19 ms·

OpenERV

849 points by graboy 2y ago

KETpXDDzR 2y ago
Feature request: Possibility to have more air intake than going out. This creates a positive pressure in your building, e.g., so that you don't get air from your garage into your living space.
PittleyDunkin 2y ago
> clean outdoor air Is the air outdoor or clean? It can't be both! Marketing bullshit aside, this looks great!
- 20after4 2y ago
  That kind of depends on where you live. And this can be combined with air filtration.
  - PittleyDunkin 2y ago
    Definitely in some places, but is there a region where outdoor air is so clean you don't need this device?
    - viraptor 2y ago
      Almost any place away from cities. I've got AQI <30, down to 5 or so, almost the whole year for example. (Apart from during an occasional bushfire) Cities and industrial sites are the exception with bad air quality, not the default.
      - cyberax 2y ago
        That depends, really. If you have an inversion layer going, you can get pretty poor air quality in lots of locations because people use crappy wood-fired stoves that produce a lot of particulates.
        20after4 2y ago
        That does happen occasionally where I live, last night for example. But it's only a single digit number of days out of a year. The rest of the time air quality is very good.
      - vineyardmike 2y ago
        To be fair, "cities are the exception with bad air" neglects the reality that cities are the default for where people live. So the "air near people" is generally city air. That said, I live in SF and my AQI is usually <50. Not as great as 5, but we sometimes get down to single-digits. Cities don't have to have bad air.
    - amluto 2y ago
      The filtration is icing on the cake. You want an HRV or ERV in any location where you want heating or cooling for any non-negligible portion of the year so that you can have energy efficient fresh air.
    - dzhiurgis 2y ago
      I live in small town on NZ coast. Air is very clean. Mosquitos and neighbor's wood burners don't care. ERV is top 3 item in my house (other than induction cooktop and Japanese toilets).
      - willvarfar 2y ago
        (ok nodding to ERV and induction cooktops, but what is a japanese toilet and why are they better? Haven't heard of them from grand-designs and those kind of youtubers)
        kla-s 2y ago
        - auto lid open and close - heated seat - water jet to clean buttocks with subsequent warm air blower - relaxing music speaker (to drown out your defecating sounds and get you started) just some ideas what some (public)/most (nice home) japanese toilets offer, which might be hard to come by anywhere else
        ajolly 2y ago
        This is the first I've heard of auto lid open and close!
        dzhiurgis 2y ago
        Only available on expensive models. Seat heating and washing are the key features.
        dzhiurgis 2y ago
        > hard to come by They are $200-300 online. Not Toto quality, but plenty good enough.
    - macrolime 2y ago
      The ERV itself is for removing CO2, not dust. Especially in cold climates where houses are built to be as air-tight as possible, these are a necessity. Even if you lived in a forest cabin you'd want filters to prevent too much dust and pollen. I've got a dual filter on mine, HEPA and activated carbon filter. The HEPA filter removes dust and pollen. I've found that if I don't use the carbon filter I get higher than recommended levels of NOx.
      - open_erv2 2y ago
        You can add a filter to the TW4, there is an adapter/kit. It's a hepa filter from a car cabin filter system design. You rarely need both anti pollen and also ERV, so you would take the heat exchanger out and just use the filter and fan. As for dust, I recommend a good pc fan filter based appliance, not putting the filter in the flow path of the ERV.
    - jeroenhd 2y ago
      Most people here just open a window when they want to air out a room. That said, that does waste a lot of energy when heating/cooling your home on cold/hot days, so ERVs and HRVs are used to get the clean air in without exchanging heat with the outside world too much. They're quite cheap and effective compared to just running normal ventilation.
  - block_dagger 2y ago
    I live near a ten lane highway. I prefer to keep the outdoor air out, and the indoor air filtered. I could see this being very useful for other dwellings though.
    - amluto 2y ago
      You are either already failing to keep outdoor air out or you are getting too little ventilation. What you want is something like this device with the H13 filter option. Maybe that plus carbon.
    - positr0n 2y ago
      Think of it this way, since you aren't dying of asphyxiation when you sleep at night, you're already getting some air exchange with the outside air. With an ERV you can control how much air you get, and put whatever filter you want in between the outside air and your room. In fact the fancier systems will let you overpressure your house by running the fan pushing in slightly higher than the air pushing out, ensure air only leaks out of your house not in.
- LukeShu 2y ago
  Fairly standard language for describing what an ERV does. Low-CO2 outdoor air vs high-CO2 indoor air, if you prefer. Important for how air-tight modern energy-efficient construction is.
- throw4321 2y ago
  People breathe, so you need outdoor air to replenish the oxygen and get rid of the carbon dioxide. That's "fresh" air. Unfortunately, outdoor air has particulate and ozone pollution. Filtering it gives you "clean" air. In winter and summer, you also heat or cool the indoor air for comfort. If you just pump in outside air, you effectively also pump out the indoor air. This wastes the energy that had gone into heating or cooling it. These systems save that energy by transfering heat between the air that's getting pumped in and the air that's getting pumped out.
20after4 2y ago
This looks really cool! I started to build something like this using thin square aluminum tubing but I never finished the project.
danans 2y ago
The way I like to describe HRV/ERVs to people who don't know about them is: "Imagine you could open a window to get fresh air into your house and stale air out, but when you did so, most of the heat/humidity would stay in during the winter, or stay out during the summer, leaving you just the fresh air". In terms of the effect on environment inside a house, I usually say: "Imagine it's always a fresh-air spring day inside your house" This is a great project. One problem with ERV/HRV systems right now is that they are very expensive niche products. While this system doesn't achieve the extremely high heat recovery efficiencies of counter-flow units, the perfect is the enemy of the good, and this seems like it could be orders of magnitude cheaper.
- llm_trw 2y ago
  Do you have a source explaining how these work? Naively allowing the air columns to thermally mix would result in the average of the inside and outside temp. So how does this do better?
  - LukeShu 2y ago
    Counter-flow heat exchangers. A parallel-flow heat exchanger would result in the average, as you say; but a counter-flow exchanger means that as the formerly-warm air gets progressively cooler, it is exposed to progressively colder air.
    - llm_trw 2y ago
      Duh, thank you for reminding me air flows in a duct.
    - gwd 2y ago
      I've got a counter-flow heat exchanger, but it looks like they're using a different design: > Each OpenERV TW4 module has a very quiet pair of fans, pointed in opposite directions, and a heat exchanger in a 6 inch pipe, that goes through a wall. The hot, polluted air from inside goes out for 30 seconds, and the heat from it is stored in the heat exchanger. > Then, the fan reverses direction, moving clean air from outdoors to the indoors. On it's way in, it picks up that heat from the heat exchanger. This type of heat exchanger is called a regenerative heat exchanger, or less commonly, a regenerator. The kind shown in the video is a recuperative type, not regenerative. Recuperative types are what most people think of, consisting of a thin layer of material that separates two gas streams. Regenerative heat exchangers are different. They briefly store the energy while air flows in one direction, then release it when the air flow reverses. > The OpenERV TW4 modules are made to always work in pairs. One always sucks air while the other blows air, synchronized over WiFi. This should be done, or hot air would be pushed out from the building through the walls during the ingress phase, causing heat loss. https://www.openerv.ca/learn-more https://www.openerv.ca/learn-more
brunoqc 2y ago
Is it safe? I think I heard that home made heat exchangers cause listeria or something like that. Something about condensation.
- danans 2y ago
  IINM, listeria is usually spread by contaminated food, not air.
  - dzhiurgis 2y ago
    Probably meant Legionnaires. Melbourne recently had an outbreak when outdoor cafes used cooling towers (essentially mist sprayers) with some sus water - https://www.health.vic.gov.au/health-alerts/outbreak-of-legionnaires-disease-in-metropolitan-melbourne https://www.health.vic.gov.au/health-alerts/outbreak-of-legi...
    - brunoqc 2y ago
      My bad. Yes, I saw DIY heat exchangers posted in the past and people were worried about Legionella/Legionnaires and mold. It seems scary when we don't know what we are doing. DIY heat exchangers would be so awesome though. Only new constructions are required to have an heat exchanger here.
ilyagr 2y ago
I'm confused how the heat retention could be around 80-90% without expending a ton of energy. Naively, if on average the same amount of air goes in and out, I'd expect the temperature of the heat exchanger (on average in space and time, eventually) to be the average of the outside and inside temperatures. If the outside is hotter, the air coming in would be cooler than the outside air (which is a win), but it couldn't be cooler than the average of the temperatures. So, it would still not be anywhere as cool as the inside air, which doesn't sound like 90% heat retention. Is the heat exchanger attached to a heater or a cooler? The linked video, https://www.youtube.com/watch?v=CDCu0IbEn8Q https://www.youtube.com/watch?v=CDCu0IbEn8Q , would suggest not, as it talks about saving the energy needed for cooling or heating. Is there another clever trick?
- ailawyer 2y ago
  [flagged]
- LukeShu 2y ago
  Counter-flow heat exchangers can be very efficient, without a heater or cooler attached. That said, I don't think I've seen a commercial ERV claim to be more than 80% efficient, so I'm skeptical of the 90% measurement. (I've seen ERVs with heaters attached; but for the purpose of avoiding frost buildup when it's below freezing outside.)
  - cyberax 2y ago
    Commercial HRVs often use rotating disks, not counterflow heat exchangers. Disks are freeze-proof, but they need to be powered.
  - cheeseface 2y ago
    In my experience 80% plus is quite common in the models sold for colder environments. E.g. Mitsubishi electric Lossnay advertises 86%.
- snewman 2y ago
  There isn't a uniform temperature across the entire exchanger. There's a smooth gradient extending from one end to the other. If the outside is hotter, then the inbound air gradually cools as it gives up heat to the outbound air which is gradually warming.
nubinetwork 2y ago
Why can't I just glue a fan to an air filter?
- margalabargala 2y ago
  That won't decrease CO2 or VOC levels.
- stackghost 2y ago
  You could do this as an air purifier, but it will primarily just remove particulates and other HEPA-y things. It won't actually bring fresh outside air in. You could glue a fan to an air filter and then position the thing in a window, to bring in outside air that then gets scrubbed by the filter. But now you're bringing in cold air in the winter, or hot air in the summer. An ERV brings in fresh air and mostly solves the problem of having cold air rushing in on a winter day, or hot air rushing in on a summer day.
- jmb99 2y ago
  Air filters remove particulates down to some size, varying based on the filter. They do not scrub CO2 or CO, nor do they (generally) remove other things like VOCs - unless they’re really, really expensive filters. Opening a window exchanges all that junk to be roughly equal to the baseline of your environment, which for most people is at least lower CO2 levels.
- numpad0 2y ago
  Or open windows, but outside's cold in many places this time of the year. Energy recovery ventilators run stale outgoing air through a heatsink to pre-heat incoming fresh air to save heating costs. Sounds BS but it's a well established and widely used thing.
dzhiurgis 2y ago
I've installed ERV about a year ago. It's great, but kinda overbuilt. The core is some very thin plastic film (some are aluminum). The body around it is 2mm metal. The entire device is 2-3mm metal. There are 2 motors inside that likely need good support, but not reason for this device to cost $1k and weight 30 kg.
littlestymaar 2y ago
