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For winter WFH in a rental, there aren't many commercial options for energy efficient ventilation to keep CO2 at reasonable levels for cognition. DIY HRV with

For winter WFH in a rental, there aren't many commercial options for energy efficient ventilation to keep CO2 at reasonable levels for cognition. DIY HRV with coroplast can be customized for small spaces. For those with more room, an exhaust duct can transfer heat to cold intake air, https://www.loudawson.com/17884/how-to-build-air-cross-flow-heat-exchanger/ https://www.loudawson.com/17884/how-to-build-air-cross-flow-.... Commercial units start around $1K+, https://www.sylvane.com/search/results/?keywords=hrv https://www.sylvane.com/search/results/?keywords=hrv. One can also combine a DIY enclosure with commercial parts, e.g. crossflow, https://www.aliexpress.us/item/3256801499168685.html https://www.aliexpress.us/item/3256801499168685.html or ductless, https://www.aliexpress.us/item/3256805773352155.html https://www.aliexpress.us/item/3256805773352155.html. ERV pros/cons and review of $500 Panasonic FV-04VE1 ventilation fan: https://doctorpapadopoulos.com/in-depth-advantages-and-disadvantages-of-energy-recovery-ventilators-erv/ https://doctorpapadopoulos.com/in-depth-advantages-and-disad... & https://www.amazon.com/Panasonic-FV-04VE1-WhisperComfortTM-Ventilation-Patent-Pending/dp/B000XJNZ1Y/ https://www.amazon.com/Panasonic-FV-04VE1-WhisperComfortTM-V....

TheWoolRug 3y ago
In a rental where you can't cut through the walls introduces challenges. I wonder if anyone has created a DIY window unit that incorporates a "ZEHNDER COMFOAIR 70" which is a small contained HRV unit that has c02 detection and can ramp fan speed to match co2. https://www.smallplanetsupply.com/small-planet-blog/2020/6/6/fresh-air-in-a-tiny-size https://www.smallplanetsupply.com/small-planet-blog/2020/6/6...
- andbberger 3y ago
  you can hookup the panasonic unit to a window manifold for a portable AC and put some insulation board over that. that is the only reasonable solution I have found for the states
  - aifooh7Keew6xoo 3y ago
    I've had good success adding various utility and ventilation feed throughs in rentals with sliding glass door inserts, including large ducts for various HVAC experiments. I start with a board and cut/slot it so it fits neatly into the top and bottom tracks, then I move the latch receiver to the board, zip a few screws through the board where the holes won't be noticed. The glass door opening becomes a bit narrower, and I can cut as many holes as I want in that little bit of wall. If it's painted white it usually ends up looking better than most of the corporate maintenance work on the building.
- walterbell 3y ago
  Bionaire Everfresh (circa 2005) $150 window HRV was discontinued, https://www.youtube.com/watch?v=OcVowAsYVI4 https://www.youtube.com/watch?v=OcVowAsYVI4 $300 option from Alibaba, http://mistersustainable.blogspot.com/2021/08/another-mini-energy-recovery-ventilator.html http://mistersustainable.blogspot.com/2021/08/another-mini-e... $700+ options, https://old.reddit.com/r/hvacadvice/comments/wdl0mn/do_window_erv_or_hrv_units_exist/?rdt=63814 https://old.reddit.com/r/hvacadvice/comments/wdl0mn/do_windo... OpenERV design (writeup pending), https://x.com/open_erv https://x.com/open_erv
sarchertech 3y ago
The CO2 cognition studies are almost definitely wrong. The military has done numerous studies over the decades with much much higher CO2 levels with none of the reported cognitive results reported more recently. The CO2 cognition studies show huge results. It’s virtual impossible that none of the military CO2 studies would have picked this up with much higher CO2 levels. Also navies the world over have been running submarines for decades with astronomically high CO2 levels with no reported cognitive deficits. Whatever these recent CO2 cognitive decline studies are measuring it’s not coming from CO2. One of the commonly citied cognitive decline studies shows a 50% reduction in cognitive ability at 1,400ppm. Submarines routinely operate at much higher levels and there was a study done where they exposed subjects to 40,000ppm for 2 weeks with no measurable cognitive decline. Here’s a good summary from an old HN comment https://news.ycombinator.com/item?id=19863319 https://news.ycombinator.com/item?id=19863319
- JoshGG 3y ago
  Hi. It would be interesting to read these military studies could you provide some citations or links? Are they published in reputable journals?
  - deleted 3y ago
    [deleted]
  - sarchertech 3y ago
    If you read the comment thread I linked to, you can find links to most of them. The real kicker for me is how absurdly high the effect is in the recent studies. You should basically see A students failing tests when the teacher closes the window. You should see huge swings in standardized test scores based on building ventilation. Companies with good ventilation, should absolutely dominate their markets. And nuclear submariners operating at 10,000 ppm should basically be non functioning if there is any kind of dose dependent effect (which the studies in question say there is).
- porkbeer 3y ago
  Reminder that the military held that 4 hours sleep was plenty for a century, and had data to justify it.
dotancohen 3y ago
Are those Aliexpress ceramic heat exchangers as good as the originals? It would be a shame to install that entire system just to have an ineffective heat exchanger component.
- Open_erv 3y ago
  They vary considerably, the aliexpress ones are about as good, but none of them are very good, they give more like 70% efficiency at the medium flow rate, overall. Not what they claim. They do work though.
- Open_erv 3y ago
  You can 3d print one actually, it works pretty well. The only problem is the alumina has a higher volumetric heat capacity, of about 3.5, whereas PLA has 2.25. Which is pretty high. The thermal conductivity isn't a big deal, the main impediment to heat flow is in the air channel, not the solid material, plastic or ceramic. I commented elsewhere in this thread on how to print your own exchanger relatively easily. You can also get your own fans, so this begs the question of why you would pay $600 for them! Also you need a pair of them, you have to have two of those modules operating, one blowing air in and the other out at any given moment. Then they reverse direction. 70 seconds is a bit long for reversal time, it's better to make it shorter if you can. If you are diying one you can do that. If you try to mod an aliexpress one it's only going to cost more and probably not be as good to be honest, because you can't optimize it. Not hackable!

