Ceiling Fan Air Filter

[-]jefftk4y70

I think I want to try this out and see how well it works. Looks like covid is probably primarily transmitted in particles of 9μm or larger, even though it itself is tiny. I can measure p10 levels (and p2.5), but I'm not sure the best way to generate the particles. The Wirecutter tests by burning matches but not only isn't that all that repeatable it generates particles that are mostly much finer than we're talking about -- ~0.1-1 μm. I wonder what would be a repeatable way to generate a lot of ~10μm particles?

[-]Eggrenade4y30

Though I love the idea of a filtered ceiling fan that's out of my way and can therefore be larger and quieter, I don't think a jury-rigged solution would work at all. Fans tradeoff flow for static pressure (https://blog.orientalmotor.com/fan-basics-air-flow-static-pressure-impedance), and I'd bet ceiling fans are optimized for flow. The filters will up the impedance considerably compared to basically open air, and the flow would drop dramatically.

Also, some (most? all?) central air systems can run fan-only (no heat or AC), making additional filters unnecessary.

[-]jefftk4y20

Box fans are also optimized for flow, but do well when used as filter cubes. Part of this is that these filters do not actually offer very much resistance to flow.

A central air system is generally not spec'd to move a large amount of air: they usually work by moving a smaller amount of more conditioned air.

[-]Eggrenade4y30

I'm not so sure a central air system wouldn't be up to the task. I calculate this purifier at 150 CFM from the product page and assuming 8 ft. ceilings, and this implies 1,500 CFM would be a fairly typical residential HVAC system, so that seems roughly adequate to me.

Also, that product page suggests you should cycle air 5 times per hour, but that seems excessive to me. I use that unit in a much larger room on a low setting and it does just fine getting rid of any smoke smell from wildfires.

[-]jefftk4y20

microcovid.org thinks outside is 1/20 the risk of inside, and 5 ACH gets you to 1/4.

The purifier you link to has a CADR of 141 CFM, so roughly equivalent to bringing in outside air at a rate of 141 CFM.

If your residential system can do 1,500 CFM on a 2,000 sqft house with 8ft ceilings, I get 5.6 ACH. That's quite a bit better than I expected; not sure how typical that is?

[-]jefftk4y20

Another advantage of a ceiling fan filter is an essentially ideal airflow pattern. If you have people sitting around the outside of a room,with the fan in the center, it blows fresh air down toward the people, and then sucks up the dirty air around the perimeter of the room.

[-][anonymous]4y-10

Jeff, this is not a situation where you can do better than a prepackaged properly engineered solution. You need scale, incremental refinement, and a metric to optimize for. (In this case a mix of reliability, filter life and cost, and particle filtering effectiveness).

The simple issue with filter cubes and other improvised solutions is they leak air.

Anyways if you need cleaner air buy one of these: https://www.google.com/amp/s/www.nytimes.com/wirecutter/reviews/best-air-purifier/amp/

(I use a coway airmega bought on sale, it is always running)

[-]jefftk4y*60

Your link's top pick, the Coway AP-1512HH Mighty, has a pollen CADR of 240 CFM [1], while a filter cube has a pollen CADR of more like 464 CFM while being much cheaper. Leaks are not a critical problem for this usage, the way they would be on an intake filter, because you are repeatedly processing the same room's air. What matters is the overall effectiveness, which is what CADR ("clean air delivery rate") measures.

[1] Per Lee 2020, covid is probably primarily transmitted in particles of 9μm or larger, and when reporting "pollen" effectiveness people use 5-11μm.

[-]Elizabeth4y30

This is not a situation where you can do better than a prepackaged properly engineered solution.

Why not?

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LESSWRONG
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Ceiling Fan Air Filter

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