Comment by derefr
1 day ago
I live in an apartment over a busy road, and my building doesn’t have forced-air ventilation to the units, so I need to pull in fresh air somehow. Just leaving the windows open results in black soot accumulating in the carpets (and is probably why both my SO and my cat developed asthma while living here.) Regular air purifiers (we have two) only do so much.
What ended up making a difference for us, is buying a portable industrial air scrubber, of the kind construction/remediation sites use to clean the smoke and dust (and mold, and asbestos, etc) they’re generating out of the air before it gets vented outside (see e.g. https://a.co/d/01lTtyuZ); and plumbing this machine into our apartment in reverse: putting it out on our (covered) balcony, with it exhausting the “scrubbed” air into the apartment. (I made a little sliding-door shim of the type people use to pipe portable AC units outside, just with the hose on the other side.)
Generally works great. We run it on a very low speed, so it’s surprisingly quiet (no louder than other fans we have for air circulation, and a more pleasant frequency because of the large diameter of the fan it has inside.) The pre-filters get absolutely caked with exhaust and road dust after ~2wks, and start to let through an odd stench at that point, so we’re actually replacing those faster than even is recommended for the industrial use-case. But the actual main HEPA filter inside the unit seems to last longer than in industrial usage.
You could probably improvise something cheaper using the same filter arrangement, though now that you have it, sounds like the best thing to do might be just including an extra sacrificial initial filter to increase the lifespan of the proper ones.
The machine's pre-filters (https://www.amazon.ca/AlorAir-MERV-10-Replacement-CleanShiel...) basically are that "extra sacrificial initial filter." I'm not sure what a "pre-pre-filter" would look like that would make it any different than one of these.
Were you maybe thinking some kind of wire mesh, like the "washable pre-filters" in air purifiers tend to be? I did initially consider this; but, after running the air scrubber for a few months and seeing what actually builds up in the pre-filter, it seems like the pre-filters don't actually end up being coated in anything (dust/hair/etc) that can actually be rubbed/scratched away or even vacuumed out of them. Rather, just end up gradually blackening (due, I think, to fine [PM2.5] particulate making it partway through them before gradually embedding deep inside them); and gradually feeling more and more "skudgy" to the touch (due perhaps to some of those particulates being hygroscopic, and due to also trapping things like pollen/mold spores.) You can actually touch the surface of the fouled pre-filter and your fingertip will come away clean (but touching it won't be a nice sensory experience.)
I think, for helping with that kind of particulate, a wire mesh wouldn't do much if anything. The only "passive" thing that would help is a non-woven cross-linked fiber material, porous enough to not overwork the air scrubber's fan to the point of making it work harder / be louder / burn out sooner, yet layered and "internally labyrinthine" enough to capture particulate despite that porosity. I.e. the same material used in the pre-filter.
(If I could add an active component, I might introduce an intake-side ionizing air purifier, where particulate gets charged and then preferentially deposits onto the fins of a washable heatsink-like grille. AFAIK, those don't normally work at the sort of CFM being pushed by the air scrubber. But if anyone wants to design a better mousetrap here, that might be a direction to look into.)
Your prefilters only lasting two weeks, plus two household members developing asthma, might make me think very seriously about moving somewhere less polluted, and quickly.
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