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...

Bionaire Everfresh (circa 2005) $150 window HRV was discontinued, https://www.youtube.com/watch?v=OcVowAsYVI4

$300 option from Alibaba, http://mistersustainable.blogspot.com/2021/08/another-mini-e...

$700+ options, https://old.reddit.com/r/hvacadvice/comments/wdl0mn/do_windo...

OpenERV design (writeup pending), https://x.com/open_erv

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

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.

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

Hi. It would be interesting to read these military studies could you provide some citations or links?

Are they published in reputable journals?

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).

Reminder that the military held that 4 hours sleep was plenty for a century, and had data to justify it.

As far as I know the army said (and still says) 4 hours is enough short term in the field not routinely.

If you’re saying they suggested soldiers only need 4 hours of sleep long term, do you have any citations for this? Links to the studies they used to justify it.

Because you can read the studies on CO2 and judge the methodology yourself.

Quite, and given that we are all humans, we should have a fair idea from personal experience.

Yeah, I’m usually a very scientific man deferring to studies over personal feelings, but I can literally feel the mental fog clear up by the minute if I open a window on the afternoon in my study/work room after forgetting to do so in the morning.

Hell, if I have a day where I am quasi-forced to spend most of it in musty rooms, I get a guaranteed headache.

There are so many things other than CO2 that can affect your feeling of mental fog. In addition the placebo effect is very very real.

ISS astronauts are routinely living in a 5000ppm environment. If the size of the effects of these studies were real, they’d be noticeable.

The most commonly cited study shows that 1400ppm cuts basic decision making ability by 25% and complex decision making ability by 50%. The study also shows a dose dependent response.

So how are people routinely operating at nearly 5 times that level for weeks at a time with no noticeable decline?

Results this large should by very easy to detect by simply measuring the CO2 levels at multiple SAT test taking sites and comparing scores.

Even without looking, an effect this large is the kind of thing that would jump out at the College Board or any other standardized test creator anytime they’re looking through their data to normalize scores or detect cheating.

Here in The Netherlands for classrooms we have regulations that aim for a classroom to stay below 950ppm CO2. I think almost every high school kid can remember how drowsy a full, poorly ventilated classroom would get.

Like I said I’m usually a scientific man but this is such a basic thing that anyone with any daily life experience would immediately recognize this 4000ppm (or whatever) as wrong.

Humans are also quite sensitive to noticing when a room is “stuffy”, so, yeah.

Stuffiness is mostly a function of humidity.

The problem with these casual discussions about CO2 levels is they don’t control for other factors. Opening a window definitely wakes you up, but is it the cold breeze or the CO2?

What's the typical temperature change associated with opening the window?

I had some more time today, just with a cursory google I could find at least 5 studies that show cognitive decline with rising CO2 (and PM2.5, but that’s another discussion).

So yeah, my gut feeling was right. It’s probably good to not consider one negative study disproving a body of positive studies.

There’s not one negative study, there’s many studies over many years.

Here’s a good walkthrough of a meta study attempting to figure out what’s going on.

https://www.construction-physics.com/p/we-need-more-research...

The human brain is a hell of a drug.

This is why we do randomized, placebo controlled studies.

Saying “you can feel the mental fog clear” is likely a placebo effect.

As said elsewhere, there’s at least 5 studies that prove what I felt.

Studies that go against more rigorous studies done over the past 50 years.

  > 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.

So dozens of studies by disinterested parties are wrong, yet the studies by a single interested party is right? If you really have good standing for believing this, I would like some more information. I am considering installing such a system.

Thank you.

1. It’s not a single interested party. What I called military studies were by at least 3 completely separate groups. The Navy, the Air Force, and NASA. There have also been studies by the EPA, and “disinterested” academic groups.

2. There aren’t dozens of positive studies. There are a handful by 1 or 2 research groups.

There was a meta analysis in 2020 looking at only the academic literature (so excluding military studies). It found that for every positive result there was at least 1 negative one.

Here’s a good walkthrough of that paper.

https://www.construction-physics.com/p/we-need-more-research...

Thank you, I will read a bit more l.

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.

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.

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!