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.
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.
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.
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.
It seems that the problems he had were in summer. There's many climates where HRVs are only really needed in winter - in which case those problems wouldn't happen.
Basically, as long as the outside air is drier than the inside air, an HRV will work well. The moment the outside air contains more moisture, ventilating will just drive up the humidity of your space - causing many issues.
Interesting subject tackling two important home issues at the same time : ventilation and heat exchange.
It seems like a way to get the best of both worlds.
However, I do not know why this forum is relevant or interesting. DIY solutions are easily doable but is it really surprising ? I am sure people have done this with old fridge parts, as someone suggest in the last post.
Yes, DIY can be cheaper but reliability is key for such systems. Size can also be key.
Yes, DIY can be cheaper but reliability is key for such systems.
If you know what you're doing (not hard to these days with so much information online), and depending on where you live, DIY HVAC can be far more reliable than getting a "licensed professional" who will attempt to overcharge for mediocre work or even scam you.
Reacting to your first point: As far as I know (western europe), heatpumps mostly are used to heat water to then heat your house, and renovating generally means reducing breathability of the house itself, which, combined with the temp difference, means condensation/mold problems.
You then have to correct that by opening windows intelligently or installing air ventilation, and then a heat exchanger to not lose too much heat.
Like you say, it seems to be a no-brainer then to instead combine heat pump _and_ ventilation, so that the ventilation itself works with a heat pump.
The only counter-argument I have is that if all the heating were done using ventilation, you might have to live in a very windy house, but I feel like entirely decoupling the two is not the best solution to that problem…
There was a period where I considered DIY for such machines impractical. I now think that to diy all the way through is impractical, the design process is too laborious even for those suitably skilled. However once the design is worked out it is actually pretty practical, with a 3d printer. You definitely have to own the printer, they charge way too much to have things printed at cloud services for some reason.
I have pubished my STL files for an earlier version of the TW4 energy recovery ventilator. It's totally practical to make your own with a printer, but it would take you a few days of labor time for sure to get everything working nicely.
Reliability is very much on offer even with diy. In reality I have looked at many commercial units and they have serious reliability problems for long term like 5 years or more, and we should be planning for 50 years wherever building tech is concerned, imo.
DIY is practice at learning new things and implementing what you've learned. It's a very good thing in that sense. Also, a healthy DIY (or maker, if you prefer) community is good as a check on commercial offerings. If businesses try to overcharge for something or don't offer it on acceptable terms, and you have a great need, having a 2nd way is important.
Making your own HRV may or may not be worthwhile for everyone who does so, but more people learning how to make one is doubtless a good thing.
Commercial units coupled with a heat pump rival ground source heat pumps at a massive 4 - 5 COP. They even heat water and can take in solar heat piping.
Love the idea. Curious if there's any maximal theoretical efficiency. It seems to me that if you had a wide pipe with a narrow pipe inside (each going different directions) that you could theoretically have a system that transfers heat with no loss.
You can in theory extend the length of a counter flow heat exchanger to get whatever efficiency you want. In practice, such a long heat exchanger would transfer significant amounts of heat to/from its environment. So then you are limited by how well you can insulate things.
Dang. Read a comment in this discussion pointing out that an always-on ERV would work well in bathroom / laundry. I just installed a Panasonic ERV for a whole (~500sq ft) space and a Panasonic whisperquiet vent fan turned down to about the same CFM as the ERV in the bathroom as well. Missed opportunity to simplify, consolidate, and make more efficient the necessary moisture control in the bath by solely having the ERV there.
GOLogic homes[1], IIRC, use a ducted ERV with return from bath, laundry, and kitchen, and supply to bedrooms.
In this one the heat exchanger construction is closer to OP, with coroplast sheets glued together. However in a follow-up video, he says this was a bad idea for his humid climate.
i have a couple of big unknowns about ventilation heat exchangers for houses, and i'm wondering if anybody knows the answers to these questions:
- why is everybody using recuperators when a regenerator would be mechanically much simpler? i'd understand if preventing mass flow was important, but in fact this thread says that in some cases they build their recuperators with water-permeable heat exchange membranes in order to facilitate mass flow of water, which is the main mass flow that a regenerator would introduce here. why don't people use regenerators?
