Thanks for the article! Using incense for testing seems like a good approach. And yes, the lack of difference between "taped" and "non-taped" is definitely interesting. I'm wondering if this might be in part because of your choice to use thin and small HEPA filters instead of the more common thicker and full size MERV filters. Intuitively, what matters is the product of the efficiency of the filter and the amount of air passing through the filter. It's possible that because the resistance of the small HEPA filters is so high, the unfiltered air passing around the filters generates a lower pressure in front of the filter than the non-moving air after the back is taped.
I recently built up a couple similar box fan filters, but using 20"x20"x5" MERV 15 filters bought "used" off Amazon for about $20 each. Note that the total surface area of the folded filter matters for air resistance, not just the height and width of the filter. That is, depth matters, because all else equal the folds increase the amount of filter area.
I sealed well, because I thought it would matter. I removed the back plastic grill to reduce resistance a bit more, and also added a cardboard cowling on the front of the fan, based on the research here: https://www.texairfilters.com/how-to-improve-the-efficiency-.... The idea is that with a high resistance filter on the back, in the absence of cowling you get unhelpful recirculation from the front corners of the fan, although maybe this recirculation might actually be helping reduce pressure in front of the filter in your taped example?
I haven't done any air quality measurements, but I think the system is working the way I'd expect. Noise at low speed is tolerable when in another room, but I only use higher speeds when leaving the house. I'd be interested in more details about your particulate monitor, especially if you are satisfied with it and if it's available in the US.
The problem with ozone generators in cars is that they often react with some plastics and do more harm than good. Unfortunately they are the only way of getting in the nooks and crannies and inside the ac vents to clean mold and that kind of stuff.
I’ve had steering wheels turn to gel using ozone and they smell funkier than what was in there.
Most things that smell are very very small particles not captured by even HEPA filters and require a different kind of filtration. Most commonly activated carbon is used, either as granule or deposited on fibers.
HEPA filters are actually more efficient at capturing very very small particles (<0.1 micron) than they are at capturing simply small particles (≈0.3 micron). The tiniest particles are light enough to be captured using electrostatic forces rather than the more typical mechanical filtration that is effective at capturing large particles.
More precisely, many odors are not particles at all but rather gases/vapors. Activated charcoal can capture larger organic molecules because it has an incredibly jagged/porous surface - just 100 grams of activated charcoal provides over 1,000,000 square feet of "effective" filtration surface area.
Yes, that's true that HEPA is very efficient at particles in the 0.01 to 0.1 micron range. It may also be below that, but I personally haven't seen that data. But because HEPA fails to filter gases/vapors, its performance must fall off before 1 angstrom = 0.0001 micron.
> odors are not particles at all but rather gases/vapors
I think the confusion comes from people referring to "particulate" as particles of >= 0.01 micron, whereas in physics we say that gases/vapors are also composed of particles. They may be single atoms floating (can't actually come up with an example though) or small molecules like O^2, CO, etc, but I'd still call those particles.
I don't know any way to filter NO2 effectively from air, and I have tried practically all commercial air filters with the largest carbon filters on the market. The worst parts of air pollution cannot be filtered out without industrial devices (that are part of the air filteration system) as far as I know.
NO2 and other acidic gases are typically filtered using activated alumina balls impregnated with an oxidizing agent such as potassium permanganate or sodium permanganate.
There are residential air purifiers available that use this in combination with activated carbon for their gas stage.
I bought IQAir and tried multiple filters (I think they use potassium permanganate), and I wasn't able to significantly reduce NO2 in my room. 3M masks similarly may work if the toxic gas concentration is far above the high levels, but I couldn't get it from normal/high to low levels.
Maybe you are talking about an integrated air filtration system, as I haven't tried that yet (though I'm planning to try it).
That 200 USD fine for smoking in hotel rooms? What do you think happens afterwards? Buy a bunch of activated carbon filters? Or get a professional ozone odor removal provider to roll in their with their gear?
I lit a candle in a room where I had one running, and the filter darkened pretty quickly. It seemed to have caught some of the smoke particles, which can be pretty small at under a micron.
Smells are usually VOCs (volatile organic compound). Those need to be trapped in an active carbon filter. An alternative is to destroy them with ozone (also called "activated air", "ionized air"), but to do so one needs ozone concentrations that are unhealthy for living beings. Ozone is very unhealthy! Ozone is generated electrically or via UVC lamps. An especially common and harmful VOC, formaldehyde, can be destroyed by the extremely overpriced dyson air filters via their cryptomic technology.