What happens to the humidity in the outflow air when it cools down and condense?
- open_erv2 2y ago
  It condenses on the heat exchanger, then it evaporates when the airflow reverses direction. That's if you don't have sorbent. If you have sorbent, it gets grabbed out of the air before it can condense.
ra 2y ago
I'm confused if this is true open source hardware and software or not?
- thanzex 2y ago
  Me too, when reading "open source" I was expecting some design docs or the like. Aside from the general confusion of the website, I haven't been able to find some of the most important information. For example, there's no diagram or immediate explanation of the general working principle and airflow path. The heat exchanger itself is published only as-is for those designs, while the author writes that he uses a custom python script tuned for the design size and his 3d printer to generate it. When i saw this I immediately thought of studying it and reuse some of its designs for my custom use case, which does not appear to be currently possible. At first glance it appears to be "open source" in the sense that you can buy it, but if and when something breaks you can print/reorder it easily. Correct me if i'm wrong
- jeroenhd 2y ago
  Under "source code", there's a link to a GDrive with a ton of design files and documentation, as well as source code. These are licensed CC BY-NC-SA 4.0, so depending on your personal definitions, they may or may not be "open source" (IMO they're open source but not FOSS but I've seen others equate open source with FOSS).
  - open_erv2 2y ago
    As a community we need to do some thinking on how open source may sensibly be applied to hardware. Unfortunately Prusa, who used to be a real champion, has departed from the assumed True Path, and they have discussed their reasons, which are largely valid. That said their design at a more fundamental level has also departed from a maintainable, simple and elegant design. The purpose of the source code is to enable maintenance, not cloning, I say that on the website. That is this context, there are many others. It improves the economics because the machine lasts longer and there is no planned obsolescence. People are welcome to make their own units from the source if they have the skill, but although it would be fun, I don't really have time to make it easy. Some day there may be a kit which is very economical but it will still take a whole day of work to assemble, probably.
ltbarcly3 2y ago
This is so cool!
madduci 2y ago
Nice idea, but why do they use Google Drive for sharing their code?
- m12k 2y ago
  Poor man's CDN?
  - zo1 2y ago
    Or a very quick way to get your personal email address blocked. Pretty sure this will eventually trigger some sort of automated spam response and that account will promptly get blocked. Hope they used a throwaway google account with absolutely no link to his domains or main email address.
gardenhedge 2y ago
I have a full system in my house. The unit is in the attic space. It's great although it makes a lot of noise, especially in the bedroom below the unit
jsiepkes 2y ago
In the Netherlands these systems are fairly common in new houses. Mostly because the law mandates a certain level of energy efficiency of new houses. There are other ways of obtaining this required efficiency level, but an ERV unit is pretty cost effective. I've personally been looking at installing such a system [1]. However since houses in the Netherlands are almost all made out of concrete installing such a system in an existing house is pretty hard. [1] https://www.duco.eu/uk-ie/products/mechanical-ventilation/ventilation-units/ducobox-energy-premium https://www.duco.eu/uk-ie/products/mechanical-ventilation/ve...
- jacobgorm 2y ago
  Same in Denmark, we pretty much had to install one when building our house, to make up for energy loss from the large window area we wanted. We didn't have it properly calibrated at first, but once that was (professionally) done it has worked perfectly and kept a pleasant indoor-climate ever since. The old-and-trusted brand here is https://www.genvex.com/en https://www.genvex.com/en (ours was supplied by Ecovent though https://ecovent.dk/?lang=en https://ecovent.dk/?lang=en )
- moooo99 2y ago
  Similar story here in Germany. New energy standards require a ventilation concept. Some people choose to rely on daily ventilation to save some money, but most people nowadays opt for an ERV. At least here in Germany, for some reason there are quite a lot of people who are super against the idea of having an ERV. Personally, I wouldn't want to miss is for having fresh air alone, not having to deal with pollen is an added bonus
- open_erv2 2y ago
  My basic understanding is that the thermal energy also costs a lot more over there than it does in north america, like 4x as much.
ggeorg 2y ago
This sounds great! The site left me a bit confused however. Is it open in respect to software/firmware? Or also the hardware? Can I just build my own with stock components? Something was mentioned about a DIY kit... The WM12 is basically two TW4 modules ... Um, TW4? As an ignoramus I need some introduction please...
- ensignavenger 2y ago
  Apparently it isn't open source at all, firmware is CC BY-NC-SA 4.0. It appears that the author does not know what open source means.
Hippocrates 2y ago
What’s so good about fresh air? Like I don’t want stinky stuffy air but as someone with central HVAC I had no issues with my indoor air. Are we trying to get outdoor smells? Or is it something else?
- Slurpee99 2y ago
  Possibly could help with radon poisoning
- reubenmorais 2y ago
  High CO2 levels impair cognition and stale air accumulates pathogens, not just smells. The V in your HVAC stands for Ventilation, so you're already getting fresh air, that's probably why you have no complaints. If you live in an air tight apartment with no forced circulation where CO2 levels spike super fast requiring ventilation several times a day, it's a different story.
- ghosty141 2y ago
  In the winter it's cold outside and opening the window cools down the room -> no ventilation most of the time. In the summer it's not a problem for me, I leave my windows partially open all the time but in the winter especially when working from home this would be quite neat. Also, I live in a small town in germany so the air quality here is comparatively good to many of the city folks here.
wtcactus 2y ago
I'm not understanding if it also filters the outdoor air coming in. I live in a place where supposedly the air is of good quality, and yet, when I open the windows, the all place gets a thin film of black dust on all surfaces - most probably due to the particle emissions and tire degradation dust from vehicles from the highway nearby. The solution I've found is to open the windows every day for about half an hour and then put an air purifier to work.
- londons_explore 2y ago
  it appears the air filter is an optional extra, but incompatible with the storm vent.
  - open_erv2 2y ago
    The filter is a bit messed up right now, you can put one on the TW4 but not the WM12.
torginus 2y ago
This looks wonderful, but it operates on the assumption that outdoor air is something you'd actually want to breathe where you live :) Unfortunately, due to cars and dirty heating systems around where I live, outdoor air tends to be not great.
alextingle 2y ago
How does it avoid short-circuiting when the supply and exhaust vents are so close together? There's lots of text on that web-site, but details of the actual design of the thing are pretty scant.
MichaelRazum 2y ago
Looks interesting. Especially since it seems to be much cheaper that the closed solutions... Have looked in this kind of systems, for my parents. The use case was basically, not about energy efficiency, but rather noise protection - to be able to sleep with a closed windows. I think so far I always had two issues (in that usecase). - First the device by itself - produces a bit noise like 42db might be too much for some people if you want to sleep. Especially some of the devices are using one ventilator, which switches directions and won't produce homogeneous noise. - Second 60 CFM is fine, but if you want to have the feeling of an open window - it should be much more and most devices can't deliver that. Also the heat exchange thing is kind of cool in the winter for sure. In the summer, you often have the case that in the evening you house is much warmer than the air outside - so you would like to turn the heat exchange off in the winter. PS: Actually, maybe looking for a complete different use case. But I think what would be very cool, would be some idea to make at least one room 100% quite (with fresh air ) in a cheap way. Guess this would be a huge life changer for a lot of people, who suffer from noise pollution.
- leoedin 2y ago
  I think that summer/winter distinction is really important. In the UK where most houses don't have air conditioning, you really don't want heat recovery for 1/3 of the year. On really hot days you might want to use heat recovery during the peak few hours, but otherwise you are trying to cool the house down with colder outside air. I would love some sort of intelligent house ventilation system which could do all that. Heat recovery when it makes sense, normal ventilation when it doesn't. All automated based on dT and relative humidities.
  - ZeroGravitas 2y ago
    I think with this model you can do this as long as you install them in a synced pair (which I think is the baseline assumption). Normal (heat recovery mode) you have them reverse flow every 60 seconds or so to swap heat. In cooling mode you just run then continually. One is bringing in fresh air and the other is removing stale air. The heat store in the intake will soon cool to the outside temp and the heat store in the output is irrelevant (apart from maybe slowing the air flow and creating noise). If you manually control the system you could combine with a few open windows to create cross breezes even on still evenings.
4gotunameagain 2y ago
That is very nice, and I really appreciate that the design files are open source. Great work. I cannot help to wonder what brings the total cost to $600, the price of a modern, powerful computer. And yes, I am familiar with the economy of scale :)
- londons_explore 2y ago
  Looks to me like a low cost version of the same could be designed with 2 CPU fans ($1), and a large 3D print ($1 - for the DIY version) or injection moulding for a commercial version ($0.30). Do time-sync between the units with grid frequency sampling (free), and have the whole thing controlled by a 2 cent microcontroller and a pair of triacs. The whole thing, designed and made in China could probably come to a BOM under $4, and retail in the USA for $12.
  - 4gotunameagain 2y ago
    While I agree with your points, $0.30 for injection moulding would need quite the scale, and I have doubts about whether two CPU fans would have enough power to flow enough air even in the absence of a HEPA filter.
    - londons_explore 2y ago
      Injection moulding is cheaper than you imagine now. The cheapest moulds start from about $250, and there are plenty of companies who will make a mould and make and ship 5k parts within 7 days. These designs would need quite a few changes to be injection moulding compatible - for one thing the fins are probably going to have to be flat not circular due to draft angle requirements. Changing the core to a roll of embossed steel foil might be a better bet, and whilst that would add about $1 to the price, it would also make the product work better and be more compact or more efficient due to a higher thermal mass in the core.
      - 4gotunameagain 2y ago
        Got any links for the $250 moulds and companies ? Maybe I could use them in my own project :)
kennethh 2y ago
What would be the advantage compared to commercial products like: https://les.mitsubishielectric.it/en/products/ventilation_377/residential-ventilation_378/de-centralized_528/vl-sr2-vl-eu5_4049.html https://les.mitsubishielectric.it/en/products/ventilation_37... This product cost around 500$ and also has heat exchange. A friend of mine has installed it and is very happy with it.
- open_erv2 2y ago
  It's better compared to a blauberg vento or lunos e2. That product probably gets poor efficiency, I have not checked the technical sheet but if they say 80% that means at the minimal flow levels, which are only 10 cfm or something. The TW4 gets >85% sensible and comparable latent efficiency, at 60 cfm. It also has twice the maximal flow of that device. It's got many other features as well, and is more durable. Ultimately, it's about return on investment. You have to make a spreadsheet and see which one is best, given the actual tested values for efficiency flow, maintenance cost, etc. If that's not possible, it's a shot in the dark.
teekert 2y ago
