4 ms·

If anyone's interested in a cheaper and less powerful version I've done tests on a DIY purifier that's based on a similar design: https://dynomight.net/better-D

by dynm 4y ago

If anyone's interested in a cheaper and less powerful version I've done tests on a DIY purifier that's based on a similar design: https://dynomight.net/better-DIY-air-purifier.html https://dynomight.net/better-DIY-air-purifier.html It costs around $100 to build and delivers around 104 CFM (2.95 m^3/min) on high and around 71 CFM (2.02 m^3/min) on medium (where it's pretty quiet). Interestingly, this is nearly an equal "deal" to your solution: it's around 1/5 the price and around 1/4 as powerful. If people are put off of installing an air purifier because of they price, I think they should try not to make perfect the enemy of good: Due to the way half-lives work, you get the biggest benefit in terms of cleaner air from the "first" CFM of power that you install.

hcurtiss 4y ago
That dude (you?) compares his contraption to the same three filters taped randomly on a box fan. That's a little silly. I'm surprised it filters anything at all, as the air would simply flow between and around the filters. During Oregon's 2020 Labor Day fires many of us just taped standard 20"x20"x1" home filters to a standard box fan. You can tape all the way around it ensuring that all air passes through the filter, and the filters have pretty good ratings (we used MERV 11 and 13 filters). We found that they worked very well. Here's a picture of one of ours (we had three running in different places): https://photos.app.goo.gl/XkEKBdt5m8nN8NU7A https://photos.app.goo.gl/XkEKBdt5m8nN8NU7A I don't have any numbers, but I strongly suspect for purposes of wildfire smoke they work as well as what that article is proposing.
- dynm 4y ago
  It is me! I'll note that I've also done experiments comparing the effects of taping and not taping around the filters, which you can see here: https://dynomight.net/2020/12/15/some-real-data-on-a-DIY-box-fan-air-purifier/#taping https://dynomight.net/2020/12/15/some-real-data-on-a-DIY-box...
  - hcurtiss 4y ago
    It's awesome that you've done all this work. I have to say, though, that this could just as well be evidence that your experiment is not designed terribly well. One would never build a home furnace with a filter that has gaps all the way around it.
    - dynm 4y ago
      Certainly you wouldn't, but keep in mind the blower in a home furnace is designed to push air through a filter. This is not the case with box fans, where (at least with the filters I used) the fan throughput vastly decreases when you add the tape. I'm pretty confident in my experiments, but I wouldn't claim this as a general result: It's just a sort of coincidence that the two factors (pushing more air overall and funneling a larger fraction of that air through the filters) happen to almost exactly cancel out. If you have a more powerful fan or you have filter media that creates less of a pressure barrier, then I'm pretty sure you will see a benefit from taping. But I was just worried about the box fan motor so I decided to remove them.
    - amluto 4y ago
      The purpose of these filters is entirely different. A furnace filter needs to prevent large particles from passing it, as such particles can deposit on the coil. Its utility is essentially -(particles missed). A room air purifier exists to remove particles. Its utility is (particles removed). Blowing additional air around that bypass the filter in an air purifier is harmless, whereas it can destroy your furnace or especially your A/C. This is why the IKEA air purifier is a better design than a HEPA purifier. Also people most certainly do build furnaces with gaps around the filter.
      - hcurtiss 4y ago
        This is all wrong. Our furnace filters (and all furnace filters) filter particles specifically to clean the air. And with a MERV 13 or higher rating, they even filter Pm 2.5. And, no, I’ve never seen a single furnace filter with intentional gaps around the filter.

by dynm 4y ago

hcurtiss 4y ago

That dude (you?) compares his contraption to the same three filters taped randomly on a box fan. That's a little silly. I'm surprised it filters anything at all, as the air would simply flow between and around the filters. During Oregon's 2020 Labor Day fires many of us just taped standard 20"x20"x1" home filters to a standard box fan. You can tape all the way around it ensuring that all air passes through the filter, and the filters have pretty good ratings (we used MERV 11 and 13 filters). We found that they worked very well. Here's a picture of one of ours (we had three running in different places): https://photos.app.goo.gl/XkEKBdt5m8nN8NU7A https://photos.app.goo.gl/XkEKBdt5m8nN8NU7A I don't have any numbers, but I strongly suspect for purposes of wildfire smoke they work as well as what that article is proposing.

dynm 4y ago
It is me! I'll note that I've also done experiments comparing the effects of taping and not taping around the filters, which you can see here: https://dynomight.net/2020/12/15/some-real-data-on-a-DIY-box-fan-air-purifier/#taping https://dynomight.net/2020/12/15/some-real-data-on-a-DIY-box...
- hcurtiss 4y ago
  It's awesome that you've done all this work. I have to say, though, that this could just as well be evidence that your experiment is not designed terribly well. One would never build a home furnace with a filter that has gaps all the way around it.
  - dynm 4y ago
    Certainly you wouldn't, but keep in mind the blower in a home furnace is designed to push air through a filter. This is not the case with box fans, where (at least with the filters I used) the fan throughput vastly decreases when you add the tape. I'm pretty confident in my experiments, but I wouldn't claim this as a general result: It's just a sort of coincidence that the two factors (pushing more air overall and funneling a larger fraction of that air through the filters) happen to almost exactly cancel out. If you have a more powerful fan or you have filter media that creates less of a pressure barrier, then I'm pretty sure you will see a benefit from taping. But I was just worried about the box fan motor so I decided to remove them.
  - amluto 4y ago
    The purpose of these filters is entirely different. A furnace filter needs to prevent large particles from passing it, as such particles can deposit on the coil. Its utility is essentially -(particles missed). A room air purifier exists to remove particles. Its utility is (particles removed). Blowing additional air around that bypass the filter in an air purifier is harmless, whereas it can destroy your furnace or especially your A/C. This is why the IKEA air purifier is a better design than a HEPA purifier. Also people most certainly do build furnaces with gaps around the filter.
    - hcurtiss 4y ago
      This is all wrong. Our furnace filters (and all furnace filters) filter particles specifically to clean the air. And with a MERV 13 or higher rating, they even filter Pm 2.5. And, no, I’ve never seen a single furnace filter with intentional gaps around the filter.