[HN Gopher] The Cuboid: A DIY air purifier that's better than a ...
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The Cuboid: A DIY air purifier that's better than a box fan
Author : dynm
Score : 140 points
Date : 2021-02-26 14:29 UTC (8 hours ago)
(HTM) web link (dynomight.net)
(TXT) w3m dump (dynomight.net)
| gregschlom wrote:
| One thing that people never talk about the box fan air purifier
| design is how it _pushes_ air through the filter, rather than
| pulling it. If you look at any commercial air purifier, you 'll
| see that they pull the air through.
|
| Pushing the air through the filter has the major downside that
| some of that air will bounce back out, and may help disperse the
| dust and bad particles that have been accumulating on the back
| side of the filter.
| rachelbythebay wrote:
| IQAir GC MultiGas models do both. There's the 'prefilter' on
| the bottom (inlet), a big fan in the middle, and a bunch of gas
| filter canisters on top.
| qw3rty01 wrote:
| The internal components also don't get dusty if it's sucking
| instead of blowing air through the filter
| chrismeller wrote:
| Most designs I've seen have it pulling. Pressure attaches it,
| rather than tape.
| Tostino wrote:
| Yeah, you can just as easily make it a puller design. I made
| mine not long ago, simply taped a MERV13 4" filter to the back
| of a 20x20 box fan. Works like a charm, no dust getting pushed
| off the filter.
| jdhawk wrote:
| put the filter on the other side of the fan?
| aidenn0 wrote:
| All articles I've read on DIY box fan purifiers suggest sealing
| the filter to the fan with tape; the box fan filter they used for
| this definitely does not do so.
| dynm wrote:
| There's experiments on this in a different post!
|
| https://dynomight.net/2020/12/15/some-real-data-on-a-DIY-box...
| sgc wrote:
| The one error in that post is he worries about wearing out
| the fan. If air flow is restricted the fan is doing less
| work, and will last longer while consuming less electricity.
| An easy and fun experiment.
| mnw21cam wrote:
| But it may overheat due to a lack of cooling airflow.
| wgjordan wrote:
| "Advice" section has an unfinished sentence ('you')
| carabiner wrote:
| Most important thing is to buy these HEPA filters now. They will
| all sell out next fire season.
| bluGill wrote:
| they should be sold out now. They reduce covid in the room.
| Granted they probably reduce your chances of getting covid by
| only 5% compared to not having them, but unless you are one of
| the lucky ones who got a vaccine a few weeks ago that is one of
| the few things you can do.
| acidbaseextract wrote:
| Great site! I love the "What happens if you drink acetone?"
| article: https://dynomight.net/2020/09/14/what-happens-if-you-
| drink-a...
| grawprog wrote:
| I accidentally drank acetone once. It tasted like icy death. I
| learned after that hastily, worried i was going to die, you can
| consume up to a pop can's worth and not suffer ill effects as
| your body can actually break it down.
|
| It's not a very pleasant experience though.
| 52-6F-62 wrote:
| Would the experience be similar to a hangover? Or is my
| understanding biology that bad?
| jessaustin wrote:
| It's difficult to imagine how one could accidentally consume
| more than a swallow.
| sgc wrote:
| You think you are shotgunning a beer, but it's an acetone.
| Happens all the time.
| nightfly wrote:
| I've had a family member take a swig of gasoline from an
| old beer bottle while working on a car.
| danudey wrote:
| The obvious fix here is not to store your molotov
| cocktails next to your regular cocktails.
| jandrese wrote:
| Personal Note: Stop storing acetone in beer steins on the
| dining room table.
| function_seven wrote:
| So my problem with acetone is how quickly it evaporates.
| I figured that cooling it down would slow the rate, so I
| kept my beer steins of acetone in the refrigerator.
|
| Still didn't prevent accidental chugging. Any other
| suggestions?
| laurent92 wrote:
| I suppose you know what you are doing, but high risk of
| explosion/fire with the fumes, that is why the original
| container usually have a correct seal, the beer bottles
| don't. Twice treacherous:
|
| - For most gases, the stoechiometric proportion is very
| low (6-9% for methane -- won't ignite well above that) so
| it's not like you have to keep a large quantity to be at
| risk,
|
| - Artist houses and painting schools often burn because
| rags are kept in a corner and self-ignite.
