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A small DIY air purifier

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Re: A small DIY air purifier

#11

Post by chrisparton1991 »

wiradikusuma wrote: post #7

Do air purifiers really work? I always have impression they're just sham, or at least placebo.

I decided to buy one when the smoke from the Sydney bushfires blanketed my town.

In my bedroom I could see and taste the smoke. The air purifier struggled, but it cleared the air around my computer quite well. I have dividing curtains in my room that I was able to close, which made it easier on the purifier.

All in all I think it was definitely worth the buy. FWIW I picked up a secondhand Kogan SmarterHome air purifier for AUD$60.

Re: A small DIY air purifier

#12

Post by jwr »

wiradikusuma wrote: post #7

Do air purifiers really work? I always have impression they're just sham, or at least placebo.

Yes, they definitely do, although to a various degree of effectiveness. If you get a Xiaomi Mi Air 2, for example, it will be very effective. If you get a Dyson fanless thing, not so much.

In general, there is no escaping physics: you need to move a large quantity of air through something that traps dust particles. The low-tech solution of a fan and a HEPA filter is a very good one, but I would suggest getting a filter that traps PM2.5 particles as well.

Re: A small DIY air purifier

#13

Post by lmilcin »

Air quality test before and after or it doesn't work.

I am very suspicious with regards to air purifiers. Have you ever seen real HEPA filter? It is thick and it is quite difficult to push air through it. I can't imagine small PC fan that is designed to push air through UNOBSTRUCTED space will make any significant flow of air. I have spent some time with the guys who build PCs and who know great deal about fans and one thing I learned even an object that the air has to pass around or any kink in the path of air can severly impact performance of PC fan. Because they are designed to be quiet and still provide good flow of air they produce almost no pressure differential to speak of and the flow can be halved by a wire mesh that is a bit too dense.

You need to cycle the air in your room through the filter couple of times to clean it, assuming your filter is any good.

The cheap fan in the picture would barely be able to cycle the air in a small room maybe once an hour, if it was completely unobstructed. It is very likely that with any kind of HEPA filter the flow will drop by an order of magnitude.

Go with suggestion of other readers. If you want good, cheap filter, use a box fan and especially one that was designed to give good pressure difference. Take large cardboard or plastic box and mount large HEPA filter in it so that the air has to pass through. The larger the surface of the filter the easier time the fan will have to push the air through it and more efficient it will be.

Re: A small DIY air purifier

#15

Post by starpilot »

packetslave wrote: post #4
adrianN wrote: post #3

You could probably buy a box fan and tape a HEPA filter in front.

This works shockingly well. They were quite popular during last year's California fires when "real" air purifiers were sold out everywhere.

Also worked well in Seattle last summer.

Re: A small DIY air purifier

#16

Post by ddeck »

lmilcin wrote: post #13

Air quality test before and after or it doesn't work. I am very suspicious with regards to air purifiers. Have you ever seen real HEPA filter? It is thick and it is quite difficult to push air through it. I can't imagine small PC fan that is designed to push air through UNOBSTRUCTED space will make any significant flow of air. I have spent some time with the guys who build PCs and who know great deal about fans and o…

>The larger the surface of the filter the easier time the fan will have to push the air through it and more efficient it will be.

This is quite true. Assuming the media in your particle filter is of sufficient quality, the most important metric to look at is the aggregate surface area. The larger the surface area, the more air you will be able to move through it and the more particulate matter it will hold before requiring replacement.

Particle filters use pleated media for this reason. It's not uncommon to see a filter with 1 square foot face having 50 square feet or more of media. Without specs, the thickness of the filter and the density of the pleating will give you a decent estimate of the filter area. To improve performance and longevity further, it's also typical to have a coarser, pre-filter.

The machine itself is just a fan to push air through the filter and as noted, any reasonably powerful fan will do a sufficiently good job. High quality machines are only really required where you're filtering air before it enters a given area (e.g. LCD/semiconductor plants), and thus cannot afford to have any unfiltered air leak past the filter.

Re: A small DIY air purifier

#17

Post by dandare »

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…

I came here to post the very same link :D

Re: A small DIY air purifier

#18

Post by ivanhoe »

if you don't mind a noise you could buy a 2nd hand vacuum cleaner with a built-in hepa or water filter (ideally also with adjustable speed to make it less noisy) and just let it run without a hose, sucking the air and pushing it through the filter...

Re: A small DIY air purifier

#19

Post by chewz »

jwr wrote: post #12
wiradikusuma wrote: post #7

Do air purifiers really work? I always have impression they're just sham, or at least placebo.

Yes, they definitely do, although to a various degree of effectiveness. If you get a Xiaomi Mi Air 2, for example, it will be very effective. If you get a Dyson fanless thing, not so much. In general, there is no escaping physics: you need to move a large quantity of air through something that traps dust particles. The low-tech solution of a fan and a HEPA filter is a very good one, but I would suggest getting a filt…

> a HEPA filter is a very good one, but I would suggest getting a filter that traps PM2.5 particles as well

Or read the specs and compare with norm

https://en.wikipedia.org/wiki/HEPA#Specifications

Re: A small DIY air purifier

#20

Post by Zardoz84 »

I would say that there are electronic schemes and plans to build DIY ion air cleaners. They works nice to remove dust or tabacoo from air.

Also, ozone air purifier make wonders to keep at bay smells and fats (wonderful to have on the kitchen), and kills bacterias, spores and fungus.

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