As most home woodworkers could confirm, a filter-on-a-box-fan works wonders in a (saw)dusty garage. Even after sanding or sawing MDF, the air is clean after about 10-15 minutes. From personal observation, I'd suggest that non-taped is a good idea, as any non-filtered air is routed through the fan to help overall circulation; ideally you want to displace all the air in the room quickly.
Right the heavy stuff falls pretty quickly. The light particles will take quite a long time, and in the meantime, you're potentially breathing all that. I use a large cyclone for the machinery, a filter-on-a-fan, and a mask. My shop is a lot cleaner than it used to be, and I'm sure my lungs are too.
Love the testing. I think the taped/non-taped results may diverge as time goes on and the filter becomes loaded. The static pressure of air filters approximately doubles over the lifetime of the filter, and in an unconstrained system more and more air will be going around the filter instead of through it.
I wish there were multiple reps of each experiment, especially with how noisy the results were and the difficulties of reproducing smoke
Regardless, this project actually makes me feel better about buying my fancy air filter
Instead of buying 2 filters (both HEPA), a fan, and a poorly calibrated air quality sensor for $150 like the author, I bought an air purifier that contains 2 filters (1 HEPA, 1 activated charcoal) a fan and a poorly calibrated air sensor for $153.
However since my air quality sensor is integrated with my purifier, it only pulls ~60 watts at the times when I'm cooking or if something is on fire. That probably saves me $50/year on electricity
Yeah, same thought. Something like the Coway air filter ( https://www.youtube.com/watch?v=zxiDrEnjYEo ) regularly sells for under $200, and it is going to be much quieter than this option. It also has been tested fairly extensively from what I've seen, it's EnergyStar approved, etc, and it has a built in sensor. It doesn't look too bad either.
But I understand the point, especially in times when you can't find a purifier.
Exactly! I have the uglier but slightly cheaper version of that air purifier (the Coway Airmega 200M). I think the faceplate is the only difference. I forgot to mention in my original comment that it also has a prefilter for larger dust particles, which I imagine probably improves the lifetime of the other filters.
Be aware that the air quality sensor on most units is a cheap VOC sensor. It detects gasses, not particles. It'll trigger if you fart near it or cook something odorous, but not for dust or smoke.
I have the Winix 5300 and 5500 purifiers (which I highly recommend), and typically run on mode 3 out of 4 because it pulls about 12 watts (and is quiet) but is not massively different airflow than mode 4 which draws about 70 watts (and is noisy).
Another way to do it is to bubble the air through water. As a kid, we did an experiment where a cigarette was "smoked" by attaching a tube to the cigarette filter, the tube exited at the bottom of a flask filled with water, and a pump would suck the air from the top of the flask.
It didn't take long before the water would turn black.
Quite a turnoff for wannabee smokers, which was the obvious point of the experiment.
It's the same idea as the Rainbow vacuum cleaner, which uses a tank of water as its filter.
That's essentially a Shisha you built there, so smoking that way is a thing ;) The tobacco is different, as is the heat source, but I can confirm that the water still turns rather unpleasant.
Another way to do it is to bubble the air through water. As a kid, we did an experiment where a cigarette was "smoked" by attaching a tube to the cigarette filter, the tube exited at the bottom of a flask filled with water, and a pump would suck the air from the top of the flask.
"We built a bong and discovered that bong water is really nasty."
The limitation for me would simply be the appearance factor; I want my filter to blend in quietly, not to draw attention. I think appearance and noise are part of why people pay so much for fancy purifiers.
Also, I imagine a centrifugal fan would draw less electricity per CFM under load (air resistance through the filter).
With the same throughput radial fans are much bigger than an axial fan. But they can deliver differential pressures in the range of several 100 Pa, which axial fans cannot.
Depends how long you run it and on what speed. I seem to remember we were working on the basis of changing it every three months if we ran it continuously during that time
What I am wondering about: I worked with and designed clean room equipment in the nineties. I remember that HEPA requires a considerable pressure difference which cannot be delivered by an axial fan. You'd need a radial one which can deliver a considerable differential pressure, at cost of throughput (where the axial fan shine). If you strap a HEPA to an axial fan and seal it, the fan runs effectively "empty", i.e. it displaces only little air which most likely even doesn't pass the filter. That's why HEPA filters work in vacuum cleaners since they have radial fans. I am astounded by the results of the post.
I tested simply with a laser. In a normal room you can see the laser beam in dark. If you have a good purifier, you can't.
Especially given the relatively wide range for age and consequently construction type. I've found that newer drywall construction tends to be more dusty in my limited experience than well maintained plaster and lath.
My house has tile floors which get visibly filthy really quickly. I have a roomba and I personally clean the floors quite often manually. In my parents house which had wall to wall carpet, they would vacuum relatively infrequently but the same amount of dirt was likely being tracked in and around. Their house was more dusty than mine seems to be because of the fact that carpet tends to hide how "dirty" it is.