I so need this, and I so need it to function with Home Assistant. I would love to ventilate based on values of my Aranet 4 (a bluetooth CO2 sensor). Also, would be nice if it coordinates with multiple units, ie what this brand does: [0] EDIT: It does, if you click on "learn more", you'll learn more: "The OpenERV TW4 modules are made to always work in pairs. One always sucks air while the other blows air, synchronized over WiFi. This should be done, or hot air would be pushed out from the building through the walls during the ingress phase, causing heat loss." ...Perfect! Currently I have two holes in my wall for ventilation, when it is windy it's too much (feel the wind blowing inside), when some people visit and there is no wind, boom, >3000 ppm CO2 in 20 minutes. I just really hope it is very quiet, although it says ~37 dBa (which is quite a lot imho), I replaced my bathroom ventilator recently, it produces 25 db! [1]). The previous one [2] produced 52 dB (cheapest around), that was pretty annoying, you'd hear it in the bedrooms above the room it was used in. Maybe 37 dB it isn't so bad, especially since you can wind it down and mostly need it when it's busy/noisy (many people) anyway. Btw, don't buy a CO2 sensor, pretty soon you're a ventilation nerd, or as my wife would call it, a ventilation curmudgeon. [0] https://blaubergventilatoren.de/en/series/vento-expert-a50-1-w https://blaubergventilatoren.de/en/series/vento-expert-a50-1... [1] https://www.filterfabriek.nl/ventilatoren/badkamerventilatoren/blauberg/blauberg-sileo-100mm-aanuit/ https://www.filterfabriek.nl/ventilatoren/badkamerventilator... [2] https://www.hornbach.nl/p/rotheigner-toilet-badkamerventilator-air-basic-100-mm/8626717/ https://www.hornbach.nl/p/rotheigner-toilet-badkamerventilat...
- gcormier 2y ago
  Why not just buy an ERV? It's available, comparable in costs, and in 5-10 years, there will still be parts, unlike this project where the author hasn't actually shared the most crucial component, the exchanger.
- Y_Y 2y ago
  > One always sucks air while the other blows air, synchronized over WiFi. This should be done, or hot air would be pushed out from the building through the walls during the ingress phase, causing heat loss." ...Perfect! Absolutely. > A room is not heated by increasing its internal energy but by decreasing its entropy due to the fact that during heating, the volume and pressure remain constant and air is expelled. https://pubs.aip.org/aapt/ajp/article-abstract/79/1/74/1041804/Thermodynamics-of-heating-a-room?redirectedFrom=fulltext https://pubs.aip.org/aapt/ajp/article-abstract/79/1/74/10418... The point about balancing airflow is crucial, but I think underappreciated by non-professionals. Thermodynamics is highly non-intuitive in places, and the enclosed climate-controlled spaces we love to inhabit are certainly included in that. Don't get me started on the idea that you can cool a closed room by running a fan or opening a fridge.
xnx 2y ago
Great project. Hrv and erv should be a lot more common. Is there a diagram of the airflow in that unit? It looks like the intakes and exhaust on both sides might be very close to each other.
ZeroGravitas 2y ago
There's some comments here suggesting that the incoming and outgoing air pass each other in a heat exchanger. But this is a different model that passes he two streams in turn through a heat sink: > Recuperative types are what most people think of, consisting of a thin layer of material that separates two gas streams. Regenerative heat exchangers are different. They briefly store the energy while air flows in one direction, then release it when the air flow reverses. I have to admit I am slightly more dubious about this type as they are new to me, though I did see a YouTube video about a commercial one recently and they seem to be a hot new thing. Possibly this is something sensible that only becomes practical with software and wireless communication? Rather than running ducts to a central location. Though then fitting two side by side in a window seems odd. Why not use the traditional type in that case?
- mrspuratic 2y ago
  I have two equivalent regenerative commercial units (HRV, no vapour handling) fitted at opposite sides of a mostly open plan ground floor. They use a heavy ceramic core, and sync for opposite or coordinated flow (optional). They go up to 60m3/h (~35CFM) which is extractor fan level for me, 60CFM (~100m3/h) is quite a step up. They were under €200 a unit about 18 months ago. They are rated 90% recovery at low speed. Today it's 11C 75%RH outside, 18C 65%RH inside, at low speed (15m3/h rated at 1.2W) there's barely a difference: 17.8-17.9C air intake temperature. They keep the air noticeably fresh, drier and also keep the CO2 down (<600ppm right now). I'm running them below the "recommended" 50% air-change per hour (ACH about 35%), and boost when needed. There's a recuperative ducted type in the attic for the first floor, when I checked last month it was 4C outside, 18C at the outlet vent, and 17C at the inlet vents. That runs at 50% ACH. The reasoning for the paired up window model isn't obvious, maybe a simple increase in capacity. The website is quite clear you need a push/pull pair to be efficient, and an immediately adjacent such pair is not going to work so well.
  - open_erv2 2y ago
    I have traced the air with a smoke generator, there is a youtube video of me doing this on my youtube channel. There is not significant re-inhalation (short circuiting) of the air. The reason for the window mount is that a lot of people rent or otherwise cannot punch holes in their walls. However the reason the window mount is nearly the same as the TW4 (through wall) type, is that I cannot invest the time and money to re-design a whole new machine for a window. The primary value is in the TW4, but a lot of people wanted window mount ones so I helped some people out by deving a quick window adapter and then they helped me out by testing some of the components/the fundamentals of the system in the real world. Unfortunately the window mount units nobody is willing to really pay the cost of manufacture for, so they have to use grade B parts etc. and they have to serve the purpose of testing the TW4 or they aren't worth making.
londons_explore 2y ago
So, this doesn't use a traditional heat exchanger. Instead it appears to "pulse" air inwards then outwards through a series of fins. It effectively heats the fins slightly in one direction, then cools them again slightly in the opposite direction. Same with wetting and drying for recovering moisture. I am surprised that the fins appear to be plastic - one would imagine that steel fins would have far better thermal capacity
londons_explore 2y ago
Less "open" than the name suggests, because the design is for non commercial use only, yet this is very much the kind of product that needs to be sold to see widespread adoption.
- sesm 2y ago
  Mass market product would have a different design, intended for manufacturing at scale. This design is intended for DIY, mass producing with DIY-intended design is too expensive (see Ergodox as an example).
boomskats 2y ago
I was reading up on counter-flow heat exchangers a few weeks ago after I'd just installed a MVHR system and realised that the actual heat exchanger components themselves were, counter-intuitively, a fraction of the price of the whole unit. I was surprised when I saw they're mostly made of thin plastic and don't depend on thermal capacity at all (unlike, say, HX espresso machines). The way they work is quite simple: c w o a │ │ l r └─────────────────────────────────────────────────────┘ d m air at 50 deg ────────────────────────► air now 5 deg o i u d ───┬──┬──┬──── heat exchanging surface─────┬──┬──┬───── t o ── ▼ ▼ ▼ ─────────────────────────────── ▼ ▼ ▼ ──── d o o r air now 45 deg ◄─────────────────────────air at 0 deg o r a ┌─────────────────────────────────────────────────────┐ i │ │ a r i r It's just a bunch of thin parallel channels where warm and cold air flow in opposite directions, separated by thin plastic walls. Because the flows are counter to each other, there's always a temperature difference driving heat transfer across the dividing walls, even as the warm air gradually cools and the cold air gradually warms. The lightweight plastic walls are advantageous here - while plastic isn't particularly conductive, the walls are so thin that heat transfers readily. It's how these heat exchangers can achieve 80-90% efficiency without needing any expensive materials or thermal mass. The warm exhaust air leaves only slightly warmer than the incoming cold air, having transferred most of its heat to the incoming stream. Clever design.
- ent 2y ago
  Thank you for the illustration! I was sitting here, wondering that the whole system sounds paradoxical but seeing it drawn down with the arrows really helped grasp how this works!
- turtlebits 2y ago
  Not sure what you mean by the heat exchanger core being a fraction of the price, but I've seen replacement cores cost around 1/3 of the total unit. They should be made of high thermal conductivity material like resin or ceramic.
mreiner 2y ago
Cool project! Around that topic I can also recommend a channel of this engineer (switch to auto-translate): https://www.youtube.com/watch?v=Cv0s6TgwbJg https://www.youtube.com/watch?v=Cv0s6TgwbJg Paraphrased: - push-pull ventilation is easy to install and comparatively cheap - it's prone to hygiene issues like blowing dirt out of the filters back into the air and providing a moist environment for microorganisms in some operational conditions - it's prone to windy conditions - the numbers stated by commercial vendors seem to have no basis in reality, there seems to be no vendor providing data based on the relevant testing standard for these systems. OPenERV states they want to get it tested by Passivehause institute but also say no lab data measured yet. Might be just my counter-factual gut-feeling, maybe a mechanical window opener based on EspHome for short pulsed passive ventilation intervals is actually more efficient, easier to implement and need less maintenance? Not aware of any comparisons though and last time I checked I could only find some finicky 3d printed actors that might not survive a guest opening the window.
- open_erv2 2y ago
  The TW4 is light years ahead. Higher flow, better efficiency, much quieter, wind compensation, Internet of things functionality. It's not just yet another machine of the same kind. The heat exchanger is very different, the whole design and construction is quite different.
  - deleted 2y ago
    [deleted]
snickerer 2y ago
I use similar decentralized (single-room) ventilation units here in Northern Germany: https://www.bayernluft.de/de/frame.cgi?page=start https://www.bayernluft.de/de/frame.cgi?page=start. I am super happy with them. We now always have air that feels fresh and warm in winter, and the humidity has dropped significantly. There are two types of such ERV devices: 1. Those with only one air channel that switches directions periodically. They use a heat storage element in the airflow. OpenERV belongs to this group. 2. Those with two separate air channels for intake and exhaust at the same time. The air does not mix but passes through a heat exchanger. Bayernlüfter works like this. The only thing I don't like about Bayernlüfter is that it is not open source. It is controlled by a Raspberry Pi (or a similar clone), and I don't have access to it.
woolion 2y ago
Is there any reason the source is available as a Google Drive link and not on Github (or whatever alternative, Gitlab, etc)? Having been burned out by open-source hardware project, checking how healthy the git looks is a good indicator.
- open_erv2 2y ago
  The file limit sizes on github are a problem, there is some workaround but I haven't gotten around to dealing with it yet.
  - dangoodmanUT 2y ago
    Try git lfs
  - sthoward 2y ago
    Try Oxen.ai
    - open_erv2 2y ago
      thanks will do
GistNoesis 2y ago
Here OpenERV use a push-pull ventilation design where air direction is reversed every 30s. This allows energy recuperation and dispense connecting the inlet and the outlet to each other, as each ventilation port alternate role simultaneously. The alternative design is a counter-flow heat exchanger. Using 3d printing and gyroids it seems possible to build quite compact ones. (metal 3d printed heat exchanger for helicopter https://www.youtube.com/watch?v=1qifd3yn9S0 https://www.youtube.com/watch?v=1qifd3yn9S0 ) 3d-printing a counter-flowing heat-exchanger seems interesting but maybe there are some molding issues that need to be taken care of (maybe HEPA filters on the inside in/outlet are sufficient). The main advantage of the heat-exchanger solution is that you won't need specific electronic control and can reuse the standard fans for controlled ventilation, but there is more thermally isolated piping required (and the pipes are quite big (~10cm diameter) because they need to move a lot of air even if the fans are weak). The push-pull system is harder to DIY because most of the off-the shelf fans can't be reversed easily (and 3d printed fans are noisy and inefficient).
deleted 2y ago
