In the years since the start of the coronavirus pandemic, it’s fair to say we’ve all become a lot more aware of the air quality surrounding us. Many of us have added a CO2 monitor to our collection of tools, and quite a few will have an air filtration system too. There are plenty of devices on the market that fulfill this niche at varying qualities and prices, but shouldn’t a decent filter be something to make for yourself? [Naomi Wu] thinks so, and she’s put up the design for her Nukit open air purifier online under the GPLv3.
The principle of the unit is simple enough: it’s a box with an HVAC filter on the front and a set of computer fans on its side to draw air through. But it’s more than just a box, as there are three separate versions for wall-mount, hanging mount or a freestanding tower, and each one comes as a DXF file with all parts ready for laser cutting. It’s about as straightforward a way to get your hands on a well-designed and high quality air purifier as could be imagined.
[Naomi] has been quiet for a while in her familiar role as YouTube maker and guide to the nooks and crannies of her native Shenzhen, so it’s very positive to see her still active and producing projects after being warned off social media by the authorities. If you’d like to see another recent project of hers, look no further than her update to [Bunnie Huang]’s Shenzhen guide.
This seems to be reinventing the wheel. Adding a couple brackets (or a bungie cord) to the intake side of a 20″ box fan gives better air flow and is cheaper.
I sorta agree. I have a 20 inch box fan build sitting next to me. It’s taped together, really low effort, and it works great.
I still like her build tho, it’s much nicer looking, and has a wall mount. I might build one for my mom. She has an air filter with some proprietary garbo filters instead of basic 20×20.
Also a lot more noisy.
Aside from being noiser, box fans are not widely available in many parts of the world. They seem to be a North American thing, hard to get and of poor quality in Europe, for example. Never seen them in east Asia either.
These look lighter and more compact, handy for people with CFS/ME or Long COVID.
If you can save money doing it that way and don’t mind the noise, go for it.
I have always wanted to make a HEPA filter computer case. It would kill two birds with one stone. Keep the computer cool (and clean) as well as cleaning the air.
Indeed, and if you can get hold of one or two of those giant PC fans and an external speed controller you can have the choice of quiet or extreme air cleaning very easily. (I guess you could use custom fan profiles on the computer – but then the computer actually has to be on for the filter to work, which may or not be how you want to use it)
My computers are always on and crunching background tasks. It reduces thermal cycling stress.
That is a theory… And the one that I ascribe to.
I did one with a Lian Li O11 case and a K&N reusable filter (they’re washable). The case is great because it has more room on the side opposite the motherboard and 3x 120mm fans to pull from that side.
I configured all the fans to exhaust except the 3 sidewall ones and the bottom ones, those are intake. I then built a new side panel that has a slot for the filter to go into and an elevated the case on a 3″ sealed box (allowing the bottom intake fans to pull through the side filter). Then I sealed up any cracks.
I haven’t had to dust the thing in years and because the filter is large it has plenty of surface area (plus the buffer volume I added) to run without straining.
I did one with a Lian Li O11 case and a K&N reusable filter (they’re washable). The case is great because it has more room on the side opposite the motherboard and 3x 120mm fans to pull from that side.
I configured all the fans to exhaust except the 3 sidewall ones and the bottom ones, those are intake. I then built a new side panel that has a slot for the filter to go into and an elevated the case on a 3″ sealed box (allowing the bottom intake fans to pull through the side filter). Then I sealed up any cracks.
I haven’t had to dust the thing in years and because the filter is large it has plenty of surface area (plus the buffer volume I added) to run without straining.
*Sorry if this shows as a double post, the last one disappeared into the void .. so not sure if it go through or not.*
+1 to this. This has been my goal as well. It’s really difficult to try and figure out how multiple PC fans handle static pressure… And what the minimum clearances are for parts to prevent thermal problems.
My cardboard mock up put the video card horizontally, but reduced the z height down to just over the slots. I don’t know if that would have cooked the SSD or not so I never bothered to finish the build.
The issue will be that the reduced airflow makes cooling the computer adequately quite difficult. A better solution is to clean the air in the room with something like this, and raise the computer up off the floor to avoid hoovering up heavier particles.
You could probably get away with a HPEA filters on the computer if it had a lot of fans, but it might get noisy.
I made mine with a 5 gallon cat litter bucket, hepa filters and a couple of computer fans.
Are PC case fans designed to deal with that much back pressure?
I know most fan designs either prioritize pressure difference or airflow, and I thought most case fans were designed for high flow at low pressure. But adding filters increases the pressure needed.
We are in the age of watercooling radiators and air towers with really dense fins having been around for ages in the PC space – so PC fans that are good at dealing with resistance are actually quite common. I’d even suggest (though with no real evidence) that almost any PC fan you buy now will be at least moderately designed with static pressure in mind now because of it – may not be the most optimal but a design for highest flow rate isn’t going to be good for the fan builders really – too many unhappy customers that put the fan against a radiator and had it fail to do anything much for every customer that just needed to bring in some fresh air to an unrestricted case.
The ventilation extractor fans are a good bet, in my opinion. Some shy away from them because their use involves working with mains power but I think if you can wire a plug, you can use them safely.
What about the Corsi-Rosenthal box? It’s even cheaper. https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box It isn’t as pretty though.
And very noisy and bulky.
And less efficient: ~60W on high for a box fan vs ~10W for an array of computer fans. If you’re going to keep something on most or all of the time efficiency matters a lot.