- now that the price of solar energy has fallen so much, and in particular solar panels cost half what they did even a year ago, will house ventilation heat exchangers remain economical?
I suppose that heat exchanger ventilation makes most sense at winter time. Not everybody lives in San Diego, a lot of people live in New York, Boston, Chicago, Seattle, etc, where a winter is a thing.
>why is everybody using recuperators when a regenerator would be mechanically much simpler?
They exist, search for "ductless HRV."
They're simply a small fan that reverses every few minutes and a heat storage material. They also have wireless ones that coordinate the fan direction between them.
I would absolutely love to simply have a system that moved air around the house. If you have a house that is 3 stories (one of them an underground basement), you could probably get away with a heat exchanger on the ground floor and simply running the circulation either up or down depending on the season.
Yet I have never seen a system in a house that just moves air between different levels of a house.
I'm the OpenERV guy. It's been a long road and it's not very open source any more I'll admit, however I did publish a bit Wikifactory article with all the cad etc. for a quite efficient window mount unit. I now have the know how to boost the flow through that thing by 2.5x or so so it could actually be a viable product/machine. However it's not a good business proposition.
There is a whole class of energy recovery ventilators called decentralized, ductless or sometimes push-pull which are quite amenable to DIY. All you need is a good reversible fan and the regenerator and a pipe.
I have shared elsewhere how to 3d print a regenerator. I use a 0.3 mm nozzle and it takes about 24 hours to print a regenerator that can do about 45 cfm at about 80 percent sensible efficiency. Basically just take a cylinder in Cura of the desired diameter, and use lines infill, no top layer, no bottom layer. That's basically it. Make the lines as thin as you can and the line spacing as small as you can while getting the desired airflow. About 2.7 mm on center spacing was about right for me and a typical fan with 6.5 mm stall pressure. The operating point was about 3.5 mm h2o and 45 cfm at maximal fan power.
These devices do capture some water vapor during cold weather because the water vapor condenses on the heat exchanger then re-evaporates.
I have tried sprinkling zeolite and silica gel in there to get good latent heat recover as well and it seems to work pretty well. You don't need much, only about 5 grams of silica gel, more for zeolite 3A molecular sieve.
I have built two window mount units. One for myself, the mega sized one, which there are pics of on my twitter (@open_erv) and also one for my friend Alex, whose landlord wouldn't let him use it, so I sold it for the cost of the parts.
It took forever to sell that thing even at the cost of the parts, so clearly window mount units are not a great business proposition. Also for other reasons, mostly people don't think of them as long term propositions so they aren't willing to amortize the cost of manufacturing a good machine over long periods.
There is one called the purifresh, for windows too.
The ductless models for houses include the lunos e2 for about $1800 CAD and only 25 cfm, and the blauberg Vento (there is another related one called Twinfresh), however I don't believe their noise or efficiency claims, and I have investigated.
There are many cheap chinese knockoffs and some of them aren't too bad Holtop makes one. But mostly they are very poor.
Ultimately I would like to make a hackaday or something that explains how to do all this, with a raspberry pi pico etc. Also an anemometer based on thermistors and the hot wire technique is useful to regulate flow, any extra flow in either direction hurts efficiency.
Thanks for posting with tech details and biz context!
Both Window HRV and Quiet Corsi-Rosenthal MERV13 Air Filter are business projects which deserve attention from those with more money than time. They are compatible with decentralized manufacturing, field testing and new building regulations for indoor air quality.
The US Centers for Disease Control and Prevention has extensively updated its ventilation guidance on helping prevent indoor transmission of the virus that causes Covid-19. The agency had advised people to ventilate indoor air before, but this is the first time a federal agency has set a target – five air changes per hour – for how much rooms and buildings should be ventilated.
Air quality experts cheered the updated recommendations. “It’s a monumental shift. We haven’t had this. We haven’t had health-based ventilation standards,” said Joseph Allen, director of the Harvard Healthy Buildings Program. Allen says that although it’s easy to see the guidance only in the context of Covid-19, it will help with many other airborne hazards like wildfire smoke, allergens and other infectious diseases, such as the flu.