Red laser, sure, but in my experience green lasers are significantly brighter and it's much easier to see the beam in clear air (though if you're human you probably need to look down the beam to spot it, my cats can see the beam horizontally and they swat at it).
>If you strap a HEPA to an axial fan and seal it, the fan runs effectively "empty", i.e. it displaces only little air which most likely even doesn't pass the filter
This. I tried a 3M MERV 12 filter taped to the intake of a cheap $12 box fan and the airflow through the fan went to effectively zero. The fan actually was pulling more air from the front of the fan around the sides of the fanbox than through the filter. Increasing the fan speed just increased this backflow. You are spot on with a radial fan being what you want here, and I notice that basically every commercial air purifier uses such a fan.
We have tested it extensively and it is very accurate for the fraction of the costs of commercial sensors. You can build it for less than USD 20 and send the data to our cloud server or any other backend.
We also measure CO2 because if you have purifiers running you often do not have enough fresh air ventilation and your CO2 often gets very high (often >1500ppm) causing headaches and reduce cognitive performance.
We measured this in classrooms some time ago and the results were not very good.
This. I no longer have access to a soldering iron and want a bunch of these, not enough that it's worth the cost of buying equipment and the time spent making them.
I appreciate your DIY instructions, but I really dislike how your website goes through the effort of hiding what you actually sell and also how much it costs. I don't want to "contact you" to get that information. We've been long enough in the 21st century that it has become an adult, and still I keep running into this archaic nonsense.
For example, you mention your "sensor package" in the FAQ and that's it. Your DIY instructions mention the "AirGradient PCB", _but there is no place where I can buy it_. For the love of god, put a 'buy' button on your website.
They want to change what they charge from time to time so putting a price up front will force them to leave money on the table. Not gonna happen. Contact them instead.
Instead of contacting them, I will spend a little time investigating whether there's someone else I can buy from, who doesn't consider being "forced to leave money on the table" makes this a reasonable way t treat potential customers, and will choose to spend money at a less customer hostile business - or possibly do without the product.
Contacting some random "enterprise sales" team? Not gonna happen.
Increasing friction is increasing friction. The GP wants to reduce friction, and your proposal likely doesn’t do that for the majority of potential customers.
That said, too many people (myself included) are so used to being courted as a customer (or really, user to try and upsell to or datamine from) that we’ve forgotten that not everyone wants our business and custom.
Splashing some cold water on your face and reminding yourself that you’re not the centre of the universe from time to time isn’t a bad habit to reduce behaving like entitled children. I still struggle with this, but baby steps... (pun not intended)
It might not be worth it to organize a big order nowadays, PCB fabrication is already super cheap. JLCPCB (and others, but I have the most experience with them) will do 5 boards for $2 + shipping and the first order gets free shipping. I've used this service for prototyping many times and had great experiences.
I had been planning to build almost the exact same thing as what the parent posted but had been putting it off because I didn't want to draw up a PCB, so this is perfect.
Usually this means the company does not sell to consumers and is b2b only, similar to how you just can't buy something anonymously online from a wholesale distributor.
Volume sales “for homes”means apartments (or condos). “For Homeowners” is a different market. Usually there will be a different website for that market. It will need to mitigate “the customer is always right” attitude prevalent among consumers.
It looks like you're using a Plantower PMS5003. I have one of those hooked up to a Raspberry Pi and it works well but I also built a few of these with ESPs: https://sensor.community/en/sensors/airrohr/
They support the PMS but I used the default SDS011. They both seem reasonable for relative values but I'm not sure about the accuracy without proper calibration. They don't appear to give similar readings to my Plume Flow 2: https://plumelabs.com/en/flow/
I've seen references to this sensor before and find it a bit concerning that there's no information about how to properly use the CO2 sensor.
This sensor uses a SenseAir S8, which like most CO2 sensors, has an automatic baseline calibration algorithm enabled [0], which expects to see pure, undiluted fresh air at least once every 8 days. The only way to disable it is explicitly, through the MODBUS interface [1].
Leaving it enabled makes perfect sense in a business or businesslike environment because these environments will be completely unoccupied overnight and have air conditioning, which usually does a daily fresh-air purge, ensuring that the sensor will have regular exposure to fresh air.
However in a residential environment, the auto baseline calibration often doesn't make sense, especially in winter. When the windows are closed and/or people or pets are around, it's very rare for the sensor to see uncontaminated fresh air, so it will see say 500ppm of CO2 and assume it's fresh air when it really isn't. I have measured this and it's a real problem.