|
| Maybe not valid for you, maybe I've just heard horror
| stories ;)
| wiml wrote:
| The other classic "rags in a corner" ignition source is
| that drying oils, ie vegetable oils like you'd use for
| paint or wood finish, generate heat as they "dry"
| (actually polymerize).
| donclark wrote:
| Upon searching for videos, there is a similar design
| "Comparetto":
|
| https://www.youtube.com/results?search_query=cuboid+air+puri...
| giantg2 wrote:
| I would have liked a little more detail in the fan/filter trade
| off section.
|
| It's not entirely true that you need a loud fan to move more air
| through a filter. That looks like a duct booster fan in the
| picture. Those have very weak (and usually inefficient) motors
| and impeller design. You could use a PSC motor running a squirrel
| cage fan. PSC motors are efficient and can handle higher torque.
| The torque can be used with an appropriate fan/impeller design
| (like a squirrel cage) to handle the pressure drop through the
| filters.
|
| That said, the duct boosters are cheap and readily available.
| Here's a homemade hybrid flow/glove box for inoculating mushroom
| substrate.
|
| https://postimg.cc/NKrGGRFH
| ydant wrote:
| The article does address the type of fan and tradeoffs:
| > An 8inch (20.32cm) diameter inline duct booster fan ($30).
| > Inline duct booster fans are fairly weak fans often >
| used to help with grow rooms or range hoods. An inline >
| duct fan would probably perform even better (see the >
| discussion) but at a higher cost. The one I bought > is
| rated to push around 12 m3 of air per minute.
| giantg2 wrote:
| Yeah, but they didn't really go into fan efficiency with
| pressure drops or motor efficiency.
|
| One other thing is longevity and even safety. Maybe their use
| of multiple filters reduces the pressure enough. But if it
| doesn't, then the motor will wear out pretty quickly and
| could potentially start a fire if it's generating enough
| heat. The motor in my setup gets pretty hot when running at
| full power.
| manishsharan wrote:
| Can any of these DIY filters eliminate the odours from cooking
| fish ? I love fish but I cant stand the smell of it cooking -- it
| literally gets into everything.
| jjeaff wrote:
| Pretty much your only and best option for odors is going to be
| active charcoal filters. Which you can by and attach under the
| filters in any regular air filter or diy filter like this one.
| I have one behind the filter in my hvac air intake.
|
| From testing I have seen, baking soda does nothing.
| netrap wrote:
| Looks like the same concept as the BlueAir 211+ but way cheaper!
| Unfortunately, for me, it needs to look somewhat nice.
| TrevorJ wrote:
| Seems like that issue would be fairly simple to solve.
| dynm wrote:
| I think a good solution would be some kind of box that you
| could just put over the whole thing while maintaining
| airflow. Ideally you'd also be able to sit on it or use it as
| a kind of side table.
|
| It wouldn't be too hard to build something, e.g. out of wood,
| to do the job, but that would surely increase the total build
| time and tools needed by at least 10x.
|
| There's got to be some cheap and widely available product out
| there that you can just buy and use. (Something from IKEA?) I
| looked around but haven't found any good options so far.
| Meleagris wrote:
| This Old House made a great video on the subject of using box
| fans with filters:
|
| https://youtu.be/aw7fUMhNov8
|
| I've been using the design they showed in the video, but I will
| definitely try this duct-fan method, saving electricity is always
| a bonus.
| alhirzel wrote:
| "Resembles IED", a most interesting metric
| abeppu wrote:
| Regarding power consumption, the calculation seems to assume you
| run the thing constantly. Is it a mistake to run these things
| constantly? Presumably if it does that good a job pulling out
| incense, and if you're not constantly smoking or burning stuff,
| and you're in a reasonably sealed building (and if those
| assumptions don't hold, why would a filter help?), you should be
| able to get most of the benefit from only turning it on when
| something has added a bunch of particulate matter (like, you're
| cooking or cleaning, or you opened the window and there's pollen
| out)?
| chrismeller wrote:
| Why is the comparison 3 small filters on a box fan? One large one
| fits perfectly over the box fan.
| klyrs wrote:
| I found this strange, too. They don't actually cover the fan as
| well as the intake to the cuboid. I think comparing to the
| single large filter would be more honest.
| ktta wrote:
| The fan will burn out if you use a single filter. See my
| other comment in the thread.
