10 ms·

DIY ventilation heat exchanger (2010)

142 points by walterbell 3y ago

0wis 3y ago
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.
- notyoutube 3y ago
  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…
  - rocqua 3y ago
    It makes a lot of sense to feed your ventilation output to a heatpump input for energy recovery with an air-source heatpump. But otherwise I think there is a lot of value in other forms of heating. Specifically in radiative heating. Floor heating is great for that, but other water-based systems are also possible.
  - geon 3y ago
    > if all the heating were done using ventilation, you might have to live in a very windy house Not an issue at all. A properly installed ceiling vent will blow air along the ceiling, where Bernoulli's principle makes the fast moving air stick to the ceiling until the speed drops enough for the higher density to make it sink gently. https://blog.swegon.com/hs-fs/hubfs/Bild4-1.png?width=1100&name=Bild4-1.png https://blog.swegon.com/hs-fs/hubfs/Bild4-1.png?width=1100&n...
    - briHass 3y ago
      There's also significant engineering calculations and guidelines/rules about the expected volume of air that is expected to enter/exit vents vs their size and grille restrictions. This is more to prevent loud airflow, but there's also charts for air distribution for room sizes. Now, most HVAC contractors go by gut feel/rules of thumb, but if you want to pay for it, a well designed system would never be 'windy' or noisy.
  - ClumsyPilot 3y ago
    > renovating generally means reducing breathability of the house itself, which, combined with the temp difference, means condensation/mold problems Look up Passivehouse standard, modern construction can make extremely effocient buildings, but it relies on the building being nesrly airtight, so it must have ventillation. 'Natural' ventillation naturally steals your heat, it's incompatiable with efficiency
- userbinator 3y ago
  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.
- Open_erv 3y ago
  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.
- smolder 3y ago
  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.
mnw21cam 3y ago
See also https://www.instructables.com/heat-recovery-ventilation/ https://www.instructables.com/heat-recovery-ventilation/
- schiffern 3y ago
  See also also https://youtu.be/w5sR-0oX1dg?t=184 https://youtu.be/w5sR-0oX1dg?t=184 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 https://www.youtube.com/watch?v=LiptsaKmq80
kragen 3y ago
heat exchangers are pretty important. does anyone have a summary of the high points in this thread? https://ecorenovator.org/forum/showpost.php?p=54888&postcount=518 https://ecorenovator.org/forum/showpost.php?p=54888&postcoun... seems to be kostas's summary of their completed build, documented in more detail at https://diyvmc.wordpress.com/ https://diyvmc.wordpress.com/ and with an overview video at https://youtu.be/phIWQD5LAcA https://youtu.be/phIWQD5LAcA 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 3y ago
  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.
  - genman 3y ago
    Also during hot summer when outside temperature is hotter than inside - you don't want ventilation to bring in hot air.
  - kragen 3y ago
    i think heat exchanger ventilation makes roughly the same amount of sense whenever you're spending costly energy to change the temperature of your space, doesn't it? it works just as well to keep summer heat out as to keep winter heat in, and staying cool in summer can be just as critical as staying warm in winter, depending on where you live the main difference is that you can heat up a house (inefficiently) with a nichrome wire or a gas burner, while cooling it requires considerably more elaborate equipment but if electricity costs 2¢ per kilowatt hour and daytime electricity is free, will the savings of a heat exchanger be enough to pay for the device?
jnsaff2 3y ago
This dude built their own and got bad mold problems https://youtu.be/LiptsaKmq80?feature=shared https://youtu.be/LiptsaKmq80?feature=shared
- keep_reading 3y ago
  Exactly my concern... Just buy the Aprilaire 8100 and don't risk mold...
  - dotancohen 3y ago
    What does that system cost? There is no pricing information on the website.
  - persolb 3y ago
    How does that remove the condensation though? That's the cause of the mold problem. Edit: looks like somehow it moves moisture between the exhaust/intake somehow... not just heat.
- zug_zug 3y ago
  Fascinating video. There was a comment on his video asking "Wouldn't this introduce the same amount of humidity/mold as opening a window?" Curious if anybody has any more insight.
  - geon 3y ago
    There could be some issue with condensation. The moisture from the indoor air could get trapped and leak.
  - aifooh7Keew6xoo 3y ago
    I think the issue is that when the heat exchange occurs one way, the HRV is effectively a condenser. Moisture builds on the heat exchange surfaces of the heat exchanger, particulates, spores, etc. in the air deposit nutrients and viable life in the crud, it thrives and multiples right into the incoming airstream for your residence. When the window is opened the air mixes without a surface for condensation and there's much less immediate deposition so there's not an enriched medium to sustain accelerated growth entirely in the air stream, but it still probably occurs to some extent in a more diffuse manner that produces a significantly lower ambient spore/toxin/particulate load
walterbell 3y ago
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.
a1o 3y ago
Wtf are the Ads that replace the images attached to the forum posts?
zug_zug 3y ago
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.
- upofadown 3y ago
  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.
  - Open_erv 3y ago
    This is approximately correct, except for one big problem with counterflow exchangers, which is frost. Even the membrane types still frost up. What you really want is a regenerator, either a thermal wheel or a fixed matrix regenerator, if you really want maximal efficiency. And it should be what they call the total sorption type, so it has some adsorbent in it. Even then the latent efficiency could be improved with a better adsorbent, the industry standard is zeolite 3A. It's good because it lasts. Silica gel becomes slowly inactive as it adsorbs other stuff that clogs the adsorptions sites basically. But the adsorbent only starts adsorbing at about 60% RH. So in some cases that actually leads to efficiency loss, compared to some kind of ideal adsorbent that adsorbed at any differential.
doctorhandshake 3y ago
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. 1 https://www.gologic.us/ https://www.gologic.us/
scotty79 3y ago
Shouldn't it also recapture moisture as well?
Open_erv 3y ago
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.
aurizon 3y ago
A number of youtubes pop up. https://www.youtube.com/results?search_query=DIY+recuperator https://www.youtube.com/results?search_query=DIY+recuperator and the goog has a few more. https://www.google.com/search?q=DIY%2Brecuperator&rlz=1C1CHBF_enCA924CA924&oq=DIY%2Brecuperator&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIGCAEQRRg80gEJMzY0NWowajE1qAIAsAIA&sourceid=chrome&ie=UTF-8 https://www.google.com/search?q=DIY%2Brecuperator&rlz=1C1CHB...
symlinkk 3y ago
Why is HN obsessed with air quality?
serpix 3y ago
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. https://www.nilan.fi/tuotteet/poistoilmalampopumput/vgu/vgu-250-sol/ https://www.nilan.fi/tuotteet/poistoilmalampopumput/vgu/vgu-...
dclowd9901 3y ago
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.