[deleted]
open_erv2 2y ago
Hey guys, I am the guy behind the OpenERV company, who designed the TW4 and WM12 ERV units. I'm sorry I don't have a bunch of units ready to ship out, as the site says it's still in beta, I am to be honest kind of taking my time because I have another project, the big quiet fan, which is actually funded a little better, and thus I've been directing most of my time to that. But I do advance this a bit most days. I have a twitter where I tweet my progress : @open_erv, and also I'm on bluesky. I have shipped a few units to other engineers who have/will test the units so I can share third party confirmation for any skeptics. To clarify some of the discussion, it is not a counterflow heat exhanger, it is a regenerative type. https://en.wikipedia.org/wiki/Regenerative_heat_exchanger https://en.wikipedia.org/wiki/Regenerative_heat_exchanger. I prefer this type because they can recover latent heat more effectively than recouperative (such as counterflow) type, and latent heat is 40-50% of the total energy content of the air, seasonal average in Ottawa or Toronto. I am hoping to get the machine tested by the PassiveHaus institute to show beyond doubt how good the efficiency is with a third party test. I have no doubt, I have tested it myself, though. These can theoretically handy any temperature differential, but the TW4 and WM12 are currently made of a polymer that I wouldn't trust in an extremely hot climate combined with direct sunlight. For that reason, I am focussed on cold climate scenarios. I am pretty sure it will not frost up even in extremely cold weather like -30. I used it last year in my window and had no problem, and it did get to like -25 at least iirc.
- open_erv2 2y ago
  Well this was fun and thanks for the discussion, everyone. People are surprisingly nice and sensible and positive here! I used to have another account but lost the password. Perhaps I'll be a reader here in the future. Anyway, I've tried to turn the very temporary influx of interest into something positive and lasting by searching for 2 people who can install and document the install of a pair of TW4 energy recovery ventilators, so anyone who wishes to buy thereafter can know what they are in for on that count. There is another guy Alex who will test flow and efficiency, I've already sent him the stuff. So we get things tested and verified, and I will continue getting a jump on producing units by running the printers and assembling in between when I am doing the more respectably paid work in my life. The kits are on the back burner because even I am still stabilizing the assembly methodology. I even added a new component just recently, a flow straightener that boosts flow by about 10% while allowing noise to be reduced even further. So stabilize, verify, produce, and then after that, within a couple months, I sell in a more or less ordinary way to anyone who wants them. I'm sorry it's not in time for the cold weather, but we have to remember ERV is about the big picture and long term. Like the rest of a building, it's an investment, and the machines are made for (very) good return and long lifespan. I will prepare some WM12 units for those who have asked for them. To be clear I only got 12 emails expressing interest, not an absolute flood, but it's encouraging to know some people "get it" at least. I knew there would only ever be a small trickle of relatively wise people from around the world that appreciate good performance and return on investment. I only need to sell a few pairs per month to make it worthwhile, at the eventual $1300 CAD price tag. I am open to scaling up production with more efficient production methodologies, but I am actually fairly well acquainted with injection molding, machining and other conventional approaches, and they aren't magic. They would help for sure but they wouldn't radically change the price, or the rate of return on investment, and they also take a lot of investment not just for tooling but also re-testing and re-design. I've also changed the design so, so many times after I thought it was done I am highly wary of being locked in.
vizzah 2y ago
I was just recently researching these units.. This model is available in Europe for about 900 EUR: https://www.international.zehnder-systems.com/en/comfortable-indoor-ventilation/products/units/decentralised-ventilation-units/zehnder-comfospot-50 https://www.international.zehnder-systems.com/en/comfortable...
tantalor 2y ago
> Fresh outdoor air But this is actually treating indoor air, that's very confusing. Fresh outdoor air is easy to find: just go outside!
- brodouevencode 2y ago
  You're also only going to get clean outdoor air in rural places where there is no/minimal farming and construction.
wakeforce 2y ago
I'd love to build this. I have access to a 3d printer, use Python, and have some electronics experience. I live in a northern climate and have been eyeing ERV systems for a while. Basically, I'm the perfect target for this. However, reading the docs, they seem written more to discourage any kind of DIY attempt by saying things A, B or C are difficult, than actually explaining how to do them correctly. I'd love to contribute to the project, but it feels like it's not set-up to foster community contribution. If I'm mistaken, I'd love to donate some of my time on this!
- Aurornis 2y ago
  I expected a community open source project from the title, but reading the docs led me to the same conclusion: The website is about convincing you to buy one while discouraging you from attempting to build one. It looks like a fun project. I don’t want to discount what has been designed and built. It is confusing to start reading about the project and discover that it’s more of a business than a community project while simultaneously being unavailable for purchase. The person who built it commented on HN that they’re focused on a 3rd different fan project right now, which brings the future of this project into question. It would be great if a community effort could fork this project and work on making it easier to DIY so the community could push it forward. EDIT: After exploring the files I’m not sure I’d even call this open source. I either can’t find some key files or they’re deliberately excluded. True open source projects would also include the CAD source, not only .STLs so others could adapt and modify the source. I think the open angle on this project is more marketing than substance.
  - open_erv2 2y ago
    The step files are also there, which is the best common denominator for CAD files. Again, it's open source for the purpose of maintenance and repair, not cloning, and frankly earlier on I did make it more community oriented and nobody ever contributed even a little bit, so I just gave up on that idea. The most likely scenario for longer term is that people may submit minor patches or suggestions, which I roll into the hardware or firmware. In reality, hardware is not like software. You can't make changes easily. Some wizards may take it upon themselves to spruce up the firmware with fancy features and release something, which anyone is free to do. There would then be multiple compatible versions of the firmware, one which I curate for reliability with minimal features, and others which others can provide. Same as for 3d printer firmware. The firmware is Micropython, which is extremely easy to understand and modify.
aojdwhsd 2y ago
This looks great. How well does the WM12 circulate the air, with the intake and exhaust being so close?
ucefkh 2y ago
This is amazing but needs much clearer docs rbh
NavinF 2y ago
Could you post a higher quality photo of the heat exchanger? Is it 3d printed plastic? How did you get the fans to run backwards? They look like standard PC fans
funsi 2y ago
I am looking at buying one of these and have had a look at similar (but not open-source) products available on Alibaba, e.g. https://www.alibaba.com/product-detail/Fresh-Air-Ventilation-Eco-Pair-Plus_1600706598634.html https://www.alibaba.com/product-detail/Fresh-Air-Ventilation... Prices there start at $150 + shipping. Has anyone tested these?
coryfklein 2y ago
Wait, is the air outdoors generally cleaner than the air indoors? Certainly not true in the Salt Lake valley for the 4 months of the year we get persistent inversion.
- NavinF 2y ago
  The CO2 levels outside are definitely lower than inside. Often by 4x. Fixing that without freezing is the main use case for an ERV
farawayea 2y ago
Some of these instructions have fiber glass or similar for insulation which appears to be used for this. It's not something anyone would want next to their ventilation system or inside it. This isn't something to even consider without some expert reviews. The projects are also work in progress and overall incomplete with many details missing. Be careful when you do anything involving ERV and HRV. It's very easy to cause serious damage to the property you live in, harm yourself and others in an irreversible way, or even both.
elric 2y ago
I installed a central ERV in my home, a Zehnder ComfoAir Q. Installing it was quite involved, but not hard. Definitely within reach of anyone with basic DIY skills. The hardest part is finding a good spot for the ventilation unit, which is about the size of a large, old CRT TV. You have to run ducting from there to multiple rooms, but their ducting system is easy to install. Mine draws about 20W/hour at its typical setting, and it greatly improves comfort. Keeps some of the humidity out when it's humid out, keeps some moisture in when it's dry out. Fresh air year round. Keeps mosquitos out. Keeps some dust/particulates out. Worth the effort, even in my small house. A decentralized unit would be a lot easier to install, but I imagine it's less efficient, less suitable for larger dwellings, and probably louder. YMMV.
xnx 2y ago
This guy on YouTube built a very clever DIY HRV, but got rid of it and went with a commercial ERV: https://www.youtube.com/watch?v=LiptsaKmq80 https://www.youtube.com/watch?v=LiptsaKmq80
fudged71 2y ago
What happens if power fails or one unit stops working? Without valves, you could get unwanted air exchange through a non-operating unit. The commenters discuss various aspects of the design in detail, but surprisingly no one brings up this potential failure mode.
_yb2s 2y ago
This is really cool! I try to keep CO2 at reasonable levels at home, and that occasionally results in running the heater with the windows open. My friends/family do not understand why I care or would waste energy like that, and seem to think it is a mental illness or something. The worst scenario is during high wildfire smoke events... trying to keep the house sealed enough to keep the smoke out often requires taping door seams, etc. and the CO2 skyrockets.
- willlma 2y ago
  I guess increasing atmospheric CO² by maximizing your fossil fuel usage is one way to equalize the interior and exterior CO² of your house...
  - _yb2s 2y ago
    It's actually pretty minimal- I live in a mild climate, and even doing this sometimes I probably spend under $50/year on home heating and leave the windows cracked most of the time. My home was most likely 'retrofit' in the '90s to make it airtight for efficiency, and even with the windows cracked is too airtight to be healthy, and still more so than it was probably designed for in the ~1950s.
jtbayly 2y ago
I’m interested in this, but I think I just realized that what I want it to do is impossible. We have a fireplace, which is not efficient at all, in part because it sucks cold air in from the outside. I was thinking it would be great it we could use an ERV to condition the air that gets brought in. However, as far as I can tell, the moment you exhaust air from your house in any way except through the ERV itself, the ERV cannot help you with the replacement air that comes in. Is that correct?
- tempestn 2y ago
  It would be cool if someone could build a chimney ERV: extract heat from the dirty air produced by fire, and inject it into fresh air pulled into the living space. So I guess basically it would function like a regular ERV, but with a fire in the exhaust path. (Probably not feasible with a wood fire, but maybe with gas?)
  - tempestn 2y ago
    Maybe this thing works that way? https://www.modlar.com/brands/nu-air-ventilation-systems-inc./ifp-45-condensing-fireplace-condensing-furnace-and-heat-recovery-ventilator/ https://www.modlar.com/brands/nu-air-ventilation-systems-inc...
- turtlebits 2y ago
  If you can use the exhaust heat to temper the incoming outside air, that's all an ERV does. Or, get a direct vent fireplace (draws in outdoor air)
- open_erv2 2y ago
  That is half correct. The TW4 units operate in synchronized pairs. When one is exhausting (egressing), the other is ingressing (bringing air in). This always happens. They even have quite nice pressure sensors that precisely regulate the pressure the fans exert, controlling flow precisely and preventing the house from becoming pressurized at any time, which as you say would imply heat loss.