| klyrs wrote:
| Can't argue with that, I've got two burnt out box fans ;)
| dicerson wrote:
| I saw that pic and immediately wondered why they didn't seal
| off the areas of the fan that the filters didn't cover. I'm
| willing to bet that had a negative effect on the box fan
| setup's performance.
| dynm wrote:
| I'll take that bet! https://dynomight.net/2020/12/15/some-
| real-data-on-a-DIY-box...
| ktta wrote:
| If a single filter is used, the fan might fail. Using
| additional filters decreases the load on the fan, because there
| are more ways for the air to come in, so the torque required
| for a certain CFM value (which stays fixed for a certain fan
| speed) is lower.
| neolog wrote:
| The same filters were used in the second trial. If they perform
| worse over time, that seems like an unfair comparison.
| bluGill wrote:
| Typically they filter better over time, but at the expense of
| less airflow. Thus it is really hard to draw any conclusions.
| lmilcin wrote:
| The barrel-shaped channel can be completely within the cube. The
| air will just go around.
|
| The fan should be chosen for static pressure. Typically static
| pressure fans feature less angle of attack and more blades.
|
| Sealing is very important. Make sure to use tape anywhere between
| the filters and make sure that the fan fits well its barrel.
| boromi wrote:
| What kind of fans are you recommending given the ~30$
| constraint? I'm not exactly sure what static-pressure fans are,
| care to explain.
| danudey wrote:
| Static pressure in fluid dynamics is just pressure, so the
| parent poster is suggesting a fan that can produce more
| pressure (in other words, uses more force to move air).
|
| For example, if you're just setting up a simple "fan blows
| air through filter" setup, more static pressure is needed to
| force more air through the filter; a fan that can move 30
| units of air per minute might not be able to move 30 units of
| air per minute when an obstruction, like a fine-particulate
| filter, is placed in front of it.
|
| If you look at the fan used in the article, you can see that
| the fan blades don't reach all the way to the outside of the
| cowling, meaning that some air could actually make its way
| through that gap, and that the blades are large but sparse,
| meaning there's more room for unwanted airflow; in other
| words, the air flow you're getting might not all be coming
| through the filters, but rather flowing around the fan and
| getting blown back out.
| mnw21cam wrote:
| The article is recommending a larger fan to move more air.
| However, the opposite may be true, as smaller fans tend to
| have a higher static pressure.
|
| Given that the airflow is only 1/4 of the rated airflow for
| the fan, it seems that the resistance of the filter is
| causing a pressure drop across the fan that is fairly close
| to its static pressure. Adding another fan in parallel to
| try to move more air likely won't make an iota of
| difference, as the pressure drop will be about the same.
| However, giving it a fan with a higher static pressure
| likely will increase the airflow, even if the rated airflow
| is lower. Or, add a second fan in series with the existing
| fan (with appropriate distance between the two to smooth
| out the turbulence), which could double the static pressure
| and therefore the airflow. Yes, adding more filters would
| also help.
|
| There's a reason that most fans in air filters are
| centrifugal (radial) fans rather than axial fans - they
| have a higher static pressure.
| groos wrote:
| Fans are rated by CFM (cubic feet/min) but one interesting aspect
| for builds like this is static pressure because of the need to
| push air through filters. I'm not sure you would be able to find
| a static pressure number for commercial fans.
| tgsovlerkhgsel wrote:
| To be precise, you need the intersection between the pressure-
| vs-flow graphs of the filter and the fan.
|
| Finding those for fans is _somewhat_ doable if you're buying
| fans from a components store like Mouser, but that doesn't help
| that much if you don't also have at least some values for the
| filter.
|
| Actually, for fans, you'd ideally want a 3d graph of pressure-
| vs-flow-vs-noise.
| [deleted]
| Netcob wrote:
| I connected an SDS011 dust sensor (didn't check US prices, but
| I'm guessing ~20$) to a raspberry pi and then used remote
| controlled power sockets to switch my air purifier on and off
| based on some limits I set.
|
| Of course when building the purifier yourself, it might make
| sense to attach the sensor directly, use something like an ESP32
| and maybe control the fan speed based on pollution levels.
|
| Here's some Grafana graphs: https://i.imgur.com/wYjERxW.png
|
| The dust sensor isn't absolutely silent due to the tiny fan, and
| the purifier obviously isn't either, so I have a "silent mode"
| that turns off both. There's also a CO2 sensor that shows you
| when I opened the windows. For some reason, dust didn't spike
| when I opened them in the afternoon, only in the morning and last
| night. The purifier is a BlueAir Pure 221 which is built a lot
| like the one in the article.
