WingNews logo WingNews
top | item 46099599

(no title)

ruralfam | 3 months ago

Appreciate any thoughts you all have re: this post. For years I have been using Noctua NF-P14 fans to circulate air in house to distribute heat in the winter from our wood stove. E.g. cut holes in the walls, and circulate remote rooms using the fans. Has worked great, and the Noctuas have been rock solid.

Recently a daughter moved into a really nice apartment close to a major university/freeway where she will live for the number of years it takes to get a Phd. I got concerned about tire dust. So I am about to start building a really nice air DIY air filter using eight Noctua NF-P14s (about 1000 cfm). XMas present.

I really wanted to use merv-13, but got quite worried about air flow restrictions, plus cost to replace (assume monthly). Instead I went with two 12x24 Carter reusable electrostatic merv-8 filters. I use Carter filters on my house blower, and really like them (just washed them... scary how much junk is in household air). Also, I got the 12x24 direct from Carter for a very low price as they were returns. Note: This is NOT a low cost project, but I just got scared re: merv-13 so went with what I know.

Anyway, the final product will NOT be like this guy's DIY. I will use my somewhat decent woodworking skills to fashion a good looking standing "lamp like" appliance that should look good in most living rooms. I am thinking of going with knotless cedar as I really like working with cedar, and there are some mills here in NW WA where one can go to get such wood (not a HomeDepot specialty).

My question is whether an electrostatic merv-8 filter would do well with tire dust. I am not looking to create "clean room" conditions in the apartment. Just get rid of some of the bad stuff. I am very weak re: understanding filters, mervs, etc. APPRECIATE any insights. Thx, RF

discuss

order

amluto|3 months ago

To make a nice air purifier, you want to deliver clean air at some respectable rate, where “clean air” is a notional amount of completely pure air, and you want this to work for all particle sizes. If you move 1000cfm (that’s a whole lot BTW) through a filter that removes 60% of the worst-case particles, that’s 600cfm of clean air.

At some point I found a nice chart, IIRC from the EPA, showing the efficiency plotted vs particle sizes for a variety of filters. IIRC the filters generally split into two categories: those with decent efficiency all the way down to zero microns and those with very poor efficiency at small sizes. IIRC the split was around MERV 12. Obviously your filter is not the filter in the chart.

So I would go with MERV 13 or even a bit higher. Also, keep in mind that pressure drop is related to the velocity of air through the filter, so a physically larger filter will have lower pressure drop at the same flow rate. But the need to replace a filter is related to collected gunk per unit area, so doubling your filter area will cost twice as much but last twice as long and will use less power and run quieter.

Also, electrostatic filters can lose their charge from exposure to various contaminants.

edit: it was the chart here, also mentioned down thread.

https://www.frdmtoplay.com/nagivating-air-purification/

Portable Air Cleaners, Furnace, and HVAC Filters. 3ed. EPA 402-F-09-002

And I remembered a bit wrong. Even MERV 10 will pick up the smallest particles, but MERV 8 may miss some. But for good performance at the most penetrating size, you want MERV 12-ish. For a single-pass filter (filtering outdoor air as it enters), you want much higher - MERV 16 or even HEPA or near-HEPA, if you want acceptable performance against potentially nasty outdoor conditions due to wildfire or nasty human particle sources.

bsilvereagle|3 months ago

Check out the plot in the header, and find the particulate size you care the most about: https://www.frdmtoplay.com/nagivating-air-purification/

ruralfam|3 months ago

Thanks. However note that the site dropped electrostatic filters to simplify things. My understanding is that for non-static-affected particles merv-13 would obviously out perform merv-8 for smaller particles. However the promise of electrostatics is that the materials in the filters create a e-stat field that makes them more efficient re: particles like dust. Certainly the two electrostatic merv-8 filters on my hvac blower capture A LOT of dust (fine particles). Since you clean them in a bathtub by filling the tub and washing the filters thru them, I can attest that there is A LOT of really fine particulates being captured.

The lead line for this article pretty much reflects the reason for my post: "The air purifier marketplace is an apt metaphor for how a particle must feel while being trapped in a filter - at every turn there's a new acronym or regulatory agency or purifier type."

dgacmu|3 months ago

A deep merv-13 with a lot of pleats can have a very reasonable pressure drop - you just have to shop a little more carefully.

I would stick with merv-13 because you'll get solid performance across a lot of things you might want to remove, from viruses to general pm2.5 and things like volatilized cooking oil. Clean air is awesome and tire dust isn't the only thing that's annoying.

ruralfam|3 months ago

I agree completely re: mev-13 == optimal solution. But the word "pragmatic" hits me hard. Merv-13 when new/clean start out with pretty restrictive flow. They catch a lot of particles so restriction increases rapidly. At some point the CFM loss means the filter is much less optimal. All the studies I read used new filters, smoke-filled rooms, a day's treatment. It is obviously impractical and very, very expensive to replace a merv-13 filter every few days. There are no reusable merv-13 filters that I could find. If there is a study about merv-13 effectiveness over 30 days vs. merv-8 I would love to see it. I would love to use merv-13, but just cannot get my head around how it is a practical, affordable solution across years and years of use, and let's say a month between filter renewal. Let me know if you have good insights as I am pretty worn out researching this. Thx, RF