TheWoolRug 3y ago

In a rental where you can't cut through the walls introduces challenges. I wonder if anyone has created a DIY window unit that incorporates a "ZEHNDER COMFOAIR 70" which is a small contained HRV unit that has c02 detection and can ramp fan speed to match co2. https://www.smallplanetsupply.com/small-planet-blog/2020/6/6/fresh-air-in-a-tiny-size https://www.smallplanetsupply.com/small-planet-blog/2020/6/6...

andbberger 3y ago
you can hookup the panasonic unit to a window manifold for a portable AC and put some insulation board over that. that is the only reasonable solution I have found for the states
- aifooh7Keew6xoo 3y ago
  I've had good success adding various utility and ventilation feed throughs in rentals with sliding glass door inserts, including large ducts for various HVAC experiments. I start with a board and cut/slot it so it fits neatly into the top and bottom tracks, then I move the latch receiver to the board, zip a few screws through the board where the holes won't be noticed. The glass door opening becomes a bit narrower, and I can cut as many holes as I want in that little bit of wall. If it's painted white it usually ends up looking better than most of the corporate maintenance work on the building.
walterbell 3y ago
Bionaire Everfresh (circa 2005) $150 window HRV was discontinued, https://www.youtube.com/watch?v=OcVowAsYVI4 https://www.youtube.com/watch?v=OcVowAsYVI4 $300 option from Alibaba, http://mistersustainable.blogspot.com/2021/08/another-mini-energy-recovery-ventilator.html http://mistersustainable.blogspot.com/2021/08/another-mini-e... $700+ options, https://old.reddit.com/r/hvacadvice/comments/wdl0mn/do_window_erv_or_hrv_units_exist/?rdt=63814 https://old.reddit.com/r/hvacadvice/comments/wdl0mn/do_windo... OpenERV design (writeup pending), https://x.com/open_erv https://x.com/open_erv

sarchertech 3y ago

The CO2 cognition studies are almost definitely wrong. The military has done numerous studies over the decades with much much higher CO2 levels with none of the reported cognitive results reported more recently. The CO2 cognition studies show huge results. It’s virtual impossible that none of the military CO2 studies would have picked this up with much higher CO2 levels. Also navies the world over have been running submarines for decades with astronomically high CO2 levels with no reported cognitive deficits. Whatever these recent CO2 cognitive decline studies are measuring it’s not coming from CO2. One of the commonly citied cognitive decline studies shows a 50% reduction in cognitive ability at 1,400ppm. Submarines routinely operate at much higher levels and there was a study done where they exposed subjects to 40,000ppm for 2 weeks with no measurable cognitive decline. Here’s a good summary from an old HN comment https://news.ycombinator.com/item?id=19863319 https://news.ycombinator.com/item?id=19863319

JoshGG 3y ago
Hi. It would be interesting to read these military studies could you provide some citations or links? Are they published in reputable journals?
- deleted 3y ago
  [deleted]
- sarchertech 3y ago
  If you read the comment thread I linked to, you can find links to most of them. The real kicker for me is how absurdly high the effect is in the recent studies. You should basically see A students failing tests when the teacher closes the window. You should see huge swings in standardized test scores based on building ventilation. Companies with good ventilation, should absolutely dominate their markets. And nuclear submariners operating at 10,000 ppm should basically be non functioning if there is any kind of dose dependent effect (which the studies in question say there is).
porkbeer 3y ago
Reminder that the military held that 4 hours sleep was plenty for a century, and had data to justify it.

dotancohen 3y ago

Are those Aliexpress ceramic heat exchangers as good as the originals? It would be a shame to install that entire system just to have an ineffective heat exchanger component.

Open_erv 3y ago
They vary considerably, the aliexpress ones are about as good, but none of them are very good, they give more like 70% efficiency at the medium flow rate, overall. Not what they claim. They do work though.
Open_erv 3y ago
You can 3d print one actually, it works pretty well. The only problem is the alumina has a higher volumetric heat capacity, of about 3.5, whereas PLA has 2.25. Which is pretty high. The thermal conductivity isn't a big deal, the main impediment to heat flow is in the air channel, not the solid material, plastic or ceramic. I commented elsewhere in this thread on how to print your own exchanger relatively easily. You can also get your own fans, so this begs the question of why you would pay $600 for them! Also you need a pair of them, you have to have two of those modules operating, one blowing air in and the other out at any given moment. Then they reverse direction. 70 seconds is a bit long for reversal time, it's better to make it shorter if you can. If you are diying one you can do that. If you try to mod an aliexpress one it's only going to cost more and probably not be as good to be honest, because you can't optimize it. Not hackable!