| everdrive wrote:
| What accounts for the CO2 cycling?
| Netcob wrote:
| Me opening my windows for a few minutes, but leaving them
| closed in general.
| jxy wrote:
| I never measured indoor CO2 level, but yours approaching
| 1400 ppm seems to be alarmingly high. I thought any level
| above 1000 ppm requires some intervention.
| RL_Quine wrote:
| It's also notable that CO2 sensors utterly suck, none of
| the consumer ones do absolute measurement, they assume a
| baseline and calibrate their output to that.
| fpgaminer wrote:
| Curious. I have a HPMA115S0-XXX dust sensor and I can't hear
| any noise from its fan at all.
| thombee wrote:
| Bit off topic, but seeing a lot of talk about air purifiers here
| recently. I've never even considered purchasing one, but now my
| interest is a little piqued. I've never really felt my air to be
| unclean, and I don't really have allergies. Still worth looking
| into? Anyone w experience tell me any benefits? cheers
| epmaybe wrote:
| I bought one cause my wife had bad allergies in our bedroom
| even after cleaning, most likely because of our dog.
|
| I get itchy eyes with allergies, and I don't think the purifier
| helped at all. Just my anecdote. An allergy pill helped me more
| haha.
| Netcob wrote:
| Look up the air quality in your area. If it's bad, an air
| purifier is probably a good idea for your long-term lung
| health.
|
| If you leave your windows open for longer periods of time, then
| an air purifier might be ineffective.
| danudey wrote:
| We live in British Columbia, and now that we have "wildfire
| season" every year, it's very easy to tell the difference
| between good air and bad air. I suspect a lot of people are
| jumping on this as well for the same reason - Silicon Valley is
| in California, and they're harder hit than anyone else with
| this.
| bogdanu wrote:
| Just because you don't have allergies now it doesn't mean
| you'll never have one. Until a few years ago, I've never heard
| of ragweed alleries. Guess who's allergic to it now?!
| cmckn wrote:
| I bought one last summer when the air quality outside was
| terrible (Pacific northwest, fire season yay). It was actually
| necessary, the air quality in my home had gotten really bad,
| like to 200 AQI. I don't have asthma, allergies, etc. but my
| esophagus was irritated and I felt generally awful.
|
| I got the Coway purifier that's currently the Wirecutter pick.
| It was about $150, has a HEPA filter and an ionizer. The
| replacement filters are pretty cheap. I leave it on 'auto' in
| my bedroom 24/7.
|
| Am I getting great benefit from it right now, when the AQI
| outside is 10? Probably not. Opening your windows for 5 minutes
| every morning is totally sufficient to keep your indoor air in
| the green. But it will be great to have around when the
| inevitable fires start later this summer. If you're in a
| similar region, pick one up while they're cheap and in stock!
| driverdan wrote:
| Use 4" thick furnace filters. They cost less than specialized air
| purifier filters and flow a lot more air.
| ska wrote:
| They don't filter the same things, which may or may not be an
| issue for you.
| Der_Einzige wrote:
| That's BS. Look at the MERV rating. MERV 14 and above filters
| out increasingly large quantities of particles at the sizes
| of COVID virus particles and pollen. 4 inch thick furnace
| filters can easily be rated above MERV 16 (I run a MERV 16
| filter in my home). For most peoples purposes, they are
| almost as good (and far cheaper) than HEPA.
| ska wrote:
| > For most peoples purposes, they are almost as good
|
| That's what "may or may not be an issue for you" meant.
| Scene_Cast2 wrote:
| Do they not? They have the same ratings scale, based on
| filtering certain particulate sizes.
| CarVac wrote:
| http://imgur.com/a/u1Ti7
|
| You can also build your computer into an air filter like I did.
|
| I'm currently running MERV 13 filters and it pulls over 100 CFM
| at a very livable noise level, currently equipped with Noctua
| NF-A12x25 fans.
|
| The computer stays very cool but also incredibly clean.
| dynm wrote:
| That's freaking brilliant. You simultaneously cool the CPU,
| keep the CPU clean, and clean your air. I might be
| sslliigghllyyy worried about the filter decreasing airflow if
| you used a HEPA filter, but probably not much of an issue with
| a MERV filter.