The move comes the day after the US ended its public health emergency for Covid-19.
Very cool project. Thank you for sharing your work.
> Also... useful to regulate flow, any extra flow in either direction hurts efficiency.
I think this factor is what ultimately tips the balance in favor of a centralized "smart" auto-calibrating unit[0] (using simple and reliable pressure sensors) over distributed ductless. However centralized units do have other advantages.[1][2]
I wouldn't get too discouraged just because you had difficulty selling an early unit. Marketing and sales is hard. Reaching the right people and then effectively communicating a product's value is both an art and a science.
BTW don't know if I said this, but there are some reversible fans on digikey that should work. I was going to open them up and paint them with dielectric grease for water resistance. I ordered the 136 mm diameter one, they are pretty expensive and we will see how quiet they are.
[+] [-] walterbell|2 years ago|reply
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-.... Commercial units start around $1K+, 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 or ductless, 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-disad... & https://www.amazon.com/Panasonic-FV-04VE1-WhisperComfortTM-V....
[+] [-] sarchertech|2 years ago|reply
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
[+] [-] TheWoolRug|2 years ago|reply
https://www.smallplanetsupply.com/small-planet-blog/2020/6/6...
[+] [-] dotancohen|2 years ago|reply
[+] [-] jnsaff2|2 years ago|reply
[+] [-] schneems|2 years ago|reply
- ERV - Dehumidifier - HVAC
And basically no regular installer does it right. Lots of efficiency nerds over at Green Home Builders, subscription required.
[+] [-] thadk|2 years ago|reply
[+] [-] leoedin|2 years ago|reply
Basically, as long as the outside air is drier than the inside air, an HRV will work well. The moment the outside air contains more moisture, ventilating will just drive up the humidity of your space - causing many issues.
[+] [-] zug_zug|2 years ago|reply
Curious if anybody has any more insight.
[+] [-] keep_reading|2 years ago|reply
[+] [-] 0wis|2 years ago|reply
[+] [-] userbinator|2 years ago|reply
If you know what you're doing (not hard to these days with so much information online), and depending on where you live, DIY HVAC can be far more reliable than getting a "licensed professional" who will attempt to overcharge for mediocre work or even scam you.
[+] [-] notyoutube|2 years ago|reply
The only counter-argument I have is that if all the heating were done using ventilation, you might have to live in a very windy house, but I feel like entirely decoupling the two is not the best solution to that problem…
[+] [-] Open_erv|2 years ago|reply
I have pubished my STL files for an earlier version of the TW4 energy recovery ventilator. It's totally practical to make your own with a printer, but it would take you a few days of labor time for sure to get everything working nicely.
Reliability is very much on offer even with diy. In reality I have looked at many commercial units and they have serious reliability problems for long term like 5 years or more, and we should be planning for 50 years wherever building tech is concerned, imo.
[+] [-] smolder|2 years ago|reply
Making your own HRV may or may not be worthwhile for everyone who does so, but more people learning how to make one is doubtless a good thing.
[+] [-] serpix|2 years ago|reply
https://www.nilan.fi/tuotteet/poistoilmalampopumput/vgu/vgu-...
[+] [-] zug_zug|2 years ago|reply
[+] [-] upofadown|2 years ago|reply
[+] [-] doctorhandshake|2 years ago|reply
GOLogic homes[1], IIRC, use a ducted ERV with return from bath, laundry, and kitchen, and supply to bedrooms.
1 https://www.gologic.us/
[+] [-] aurizon|2 years ago|reply
and the goog has a few more. https://www.google.com/search?q=DIY%2Brecuperator&rlz=1C1CHB...