In a residential environment, unless you're sure you have good, frequent exposure to pure fresh air, you're better off doing a fixed calibration once a year or so.
AirGradient also seems to be a hardware-only design. The ESPHome project [2] has great software support for a variety of sensors (including the SenseAir S8, so it should be compatible with the AirGradient hardware) as well as a very well-documented hardware project [3]. After trying my own Arduino-based software and then ESP-IDF, I find esphome much more pleasant to work with.
Any CO2 sensor (part) that gives you the ability to turn off ASC should work just fine and most of them do, you just need to trigger it.
Personally, after trying out a bunch of sensors, I use the Sensirion SCD30.
As for devices, I'm not aware of a consumer device that I'd recommend. If you're willing to do at least a little bit of DIY, Watterott [0] sells an SCD30 hooked up to an Arduino-compatible MCU with WiFi, a red/green/blue indication of CO2 levels and ASC disabled by default [1].
It's an open-source hardware design and software [2] and has a few reference firmwares [3], including one [4] for MQTT.
If you want to go a little bit further, I'd recommend an ESP32 with an SCD30 and ESPHome [5]. That's what I use myself, mostly because I already had the sensors prior to Watterott's product existing.
This is certainly done with COVID-19 in mind. Is there any source that shows how effective HEPA filters are for filtering SARS-CoV-2, given that its average size is just 130nm, which is twenty times smaller than PM2.5.
HEPA is a bit of a loose term. It generally means 99.97% efficiency for 0.3 micron sized particles at some particular airflow.
0.3 micron was chosen because as noted by another commenter below, high efficiency filters typically filter better at smaller sizes than this.
A more stringent certification is EN1822, which first tests which particle size penetrates the filter the most, and then rates the efficiency based on that particle size.
With respect to viruses, a minimum of EN1822 H14 is required for use in European biological safety cabinets. An H14 filter is 99.995% efficient as it's most penetrating particle size (MPPS).
That said, it's important to realize the difference between using a filter to pass air into/out of a clean environment (e.g positive/negative pressure clean room) versus just using an air purifier in a room. In the latter case, the machine is only going to filter the air going through it, and will take a significant amount of time to turn over the air in the room, during which time it's just blowing things around.
Interesting. I only have central ventilation but my mom has central heated air in her house, in theory she could chuck a HEPA filter in front of it to get cleaner air in all of her house.
She probably has, but the heating module gives her a periodic reminder to clean it (which I then have to do because she can't reach it). It gets replaced every few years, I think she has a service contract :)
Note that this can be a really bad idea. While it might temporarily improve the air quality, extreme filtration will reduce the air flow through the system. This will in turn reduce the efficiency of the heater, possibly in a way that causes its internals to overheat and destroy themselves. Rather than "upgrading" to higher filtration, you are safer replacing whatever filter is there with a new clean one that matches the correct specs and then adding higher quality filtration separately.
I've read the same thing, that if you put a heavy duty filter on your furnace you put a heavier strain on the motor and risk burning it out. I'm not an HVAC professional so research this yourself.
Smart Air is a whole company built around a super cheap HEPA-on-a-fan, started by foreigners in China. They still sell their old DIY1.1 model for $35 shipped (in Mainland). I own and love their filters, although I miss the «smart» features of their competitors.
It would be neat to see results of a good furnace filter on the fan. Saves the cost of the bungee because the air flow holds it on pretty much, and the filters are cheaper. It is what I use in my grow house to filter the air.
You don't need a HEPA filter. HEPA is only useful when you can only pass the air through the filter once, like in hospitals. A home air filter can push the air through the filter several times, so an MERV8 is just as good as a HEPA and lasts longer.
I used a DIY filter to remove wildfire smoke from my apartment. It's just a 12"x12" MERV8 filter taped to the front of a small fan. It worked well. I periodically opened my windows to exchange the stuffy air with fresh+smokey air. After closing the windows, the filter took about 30 minutes to remove all of the smoke inside.
I build one during the forest fires earlier in the year, I bought a box fan and 6 Merv 14 furnace filters.
My best idea was cutting out the front and back wall of the box the filters came with and squishing the fan between two.
It worked well enough with the 50cm fan that it could make a 10x8m room pleasant in 10 minutes. The only improvement I would make would be buying a lower rated filter for the intake since it got clogged up with a lot of large particles that were kicked up by the fan.
I was planning a big build with an impeller fan, but there is something to be said for a solution so stupid that I can rebuild it in 5 minutes with $50 in parts.
water filters also have the incompatible proprietary filters problem. I wanted to try filtering some water so I could make coffee that wasn't bitter but every water filter seemed to want me to buy a bunch of plastic to go around a replaceable filter. In the end I settled on pyrolysized cherry wood branches, (activated carbon, or biochar). It seems them carbonated bamboo is also used in tea making. It worked but it certainly took a long time leaving the sticks in the water.