849 points by graboy 2y ago

Feature request: Possibility to have more air intake than going out. This creates a positive pressure in your building, e.g., so that you don't get air from your garage into your living space.

PittleyDunkin 2y ago

> clean outdoor air Is the air outdoor or clean? It can't be both! Marketing bullshit aside, this looks great!

20after4 2y ago
That kind of depends on where you live. And this can be combined with air filtration.
- PittleyDunkin 2y ago
  Definitely in some places, but is there a region where outdoor air is so clean you don't need this device?
  - viraptor 2y ago
    Almost any place away from cities. I've got AQI <30, down to 5 or so, almost the whole year for example. (Apart from during an occasional bushfire) Cities and industrial sites are the exception with bad air quality, not the default.
    - cyberax 2y ago
      That depends, really. If you have an inversion layer going, you can get pretty poor air quality in lots of locations because people use crappy wood-fired stoves that produce a lot of particulates.
      - 20after4 2y ago
        That does happen occasionally where I live, last night for example. But it's only a single digit number of days out of a year. The rest of the time air quality is very good.
    - vineyardmike 2y ago
      To be fair, "cities are the exception with bad air" neglects the reality that cities are the default for where people live. So the "air near people" is generally city air. That said, I live in SF and my AQI is usually <50. Not as great as 5, but we sometimes get down to single-digits. Cities don't have to have bad air.
  - amluto 2y ago
    The filtration is icing on the cake. You want an HRV or ERV in any location where you want heating or cooling for any non-negligible portion of the year so that you can have energy efficient fresh air.
  - dzhiurgis 2y ago
    I live in small town on NZ coast. Air is very clean. Mosquitos and neighbor's wood burners don't care. ERV is top 3 item in my house (other than induction cooktop and Japanese toilets).
    - willvarfar 2y ago
      (ok nodding to ERV and induction cooktops, but what is a japanese toilet and why are they better? Haven't heard of them from grand-designs and those kind of youtubers)
      - kla-s 2y ago
        - auto lid open and close - heated seat - water jet to clean buttocks with subsequent warm air blower - relaxing music speaker (to drown out your defecating sounds and get you started) just some ideas what some (public)/most (nice home) japanese toilets offer, which might be hard to come by anywhere else
        ajolly 2y ago
        This is the first I've heard of auto lid open and close!
        dzhiurgis 2y ago
        Only available on expensive models. Seat heating and washing are the key features.
        dzhiurgis 2y ago
        > hard to come by They are $200-300 online. Not Toto quality, but plenty good enough.
  - macrolime 2y ago
    The ERV itself is for removing CO2, not dust. Especially in cold climates where houses are built to be as air-tight as possible, these are a necessity. Even if you lived in a forest cabin you'd want filters to prevent too much dust and pollen. I've got a dual filter on mine, HEPA and activated carbon filter. The HEPA filter removes dust and pollen. I've found that if I don't use the carbon filter I get higher than recommended levels of NOx.
    - open_erv2 2y ago
      You can add a filter to the TW4, there is an adapter/kit. It's a hepa filter from a car cabin filter system design. You rarely need both anti pollen and also ERV, so you would take the heat exchanger out and just use the filter and fan. As for dust, I recommend a good pc fan filter based appliance, not putting the filter in the flow path of the ERV.
  - jeroenhd 2y ago
    Most people here just open a window when they want to air out a room. That said, that does waste a lot of energy when heating/cooling your home on cold/hot days, so ERVs and HRVs are used to get the clean air in without exchanging heat with the outside world too much. They're quite cheap and effective compared to just running normal ventilation.
- block_dagger 2y ago
  I live near a ten lane highway. I prefer to keep the outdoor air out, and the indoor air filtered. I could see this being very useful for other dwellings though.
  - amluto 2y ago
    You are either already failing to keep outdoor air out or you are getting too little ventilation. What you want is something like this device with the H13 filter option. Maybe that plus carbon.
  - positr0n 2y ago
    Think of it this way, since you aren't dying of asphyxiation when you sleep at night, you're already getting some air exchange with the outside air. With an ERV you can control how much air you get, and put whatever filter you want in between the outside air and your room. In fact the fancier systems will let you overpressure your house by running the fan pushing in slightly higher than the air pushing out, ensure air only leaks out of your house not in.
LukeShu 2y ago
Fairly standard language for describing what an ERV does. Low-CO2 outdoor air vs high-CO2 indoor air, if you prefer. Important for how air-tight modern energy-efficient construction is.
throw4321 2y ago
People breathe, so you need outdoor air to replenish the oxygen and get rid of the carbon dioxide. That's "fresh" air. Unfortunately, outdoor air has particulate and ozone pollution. Filtering it gives you "clean" air. In winter and summer, you also heat or cool the indoor air for comfort. If you just pump in outside air, you effectively also pump out the indoor air. This wastes the energy that had gone into heating or cooling it. These systems save that energy by transfering heat between the air that's getting pumped in and the air that's getting pumped out.

20after4 2y ago

This looks really cool! I started to build something like this using thin square aluminum tubing but I never finished the project.

danans 2y ago

The way I like to describe HRV/ERVs to people who don't know about them is: "Imagine you could open a window to get fresh air into your house and stale air out, but when you did so, most of the heat/humidity would stay in during the winter, or stay out during the summer, leaving you just the fresh air". In terms of the effect on environment inside a house, I usually say: "Imagine it's always a fresh-air spring day inside your house" This is a great project. One problem with ERV/HRV systems right now is that they are very expensive niche products. While this system doesn't achieve the extremely high heat recovery efficiencies of counter-flow units, the perfect is the enemy of the good, and this seems like it could be orders of magnitude cheaper.

llm_trw 2y ago
Do you have a source explaining how these work? Naively allowing the air columns to thermally mix would result in the average of the inside and outside temp. So how does this do better?
- LukeShu 2y ago
  Counter-flow heat exchangers. A parallel-flow heat exchanger would result in the average, as you say; but a counter-flow exchanger means that as the formerly-warm air gets progressively cooler, it is exposed to progressively colder air.
  - llm_trw 2y ago
    Duh, thank you for reminding me air flows in a duct.
  - gwd 2y ago
    I've got a counter-flow heat exchanger, but it looks like they're using a different design: > Each OpenERV TW4 module has a very quiet pair of fans, pointed in opposite directions, and a heat exchanger in a 6 inch pipe, that goes through a wall. The hot, polluted air from inside goes out for 30 seconds, and the heat from it is stored in the heat exchanger. > Then, the fan reverses direction, moving clean air from outdoors to the indoors. On it's way in, it picks up that heat from the heat exchanger. This type of heat exchanger is called a regenerative heat exchanger, or less commonly, a regenerator. The kind shown in the video is a recuperative type, not regenerative. Recuperative types are what most people think of, consisting of a thin layer of material that separates two gas streams. Regenerative heat exchangers are different. They briefly store the energy while air flows in one direction, then release it when the air flow reverses. > The OpenERV TW4 modules are made to always work in pairs. One always sucks air while the other blows air, synchronized over WiFi. This should be done, or hot air would be pushed out from the building through the walls during the ingress phase, causing heat loss. https://www.openerv.ca/learn-more https://www.openerv.ca/learn-more

brunoqc 2y ago

Is it safe? I think I heard that home made heat exchangers cause listeria or something like that. Something about condensation.

danans 2y ago
IINM, listeria is usually spread by contaminated food, not air.
- dzhiurgis 2y ago
  Probably meant Legionnaires. Melbourne recently had an outbreak when outdoor cafes used cooling towers (essentially mist sprayers) with some sus water - https://www.health.vic.gov.au/health-alerts/outbreak-of-legionnaires-disease-in-metropolitan-melbourne https://www.health.vic.gov.au/health-alerts/outbreak-of-legi...
  - brunoqc 2y ago
    My bad. Yes, I saw DIY heat exchangers posted in the past and people were worried about Legionella/Legionnaires and mold. It seems scary when we don't know what we are doing. DIY heat exchangers would be so awesome though. Only new constructions are required to have an heat exchanger here.

ilyagr 2y ago

I'm confused how the heat retention could be around 80-90% without expending a ton of energy. Naively, if on average the same amount of air goes in and out, I'd expect the temperature of the heat exchanger (on average in space and time, eventually) to be the average of the outside and inside temperatures. If the outside is hotter, the air coming in would be cooler than the outside air (which is a win), but it couldn't be cooler than the average of the temperatures. So, it would still not be anywhere as cool as the inside air, which doesn't sound like 90% heat retention. Is the heat exchanger attached to a heater or a cooler? The linked video, https://www.youtube.com/watch?v=CDCu0IbEn8Q https://www.youtube.com/watch?v=CDCu0IbEn8Q , would suggest not, as it talks about saving the energy needed for cooling or heating. Is there another clever trick?

ailawyer 2y ago
[flagged]
LukeShu 2y ago
Counter-flow heat exchangers can be very efficient, without a heater or cooler attached. That said, I don't think I've seen a commercial ERV claim to be more than 80% efficient, so I'm skeptical of the 90% measurement. (I've seen ERVs with heaters attached; but for the purpose of avoiding frost buildup when it's below freezing outside.)
- cyberax 2y ago
  Commercial HRVs often use rotating disks, not counterflow heat exchangers. Disks are freeze-proof, but they need to be powered.
- cheeseface 2y ago
  In my experience 80% plus is quite common in the models sold for colder environments. E.g. Mitsubishi electric Lossnay advertises 86%.
snewman 2y ago
There isn't a uniform temperature across the entire exchanger. There's a smooth gradient extending from one end to the other. If the outside is hotter, then the inbound air gradually cools as it gives up heat to the outbound air which is gradually warming.

nubinetwork 2y ago

Why can't I just glue a fan to an air filter?

margalabargala 2y ago
That won't decrease CO2 or VOC levels.
stackghost 2y ago
You could do this as an air purifier, but it will primarily just remove particulates and other HEPA-y things. It won't actually bring fresh outside air in. You could glue a fan to an air filter and then position the thing in a window, to bring in outside air that then gets scrubbed by the filter. But now you're bringing in cold air in the winter, or hot air in the summer. An ERV brings in fresh air and mostly solves the problem of having cold air rushing in on a winter day, or hot air rushing in on a summer day.
jmb99 2y ago
Air filters remove particulates down to some size, varying based on the filter. They do not scrub CO2 or CO, nor do they (generally) remove other things like VOCs - unless they’re really, really expensive filters. Opening a window exchanges all that junk to be roughly equal to the baseline of your environment, which for most people is at least lower CO2 levels.
numpad0 2y ago
Or open windows, but outside's cold in many places this time of the year. Energy recovery ventilators run stale outgoing air through a heatsink to pre-heat incoming fresh air to save heating costs. Sounds BS but it's a well established and widely used thing.

