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A small DIY air purifier

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Re: A small DIY air purifier

#101

Post by showerst »

sl1ck731 wrote: post #98
majos wrote: post #94

May as well ask here: do air purifiers have meaningful health benefits for generally healthy people? I get that you change the filter and it's filled with grey muck and that's gross, and that the filters change particulate content in air, but is there good evidence that doing those things improves health if you don't already have some sensitivity to air pollution or live in a highly polluted area? I don't know if "Lu…

I would assume the majority of people (in the US, anyway) are already filtering their air enough through their central air to make any additional "room-sized" filtering negligible. Similarly they make some very dense HVAC filters if standard ones aren't catching the level of particles you need, so I'm not sure what the purpose of these filter-fan things are for most people.

In a previous house I rented, we swapped the furnace filter for a much finer one (from 8 to 13 on whatever scale they market these things in), and it made the HVAC system run noticeably worse. Lower airflow, noisier, etc. It seemed to me that the intake system couldn't keep up with the reduced flow of the denser filter.

Could moving to a coarser filter but adding room filters be useful in that context?

Re: A small DIY air purifier

#102

Post by driverdan »

cosmolev wrote: post #97
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 have smartairfilter's Cannon purifier. As all those standalone purifiers it works only with windows completely closed. I went for ventilation systems that take air from outside, filter it and then bring it inside the room. Namely Xiaomi MJXFJ-300-G1: https://www.xiaomitoday.com/xiaomi-mijia-air-purifier-mjxfj-... I've installed one in every bedroom.

That seems quite expensive for what it is. For that price I'd expect it to have an efficient heat exchanger.

Re: A small DIY air purifier

#103

Post by cptskippy »

sl1ck731 wrote: post #98
majos wrote: post #94

May as well ask here: do air purifiers have meaningful health benefits for generally healthy people? I get that you change the filter and it's filled with grey muck and that's gross, and that the filters change particulate content in air, but is there good evidence that doing those things improves health if you don't already have some sensitivity to air pollution or live in a highly polluted area? I don't know if "Lu…

I would assume the majority of people (in the US, anyway) are already filtering their air enough through their central air to make any additional "room-sized" filtering negligible. Similarly they make some very dense HVAC filters if standard ones aren't catching the level of particles you need, so I'm not sure what the purpose of these filter-fan things are for most people.

That assumes that your HVAC runs regularly. Apart from deep summer and winter we rarely run our house HVAC.

We have a filter that runs constantly at low speed because we have pets and without the filter there would be issues for members of my family.

Re: A small DIY air purifier

#104

Post by driverdan »

Eric_WVGG wrote: post #65
wiradikusuma wrote: post #7

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

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…

Being able to detect particulates in the air isn't what's important. You need to know if it's actually improving the air quality.

Re: A small DIY air purifier

#105

Post by leetbulb »

qpiox wrote: post #28
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…

It depends on what noise level is acceptable for you and the room size. Out of 30 or so air purifiers available in shops here, of all the ones that are in the $100-500 category, the Winix P/U450 are able to push the largest amount of air under the constraint of HEPA filters are rated at which air speed they are most effective and how much pressure is needed. The ammount of pressure will only rise as the filter is sat…

I have two Winix HR1000. They have extremely powerful blowers and are quiet when not in "turbo" mode. The turbo mode is actually pretty good for white noise when sleeping. I've been running them 24/7 for years now and they are still working great.

Re: A small DIY air purifier

#106

Post by logfromblammo »

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

Or ditch the cardboard, and use 5 square HVAC filters to make a true "box fan".

Re: A small DIY air purifier

#107

Post by dr_orpheus »

sl1ck731 wrote: post #98
majos wrote: post #94

May as well ask here: do air purifiers have meaningful health benefits for generally healthy people? I get that you change the filter and it's filled with grey muck and that's gross, and that the filters change particulate content in air, but is there good evidence that doing those things improves health if you don't already have some sensitivity to air pollution or live in a highly polluted area? I don't know if "Lu…

I would assume the majority of people (in the US, anyway) are already filtering their air enough through their central air to make any additional "room-sized" filtering negligible. Similarly they make some very dense HVAC filters if standard ones aren't catching the level of particles you need, so I'm not sure what the purpose of these filter-fan things are for most people.

Dense HVAC filters make your HVAC systems run much less efficiently. There is less airflow and less heat transfer (either cooling or heating). Anyone that has come to service my air conditioner or furnace has always checked the filter and recommended never getting a denser filter. The filters in the HVAC system are more there to prevent your furnace from getting clogged up with larger particles than to help the indoor air quality.

Re: A small DIY air purifier

#109

Post by jbob2000 »

logfromblammo wrote: post #108

Please don't use an iPhone X "for scale". The dual-ruled calipers used in the next photo would be an acceptable substitute for just using a plain old ruler.

Most people know what an iPhone X (or similar device) feels like. Not many people have held calipers (or remember what holding them feels like) and not many people can put into context what a marking on a ruler actually means.

For a quick scale judgment, a smartphone is perfect. It's not supposed to be precise.

Re: A small DIY air purifier

#110

Post by Nexxxeh »

apta wrote: post #84
kevinconroy wrote: post #68

Earlier quoted context omitted.

Yes! We have two box fans with HEPA filters in our bedroom to combat the cat fur/dander. It's made a world of difference. You can see it working as the filter captures everything. Have to change them monthly... but so worth it. #YMMV #YouCatsMayVary

Do you strap them to the front or the rear of the fan? Doesn't having them on the front (i.e. where the air blows out) mean that the fan will get dirty since it's sucking the air in?

You may wish to use a cheap thin washable pre-filter either way. It will catch a lot of the hair before it hits the fine filtration, which you can then just wash off the pre-filter, making it easier and cheaper to maintain.
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