In the spirit of DIY/OSS here, I think ideally you’d want to emulate something like a Berkey water filter, these are basically just steel tanks with large threaded cylindrical charcoal filters (2” diameter, ~10” long) that use gravity to pull the water from the top to the bottom.
A simple 3D printed housing filled with some charcoal/carbon media to trickle filter like a Brita would be interesting to see its effectiveness.
At my parents house, we set up a whole-house water filtration system by repurposing water softeners. empty the guts of one, refill with aquarium supply activated carbon, then adjust the electronics to your liking and you're good to go. Those systems are designed to run 24/7 and soften/filter all the water going into your house.
There are standard sizes and housings for water filters. No fridge uses anything standard, but you can find them. you need some sort of plastic (or at least something food safe) around the filter though.
> Air purifiers can be expensive and you've probably seen articles recommending to just put a 20" x 20" x 1" furnace filter on a cheap 20" box fan and POOF! instant cleaner air for not a lot of money. It really does clean the air pretty cheap.
> There's a problem with this though. These fans weren't designed to be run with a filter. The filter will restrict air flow which will put a higher strain on the motor causing it to use more electricity and in worse cases could be a fire hazard. The higher the MERV rating (cleaning efficiency) of the filter the more stress it will put on the fan.
> Don't worry! You can still have your cheap air purifier as long as the filter area is increased to decrease the effect of air resistance. Instead of using one 20x20x1 filter we'll use two 20x25x1 filters which increases the filter surface area over 250%. It's a little more expensive because you're using two filters instead of one but the increased filter surface area also helps the filter last longer before it gets clogged up and we're saving on energy use compared to a single filter.
I used a 25x20x4 which was easy to find. Even though I didn't do anything to stop air from flowing around the backside of the filter to the fan it still gets noticeably black fast.
But more difficult, yes? Stacking filters is very different from getting a thicker filter. The former increases air resistance, the latter decreases it. So to get the equivalent behavior from two 20x20 filters, you'd have to device some way of routing air through both of them in parallel.
> There's a problem with this though. These fans weren't designed to be run with a filter. The filter will restrict air flow which will put a higher strain on the motor causing it to use more electricity and in worse cases could be a fire hazard. The higher the MERV rating (cleaning efficiency) of the filter the more stress it will put on the fan.
I'm fairly certain the opposite is true. In fact, most rowing machines work on this principle. The easiest setting is the one where the fan is as closed off as possible because it's pulling a vacuum. Less air, less resistance, easier to row / less power required to spin the fan. If anything, fans should draw less current with air flow on the inlet side restricted.
A. Putting two [larger] filters in a 'V' with cardboard to fill the top and bottom pulls the same amount of air through a larger area of filters
B. pulling the same volume of air through greater surface area results in greater pressure between the filter and fan than one filter directly affixed to the fan
C. The lower air pressure / "suction" due to an obstructed intake causes an electric fan motor to fail more quickly.
D. Increasing the air pressure that the motor is in reduces the failure rate?
The only downside of the DIY route is the noise. Most box fans that I've seen are very noisy relative to "real" air cleaners/purifiers.
I've used a box fan plus furnace filter for years to deal with cat litter dust. Since the particles I want to filter are quite large, I can get away with using a fairly cheap furnace filter. The nice thing about this is that it's really easy to scale it to your requirements.
To deal with the noise, I used a motion sensor and switched outlet to only run it for 10 minutes after the litter has been used. This runs through my existing home automation stuff (Home Assistant+Node-RED), but it could also be done with an Arduino (you don't even something that powerful - two I/O lines is enough), a PIR sensor, and a solid state relay for the fan control.
I've tried a number of low-dust/no-dust litters, but most of have lead to the cats finding other places to do their business or have disappeared from store shelves when I've needed to replenish it. Everything about this is a compromise between litter acceptance, litter availability, litter cost, filter cost, filter life, noise, and dust production.
I'm using Vornado fan with 2 16x20x1 merv 11 filters from lowes (2 to make triangle). And in lowest speed it's very quiet. I have commercial air cleaner and my diy is way cheaper to run and as quiet.
https://tombuildsstuff.blogspot.com/2013/06/better-box-fan-a... - like this.
I swear I came across that post at one point - it looks very familiar!
I really want to do this because 20x25x1 filters are a LOT easier to find (where I am anyway) than 20x20x1 filters. The only obstacle is that the resulting unit ends up taking a lot more space, and that's at a bit of a premium in the place I need it.
If I move the litter boxes to somewhere with more space I will definitely switch to this design.