[+] [-] mnw21cam|2 years ago|reply
[+] [-] schiffern|2 years ago|reply
In this one the heat exchanger construction is closer to OP, with coroplast sheets glued together. However in a follow-up video, he says this was a bad idea for his humid climate.
https://www.youtube.com/watch?v=LiptsaKmq80
[+] [-] kragen|2 years ago|reply
i have a couple of big unknowns about ventilation heat exchangers for houses, and i'm wondering if anybody knows the answers to these questions:
- why is everybody using recuperators when a regenerator would be mechanically much simpler? i'd understand if preventing mass flow was important, but in fact this thread says that in some cases they build their recuperators with water-permeable heat exchange membranes in order to facilitate mass flow of water, which is the main mass flow that a regenerator would introduce here. why don't people use regenerators?
- now that the price of solar energy has fallen so much, and in particular solar panels cost half what they did even a year ago, will house ventilation heat exchangers remain economical?
[+] [-] nine_k|2 years ago|reply
[+] [-] schiffern|2 years ago|reply
They're simply a small fan that reverses every few minutes and a heat storage material. They also have wireless ones that coordinate the fan direction between them.
[+] [-] andbberger|2 years ago|reply
[+] [-] dclowd9901|2 years ago|reply
Yet I have never seen a system in a house that just moves air between different levels of a house.
[+] [-] Open_erv|2 years ago|reply
There is a whole class of energy recovery ventilators called decentralized, ductless or sometimes push-pull which are quite amenable to DIY. All you need is a good reversible fan and the regenerator and a pipe.
I have shared elsewhere how to 3d print a regenerator. I use a 0.3 mm nozzle and it takes about 24 hours to print a regenerator that can do about 45 cfm at about 80 percent sensible efficiency. Basically just take a cylinder in Cura of the desired diameter, and use lines infill, no top layer, no bottom layer. That's basically it. Make the lines as thin as you can and the line spacing as small as you can while getting the desired airflow. About 2.7 mm on center spacing was about right for me and a typical fan with 6.5 mm stall pressure. The operating point was about 3.5 mm h2o and 45 cfm at maximal fan power.
These devices do capture some water vapor during cold weather because the water vapor condenses on the heat exchanger then re-evaporates.
I have tried sprinkling zeolite and silica gel in there to get good latent heat recover as well and it seems to work pretty well. You don't need much, only about 5 grams of silica gel, more for zeolite 3A molecular sieve.
I have built two window mount units. One for myself, the mega sized one, which there are pics of on my twitter (@open_erv) and also one for my friend Alex, whose landlord wouldn't let him use it, so I sold it for the cost of the parts.
It took forever to sell that thing even at the cost of the parts, so clearly window mount units are not a great business proposition. Also for other reasons, mostly people don't think of them as long term propositions so they aren't willing to amortize the cost of manufacturing a good machine over long periods.
There is one called the purifresh, for windows too.
The ductless models for houses include the lunos e2 for about $1800 CAD and only 25 cfm, and the blauberg Vento (there is another related one called Twinfresh), however I don't believe their noise or efficiency claims, and I have investigated.
There are many cheap chinese knockoffs and some of them aren't too bad Holtop makes one. But mostly they are very poor.
Ultimately I would like to make a hackaday or something that explains how to do all this, with a raspberry pi pico etc. Also an anemometer based on thermistors and the hot wire technique is useful to regulate flow, any extra flow in either direction hurts efficiency.
[+] [-] walterbell|2 years ago|reply
Both Window HRV and Quiet Corsi-Rosenthal MERV13 Air Filter are business projects which deserve attention from those with more money than time. They are compatible with decentralized manufacturing, field testing and new building regulations for indoor air quality.
12 May 2023, https://news.ycombinator.com/item?id=36238958
[+] [-] schiffern|2 years ago|reply
I wouldn't get too discouraged just because you had difficulty selling an early unit. Marketing and sales is hard. Reaching the right people and then effectively communicating a product's value is both an art and a science.
[0] https://www.youtube.com/watch?v=LGB83pSLMiI
[1] https://news.ycombinator.com/item?id=38743885
[2] https://www.youtube.com/watch?v=TChYcSSNXrI
[+] [-] Open_erv|2 years ago|reply
[+] [-] Open_erv|2 years ago|reply
[+] [-] scotty79|2 years ago|reply
[+] [-] a1o|2 years ago|reply
[+] [-] symlinkk|2 years ago|reply