142 points by walterbell 3y ago

0wis 3y ago

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.

notyoutube 3y ago
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…
- rocqua 3y ago
  It makes a lot of sense to feed your ventilation output to a heatpump input for energy recovery with an air-source heatpump. But otherwise I think there is a lot of value in other forms of heating. Specifically in radiative heating. Floor heating is great for that, but other water-based systems are also possible.
- geon 3y ago
  > if all the heating were done using ventilation, you might have to live in a very windy house Not an issue at all. A properly installed ceiling vent will blow air along the ceiling, where Bernoulli's principle makes the fast moving air stick to the ceiling until the speed drops enough for the higher density to make it sink gently. https://blog.swegon.com/hs-fs/hubfs/Bild4-1.png?width=1100&name=Bild4-1.png https://blog.swegon.com/hs-fs/hubfs/Bild4-1.png?width=1100&n...
  - briHass 3y ago
    There's also significant engineering calculations and guidelines/rules about the expected volume of air that is expected to enter/exit vents vs their size and grille restrictions. This is more to prevent loud airflow, but there's also charts for air distribution for room sizes. Now, most HVAC contractors go by gut feel/rules of thumb, but if you want to pay for it, a well designed system would never be 'windy' or noisy.
- ClumsyPilot 3y ago
  > renovating generally means reducing breathability of the house itself, which, combined with the temp difference, means condensation/mold problems Look up Passivehouse standard, modern construction can make extremely effocient buildings, but it relies on the building being nesrly airtight, so it must have ventillation. 'Natural' ventillation naturally steals your heat, it's incompatiable with efficiency
userbinator 3y ago
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.
Open_erv 3y ago
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.
smolder 3y ago
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.