Did this with a small fan (around 6" in diameter) and it died out within a week of use. To be fair, the HEPA filter I used was really restrictive but anyone who plans to do this should probably keep that in mind.
I agree. When we had wildfire smoke descend on our area, the stores sold out within hours. If you live in an area which routinely experiences wildfire smoke, it's worth stocking a few filters, both 20x20x4 for box fans and whatever size your furnace uses. It made a huge difference to have fresh filters to swap out every few days.
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[ 3.2 ms ] story [ 218 ms ] threadI recently built up a couple similar box fan filters, but using 20"x20"x5" MERV 15 filters bought "used" off Amazon for about $20 each. Note that the total surface area of the folded filter matters for air resistance, not just the height and width of the filter. That is, depth matters, because all else equal the folds increase the amount of filter area.
I sealed well, because I thought it would matter. I removed the back plastic grill to reduce resistance a bit more, and also added a cardboard cowling on the front of the fan, based on the research here: https://www.texairfilters.com/how-to-improve-the-efficiency-.... The idea is that with a high resistance filter on the back, in the absence of cowling you get unhelpful recirculation from the front corners of the fan, although maybe this recirculation might actually be helping reduce pressure in front of the filter in your taped example?
I haven't done any air quality measurements, but I think the system is working the way I'd expect. Noise at low speed is tolerable when in another room, but I only use higher speeds when leaving the house. I'd be interested in more details about your particulate monitor, especially if you are satisfied with it and if it's available in the US.
I also know that one trick to remove the smoke smell from a used car is to use an ozone generator in the car.
I’ve had steering wheels turn to gel using ozone and they smell funkier than what was in there.
More precisely, many odors are not particles at all but rather gases/vapors. Activated charcoal can capture larger organic molecules because it has an incredibly jagged/porous surface - just 100 grams of activated charcoal provides over 1,000,000 square feet of "effective" filtration surface area.
> odors are not particles at all but rather gases/vapors
I think the confusion comes from people referring to "particulate" as particles of >= 0.01 micron, whereas in physics we say that gases/vapors are also composed of particles. They may be single atoms floating (can't actually come up with an example though) or small molecules like O^2, CO, etc, but I'd still call those particles.
But then in your world there are no such things as gasses? If so, the world uses all usefullness
There are residential air purifiers available that use this in combination with activated carbon for their gas stage.
Maybe you are talking about an integrated air filtration system, as I haven't tried that yet (though I'm planning to try it).
To remove smells ozone generators are used. That stuff is really dangerous though
No it's not.
That 200 USD fine for smoking in hotel rooms? What do you think happens afterwards? Buy a bunch of activated carbon filters? Or get a professional ozone odor removal provider to roll in their with their gear?
Regardless, this project actually makes me feel better about buying my fancy air filter
Instead of buying 2 filters (both HEPA), a fan, and a poorly calibrated air quality sensor for $150 like the author, I bought an air purifier that contains 2 filters (1 HEPA, 1 activated charcoal) a fan and a poorly calibrated air sensor for $153.
However since my air quality sensor is integrated with my purifier, it only pulls ~60 watts at the times when I'm cooking or if something is on fire. That probably saves me $50/year on electricity
But I understand the point, especially in times when you can't find a purifier.
Also, good video on all this: https://www.youtube.com/watch?v=kH5APw_SLUU
I have the Winix 5300 and 5500 purifiers (which I highly recommend), and typically run on mode 3 out of 4 because it pulls about 12 watts (and is quiet) but is not massively different airflow than mode 4 which draws about 70 watts (and is noisy).
[0] https://kylebenzle.medium.com/adding-an-air-purifier-to-your...
It didn't take long before the water would turn black.
Quite a turnoff for wannabee smokers, which was the obvious point of the experiment.
It's the same idea as the Rainbow vacuum cleaner, which uses a tank of water as its filter.
"We built a bong and discovered that bong water is really nasty."
Just think of that nasty bong water being what the smoke does to the fluids in your lungs.
The limitation for me would simply be the appearance factor; I want my filter to blend in quietly, not to draw attention. I think appearance and noise are part of why people pay so much for fancy purifiers.
Also, I imagine a centrifugal fan would draw less electricity per CFM under load (air resistance through the filter).
It’s a fan + a HEPA filter and it’s kinda pretty
I tested simply with a laser. In a normal room you can see the laser beam in dark. If you have a good purifier, you can't.
Dear god, do you live next to a coal plant? I would argue that in a normal room one should NOT be able to see the laser beam!
