Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Experiments on a $50 DIY air purifier that takes 30s to assemble

dyno-might.github.io

Post reply on HN
Print view View original

41–50 of 149 posts

Re: Experiments on a $50 DIY air purifier that takes 30s to assemble

#41

Post by Traubenfuchs »

chopin wrote: post #19

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. i…

> In a normal room you can see the laser beam in dark.

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!

Re: Experiments on a $50 DIY air purifier that takes 30s to assemble

#42

Post by Traubenfuchs »

artvark11 wrote: post #3

Are diy filters effective at removing smells or only removing the measurable particles?

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.

Re: Experiments on a $50 DIY air purifier that takes 30s to assemble

#44

Post by throwaway9d0291 »

ahaucnx wrote: post #21

We have open source, open hardware build instructions for a very reliable Air quality sensor that can be used to measure PM2.5 and also CO2. 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 p…

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.

[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

Re: Experiments on a $50 DIY air purifier that takes 30s to assemble

#45

Post by bigiain »

xwdv wrote: post #38
shared_frog wrote: post #33

Earlier quoted context omitted.

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…

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.

Re: Experiments on a $50 DIY air purifier that takes 30s to assemble

#46

Post by xwdv »

bigiain wrote: post #45
xwdv wrote: post #38

Earlier quoted context omitted.

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.

What if they put an upfront price of $100 dollars but cheaper prices available if you contact them?

Re: Experiments on a $50 DIY air purifier that takes 30s to assemble

#47

Post by ClumsyPilot »

cyounkins wrote: post #11
rckoepke wrote: post #9

Earlier quoted context omitted.

HEPA filters are actually more efficient at capturing very very small 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 m…

> '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

Re: Experiments on a $50 DIY air purifier that takes 30s to assemble

#48

Post by xiphias2 »

ddeck wrote: post #24
xiphias2 wrote: post #18

Earlier quoted context omitted.

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).

Re: Experiments on a $50 DIY air purifier that takes 30s to assemble

#49

Post by mleonhard »

Any MERV8 or higher filter will work.

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.

Re: Experiments on a $50 DIY air purifier that takes 30s to assemble

#50

Post by konjin »

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.

Post reply on HN