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derefr 14 hours ago [-]
I live in an apartment over a busy road, and my building doesn’t have forced-air ventilation to the units, so I need to pull in fresh air somehow. Just leaving the windows open results in black soot accumulating in the carpets (and is probably why both my SO and my cat developed asthma while living here.) Regular air purifiers (we have two) only do so much.
What ended up making a difference for us, is buying a portable industrial air scrubber, of the kind construction/remediation sites use to clean the smoke and dust (and mold, and asbestos, etc) they’re generating out of the air before it gets vented outside (see e.g. https://a.co/d/01lTtyuZ); and plumbing this machine into our apartment in reverse: putting it out on our (covered) balcony, with it exhausting the “scrubbed” air into the apartment. (I made a little sliding-door shim of the type people use to pipe portable AC units outside, just with the hose on the other side.)
Generally works great. We run it on a very low speed, so it’s surprisingly quiet (no louder than other fans we have for air circulation, and a more pleasant frequency because of the large diameter of the fan it has inside.) The pre-filters get absolutely caked with exhaust and road dust after ~2wks, and start to let through an odd stench at that point, so we’re actually replacing those faster than even is recommended for the industrial use-case. But the actual main HEPA filter inside the unit seems to last longer than in industrial usage.
Llamamoe 3 hours ago [-]
You could probably improvise something cheaper using the same filter arrangement, though now that you have it, sounds like the best thing to do might be just including an extra sacrificial initial filter to increase the lifespan of the proper ones.
mft_ 4 hours ago [-]
Your prefilters only lasting two weeks, plus two household members developing asthma, might make me think very seriously about moving somewhere less polluted, and quickly.
mitxela 11 hours ago [-]
Cars are the best form of transportation ever invented.
nwah1 15 hours ago [-]
There was some talk on here during Covid about the feasibility of making all structures up to BSL4 standards. Seems kind of nuts, but it would certainly contain a lot of biosafety threats. With AI it now seems borderline urgent.
ungreased0675 13 hours ago [-]
I was very disappointed that COVID did not inspire more interest in indoor air quality, especially in public spaces.
Llamamoe 3 hours ago [-]
Agreed. It was literally the wake up call for the fact that air quality standards are as important as soap and handwashinhg are, and yet... nothing happened.
And so the question of what effects getting rid of several-yearly respiratory infections would have on our health and the development of children remains open.
dgacmu 12 hours ago [-]
I don't know how general it is, but my dentist and kid's school kept the HEPA filters after covid. It's at least... a little better?
(Speaking personally, my home indoor air quality is now awesome and I love it. Wish it hadn't taken a pandemic to clue me in, though.)
schiffern 15 hours ago [-]
AirFanta creator Adam Wong has a version using a 3D-printed adapter to 8" circular duct.[0]
In newer builds he places the purifier box indoors and simply reverses the orientation of the fans and filters. This keeps the box protected from weather, and the duct can be run in such a way as to keep out rain or dripping.
The AirFanta is actually rated as EPA E11 (95%) not HEPA H13 (99.97%), so if you're trying to keep out everything in one single pass like a clean room then AirFanta might not be best. It may be a good idea to check the real-world interception performance with a particle counter.
An ERV with HEPA filter may be a better, less improvised option. Most systems can be adjusted for positive pressure, although the intent is balanced airflow.
schiffern 4 hours ago [-]
If the airflow isn't balanced, there's little point to using an ERV. If half the air is escaping elsewhere, none of that heat is being recovered. You might as well delete the ERV and just use half the airflow, because that will get the same positive pressure for the same energy loss.
mitxela 3 hours ago [-]
What if it's only 1% of air escaping
schiffern 2 hours ago [-]
Then it's 100x oversized for the purpose of pressurizing the structure. ;)
ERVs are great for increasing air exchange (two-way flow), but unnecessary when pressurizing because that's one-way flow by definition.
If you already bought an ERV it makes sense to combine the functions, simply because you already bought the expensive ERV hardware. But if you weren't planning to install an ERV anyway, it doesn't make sense to install one just for this project, because it won't do anything to reduce the heating/cooling loss from this type of system.
The one-way component of flow is still 100% non-recuperated. If you install a cheap 100 CFM positive pressure system and it burns an extra $100, then setting your ERV to be unbalanced by 100 CFM will cost that same $100. Same leak rate, same heat loss, same cost!
