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A small DIY air purifier

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Re: A small DIY air purifier

#171

Post by emrehan »

frank2 wrote: post #131
clarry wrote: post #24

Speaking of air purifiers, does anyone have recommendations for one that is quiet and still effective? I have a pair of Electrolux EAP300s, in small rooms. Unfortunately on the lowest manual setting ("Quiet") they hardly do anything for air quality. And they're still louder than I like. I think they really optimized for cost; these devices feel very light and plasticy, the fan sounds cheap and has an uneven tone to i…

One thing to keep in mind is that an air purifier with a squirrel-cage fan (the kind of fan needed to pull enough air through a HEPA filter) makes a very pleasant sound that is good for masking, e.g., banging noises from neighboring apartments. I regularly run mine just to mask noise. So being loud can be considered a feature.

Exposure to noise degrades hearing and have psychological consequences.

Re: A small DIY air purifier

#172

Post by chewz »

yboris wrote: post #85
chewz wrote: post #23

This seems like useless toy. You should be aiming for something larger that would work for an apartment. [1] https://youtu.be/kH5APw_SLUU [2] https://youtu.be/8Hkdpx-59kk There is thousand vidoes on Youtube on how to DYI one.

Thank you for sharing these two videos! I really like the 1st one with the air-quality-measuring-instrument.

You welcome.

You can also make DYI air-quality instrument on a cheap using SDS011 sensor and Raspberry Pi. [2]

[1] https://aqicn.org/sensor/sds011/

[2] https://www.raspberrypi.org/blog/monitor-air-quality-with-a-...

Re: A small DIY air purifier

#173

Post by labawi »

avian wrote: post #170
labawi wrote: post #146

Earlier quoted context omitted.

IMO, absolute pressure doesn't give much of a perspective. Car tire pressure is about 1.8-2.5 Bar. Your 2000 Pa atmospheric pressure change is about 20 mBar. Pressure in an inflated balloon is about 2 mBar (0.002 Bar). Noctua's static pressure is 0.8 mBar. Let's call it 0.5 mBar dynamic working pressure. Not as low as I expected. Not sure if it will have a semi-reasonable speed, but that will definitely push some air…

That balloon figure doesn’t make sense to me in relation to atmospheric pressure changes. It would mean that a tied-off balloon would randomly inflate and deflate itself depending on weather.

It does, slightly. Pressure change 20 mBar = 2% of absolute atmospheric pressure -> about 2% balloon volume change, with corresponding 2% internal absolute pressure change, while keeping the same low differential inside-outside pressure.

Re: A small DIY air purifier

#174

Post by brnt »

dredmorbius wrote: post #151
chewz wrote: post #23

This seems like useless toy. You should be aiming for something larger that would work for an apartment. [1] https://youtu.be/kH5APw_SLUU [2] https://youtu.be/8Hkdpx-59kk There is thousand vidoes on Youtube on how to DYI one.

The problem for areas presently affected by high PM2.5 concentrations, most notably Australia, is that materials which are commonplace in the US, box fans, but especially box-fan-sized square HEPA furnace filters, are rare as hen's teeth. So alternate designs using available materials are required. (Or someone might drop ship a few containers worth of box fans and HEPA furnace filters down under.)

Same problem here. I've just spent close to an hour trying to locate a box fan for sale in Europe, couldn't find any resembling those I can easily find on amazon.com!

Re: A small DIY air purifier

#175

Post by verdverm »

dredmorbius wrote: post #168
verdverm wrote: post #167

Earlier quoted context omitted.

It works with two and not with one, so pretty much required. The effect is far from marginal in my setup. Also far cheaper then the post link, less than half.

Numerous documented and tested builds with only one. https://invidio.us/watch?v=kH5APw_SLUU YMMV.

Cool, don't really care, happy with my double filtered setup

Re: A small DIY air purifier

#176

Post by amluto »

dredmorbius wrote: post #155
amluto wrote: post #127

My general theory is that HEPA makes sense for filtration where a single pass is all you get. So it makes sense for vacuum cleaners, air intakes, and such. But, for room air cleaning, what matters is the rate at which particles are removed, not the cleanness of the air coming out. So, for recirculating, something like a MERV 13 filter seems like a better choice: it lets more particles through on each pass, but it als…

PM2.5 particles are small enough that they pass through many materials. You can use lower-efficiency (higher effective particle-size) filters ... but you'll just be blowing the bad stuff through them rather than removing it. The net metric is how fast the room particulate level drops , which is the treatment goal. Flow rate is a red herring.

That’s why I suggested MERV 13 and not, say, MERV 8. If your filter removes a mere 50% of particles at a given size but moves twice as much air as a HEPA filter, you’re doing fine for a recirculating filter.

Re: A small DIY air purifier

#177

Post by 91aintprime »

post_break wrote: post #67
kn100 wrote: post #6

This is a really cool project but frankly you can do it a lot cheaper. Find the cheapest box fan you can find, and find the cheapest HEPA filter you can, and strap the HEPA filter to the front. To improve air purification even futher, slap an activated carbon filter on the front too, and your air purifier now filters VoCs! For cheap Activated Carbon Filters, look into the kind used for Aquarium filters. They'll work…

If you want this to actually work, you take a box fan, and 2 filters. You make a triangle and then some cardboard on the top and bottom to fill the gap. This increases surface area and reduces the stress on the fan due to pressure drop. Slapping a filter directly on to the box fan is going to kill the fan very quickly. https://i.imgur.com/SX1RloH.jpg

something something impedance matching

Re: A small DIY air purifier

#178

Post by bradknowles »

Eric_WVGG wrote: post #79
Eric_WVGG wrote: post #65

Earlier quoted context omitted.

I felt similarly, but I have a family member who is bed-bound, there’s some asbestos removal going on, so I decided to take the plunge. I can vouch for their ability to detect impure air. If I start cooking anything, it switches on within seconds. It’ll turn on within about three minutes of sweeping the floor. And if the detectors can turn on when the air is dirty, it stands to reason that they can tell when the air…

(A few minutes after posting this, morning rooftop construction started. Sounds of saws and drills buzzing, large objects and beams being dropped directly overhead. Air purifier just kicked into high gear. Yes, I’m definitely into this thing.) https://thewirecutter.com/reviews/best-air-purifier/

I’m a big fan of thewirecutter, and I reference them frequently on most things I’m buying. But for HEPA air filters, I don’t feel like they test the models that I feel are best for someone with asthma, or other similar breathing problems.

We have several IQAir units, of at least a couple different models. None of them have sensors to automatically ramp up the filtering when they detect pollution, that would be nice. But according to the air quality sensors I have in the house, they do an amazingly good job of filtering the air, at least if you turn them up to high enough levels.

I have yet to see demonstrated clear benefit of the units with activated charcoal filters for removing VOCs from the air, but my gut feeling is they do help in those areas where VOCs are a concern. Not all parts of our house needs that, however.

Having four furballs does greatly increase the dander and other allergens we have to deal with, but we wouldn’t give them up for anything, so the IQAir units at least make our lives a bit more livable. Especially during “Cedar Fever” season.

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