| whoomp12342 wrote:
| meh, just buy more fans. Also, putting a filter coming in
| will significantly reduce the amount of dust that your fans
| and other parts suck in
| dynm wrote:
| More (or more powerful) fans will definitely work, but
| isn't "free" in terms of noise or electricity. Unlike a
| normal desktop it doesn't work to put this one in a
| different room. Still, with a MERV filter, I doubt it's too
| big a deal.
| CarVac wrote:
| I'd be all for a case manufacturer to clone my design in
| metal but I doubt that common HVAC air filter form factors
| are the same around the world; you'd either need an oversized
| design with adapter plates, or many case size variants.
| Scene_Cast2 wrote:
| Silverstone MM01 is such a PC case, it's been out for a
| while
| Forbo wrote:
| $500+ for the case, $160+ for new filters. Ouch.
| CarVac wrote:
| I knew the Mammoth existed when I made mine, but it's not
| what I wanted.
|
| The Mammoth is designed to withstand water spray and dust
| and still cool the components satisfactorily, while mine
| is designed to clean as much air as possible for the
| synergy with computer cooling.
|
| Additionally, I wanted to use HVAC filters due to their
| price/availability and large area, and I wanted a
| vertical motherboard like the Raven so I could access all
| the motherboard ports on the top.
|
| If anybody would do it, I think Silverstone would. They
| think out of the box.
|
| Modern design considerations would be allowing for top-
| mounted radiators on the exhaust side, and having the
| power supply attached to the motherboard tray so you
| could route power cables behind.
| tyingq wrote:
| Custom cut acrylic (or other plastic sheet) might be an
| option too. Pretty cheap if you stick to rectangles, though
| there are places that will cut based on your 2D vector
| files also.
| nullserver wrote:
| When I was a teen I worked a few months in an office where
| people chain smoked constantly. My computer kept dying, and I
| started ranting about how much old these computers were. Based
| on how much yellow gunk was inside it. Like quarter inch layer
| on everythin.
|
| I was informed they were less then six months old. Resigned by
| end of month.
| edoceo wrote:
| This is super well written and explained and shows the research
| and methods used.
| pugworthy wrote:
| The "I built a better DIY air purifier" trend really reminds me
| of swamp coolers for Burning Man, except it doesn't yet have its
| FIGJAM.
|
| Both have people doing interesting experiments, suggesting
| alternatives, pointing out inefficiencies, etc.
| tyingq wrote:
| Despite the low cost construction, it actually looks decent. Swap
| in some black bungee cords and it would look even better.
| jackfoxy wrote:
| This sew shop in L.A. https://suayla.com/pages/our-mission was
| claiming you could use a double layer of common blue shop towels
| as an N95 filter. I can't find that information on their site
| anymore.
|
| If it is N95 effective, to my understanding it's pretty
| equivalent to HEPA air filter standard. It's on my to do list to
| make an indoor filter this way. If nothing else I hope to reduce
| the volume of indoor dust that settles in my office. Cheaper than
| HEPA filters.
| TylerE wrote:
| HEPA is more like N100 than N95.
| ipsum2 wrote:
| It was probably removed for being inaccurate. If using blue
| shop towels worked as well, then manufacturing N95s would be a
| lot simpler.
| jacob019 wrote:
| Shop towels are not going to offer anywhere near the filtering
| performance of melt-blown polypropylene for N95 masks.
| colechristensen wrote:
| HEPA is 99.95% of particles > 0.3 micrometers
|
| N95 is 95% of particles.
|
| They aren't equivalent.
| starpilot wrote:
| It takes a lot of specialized aerosol science equipment and
| expertise to measure the percentage filtration, so it's
| questionable that they could claim to replace N95 filter with
| towels.
| avmich wrote:
| > I wanted a new design that preserves the best aspects of using
| a box-fan: ... No proprietary parts.
|
| Does HEPA filter qualifies as a proprietary part? Can it be
| created at home?
| klyrs wrote:
| It's a commodity part that you can pick up at many hardware
| stores, and if the filters you get are different size from the
| article, it's easy to modify the design to match. Contrast to,
| say, a Dyson air purifier: you need to buy Dyson-brand filters
| (or a knock-off).
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(page generated 2021-02-26 23:00 UTC)