Make Your Own DIY Air Filter for RMB 166

Nimo Wanjau | Jul 25, 2013 11:00 am | 5 comments | 8922 reads

After staying in Beijing for nearly four years, I've learned to look for good bargains, so when I came across this do-it-yourself purifier post I could feel my sense of cheapness being called upon (despite the fact that the picture looks like a broken air conditioning unit).

The post on Tumblr by particlecounting, who just started blogging about a week ago, claims that you can make an effective indoor air purifier simply by taking a flat front motor run fan and strapping a HEPA filter (purchasable from Taobao for RMB 58) for a total of just RMB 166 (as opposed to the RMB 11,000 or so you'd pay for a high-end filter).

The author, a self-professed "nerd" who says he is a 2012-2013 Fulbright Scholar based in Beijing and a PhD student in cultural psychology at the University of Virginia, gives a step-by-step guide on how to make your own, accompanied by pictures.
In a subsequent post, the author also documents a series of tests he conducted to study the effectiveness of his DIY purifier. He conducted a particle count of the air inside the room before switching the purifier on and used the US Embassy's AQI to correlate with his particle counter and tested the air for eight hours in his bedroom with the windows and doors closed. He also took into account variables like someone entering and leaving the room which might cause a gust of wind to blow into the room.
The author compares the effectiveness of the DIY with a state of the art purifier based on data collected by myhealthbeijing blogger and Beijing United Family Hospital Doctor Richard St. Cyr, who calculated his air quality reductions on the air outside as opposed to the inside air, which the author believes is a better approach (he later updated the post by noting Dr. Richard conducted his tests with the doors closed for one hour).
In the end he acknowledges that variables like room size (his room is 6.5m smaller than Dr Richard's) make the comparisons imperfect but concludes that his DIY filter is "roughly comparable to an expensive filter at far lower cost."
Photo courtesy of farm7 via Flickr

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tomuw's picture tomuw Submitted by Guest on Tue, 10/01/2013 - 11:24

This is Thomas, the guy behind the DIY filter site.

And that's an excellent question! Does it work? I'm a believer in open data (and a nerd), so I've done many tests of the filter with a particle counter. You can see the data:

1. You can see a video of a test of the air coming out of the DIY filter here:

http://particlecounting.tumblr.com/post/55491154130/heres-test-1-is-the-air-thats-coming-out-of-the

2. I've done tests of ambient room air before and after turning the DIY filter on. You can see my data here:

http://particlecounting.tumblr.com/post/55665836265/purifier-tests

and here:

http://particlecounting.tumblr.com/post/55947941919/diy-compared-to-expensive-filters

3. And you can come to our workshops and test the DIY filters live on the spot with the particle counter.

http://smartairfilters.com/#workshops

As far as the seal goes, ours get a pretty good seal around the filter. For an improved seal, you can try using the more flexible pre-filter that comes with some filters. Perhaps your HEPA was different from the ones we use? Nowadays, I've been using velcro straps, which gets a tighter seal. Pictures here:

http://smartairfilters.com/#steps

Finally, this is a bit of a philosophical point, but how much the seal matters depends on whether you're (1) sending out air from a very dirty source into a clean room, as in a vacuum cleaner or (2) pushing air that's already in your room through a filter. In case 1, the seal is very important. In the second case, the seal is important, but a less-than-100% seal does not render it "useless," as you suggest. All you need is for some air to be going through the filter for it to be removing particulates from the air. But you don't have to take my word for it. Doctors at the University of Michigan have tests with a similar set up, and you can see their seal is not perfect:

http://particlecounting.tumblr.com/post/56577062878/independent-confirmation-ive-always-suspected

Thomas Talhelm

http://particlecounting.tumblr.com/

admin's picture admin Submitted by Guest on Thu, 09/26/2013 - 12:57

The Beijing Deva wrote:
I gave it a try but it appears that without the filter being properly sealed against the fan, the air fails to penetrate it and escapes round the sides and back through the intake side, rendering it completely useless.

The pictures in the blog show the filter being attached by a single ribbon so not really sure what to think.

Hmm, that's too bad. I use IQ Air as well (at home) but our office is too big to afford to buy a bunch of those to keep the place clean and I was thinking about implementing this low-cost solution... I wonder what it would take to make one that would really work?

 

Books by current and former Beijinger staffers

http://astore.amazon.com/truerunmedia-20

The Beijing Deva's picture The Beijing Deva Submitted by Guest on Wed, 09/25/2013 - 12:30

I gave it a try but it appears that without the filter being properly sealed against the fan, the air fails to penetrate it and escapes round the sides and back through the intake side, rendering it completely useless.

The pictures in the blog show the filter being attached by a single ribbon so not really sure what to think.

We just went and bought an IQ Air instead, lot less hassle!

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