Experiments on a $50 DIY air purifier that takes 30s to assemble
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Experiments on a $50 DIY air purifier that takes 30s to assemble
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Re: Experiments on a $50 DIY air purifier that takes 30s to assemble
#2Thanks for the article! Using incense for testing seems like a good approach. And yes, the lack of difference between "taped" and "non-taped" is definitely interesting. I'm wondering if this might be in part because of your choice to use thin and small HEPA filters instead of the more common thicker and full size MERV filters. Intuitively, what matters is the product of the efficiency of the filter and the amount of air passing through the filter. It's possible that because the resistance of the small HEPA filters is so high, the unfiltered air passing around the filters generates a lower pressure in front of the filter than the non-moving air after the back is taped.
I recently built up a couple similar box fan filters, but using 20"x20"x5" MERV 15 filters bought "used" off Amazon for about $20 each. Note that the total surface area of the folded filter matters for air resistance, not just the height and width of the filter. That is, depth matters, because all else equal the folds increase the amount of filter area.
I sealed well, because I thought it would matter. I removed the back plastic grill to reduce resistance a bit more, and also added a cardboard cowling on the front of the fan, based on the research here: https://www.texairfilters.com/how-to-improve-the-efficiency-.... The idea is that with a high resistance filter on the back, in the absence of cowling you get unhelpful recirculation from the front corners of the fan, although maybe this recirculation might actually be helping reduce pressure in front of the filter in your taped example?
I haven't done any air quality measurements, but I think the system is working the way I'd expect. Noise at low speed is tolerable when in another room, but I only use higher speeds when leaving the house. I'd be interested in more details about your particulate monitor, especially if you are satisfied with it and if it's available in the US.
Re: Experiments on a $50 DIY air purifier that takes 30s to assemble
#3Are diy filters effective at removing smells or only removing the measurable particles?
Re: Experiments on a $50 DIY air purifier that takes 30s to assemble
#4Are diy filters effective at removing smells or only removing the measurable particles?
Not sure, but I know my commercial air filter has an optional activated charcoal filter screen in order to do smell removal.
I also know that one trick to remove the smoke smell from a used car is to use an ozone generator in the car.
Re: Experiments on a $50 DIY air purifier that takes 30s to assemble
#5As most home woodworkers could confirm, a filter-on-a-box-fan works wonders in a (saw)dusty garage. Even after sanding or sawing MDF, the air is clean after about 10-15 minutes. From personal observation, I'd suggest that non-taped is a good idea, as any non-filtered air is routed through the fan to help overall circulation; ideally you want to displace all the air in the room quickly.
Re: Experiments on a $50 DIY air purifier that takes 30s to assemble
#6Are diy filters effective at removing smells or only removing the measurable particles?
Most things that smell are very very small particles not captured by even HEPA filters and require a different kind of filtration. Most commonly activated carbon is used, either as granule or deposited on fibers.
Re: Experiments on a $50 DIY air purifier that takes 30s to assemble
#7Love the testing. I think the taped/non-taped results may diverge as time goes on and the filter becomes loaded. The static pressure of air filters approximately doubles over the lifetime of the filter, and in an unconstrained system more and more air will be going around the filter instead of through it.
Re: Experiments on a $50 DIY air purifier that takes 30s to assemble
#8Nice article! Which EPA filters you ended up using? Thinking of building one myself.
Re: Experiments on a $50 DIY air purifier that takes 30s to assemble
#9Are diy filters effective at removing smells or only removing the measurable particles?
Most things that smell are very very small particles not captured by even HEPA filters and require a different kind of filtration. Most commonly activated carbon is used, either as granule or deposited on fibers.
HEPA filters are actually more efficient at capturing very very small particles (More precisely, many odors are not particles at all but rather gases/vapors. Activated charcoal can capture larger organic molecules because it has an incredibly jagged/porous surface - just 100 grams of activated charcoal provides over 1,000,000 square feet of "effective" filtration surface area.
Re: Experiments on a $50 DIY air purifier that takes 30s to assemble
#10Are diy filters effective at removing smells or only removing the measurable particles?
Not really.
To remove smells ozone generators are used. That stuff is really dangerous though