This. I tried a 3M MERV 12 filter taped to the intake of a cheap $12 box fan and the airflow through the fan went to effectively zero. The fan actually was pulling more air from the front of the fan around the sides of the fanbox than through the filter. Increasing the fan speed just increased this backflow. You are spot on with a radial fan being what you want here, and I notice that basically every commercial air purifier uses such a fan.
Wish I could find a room humidifier with a radial fan but all I can find are axial fan designs :p
https://www.airgradient.com/diy/
We have tested it extensively and it is very accurate for the fraction of the costs of commercial sensors. You can build it for less than USD 20 and send the data to our cloud server or any other backend.
We also measure CO2 because if you have purifiers running you often do not have enough fresh air ventilation and your CO2 often gets very high (often >1500ppm) causing headaches and reduce cognitive performance.
We measured this in classrooms some time ago and the results were not very good.
Details. https://www.airgradient.com/blog/2020/02/07/we-measured-the-...
Help us give you money! :-)
I’d be happy to pay OP for their work and everyone wins.
Especially low-volume tings like "pre-assembled DIY kits"
For example, you mention your "sensor package" in the FAQ and that's it. Your DIY instructions mention the "AirGradient PCB", _but there is no place where I can buy it_. For the love of god, put a 'buy' button on your website.
It seems what they are selling are consulting services with possible parts depending on the results, if you don’t want to do everything yourself.
[0]: https://jlcpcb.com
Contacting some random "enterprise sales" team? Not gonna happen.
That said, too many people (myself included) are so used to being courted as a customer (or really, user to try and upsell to or datamine from) that we’ve forgotten that not everyone wants our business and custom.
Splashing some cold water on your face and reminding yourself that you’re not the centre of the universe from time to time isn’t a bad habit to reduce behaving like entitled children. I still struggle with this, but baby steps... (pun not intended)
[0] https://www.spacex.com/rideshare/
I had been planning to build almost the exact same thing as what the parent posted but had been putting it off because I didn't want to draw up a PCB, so this is perfect.
They support the PMS but I used the default SDS011. They both seem reasonable for relative values but I'm not sure about the accuracy without proper calibration. They don't appear to give similar readings to my Plume Flow 2: https://plumelabs.com/en/flow/
This sensor uses a SenseAir S8, which like most CO2 sensors, has an automatic baseline calibration algorithm enabled [0], which expects to see pure, undiluted fresh air at least once every 8 days. The only way to disable it is explicitly, through the MODBUS interface [1].
Leaving it enabled makes perfect sense in a business or businesslike environment because these environments will be completely unoccupied overnight and have air conditioning, which usually does a daily fresh-air purge, ensuring that the sensor will have regular exposure to fresh air.
However in a residential environment, the auto baseline calibration often doesn't make sense, especially in winter. When the windows are closed and/or people or pets are around, it's very rare for the sensor to see uncontaminated fresh air, so it will see say 500ppm of CO2 and assume it's fresh air when it really isn't. I have measured this and it's a real problem.
In a residential environment, unless you're sure you have good, frequent exposure to pure fresh air, you're better off doing a fixed calibration once a year or so.
AirGradient also seems to be a hardware-only design. The ESPHome project [2] has great software support for a variety of sensors (including the SenseAir S8, so it should be compatible with the AirGradient hardware) as well as a very well-documented hardware project [3]. After trying my own Arduino-based software and then ESP-IDF, I find esphome much more pleasant to work with.
[0]: https://rmtplusstoragesenseair.blob.core.windows.net/docs/pu...
[1]: https://rmtplusstoragesenseair.blob.core.windows.net/docs/De...
[2]: https://esphome.io/
[3]: https://github.com/nkitanov/iaq_board
Personally, after trying out a bunch of sensors, I use the Sensirion SCD30.
As for devices, I'm not aware of a consumer device that I'd recommend. If you're willing to do at least a little bit of DIY, Watterott [0] sells an SCD30 hooked up to an Arduino-compatible MCU with WiFi, a red/green/blue indication of CO2 levels and ASC disabled by default [1].
It's an open-source hardware design and software [2] and has a few reference firmwares [3], including one [4] for MQTT.
If you want to go a little bit further, I'd recommend an ESP32 with an SCD30 and ESPHome [5]. That's what I use myself, mostly because I already had the sensors prior to Watterott's product existing.
[0]: https://shop.watterott.com/
[1]: https://shop.watterott.com/CO2-traffic-light-Plus-version-Wi...
[2]: https://github.com/watterott/CO2-Ampel
[3]: https://learn.watterott.com/breakouts/co2-ampel/
[4]: https://github.com/mariolukas/Watterott-CO2-Ampel-Plus-Firmw...
[5]: https://esphome.io/
The only think I found was https://www.adafruit.com/product/3686, but thats 4x the price of aliexpress.