dzhiurgis 2y ago

I've installed ERV about a year ago. It's great, but kinda overbuilt. The core is some very thin plastic film (some are aluminum). The body around it is 2mm metal. The entire device is 2-3mm metal. There are 2 motors inside that likely need good support, but not reason for this device to cost $1k and weight 30 kg.

littlestymaar 2y ago

What happens to the humidity in the outflow air when it cools down and condense?

open_erv2 2y ago
It condenses on the heat exchanger, then it evaporates when the airflow reverses direction. That's if you don't have sorbent. If you have sorbent, it gets grabbed out of the air before it can condense.

ra 2y ago

I'm confused if this is true open source hardware and software or not?

thanzex 2y ago
Me too, when reading "open source" I was expecting some design docs or the like. Aside from the general confusion of the website, I haven't been able to find some of the most important information. For example, there's no diagram or immediate explanation of the general working principle and airflow path. The heat exchanger itself is published only as-is for those designs, while the author writes that he uses a custom python script tuned for the design size and his 3d printer to generate it. When i saw this I immediately thought of studying it and reuse some of its designs for my custom use case, which does not appear to be currently possible. At first glance it appears to be "open source" in the sense that you can buy it, but if and when something breaks you can print/reorder it easily. Correct me if i'm wrong
jeroenhd 2y ago
Under "source code", there's a link to a GDrive with a ton of design files and documentation, as well as source code. These are licensed CC BY-NC-SA 4.0, so depending on your personal definitions, they may or may not be "open source" (IMO they're open source but not FOSS but I've seen others equate open source with FOSS).
- open_erv2 2y ago
  As a community we need to do some thinking on how open source may sensibly be applied to hardware. Unfortunately Prusa, who used to be a real champion, has departed from the assumed True Path, and they have discussed their reasons, which are largely valid. That said their design at a more fundamental level has also departed from a maintainable, simple and elegant design. The purpose of the source code is to enable maintenance, not cloning, I say that on the website. That is this context, there are many others. It improves the economics because the machine lasts longer and there is no planned obsolescence. People are welcome to make their own units from the source if they have the skill, but although it would be fun, I don't really have time to make it easy. Some day there may be a kit which is very economical but it will still take a whole day of work to assemble, probably.

ltbarcly3 2y ago

This is so cool!

madduci 2y ago

Nice idea, but why do they use Google Drive for sharing their code?

m12k 2y ago
Poor man's CDN?
- zo1 2y ago
  Or a very quick way to get your personal email address blocked. Pretty sure this will eventually trigger some sort of automated spam response and that account will promptly get blocked. Hope they used a throwaway google account with absolutely no link to his domains or main email address.

gardenhedge 2y ago

I have a full system in my house. The unit is in the attic space. It's great although it makes a lot of noise, especially in the bedroom below the unit

jsiepkes 2y ago

In the Netherlands these systems are fairly common in new houses. Mostly because the law mandates a certain level of energy efficiency of new houses. There are other ways of obtaining this required efficiency level, but an ERV unit is pretty cost effective. I've personally been looking at installing such a system [1]. However since houses in the Netherlands are almost all made out of concrete installing such a system in an existing house is pretty hard. [1] https://www.duco.eu/uk-ie/products/mechanical-ventilation/ventilation-units/ducobox-energy-premium https://www.duco.eu/uk-ie/products/mechanical-ventilation/ve...

jacobgorm 2y ago
Same in Denmark, we pretty much had to install one when building our house, to make up for energy loss from the large window area we wanted. We didn't have it properly calibrated at first, but once that was (professionally) done it has worked perfectly and kept a pleasant indoor-climate ever since. The old-and-trusted brand here is https://www.genvex.com/en https://www.genvex.com/en (ours was supplied by Ecovent though https://ecovent.dk/?lang=en https://ecovent.dk/?lang=en )
moooo99 2y ago
Similar story here in Germany. New energy standards require a ventilation concept. Some people choose to rely on daily ventilation to save some money, but most people nowadays opt for an ERV. At least here in Germany, for some reason there are quite a lot of people who are super against the idea of having an ERV. Personally, I wouldn't want to miss is for having fresh air alone, not having to deal with pollen is an added bonus
open_erv2 2y ago
My basic understanding is that the thermal energy also costs a lot more over there than it does in north america, like 4x as much.

ggeorg 2y ago

This sounds great! The site left me a bit confused however. Is it open in respect to software/firmware? Or also the hardware? Can I just build my own with stock components? Something was mentioned about a DIY kit... The WM12 is basically two TW4 modules ... Um, TW4? As an ignoramus I need some introduction please...

ensignavenger 2y ago
Apparently it isn't open source at all, firmware is CC BY-NC-SA 4.0. It appears that the author does not know what open source means.

Hippocrates 2y ago

What’s so good about fresh air? Like I don’t want stinky stuffy air but as someone with central HVAC I had no issues with my indoor air. Are we trying to get outdoor smells? Or is it something else?

Slurpee99 2y ago
Possibly could help with radon poisoning
reubenmorais 2y ago
High CO2 levels impair cognition and stale air accumulates pathogens, not just smells. The V in your HVAC stands for Ventilation, so you're already getting fresh air, that's probably why you have no complaints. If you live in an air tight apartment with no forced circulation where CO2 levels spike super fast requiring ventilation several times a day, it's a different story.
ghosty141 2y ago
In the winter it's cold outside and opening the window cools down the room -> no ventilation most of the time. In the summer it's not a problem for me, I leave my windows partially open all the time but in the winter especially when working from home this would be quite neat. Also, I live in a small town in germany so the air quality here is comparatively good to many of the city folks here.

wtcactus 2y ago

I'm not understanding if it also filters the outdoor air coming in. I live in a place where supposedly the air is of good quality, and yet, when I open the windows, the all place gets a thin film of black dust on all surfaces - most probably due to the particle emissions and tire degradation dust from vehicles from the highway nearby. The solution I've found is to open the windows every day for about half an hour and then put an air purifier to work.

londons_explore 2y ago
it appears the air filter is an optional extra, but incompatible with the storm vent.
- open_erv2 2y ago
  The filter is a bit messed up right now, you can put one on the TW4 but not the WM12.

torginus 2y ago

This looks wonderful, but it operates on the assumption that outdoor air is something you'd actually want to breathe where you live :) Unfortunately, due to cars and dirty heating systems around where I live, outdoor air tends to be not great.

alextingle 2y ago

How does it avoid short-circuiting when the supply and exhaust vents are so close together? There's lots of text on that web-site, but details of the actual design of the thing are pretty scant.

MichaelRazum 2y ago

Looks interesting. Especially since it seems to be much cheaper that the closed solutions... Have looked in this kind of systems, for my parents. The use case was basically, not about energy efficiency, but rather noise protection - to be able to sleep with a closed windows. I think so far I always had two issues (in that usecase). - First the device by itself - produces a bit noise like 42db might be too much for some people if you want to sleep. Especially some of the devices are using one ventilator, which switches directions and won't produce homogeneous noise. - Second 60 CFM is fine, but if you want to have the feeling of an open window - it should be much more and most devices can't deliver that. Also the heat exchange thing is kind of cool in the winter for sure. In the summer, you often have the case that in the evening you house is much warmer than the air outside - so you would like to turn the heat exchange off in the winter. PS: Actually, maybe looking for a complete different use case. But I think what would be very cool, would be some idea to make at least one room 100% quite (with fresh air ) in a cheap way. Guess this would be a huge life changer for a lot of people, who suffer from noise pollution.

leoedin 2y ago
I think that summer/winter distinction is really important. In the UK where most houses don't have air conditioning, you really don't want heat recovery for 1/3 of the year. On really hot days you might want to use heat recovery during the peak few hours, but otherwise you are trying to cool the house down with colder outside air. I would love some sort of intelligent house ventilation system which could do all that. Heat recovery when it makes sense, normal ventilation when it doesn't. All automated based on dT and relative humidities.
- ZeroGravitas 2y ago
  I think with this model you can do this as long as you install them in a synced pair (which I think is the baseline assumption). Normal (heat recovery mode) you have them reverse flow every 60 seconds or so to swap heat. In cooling mode you just run then continually. One is bringing in fresh air and the other is removing stale air. The heat store in the intake will soon cool to the outside temp and the heat store in the output is irrelevant (apart from maybe slowing the air flow and creating noise). If you manually control the system you could combine with a few open windows to create cross breezes even on still evenings.

4gotunameagain 2y ago

That is very nice, and I really appreciate that the design files are open source. Great work. I cannot help to wonder what brings the total cost to $600, the price of a modern, powerful computer. And yes, I am familiar with the economy of scale :)

londons_explore 2y ago
Looks to me like a low cost version of the same could be designed with 2 CPU fans ($1), and a large 3D print ($1 - for the DIY version) or injection moulding for a commercial version ($0.30). Do time-sync between the units with grid frequency sampling (free), and have the whole thing controlled by a 2 cent microcontroller and a pair of triacs. The whole thing, designed and made in China could probably come to a BOM under $4, and retail in the USA for $12.
- 4gotunameagain 2y ago
  While I agree with your points, $0.30 for injection moulding would need quite the scale, and I have doubts about whether two CPU fans would have enough power to flow enough air even in the absence of a HEPA filter.
  - londons_explore 2y ago
    Injection moulding is cheaper than you imagine now. The cheapest moulds start from about $250, and there are plenty of companies who will make a mould and make and ship 5k parts within 7 days. These designs would need quite a few changes to be injection moulding compatible - for one thing the fins are probably going to have to be flat not circular due to draft angle requirements. Changing the core to a roll of embossed steel foil might be a better bet, and whilst that would add about $1 to the price, it would also make the product work better and be more compact or more efficient due to a higher thermal mass in the core.
    - 4gotunameagain 2y ago
      Got any links for the $250 moulds and companies ? Maybe I could use them in my own project :)

kennethh 2y ago

What would be the advantage compared to commercial products like: https://les.mitsubishielectric.it/en/products/ventilation_377/residential-ventilation_378/de-centralized_528/vl-sr2-vl-eu5_4049.html https://les.mitsubishielectric.it/en/products/ventilation_37... This product cost around 500$ and also has heat exchange. A friend of mine has installed it and is very happy with it.

open_erv2 2y ago
It's better compared to a blauberg vento or lunos e2. That product probably gets poor efficiency, I have not checked the technical sheet but if they say 80% that means at the minimal flow levels, which are only 10 cfm or something. The TW4 gets >85% sensible and comparable latent efficiency, at 60 cfm. It also has twice the maximal flow of that device. It's got many other features as well, and is more durable. Ultimately, it's about return on investment. You have to make a spreadsheet and see which one is best, given the actual tested values for efficiency flow, maintenance cost, etc. If that's not possible, it's a shot in the dark.

