Although it would be nice, we can’t all work from home. If you have to spend the day in close quarters with other people, you might want more protection than just a mask and sanitizer. Check out [jshanna]’s DIY HEPA filtering fan — it looks like a breeze to build and uses commonly-available parts plus a few 3D-printed pieces to put it all together.
The basis of this attractive and useful office must-have is a muffin fan from Amazon that has an optional variable speed controller. A long threaded rod runs up the center of the HEPA filter, so it attaches kind of like a lampshade. The fan draws up air from underneath and blows it upward through the filter and out into the room. Whenever the HEPA filter gets dirty, just take it out and wash it.
Are you still buying disposable masks? You might save money in the long run by making your own.
A regular fan is about as good at pushing air through a filter as a crocheted pool cue is for playing pool.
indeed, better use a radial fan instead of this axial thing.
I mistakenly assumed the threaded rod was some kind of electrode for electrostatic filtering, but alas!
I shit thee not…
Fan specs, static pressure developed = 9.1 mmH20 (If it blows into a U tube it can lift a column of water 9.1mm) https://www.acinfinity.com/component-cooling/axial-ac-fan-kits/axial-1238-muffin-120v-ac-cooling-fan-120mm-x-120mm-x-38mm
Figures a manufacturer secret for the specific vacuum filter used, because you’re not expected to be engineering your own vacuum cleaner (If you need real figures to properly engineer an air cleaner, buy a filter that has a spec sheet) hence no “need to know” however, EPA states that 1″ or 25mmH2O pressure drop is typical of a clean filter meeting HEPA specs (If it’s got bigger holes in it it doesn’t meet them)
https://www3.epa.gov/ttncatc1/dir1/ff-hepa.pdf
25 is bigger than 9.1, so fan is incapable of pushing hard enough to develop any airflow significantly higher than natural diffusion rate… though maybe the motor getting hot might move a little air.
Hint: If you use a filter made for a device, such as a vacuum cleaner, and the motor of your choosing isn’t at least a quarter as powerful, in this instance 18W vs something like 800W then you’re probably not in the right ballpark, you want the one three cities over.
Not so sure you’re completely correct. The 25mm typical drop spec is for a typical operational pressure of 8″ of water (~200mm of water). Lower pressures will show a lower drop, and there will still be airflow through the filter.
I was going to post a similar comment. Even just looking at it it’s obvious this thing won’t be pushing any decent amount of air. Also, if you’re not passing the volume of air in the room at least once per hour it won’t make a big difference. There’s a reason proper sized air filters have huge filters and big chunky fans.
There are axial fans that have decent static pressure these days, like the Noctua Industrial line.
Static pressure also increases with fans in series so it’s possible to stack them for increased performance.
Whooo 10.5 mmH20 big numbers, for a fan, did I mention fans are useless? …You’re gonna need a stack of 5 of them before they start moving air through that, and that will be at about a quarter the CFM of one of them in free air… and you won’t want to put them on a speed controller, any speed below 80% may as well be an off switch.
I’m sure that 3 fans would be enough to purify a small personal space, say a desk. They aren’t useless for certain applications that don’t revolve around whole-room purification.
> RW ver 0.0.1
You’re aware of static pressure of fans and the pressure required for filters. And dis the recommended fan and all axial fans.
Why not suggest an alternative. Something like a AFB1212GHE-CF00, with 27.483 mmH2O, or another more suitable offering. Although they can be hard to get by times, due to so many people using them to create the pressure difference required to move air through filters.
delta-fan.com/products/dc-axial-fans.html
I have a feeling that the 60dB noise might get annoying.
So that’s at zero airflow. Let’s not guess though, lets do the math. If you look on the graph, bottom page, https://www.delta-fan.com/Download/Spec/AFB1212GHE-CF00.pdf going across from 25mm pressure drop of the filter, we’ll see it’s about at 0.5 m^3 a minute, about 15cfm… this seems adequate to keep up with a personal inspiration rate of about 400 cubic feet an hour. (Note you’ll see lower figures for air requirement per hour because they are for amount actually consumed, not the amount that passes through your lungs) if you had the fan pointed at you.