0.3 micron was chosen because as noted by another commenter below, high efficiency filters typically filter better at smaller sizes than this.
A more stringent certification is EN1822, which first tests which particle size penetrates the filter the most, and then rates the efficiency based on that particle size.
With respect to viruses, a minimum of EN1822 H14 is required for use in European biological safety cabinets. An H14 filter is 99.995% efficient as it's most penetrating particle size (MPPS).
That said, it's important to realize the difference between using a filter to pass air into/out of a clean environment (e.g positive/negative pressure clean room) versus just using an air purifier in a room. In the latter case, the machine is only going to filter the air going through it, and will take a significant amount of time to turn over the air in the room, during which time it's just blowing things around.
https://tinyurl.com/FAQ-aerosols
https://smartairfilters.com/en/about/our-story/
I haven't tried as cheap HEPA filters appear to be harder to get hold of in the UK. Maybe due to different heating systems.
Clearing the Air: The Beginning and the End of Air Pollution by Tim Smedley is an excellent book if you are interested in this area.
You don't need a HEPA filter. HEPA is only useful when you can only pass the air through the filter once, like in hospitals. A home air filter can push the air through the filter several times, so an MERV8 is just as good as a HEPA and lasts longer.
I used a DIY filter to remove wildfire smoke from my apartment. It's just a 12"x12" MERV8 filter taped to the front of a small fan. It worked well. I periodically opened my windows to exchange the stuffy air with fresh+smokey air. After closing the windows, the filter took about 30 minutes to remove all of the smoke inside.
My best idea was cutting out the front and back wall of the box the filters came with and squishing the fan between two.
It worked well enough with the 50cm fan that it could make a 10x8m room pleasant in 10 minutes. The only improvement I would make would be buying a lower rated filter for the intake since it got clogged up with a lot of large particles that were kicked up by the fan.
I was planning a big build with an impeller fan, but there is something to be said for a solution so stupid that I can rebuild it in 5 minutes with $50 in parts.
A simple 3D printed housing filled with some charcoal/carbon media to trickle filter like a Brita would be interesting to see its effectiveness.
> Air purifiers can be expensive and you've probably seen articles recommending to just put a 20" x 20" x 1" furnace filter on a cheap 20" box fan and POOF! instant cleaner air for not a lot of money. It really does clean the air pretty cheap.
> There's a problem with this though. These fans weren't designed to be run with a filter. The filter will restrict air flow which will put a higher strain on the motor causing it to use more electricity and in worse cases could be a fire hazard. The higher the MERV rating (cleaning efficiency) of the filter the more stress it will put on the fan.
> Don't worry! You can still have your cheap air purifier as long as the filter area is increased to decrease the effect of air resistance. Instead of using one 20x20x1 filter we'll use two 20x25x1 filters which increases the filter surface area over 250%. It's a little more expensive because you're using two filters instead of one but the increased filter surface area also helps the filter last longer before it gets clogged up and we're saving on energy use compared to a single filter.
That seems like an overly complicated first attempt, why not just switch to a 20x20x4?
I'm fairly certain the opposite is true. In fact, most rowing machines work on this principle. The easiest setting is the one where the fan is as closed off as possible because it's pulling a vacuum. Less air, less resistance, easier to row / less power required to spin the fan. If anything, fans should draw less current with air flow on the inlet side restricted.
B. pulling the same volume of air through greater surface area results in greater pressure between the filter and fan than one filter directly affixed to the fan
C. The lower air pressure / "suction" due to an obstructed intake causes an electric fan motor to fail more quickly.
D. Increasing the air pressure that the motor is in reduces the failure rate?
I've used a box fan plus furnace filter for years to deal with cat litter dust. Since the particles I want to filter are quite large, I can get away with using a fairly cheap furnace filter. The nice thing about this is that it's really easy to scale it to your requirements.
To deal with the noise, I used a motion sensor and switched outlet to only run it for 10 minutes after the litter has been used. This runs through my existing home automation stuff (Home Assistant+Node-RED), but it could also be done with an Arduino (you don't even something that powerful - two I/O lines is enough), a PIR sensor, and a solid state relay for the fan control.
I've tried a number of low-dust/no-dust litters, but most of have lead to the cats finding other places to do their business or have disappeared from store shelves when I've needed to replenish it. Everything about this is a compromise between litter acceptance, litter availability, litter cost, filter cost, filter life, noise, and dust production.
I really want to do this because 20x25x1 filters are a LOT easier to find (where I am anyway) than 20x20x1 filters. The only obstacle is that the resulting unit ends up taking a lot more space, and that's at a bit of a premium in the place I need it.
If I move the litter boxes to somewhere with more space I will definitely switch to this design.