teekert 2y ago

I so need this, and I so need it to function with Home Assistant. I would love to ventilate based on values of my Aranet 4 (a bluetooth CO2 sensor). Also, would be nice if it coordinates with multiple units, ie what this brand does: [0] EDIT: It does, if you click on "learn more", you'll learn more: "The OpenERV TW4 modules are made to always work in pairs. One always sucks air while the other blows air, synchronized over WiFi. This should be done, or hot air would be pushed out from the building through the walls during the ingress phase, causing heat loss." ...Perfect! Currently I have two holes in my wall for ventilation, when it is windy it's too much (feel the wind blowing inside), when some people visit and there is no wind, boom, >3000 ppm CO2 in 20 minutes. I just really hope it is very quiet, although it says ~37 dBa (which is quite a lot imho), I replaced my bathroom ventilator recently, it produces 25 db! [1]). The previous one [2] produced 52 dB (cheapest around), that was pretty annoying, you'd hear it in the bedrooms above the room it was used in. Maybe 37 dB it isn't so bad, especially since you can wind it down and mostly need it when it's busy/noisy (many people) anyway. Btw, don't buy a CO2 sensor, pretty soon you're a ventilation nerd, or as my wife would call it, a ventilation curmudgeon. [0] https://blaubergventilatoren.de/en/series/vento-expert-a50-1-w https://blaubergventilatoren.de/en/series/vento-expert-a50-1... [1] https://www.filterfabriek.nl/ventilatoren/badkamerventilatoren/blauberg/blauberg-sileo-100mm-aanuit/ https://www.filterfabriek.nl/ventilatoren/badkamerventilator... [2] https://www.hornbach.nl/p/rotheigner-toilet-badkamerventilator-air-basic-100-mm/8626717/ https://www.hornbach.nl/p/rotheigner-toilet-badkamerventilat...

gcormier 2y ago
Why not just buy an ERV? It's available, comparable in costs, and in 5-10 years, there will still be parts, unlike this project where the author hasn't actually shared the most crucial component, the exchanger.
Y_Y 2y ago
> One always sucks air while the other blows air, synchronized over WiFi. This should be done, or hot air would be pushed out from the building through the walls during the ingress phase, causing heat loss." ...Perfect! Absolutely. > A room is not heated by increasing its internal energy but by decreasing its entropy due to the fact that during heating, the volume and pressure remain constant and air is expelled. https://pubs.aip.org/aapt/ajp/article-abstract/79/1/74/1041804/Thermodynamics-of-heating-a-room?redirectedFrom=fulltext https://pubs.aip.org/aapt/ajp/article-abstract/79/1/74/10418... The point about balancing airflow is crucial, but I think underappreciated by non-professionals. Thermodynamics is highly non-intuitive in places, and the enclosed climate-controlled spaces we love to inhabit are certainly included in that. Don't get me started on the idea that you can cool a closed room by running a fan or opening a fridge.

xnx 2y ago

Great project. Hrv and erv should be a lot more common. Is there a diagram of the airflow in that unit? It looks like the intakes and exhaust on both sides might be very close to each other.

ZeroGravitas 2y ago

There's some comments here suggesting that the incoming and outgoing air pass each other in a heat exchanger. But this is a different model that passes he two streams in turn through a heat sink: > Recuperative types are what most people think of, consisting of a thin layer of material that separates two gas streams. Regenerative heat exchangers are different. They briefly store the energy while air flows in one direction, then release it when the air flow reverses. I have to admit I am slightly more dubious about this type as they are new to me, though I did see a YouTube video about a commercial one recently and they seem to be a hot new thing. Possibly this is something sensible that only becomes practical with software and wireless communication? Rather than running ducts to a central location. Though then fitting two side by side in a window seems odd. Why not use the traditional type in that case?

mrspuratic 2y ago
I have two equivalent regenerative commercial units (HRV, no vapour handling) fitted at opposite sides of a mostly open plan ground floor. They use a heavy ceramic core, and sync for opposite or coordinated flow (optional). They go up to 60m3/h (~35CFM) which is extractor fan level for me, 60CFM (~100m3/h) is quite a step up. They were under €200 a unit about 18 months ago. They are rated 90% recovery at low speed. Today it's 11C 75%RH outside, 18C 65%RH inside, at low speed (15m3/h rated at 1.2W) there's barely a difference: 17.8-17.9C air intake temperature. They keep the air noticeably fresh, drier and also keep the CO2 down (<600ppm right now). I'm running them below the "recommended" 50% air-change per hour (ACH about 35%), and boost when needed. There's a recuperative ducted type in the attic for the first floor, when I checked last month it was 4C outside, 18C at the outlet vent, and 17C at the inlet vents. That runs at 50% ACH. The reasoning for the paired up window model isn't obvious, maybe a simple increase in capacity. The website is quite clear you need a push/pull pair to be efficient, and an immediately adjacent such pair is not going to work so well.
- open_erv2 2y ago
  I have traced the air with a smoke generator, there is a youtube video of me doing this on my youtube channel. There is not significant re-inhalation (short circuiting) of the air. The reason for the window mount is that a lot of people rent or otherwise cannot punch holes in their walls. However the reason the window mount is nearly the same as the TW4 (through wall) type, is that I cannot invest the time and money to re-design a whole new machine for a window. The primary value is in the TW4, but a lot of people wanted window mount ones so I helped some people out by deving a quick window adapter and then they helped me out by testing some of the components/the fundamentals of the system in the real world. Unfortunately the window mount units nobody is willing to really pay the cost of manufacture for, so they have to use grade B parts etc. and they have to serve the purpose of testing the TW4 or they aren't worth making.

londons_explore 2y ago

So, this doesn't use a traditional heat exchanger. Instead it appears to "pulse" air inwards then outwards through a series of fins. It effectively heats the fins slightly in one direction, then cools them again slightly in the opposite direction. Same with wetting and drying for recovering moisture. I am surprised that the fins appear to be plastic - one would imagine that steel fins would have far better thermal capacity

londons_explore 2y ago

Less "open" than the name suggests, because the design is for non commercial use only, yet this is very much the kind of product that needs to be sold to see widespread adoption.

sesm 2y ago
Mass market product would have a different design, intended for manufacturing at scale. This design is intended for DIY, mass producing with DIY-intended design is too expensive (see Ergodox as an example).

boomskats 2y ago

I was reading up on counter-flow heat exchangers a few weeks ago after I'd just installed a MVHR system and realised that the actual heat exchanger components themselves were, counter-intuitively, a fraction of the price of the whole unit. I was surprised when I saw they're mostly made of thin plastic and don't depend on thermal capacity at all (unlike, say, HX espresso machines). The way they work is quite simple: c w o a │ │ l r └─────────────────────────────────────────────────────┘ d m air at 50 deg ────────────────────────► air now 5 deg o i u d ───┬──┬──┬──── heat exchanging surface─────┬──┬──┬───── t o ── ▼ ▼ ▼ ─────────────────────────────── ▼ ▼ ▼ ──── d o o r air now 45 deg ◄─────────────────────────air at 0 deg o r a ┌─────────────────────────────────────────────────────┐ i │ │ a r i r It's just a bunch of thin parallel channels where warm and cold air flow in opposite directions, separated by thin plastic walls. Because the flows are counter to each other, there's always a temperature difference driving heat transfer across the dividing walls, even as the warm air gradually cools and the cold air gradually warms. The lightweight plastic walls are advantageous here - while plastic isn't particularly conductive, the walls are so thin that heat transfers readily. It's how these heat exchangers can achieve 80-90% efficiency without needing any expensive materials or thermal mass. The warm exhaust air leaves only slightly warmer than the incoming cold air, having transferred most of its heat to the incoming stream. Clever design.

ent 2y ago
Thank you for the illustration! I was sitting here, wondering that the whole system sounds paradoxical but seeing it drawn down with the arrows really helped grasp how this works!
turtlebits 2y ago
Not sure what you mean by the heat exchanger core being a fraction of the price, but I've seen replacement cores cost around 1/3 of the total unit. They should be made of high thermal conductivity material like resin or ceramic.

mreiner 2y ago

Cool project! Around that topic I can also recommend a channel of this engineer (switch to auto-translate): https://www.youtube.com/watch?v=Cv0s6TgwbJg https://www.youtube.com/watch?v=Cv0s6TgwbJg Paraphrased: - push-pull ventilation is easy to install and comparatively cheap - it's prone to hygiene issues like blowing dirt out of the filters back into the air and providing a moist environment for microorganisms in some operational conditions - it's prone to windy conditions - the numbers stated by commercial vendors seem to have no basis in reality, there seems to be no vendor providing data based on the relevant testing standard for these systems. OPenERV states they want to get it tested by Passivehause institute but also say no lab data measured yet. Might be just my counter-factual gut-feeling, maybe a mechanical window opener based on EspHome for short pulsed passive ventilation intervals is actually more efficient, easier to implement and need less maintenance? Not aware of any comparisons though and last time I checked I could only find some finicky 3d printed actors that might not survive a guest opening the window.

open_erv2 2y ago
The TW4 is light years ahead. Higher flow, better efficiency, much quieter, wind compensation, Internet of things functionality. It's not just yet another machine of the same kind. The heat exchanger is very different, the whole design and construction is quite different.
- deleted 2y ago
  [deleted]

snickerer 2y ago

I use similar decentralized (single-room) ventilation units here in Northern Germany: https://www.bayernluft.de/de/frame.cgi?page=start https://www.bayernluft.de/de/frame.cgi?page=start. I am super happy with them. We now always have air that feels fresh and warm in winter, and the humidity has dropped significantly. There are two types of such ERV devices: 1. Those with only one air channel that switches directions periodically. They use a heat storage element in the airflow. OpenERV belongs to this group. 2. Those with two separate air channels for intake and exhaust at the same time. The air does not mix but passes through a heat exchanger. Bayernlüfter works like this. The only thing I don't like about Bayernlüfter is that it is not open source. It is controlled by a Raspberry Pi (or a similar clone), and I don't have access to it.

woolion 2y ago

Is there any reason the source is available as a Google Drive link and not on Github (or whatever alternative, Gitlab, etc)? Having been burned out by open-source hardware project, checking how healthy the git looks is a good indicator.

open_erv2 2y ago
The file limit sizes on github are a problem, there is some workaround but I haven't gotten around to dealing with it yet.
- dangoodmanUT 2y ago
  Try git lfs
- sthoward 2y ago
  Try Oxen.ai
  - open_erv2 2y ago
    thanks will do

GistNoesis 2y ago

Here OpenERV use a push-pull ventilation design where air direction is reversed every 30s. This allows energy recuperation and dispense connecting the inlet and the outlet to each other, as each ventilation port alternate role simultaneously. The alternative design is a counter-flow heat exchanger. Using 3d printing and gyroids it seems possible to build quite compact ones. (metal 3d printed heat exchanger for helicopter https://www.youtube.com/watch?v=1qifd3yn9S0 https://www.youtube.com/watch?v=1qifd3yn9S0 ) 3d-printing a counter-flowing heat-exchanger seems interesting but maybe there are some molding issues that need to be taken care of (maybe HEPA filters on the inside in/outlet are sufficient). The main advantage of the heat-exchanger solution is that you won't need specific electronic control and can reuse the standard fans for controlled ventilation, but there is more thermally isolated piping required (and the pipes are quite big (~10cm diameter) because they need to move a lot of air even if the fans are weak). The push-pull system is harder to DIY because most of the off-the shelf fans can't be reversed easily (and 3d printed fans are noisy and inefficient).