Be careful of what you wish for, constant exposure to pathogens keeps the innate immune system fit, because like most body systems it really is a case of “use it or lose it”. And on a related note, the following is 100% true and supported by recent research, stinky farts protect you from RNA viruses, yep a not toxic dose of hydrogen sulfide H₂S is protective. Remember that next time your dog “gets your attention”. Living in fear of the unknown will also damage your immune system via the consequences of chronically elevated stress hormones, and also activate latent viruses. Cool project though, great for mushroom growers and people doing plant tissue culture etc.
Well, yes. If the pathogen doesn’t kill you.
What are the chances of that, literally?
That’s a good question actually, so I looked into the topic more deeply. It turns out you are right, and there is no evidence of anyone ever dying from exposure to any kind of pathogen! The chances are literally zero. Amazing.
It wasn’t the exposure that harmed them but the inadequate response of their immune systems.
Constant exposure to small particles, like from soldering smoke, is not known to keep you healthy though.
I take a little dab of mercury and lead each morning to keep my cognitive abilities in tip top shape.
When you get a moment, read Going Postal by Sir Terry Pratchett. I think you’ll find a kindred spirit in Mr. Tolliver Groat. His approach to homeopathy was… unique.
For Example: His trousers, permeated as they were with charcoal, nitre and sulphur to keep disease at bay, were the only known subject of a controlled detonation in a medical environment.
Yes we can see that clearly. 😏
Yes it is good for people who actually pollute their environment and need to mitigate that.
Citation please! See the recent JAMA brief on immunity theft also.
I wish you could easily purchase these enclosures. I live in an apt and not easy to get wood cutting/fab done. A buddy made some to fit the Lasko 20″ window fans but they don’t work well with the pressure drop, low speed is still pretty loud and fast. So using PC fans could be better.
It’s simply a PC case without the I/O. So check local stores for a cheap tower with lots of fans, mount an air filter or two, and orient all the fans to create a negative pressure.
Could you post a photo of your build? It’s not exactly clear how you’re creating the airtight seal to the two filters? Or how you’re making the additional holes for the extra fans?
You can! https://www.cleanairkits.com/
By going with 12v fans is a mistake due to the relatively low pressure they have which will limit their effectiveness. Use an LED driver and hook up some industrial grade 12″ fans for significantly more airflow and pressure.
I was looking at the moss filters and seeing about using a 5 gallon cleat water bottle as a giant green house for the moss and adding moisture and a slow fan to force the air through the moss to allow the live moss to capture foreign particles
My filter kit just arrived today! I had the wood pieces professionally cut from one of those online laser cutting places. And…nothing fits. I looked at the DXF files, and figured out why: the length of the slots are exactly the same length as the tabs. Even worse, the slotted holes are exactly 3mm wide, which definitely will not fit 3.175mm (1/8″) thick material. I spent 30 minutes filing, and it still doesn’t fit together.
It’s unfortunate this design wasn’t toleranced at all. Testing would have quickly caught these problems.
I made something a bit heavier duty for our woodshop with 4x 20×30 k&n filters and a beefy ducted blower fan mounted on top. Not HEPA, but cleans the air very quickly while sanding or CNCing. Also a breeze to clean with a shop vac.
Originally used a box fan, but learned from matthias wandel that air can actually get sucked in through the corners on the front of the fan. So even if it seems like you’re getting good flow coming out, the air might just be doing a U turn on the front and simply skipping the filter. You can cover the corners, but box fans aren’t really designed to handle that much of a pressure difference. Ducted or centrifugal blowers are your best bet if you want to maximize suction through your filters and keep your CFMs high even as they get dirty.
Depending on the filter, you could end up sucking too hard with some of those blowers; if you do then the filter will pass too much of what it’s supposed to be filtering out, and you should use a greater area of filter. Good computer fans can represent plenty of flow rate depending on the size of hepa filter.
Missing a few probably obvious details but, do you configure all of the fans to blow? Do you wire them to a fan controller?
If you make the fans suck through the filter, then they stay clean. The way you control speed is up to you; if you get 4-pin fans you can get very good speed control with a controller. Any fan will run at varying speed if you vary the voltage, though it won’t be able to go as low of RPM without stalling out as with a controller.
For my wood shop at home, I found a 24″ industrial 3 blade fan in a dumpster… Cleaned it up and mounted it on a 6 sided cube frame… Other 5 sides have 2 20″ filters, rotated 90 degrees. On a timer switch, it is a beast!! Clean the cake off the external filter every so often. It really filters the air!!
There is a group of people in China called Smart Air who have been doing a better version of this for over 10 years now. Take a look at https://smartairfilters.com/en/about/our-story/
They have done tons of experiments and posted all the results on their blog if you look back through the archives.
These are MERV 13 which is much lower filtration than HEPA H13, just in case someone misread that like I did. The allergy/virus benefit is lessened, though it supports a higher flow rate. You can get hepa filters for slightly less than this, though with presumably noticeably less area even despite the higher density. I used the ones meant as cheap replacements for levoit 300 series filters, which have a central hole similar sized to a 120mm fan’s area. Then it only takes a plank of wood with a hole in it to give you something airtight to use to attach a higher-speed computer fan. The air flows along a very evenly defined path without backflow, unlike some box fan ideas. Since I had an entire board to use, I made a box to hold the electronic bits and cut a groove into which I can place one of those “bladeless” fan things – it muffles the sound and when I turn the fan up to higher speeds, can be used like a weaker version of those fans – but otherwise you’re better off without the excess restriction. I have been using it on lower speeds and changing the filter every few months; I think I may try adding prefilters next to extend the lifespan.