My personal preference would be to filter the entire volume of the room at least 4 times an hour, due to remembering reading something about the risk of catching virus from aerosols doubling every 15 mins of exposure. Can’t source that ATM.
This is all standard procedure for selection of components. Use the curves to choose the fan that comes closest to your desired criteria. Lots of people using various of the 1212 for filtered airflow applications, due to various levels of static pressure available. I’ve seen a lot of them run lower than 12 VDC, ~8 VDC.
And anyone designing for fine droplet filtration should be aware that the sieve model of filtration is not the one for fine droplets. 3m is the source for learning how file droplet filtration actually works.
Or you can go this more elaborate route with a Box Fan:
https://www.youtube.com/watch?v=aw7fUMhNov8
At my work we’ve actually tested using the noctua industrial fans, both the 12v and 24v ones, the biggest available from them basically. They don’t pass nearly enough air through a proper hepa filter (E or H class). There’s a reason they either use very very loud fans (vaccum cleaners) or very large heavy ones (hvac) when they use hepa filters. Even home purifiers like the Xiaomi ones use a very big filter (more surface area) and large diameter fan to get the required airflow.
Either way, under almost any circumstances you’re going to be much better off 3D printing clips that allow you to attach a 20x20x1 furnace filter to a $20 box fan.
Box fans are powerful enough to still have fairly decent airflow when pulling through a filter.
https://www.thingiverse.com/thing:2722621 – I have a few of these on a box fan, although at some point I need to redesign them so they’re a little more durable. (not my design, I have used it though)
Shopvac filters like this are designed to have the air sucked in through the middle, not pushed out through the middle. The pleats have less effective surface area on the inside, and will be harder (or impossible) to clean. Not to mention the fan would be sucking up unfiltered air itself.
Not sure if it matters but these shop vacuum filters are designed to have the air flowing in the opposite direction.
when it comes to projects even tangentially related to health and safety, hackaday really owes it to the public to be more skeptical of project claims.
as RW points out, this is unlikely to do anything except convert electricity into heat.
but the post will stay right where it is, because the engagement algorithm isn’t bothered by externalities.
You are missing the point. According to the headline it eliminates stale. I’m not sure how big stale is, or if it can even be blocked by a HEPA rated filter. I had thought that stale air is best treated with a dehumidifier and CO2 scrubber, but if this does it with a fan and some paper, that sounds much simpler.
Looks like a project with good intent. Inexpensive particulate sensors are available from the usual sources. One just arrived here. It’s great. While I’m not convinced of it’s accuracy, it’s presumably indicative of amount of c**p in the air. If the filter were tested systematically with one of these and proved to be doing something significant – then hurrah.
Agree stale air is stinky, unpleasant air – HEPA filters dust. Perhaps a carbon scrubber and some silica gel would be good.
I’m really taking a shot at the hyperbolic HaD headline writing.
For about $100 you can get a factory one with more cfm
Anemometers are pretty cheap, could really add some flow numbers.
Some days the comments sections are a wealth of information compared to the article. Reminds me of leadership training and even business majors differences versus engineering/science majors.
Basically, someone has to lead. I recall clearly being told that I had to accept failure… which is troublesome to me when meeting and exceeding performance is the requirement in my mind with the worse situation of just meeting objectives.
Without the leadership to get the ball rolling, albeit whatever form of embarrassing, the SME’s and followers won’t respond to do anything corrective action other than what they were doing I guess.
Interesting is I just went through a Digikey list to review what parts I have and can save on… now thinking I might add the AFB1212GHE-CF00 to the list.
To reduce the pressure drop of the HEPA filter, just use a larger filter with more surface area. You can reduce the pressure drop as much as you want with a sufficiently large filter.
As folks discover how hard it is to hack an effective air purifier from unsuitable parts, may I offer the option to BUY AN AIR PURIFIER if you’ve got nasty stuff in your shop?! And if you don’t think your 3D printer qualifies as “nasty stuff,” well your lungs don’t care what you think :D Austin Air is good, as is IQAir, and the hyped brands tend to be not great.