deleted 2y ago

[deleted]

open_erv2 2y ago

Hey guys, I am the guy behind the OpenERV company, who designed the TW4 and WM12 ERV units. I'm sorry I don't have a bunch of units ready to ship out, as the site says it's still in beta, I am to be honest kind of taking my time because I have another project, the big quiet fan, which is actually funded a little better, and thus I've been directing most of my time to that. But I do advance this a bit most days. I have a twitter where I tweet my progress : @open_erv, and also I'm on bluesky. I have shipped a few units to other engineers who have/will test the units so I can share third party confirmation for any skeptics. To clarify some of the discussion, it is not a counterflow heat exhanger, it is a regenerative type. https://en.wikipedia.org/wiki/Regenerative_heat_exchanger https://en.wikipedia.org/wiki/Regenerative_heat_exchanger. I prefer this type because they can recover latent heat more effectively than recouperative (such as counterflow) type, and latent heat is 40-50% of the total energy content of the air, seasonal average in Ottawa or Toronto. I am hoping to get the machine tested by the PassiveHaus institute to show beyond doubt how good the efficiency is with a third party test. I have no doubt, I have tested it myself, though. These can theoretically handy any temperature differential, but the TW4 and WM12 are currently made of a polymer that I wouldn't trust in an extremely hot climate combined with direct sunlight. For that reason, I am focussed on cold climate scenarios. I am pretty sure it will not frost up even in extremely cold weather like -30. I used it last year in my window and had no problem, and it did get to like -25 at least iirc.

open_erv2 2y ago
Well this was fun and thanks for the discussion, everyone. People are surprisingly nice and sensible and positive here! I used to have another account but lost the password. Perhaps I'll be a reader here in the future. Anyway, I've tried to turn the very temporary influx of interest into something positive and lasting by searching for 2 people who can install and document the install of a pair of TW4 energy recovery ventilators, so anyone who wishes to buy thereafter can know what they are in for on that count. There is another guy Alex who will test flow and efficiency, I've already sent him the stuff. So we get things tested and verified, and I will continue getting a jump on producing units by running the printers and assembling in between when I am doing the more respectably paid work in my life. The kits are on the back burner because even I am still stabilizing the assembly methodology. I even added a new component just recently, a flow straightener that boosts flow by about 10% while allowing noise to be reduced even further. So stabilize, verify, produce, and then after that, within a couple months, I sell in a more or less ordinary way to anyone who wants them. I'm sorry it's not in time for the cold weather, but we have to remember ERV is about the big picture and long term. Like the rest of a building, it's an investment, and the machines are made for (very) good return and long lifespan. I will prepare some WM12 units for those who have asked for them. To be clear I only got 12 emails expressing interest, not an absolute flood, but it's encouraging to know some people "get it" at least. I knew there would only ever be a small trickle of relatively wise people from around the world that appreciate good performance and return on investment. I only need to sell a few pairs per month to make it worthwhile, at the eventual $1300 CAD price tag. I am open to scaling up production with more efficient production methodologies, but I am actually fairly well acquainted with injection molding, machining and other conventional approaches, and they aren't magic. They would help for sure but they wouldn't radically change the price, or the rate of return on investment, and they also take a lot of investment not just for tooling but also re-testing and re-design. I've also changed the design so, so many times after I thought it was done I am highly wary of being locked in.

vizzah 2y ago

I was just recently researching these units.. This model is available in Europe for about 900 EUR: https://www.international.zehnder-systems.com/en/comfortable-indoor-ventilation/products/units/decentralised-ventilation-units/zehnder-comfospot-50 https://www.international.zehnder-systems.com/en/comfortable...

tantalor 2y ago

> Fresh outdoor air But this is actually treating indoor air, that's very confusing. Fresh outdoor air is easy to find: just go outside!

brodouevencode 2y ago
You're also only going to get clean outdoor air in rural places where there is no/minimal farming and construction.

wakeforce 2y ago

I'd love to build this. I have access to a 3d printer, use Python, and have some electronics experience. I live in a northern climate and have been eyeing ERV systems for a while. Basically, I'm the perfect target for this. However, reading the docs, they seem written more to discourage any kind of DIY attempt by saying things A, B or C are difficult, than actually explaining how to do them correctly. I'd love to contribute to the project, but it feels like it's not set-up to foster community contribution. If I'm mistaken, I'd love to donate some of my time on this!

Aurornis 2y ago
I expected a community open source project from the title, but reading the docs led me to the same conclusion: The website is about convincing you to buy one while discouraging you from attempting to build one. It looks like a fun project. I don’t want to discount what has been designed and built. It is confusing to start reading about the project and discover that it’s more of a business than a community project while simultaneously being unavailable for purchase. The person who built it commented on HN that they’re focused on a 3rd different fan project right now, which brings the future of this project into question. It would be great if a community effort could fork this project and work on making it easier to DIY so the community could push it forward. EDIT: After exploring the files I’m not sure I’d even call this open source. I either can’t find some key files or they’re deliberately excluded. True open source projects would also include the CAD source, not only .STLs so others could adapt and modify the source. I think the open angle on this project is more marketing than substance.
- open_erv2 2y ago
  The step files are also there, which is the best common denominator for CAD files. Again, it's open source for the purpose of maintenance and repair, not cloning, and frankly earlier on I did make it more community oriented and nobody ever contributed even a little bit, so I just gave up on that idea. The most likely scenario for longer term is that people may submit minor patches or suggestions, which I roll into the hardware or firmware. In reality, hardware is not like software. You can't make changes easily. Some wizards may take it upon themselves to spruce up the firmware with fancy features and release something, which anyone is free to do. There would then be multiple compatible versions of the firmware, one which I curate for reliability with minimal features, and others which others can provide. Same as for 3d printer firmware. The firmware is Micropython, which is extremely easy to understand and modify.

aojdwhsd 2y ago

This looks great. How well does the WM12 circulate the air, with the intake and exhaust being so close?

ucefkh 2y ago

This is amazing but needs much clearer docs rbh

NavinF 2y ago

Could you post a higher quality photo of the heat exchanger? Is it 3d printed plastic? How did you get the fans to run backwards? They look like standard PC fans

funsi 2y ago

I am looking at buying one of these and have had a look at similar (but not open-source) products available on Alibaba, e.g. https://www.alibaba.com/product-detail/Fresh-Air-Ventilation-Eco-Pair-Plus_1600706598634.html https://www.alibaba.com/product-detail/Fresh-Air-Ventilation... Prices there start at $150 + shipping. Has anyone tested these?

coryfklein 2y ago

Wait, is the air outdoors generally cleaner than the air indoors? Certainly not true in the Salt Lake valley for the 4 months of the year we get persistent inversion.

NavinF 2y ago
The CO2 levels outside are definitely lower than inside. Often by 4x. Fixing that without freezing is the main use case for an ERV

farawayea 2y ago

Some of these instructions have fiber glass or similar for insulation which appears to be used for this. It's not something anyone would want next to their ventilation system or inside it. This isn't something to even consider without some expert reviews. The projects are also work in progress and overall incomplete with many details missing. Be careful when you do anything involving ERV and HRV. It's very easy to cause serious damage to the property you live in, harm yourself and others in an irreversible way, or even both.

elric 2y ago

I installed a central ERV in my home, a Zehnder ComfoAir Q. Installing it was quite involved, but not hard. Definitely within reach of anyone with basic DIY skills. The hardest part is finding a good spot for the ventilation unit, which is about the size of a large, old CRT TV. You have to run ducting from there to multiple rooms, but their ducting system is easy to install. Mine draws about 20W/hour at its typical setting, and it greatly improves comfort. Keeps some of the humidity out when it's humid out, keeps some moisture in when it's dry out. Fresh air year round. Keeps mosquitos out. Keeps some dust/particulates out. Worth the effort, even in my small house. A decentralized unit would be a lot easier to install, but I imagine it's less efficient, less suitable for larger dwellings, and probably louder. YMMV.

xnx 2y ago

This guy on YouTube built a very clever DIY HRV, but got rid of it and went with a commercial ERV: https://www.youtube.com/watch?v=LiptsaKmq80 https://www.youtube.com/watch?v=LiptsaKmq80

fudged71 2y ago

What happens if power fails or one unit stops working? Without valves, you could get unwanted air exchange through a non-operating unit. The commenters discuss various aspects of the design in detail, but surprisingly no one brings up this potential failure mode.

_yb2s 2y ago

This is really cool! I try to keep CO2 at reasonable levels at home, and that occasionally results in running the heater with the windows open. My friends/family do not understand why I care or would waste energy like that, and seem to think it is a mental illness or something. The worst scenario is during high wildfire smoke events... trying to keep the house sealed enough to keep the smoke out often requires taping door seams, etc. and the CO2 skyrockets.

willlma 2y ago
I guess increasing atmospheric CO² by maximizing your fossil fuel usage is one way to equalize the interior and exterior CO² of your house...
- _yb2s 2y ago
  It's actually pretty minimal- I live in a mild climate, and even doing this sometimes I probably spend under $50/year on home heating and leave the windows cracked most of the time. My home was most likely 'retrofit' in the '90s to make it airtight for efficiency, and even with the windows cracked is too airtight to be healthy, and still more so than it was probably designed for in the ~1950s.

jtbayly 2y ago

I’m interested in this, but I think I just realized that what I want it to do is impossible. We have a fireplace, which is not efficient at all, in part because it sucks cold air in from the outside. I was thinking it would be great it we could use an ERV to condition the air that gets brought in. However, as far as I can tell, the moment you exhaust air from your house in any way except through the ERV itself, the ERV cannot help you with the replacement air that comes in. Is that correct?

tempestn 2y ago
It would be cool if someone could build a chimney ERV: extract heat from the dirty air produced by fire, and inject it into fresh air pulled into the living space. So I guess basically it would function like a regular ERV, but with a fire in the exhaust path. (Probably not feasible with a wood fire, but maybe with gas?)
- tempestn 2y ago
  Maybe this thing works that way? https://www.modlar.com/brands/nu-air-ventilation-systems-inc./ifp-45-condensing-fireplace-condensing-furnace-and-heat-recovery-ventilator/ https://www.modlar.com/brands/nu-air-ventilation-systems-inc...
turtlebits 2y ago
If you can use the exhaust heat to temper the incoming outside air, that's all an ERV does. Or, get a direct vent fireplace (draws in outdoor air)
open_erv2 2y ago
That is half correct. The TW4 units operate in synchronized pairs. When one is exhausting (egressing), the other is ingressing (bringing air in). This always happens. They even have quite nice pressure sensors that precisely regulate the pressure the fans exert, controlling flow precisely and preventing the house from becoming pressurized at any time, which as you say would imply heat loss.