mnw21cam 3y ago

See also https://www.instructables.com/heat-recovery-ventilation/ https://www.instructables.com/heat-recovery-ventilation/

schiffern 3y ago
See also also https://youtu.be/w5sR-0oX1dg?t=184 https://youtu.be/w5sR-0oX1dg?t=184 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 https://www.youtube.com/watch?v=LiptsaKmq80

kragen 3y ago

heat exchangers are pretty important. does anyone have a summary of the high points in this thread? https://ecorenovator.org/forum/showpost.php?p=54888&postcount=518 https://ecorenovator.org/forum/showpost.php?p=54888&postcoun... seems to be kostas's summary of their completed build, documented in more detail at https://diyvmc.wordpress.com/ https://diyvmc.wordpress.com/ and with an overview video at https://youtu.be/phIWQD5LAcA https://youtu.be/phIWQD5LAcA 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 3y ago
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.
- genman 3y ago
  Also during hot summer when outside temperature is hotter than inside - you don't want ventilation to bring in hot air.
- kragen 3y ago
  i think heat exchanger ventilation makes roughly the same amount of sense whenever you're spending costly energy to change the temperature of your space, doesn't it? it works just as well to keep summer heat out as to keep winter heat in, and staying cool in summer can be just as critical as staying warm in winter, depending on where you live the main difference is that you can heat up a house (inefficiently) with a nichrome wire or a gas burner, while cooling it requires considerably more elaborate equipment but if electricity costs 2¢ per kilowatt hour and daytime electricity is free, will the savings of a heat exchanger be enough to pay for the device?

jnsaff2 3y ago

This dude built their own and got bad mold problems https://youtu.be/LiptsaKmq80?feature=shared https://youtu.be/LiptsaKmq80?feature=shared

keep_reading 3y ago
Exactly my concern... Just buy the Aprilaire 8100 and don't risk mold...
- dotancohen 3y ago
  What does that system cost? There is no pricing information on the website.
- persolb 3y ago
  How does that remove the condensation though? That's the cause of the mold problem. Edit: looks like somehow it moves moisture between the exhaust/intake somehow... not just heat.
zug_zug 3y ago
Fascinating video. There was a comment on his video asking "Wouldn't this introduce the same amount of humidity/mold as opening a window?" Curious if anybody has any more insight.
- geon 3y ago
  There could be some issue with condensation. The moisture from the indoor air could get trapped and leak.
- aifooh7Keew6xoo 3y ago
  I think the issue is that when the heat exchange occurs one way, the HRV is effectively a condenser. Moisture builds on the heat exchange surfaces of the heat exchanger, particulates, spores, etc. in the air deposit nutrients and viable life in the crud, it thrives and multiples right into the incoming airstream for your residence. When the window is opened the air mixes without a surface for condensation and there's much less immediate deposition so there's not an enriched medium to sustain accelerated growth entirely in the air stream, but it still probably occurs to some extent in a more diffuse manner that produces a significantly lower ambient spore/toxin/particulate load

walterbell 3y ago

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.

a1o 3y ago

Wtf are the Ads that replace the images attached to the forum posts?

zug_zug 3y ago

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.

upofadown 3y ago
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.
- Open_erv 3y ago
  This is approximately correct, except for one big problem with counterflow exchangers, which is frost. Even the membrane types still frost up. What you really want is a regenerator, either a thermal wheel or a fixed matrix regenerator, if you really want maximal efficiency. And it should be what they call the total sorption type, so it has some adsorbent in it. Even then the latent efficiency could be improved with a better adsorbent, the industry standard is zeolite 3A. It's good because it lasts. Silica gel becomes slowly inactive as it adsorbs other stuff that clogs the adsorptions sites basically. But the adsorbent only starts adsorbing at about 60% RH. So in some cases that actually leads to efficiency loss, compared to some kind of ideal adsorbent that adsorbed at any differential.

doctorhandshake 3y ago

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. 1 https://www.gologic.us/ https://www.gologic.us/

scotty79 3y ago

Shouldn't it also recapture moisture as well?

Open_erv 3y ago

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.

aurizon 3y ago

A number of youtubes pop up. https://www.youtube.com/results?search_query=DIY+recuperator https://www.youtube.com/results?search_query=DIY+recuperator and the goog has a few more. https://www.google.com/search?q=DIY%2Brecuperator&rlz=1C1CHBF_enCA924CA924&oq=DIY%2Brecuperator&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIGCAEQRRg80gEJMzY0NWowajE1qAIAsAIA&sourceid=chrome&ie=UTF-8 https://www.google.com/search?q=DIY%2Brecuperator&rlz=1C1CHB...

symlinkk 3y ago

Why is HN obsessed with air quality?

serpix 3y ago

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. https://www.nilan.fi/tuotteet/poistoilmalampopumput/vgu/vgu-250-sol/ https://www.nilan.fi/tuotteet/poistoilmalampopumput/vgu/vgu-...

dclowd9901 3y ago

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.