Experiments on a $50 DIY air purifier that takes 30s to assemble • Hacker News Board

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

#111

Post by JJMalina » Thu, Dec 17, 2020, 6:02 PM UTC

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…

The Plantower PMS5003 PM Sensor is unavailable to ship to the US on aliexpress https://www.aliexpress.com/item/32944660534.html Do you know of another supplier that ships to/within the US?

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

#112

Post by giantg2 » Thu, Dec 17, 2020, 6:05 PM UTC

It could be more efficient if you use a old cardboard boxes and duct tape to build a custom fit shroud connecting/ mounting the filter to the fan.

I use a similar setup on a homemade glove box / flow hood type device for culturing mushrooms. I have an 8" duct booster fan pushing air into a cardboard box. Between that box and the flow hood I have a HEPA filter sandwiched between them using bolts and wing nuts. The only thing I'd change is the fan. The booster fan was cheap, but has trouble with the back pressure (lower air flow). I would probably look at using squirrel cage or maybe a radon fan. They should be able to handle the pressure.

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

#113

Post by NietTim » Thu, Dec 17, 2020, 6:15 PM UTC

nkurz wrote: post #53

NietTim wrote: post #29

Interesting. I only have central ventilation but my mom has central heated air in her house, in theory she could chuck a HEPA filter in front of it to get cleaner air in all of her house.

Note that this can be a really bad idea. While it might temporarily improve the air quality, extreme filtration will reduce the air flow through the system. This will in turn reduce the efficiency of the heater, possibly in a way that causes its internals to overheat and destroy themselves. Rather than "upgrading" to higher filtration, you are safer replacing whatever filter is there with a new clean one that matches…

This is a very good point, thanks

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

#114

Post by kingnothing » Thu, Dec 17, 2020, 6:15 PM UTC

Wirecutter also has some info on this setup compared to commercially available options. tldr: a good HEPA filter will remove 99% of impurities, their box fan setup removed 87%.

https://www.nytimes.com/wirecutter/reviews/best-air-purifier...

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

#115

Post by NietTim » Thu, Dec 17, 2020, 6:16 PM UTC

dsr_ wrote: post #51

NietTim wrote: post #29

Interesting. I only have central ventilation but my mom has central heated air in her house, in theory she could chuck a HEPA filter in front of it to get cleaner air in all of her house.

Odds are good that she has a MERV filter... and that it hasn't been changed in years.

She probably has, but the heating module gives her a periodic reminder to clean it (which I then have to do because she can't reach it). It gets replaced every few years, I think she has a service contract :)

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

#116

Post by Rebelgecko » Thu, Dec 17, 2020, 6:20 PM UTC

thomas wrote: post #71

Rebelgecko wrote: post #14

I wish there were multiple reps of each experiment, especially with how noisy the results were and the difficulties of reproducing smoke Regardless, this project actually makes me feel better about buying my fancy air filter Instead of buying 2 filters (both HEPA), a fan, and a poorly calibrated air quality sensor for $150 like the author, I bought an air purifier that contains 2 filters (1 HEPA, 1 activated charcoal…

Yeah, same thought. Something like the Coway air filter ( https://www.youtube.com/watch?v=zxiDrEnjYEo ) regularly sells for under $200, and it is going to be much quieter than this option. It also has been tested fairly extensively from what I've seen, it's EnergyStar approved, etc, and it has a built in sensor. It doesn't look too bad either. But I understand the point, especially in times when you can't find a puri…

Exactly! I have the uglier but slightly cheaper version of that air purifier (the Coway Airmega 200M). I think the faceplate is the only difference. I forgot to mention in my original comment that it also has a prefilter for larger dust particles, which I imagine probably improves the lifetime of the other filters.

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

#117

Post by ruste » Thu, Dec 17, 2020, 6:25 PM UTC

westurner wrote: post #54

From "Better Box Fan Air Purifier" https://tombuildsstuff.blogspot.com/2013/06/better-box-fan-a... : > Air purifiers can be expensive and you've probably seen articles recommending to just put a 20" x 20" x 1" furnace filter on a cheap 20" box fan and POOF! instant cleaner air for not a lot of money. It really does clean the air pretty cheap. > There's a problem with this though. These fans weren't designed to be run…

> There's a problem with this though. These fans weren't designed to be run with a filter. The filter will restrict air flow which will put a higher strain on the motor causing it to use more electricity and in worse cases could be a fire hazard. The higher the MERV rating (cleaning efficiency) of the filter the more stress it will put on the fan.

I'm fairly certain the opposite is true. In fact, most rowing machines work on this principle. The easiest setting is the one where the fan is as closed off as possible because it's pulling a vacuum. Less air, less resistance, easier to row / less power required to spin the fan. If anything, fans should draw less current with air flow on the inlet side restricted.

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

#118

Post by yborg » Thu, Dec 17, 2020, 6:26 PM UTC

metiscus wrote: post #68

joncrane wrote: post #56

Earlier quoted context omitted.

You'd be surprised how "dirty" (dusty) the air inside houses is.

Especially given the relatively wide range for age and consequently construction type. I've found that newer drywall construction tends to be more dusty in my limited experience than well maintained plaster and lath.

Wall-wall carpet, especially old carpet, is a dust factory.

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

#119

Post by yborg » Thu, Dec 17, 2020, 6:30 PM UTC

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…

>If you strap a HEPA to an axial fan and seal it, the fan runs effectively "empty", i.e. it displaces only little air which most likely even doesn't pass the filter

This. I tried a 3M MERV 12 filter taped to the intake of a cheap $12 box fan and the airflow through the fan went to effectively zero. The fan actually was pulling more air from the front of the fan around the sides of the fanbox than through the filter. Increasing the fan speed just increased this backflow. You are spot on with a radial fan being what you want here, and I notice that basically every commercial air purifier uses such a fan.

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

#120

Post by metiscus » Thu, Dec 17, 2020, 6:41 PM UTC

yborg wrote: post #118

metiscus wrote: post #68

Earlier quoted context omitted.

Especially given the relatively wide range for age and consequently construction type. I've found that newer drywall construction tends to be more dusty in my limited experience than well maintained plaster and lath.

Wall-wall carpet, especially old carpet, is a dust factory.

My house has tile floors which get visibly filthy really quickly. I have a roomba and I personally clean the floors quite often manually. In my parents house which had wall to wall carpet, they would vacuum relatively infrequently but the same amount of dirt was likely being tracked in and around. Their house was more dusty than mine seems to be because of the fact that carpet tends to hide how "dirty" it is.