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Ceiling Air Purifier

jefftk.com

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Re: Ceiling Air Purifier

#61

Post by jefftk »

flybrand wrote: post #48
sdflhasjd wrote: post #20

Earlier quoted context omitted.

It's not clear how this performs over having no fans and filters at all.

Agreed - and another wish list item would be a basic room air purifier “RAP” off the shelf, sitting in the corner. OP will also want to track performance over time. How long does it take the filters to load.

> How long does it take the filters to load

This is basically the same question as "how long does a filter cube last". See https://www.texairfilters.com/testing-the-efficiency-of-merv... where they found performance was still good at 6m, though decreasing at 10m.

Re: Ceiling Air Purifier

#62

Post by bombcar »

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…

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/

Re: Ceiling Air Purifier

#63

Post by SamBam »

tallanvor wrote: post #9

There doesn't seem to be good control tests to say what difference the filters really make - seems one was added in in the comments, but it's missing important details (is the control with everything off? What happens if the fan is running on medium or high, etc.? And, of course, it's not really practical in that most people really don't want to be sticking stuff on their ceiling, but it could be an interesting exper…

I was thinking the same thing. He has graphs for how quickly the pm2.5 levels reduce compared with a commercial machine, but not compared with running the fan alone, without filters.

I believe that it is quite possible the majority of the air is not going through the filters. It seems that much of the air might spill out down the insides of the filters, rather than being forced through. In that case, the graph could be equally explained by the fan causing outside air to be sucked in.

Re: Ceiling Air Purifier

#64

Post by jefftk »

maxk42 wrote: post #57

Is nobody going to mention what a pain in the ass it would be to change all those filters regularly? I love in a somewhat dry and dusty area and need to change my filters (near the ground) every two to three months. I'd hate to have to climb up a ladder to change eight to nine filters that often.

Unless your ceiling is very high you probably wouldn't need a ladder to change the filters on a productized version of this. Reach up, twist something to unlock, old filter slides out, slide in new filter, twist to lock. Repeat for each filter going around. Ten minutes every six months?

Re: Ceiling Air Purifier

#65

Post by ark03 »

My intuition says most airflow comes from the center(and drops linearly towards the tip of the blade and picks up at the blade)

i.e. there's no need to build a filter the size of the fan; you can cover "most" of the airflow by using something similar but extends 50-60% of blade length(pure guess) and the whole arrangement can be above the rotating plane (so easier build?)

Re: Ceiling Air Purifier

#67

Post by creaturemachine »

foobarian wrote: post #38
malfist wrote: post #35

Earlier quoted context omitted.

I've always heard this, but I don't know that that's true. The thing that dies first on an HVAC system isn't the motor, it lasts a long damn time, it's the capacitor, or contactor or some other fault not really related to the motor work load. Plus, your "motor" isn't an engine, it's not variable speed, it only has one "hardness" that it works at. It might push less air with the thicker filter, but it's not going to r…

>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.

That's true, but it's not so simple anymore. Furnace blowers are all electrically commutated brushless DC motors now, and will ramp to keep a constant torque.

Re: Ceiling Air Purifier

#68

Post by [deleted] »

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…

[deleted]

Re: Ceiling Air Purifier

#69

Post by aarongray »

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

Re: Ceiling Air Purifier

#70

Post by dr_orpheus »

bombcar wrote: post #19
discreditable wrote: post #10

Earlier quoted context omitted.

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.

You can have them do a test and adjust the system depending on the filter that's installed to make sure it's moving enough air (though that is mainly important when heating to prevent the heating element from overheating).

It is also important in the cooling cycle for two reasons.

1. If there is not enough air moving over the air-conditioner coils there is the possibility that they will ice over. This has a cascading effect where there is less transfer through the coils and more ice builds up until the whole thing is a block of ice. This most often happens though when people buy condensers that are too big for their system (the thinking being the bigger the better the more cooling, but it is a balance within some tolerance) but can also be done on the other side by reducing airflow too much.

2. Less airflow can also mean too much condensation in the air which can end up sitting in the ductwork and causing it to rust out. This happened to my parents when they installed extra filters in their HVAC system. I guess this is similar cause as #1, just different potential effects.

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