower, disassembled it, lubricated moving parts, and of course tested it out on a stand. That much blowing power is quite impressive when right next to your face.

Re: Ceiling Air Purifier

#84

Post by malfist »

devenson wrote: post #78
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…

Even a motor without a fancy control system will consume more power under load. See: https://en.m.wikipedia.org/wiki/Counter-electromotive_force

I'm not saying a motor turned off will consume the same power as a motor turned on, that's foolish.

Back pressure doesn't impact the load of a fan motor, at least not as the scale we see in HVACs, we're not making vacuum chambers.

Re: Ceiling Air Purifier

#85

Post by happyopossum »

alexpw wrote: post #71
kolencherry wrote: post #55

Earlier quoted context omitted.

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, tha…

> I never understood the purpose of the bottom filter in the Corsi-Rosenthal Box

It's for when the box fan is not sitting on the floor - either raised up on feet (which many have), sitting in a window, or hung somewhere. That said, you're right - 4 packs are easier to come by and probably work nearly as well in the real world.

Re: Ceiling Air Purifier

#86

Post by foobarian »

malfist wrote: post #84
devenson wrote: post #78

Earlier quoted context omitted.

Even a motor without a fancy control system will consume more power under load. See: https://en.m.wikipedia.org/wiki/Counter-electromotive_force

I'm not saying a motor turned off will consume the same power as a motor turned on, that's foolish. Back pressure doesn't impact the load of a fan motor, at least not as the scale we see in HVACs, we're not making vacuum chambers.

Maybe our disconnect is that we're talking about two different things, one being the rated design point of the blower system, which is presumably constant (though newer systems seem to be more sophisticated), and the other being the exact load and power consumption that depends on backpressure. A higher backpressure will certainly increase the motor power consumption on a classic induction motor - if not by 100% then by some non-zero amount.

Anyway at the end of the day I agree with the original characterization of wear and tear - motor and blower will probably outlast most other components. In the case of the one I mentioned this seemed to be true. You just may end up paying a little more for the electricity to run it.

Re: Ceiling Air Purifier

#87

Post by UI_at_80x24 »

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 common 12VDC power source it's already been stepped down.

(source: used to work for a photocopier company, and when people bought newer units, we would pickup the old units and usually junk them.)

Re: Ceiling Air Purifier

#88

Post by usefulcat »

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.

As long as the filters are adequately supported at the edges it shouldn't be a problem. I know because my house has two 12x24 HVAC filters which are only supported at the edges and are almost certainly subject to much higher rates of airflow.

Re: Ceiling Air Purifier

#89

Post by aarongray »

gonehome wrote: post #80
picture wrote: post #74

Earlier quoted context omitted.

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…

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

Re: Ceiling Air Purifier

#90

Post by aarongray »

blagie wrote: post #79
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…

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.

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