I made a quieter air purifier

The general rule about computer fans is that the bigger they are the the quieter they are (i.e. 140mm > 120mm etc.) It's a wierd market gap that large "commercial" air moving fans are so loud.

There are continuous extraction fans, they're called dMEV systems. Eg https://www.epicair.co.uk/products/vent-axia-lo-carbon-reviv...

There's also systems which can move air both ways through the whole house - https://www.ventilation-alnor.co.uk/index/support/alnor-know...

Your DIY solution looks a lot cheaper though.

Vevor makes drop-in floor/wall register fans in the $35-40 price range. The 'proper' solution is inline booster fans in each leg of the ducts, but retrofitting can be expensive depending on access.

if you have house (with attic), jump ducts are nicer solution

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.

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.

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

I recently bought one of these. It's pretty quiet (on the low setting) - you quite likely wouldn't hear it near a freeway https://www.amazon.co.uk/gp/aw/d/B071SLZRRV

vid of the noise levels https://youtu.be/wOc0TM1ErYA?t=195

Box fans are a fire hazard when used continuously to pull air through filtration media. They are not designed for that.

Computer cooling fans also might not have been designed to handle that much "load", but in the case of the box fan, we have an actual report of someone who almost burned down the house:

https://news.ycombinator.com/item?id=21382994

I use a bank of eight Noctuas to vent from the rooom with our wood stove to the main hall. Then use more units with two sets of Noctuas ganged to move from the hall to various remote rooms. Been using them for more years than I can remember. Silent, never failed yet. It has been great vs. using house fans (my initial approach). BTW: Our local thrift store has a huge amount of various DC power supplies from donations. I sift thru them to find the right volts/amp combo needed for the ganged units, and generally spend about a dollar per supply. HTH, RF.

If you’re willing to buy something off the shelf, get one of the IKEA filters. They’re more efficient, quieter, and use less expensive media.

yeah, i get why people were doing the DIY air purifier thing during covid when air purifiers were hard to come by, and the box fan version at least has cost-effectiveness going for it.

but 5x arctic cooling PC fans is ~$100. the commercial versions are easily available, more effective, no more expensive, and don't look like a box of furnace filters taped together.

You want to suck air through the filters rather than blow into them. For one, this keeps the fans cleaner but also it's more efficient, reducing turbulence inside the box.

https://old.reddit.com/r/crboxes/ is a good resource if you're looking to make your own. There's been a general shift from large box fans to PC fans because their performance/noise ratio is better.

I think it's because there are no grills on the outside. If the fans were sucking air out of the box, dust would build up on the outside, and bumping it would dislodge dust back into the environment.

With the fans blowing in, all the dust is on the inside of the box (and on the fans).

The box fan version also blows air into the box

Your question isn't very clear... Is it why do they use computer fans? (My guess is that is what they had). Or is it why do you blow instead of suck?

I think this done to create a slight overpressure which helps keep the dust out.

They're from Arctic Cooling, so 140mm at most. They don't make anything bigger than that.

It didn't really come out of academia in that way. It was an innovation borne out of necessity during Covid. I don't think I've seen anybody using a box design for it. If you have a source, I'll be happy to be corrected.

Regardless technology is often named after people who made it popular, especially when original inventors are unknown or too diffuse.