This is one of those deceptive math problems where it seems like it should work, but really it works out "six of one and half-dozen of the other."
mitxela 2 hours ago [-]
I didn't understand the purpose as pressurising the structure. I understood the purpose as ventilating the interior, providing a central place to attach a filter, and preventing air from coming in from other places.
schiffern 2 hours ago [-]
Yes, exactly! If you're ventilating the interior then using an ERV makes sense. If you're preventing air from coming in from other places, then the ERV doesn't save anything, because (intentionally) 100% of the incoming airflow is leaking out somewhere, so there's nothing for the ERV to do.
I edited my post above to hopefully make it a bit more clear, but it seems you get it right away! Cheers
mitxela 58 minutes ago [-]
Right but they didn't want to stop air coming in. They just wanted all incoming air to be filtered.
schiffern 47 minutes ago [-]
>they didn't want to stop air coming in
They did, though! The entire point of positively pressurizing a structure is that any small leaks will instead result in clean air leaking out, which prevents dirty air from leaking in. This is how (most) cleanrooms work.
mitxela 44 minutes ago [-]
That's so the one central point of air ingress is the one with the filter. Air still gets in - through the filter.
schiffern 29 minutes ago [-]
Bingo.
The neat thing is, if you're already accepting this heat loss penalty anyway (in the service of positive pressure), it greatly reduces or even eliminates the ERV you need to maintain good indoor CO2. So in addition to better indoor AQI, positive pressure can greatly reduce total equipment cost.
Seems like a win/win to me!
Buckminster Fuller proposed a similar scheme in his Dymaxion House (even removing dust via baseboard vents), but it used passive heating and cooling so there was little penalty.
What ended up making a difference for us, is buying a portable industrial air scrubber, of the kind construction/remediation sites use to clean the smoke and dust (and mold, and asbestos, etc) they’re generating out of the air before it gets vented outside (see e.g. https://a.co/d/01lTtyuZ); and plumbing this machine into our apartment in reverse: putting it out on our (covered) balcony, with it exhausting the “scrubbed” air into the apartment. (I made a little sliding-door shim of the type people use to pipe portable AC units outside, just with the hose on the other side.)
Generally works great. We run it on a very low speed, so it’s surprisingly quiet (no louder than other fans we have for air circulation, and a more pleasant frequency because of the large diameter of the fan it has inside.) The pre-filters get absolutely caked with exhaust and road dust after ~2wks, and start to let through an odd stench at that point, so we’re actually replacing those faster than even is recommended for the industrial use-case. But the actual main HEPA filter inside the unit seems to last longer than in industrial usage.
And so the question of what effects getting rid of several-yearly respiratory infections would have on our health and the development of children remains open.
(Speaking personally, my home indoor air quality is now awesome and I love it. Wish it hadn't taken a pandemic to clue me in, though.)
In newer builds he places the purifier box indoors and simply reverses the orientation of the fans and filters. This keeps the box protected from weather, and the duct can be run in such a way as to keep out rain or dripping.
The AirFanta is actually rated as EPA E11 (95%) not HEPA H13 (99.97%), so if you're trying to keep out everything in one single pass like a clean room then AirFanta might not be best. It may be a good idea to check the real-world interception performance with a particle counter.
[0] https://x.com/Engineer_Wong/status/2034098395376455946
https://www.reddit.com/r/crboxes/comments/1ef3dly/positive_p...
ERVs are great for increasing air exchange (two-way flow), but unnecessary when pressurizing because that's one-way flow by definition.
If you already bought an ERV it makes sense to combine the functions, simply because you already bought the expensive ERV hardware. But if you weren't planning to install an ERV anyway, it doesn't make sense to install one just for this project, because it won't do anything to reduce the heating/cooling loss from this type of system.
The one-way component of flow is still 100% non-recuperated. If you install a cheap 100 CFM positive pressure system and it burns an extra $100, then setting your ERV to be unbalanced by 100 CFM will cost that same $100. Same leak rate, same heat loss, same cost!
This is one of those deceptive math problems where it seems like it should work, but really it works out "six of one and half-dozen of the other."
I edited my post above to hopefully make it a bit more clear, but it seems you get it right away! Cheers
The neat thing is, if you're already accepting this heat loss penalty anyway (in the service of positive pressure), it greatly reduces or even eliminates the ERV you need to maintain good indoor CO2. So in addition to better indoor AQI, positive pressure can greatly reduce total equipment cost.
Seems like a win/win to me!
Buckminster Fuller proposed a similar scheme in his Dymaxion House (even removing dust via baseboard vents), but it used passive heating and cooling so there was little penalty.