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.
My entire "medium sized European suburban house" runs on a $2.5k 400m3/h unit with HEPA filters made in Lithuania - and that was the more expensive model that I can directly control over MODBUS / 0-10V signal (even turning it into a "dumb" unit). Most of the expenses were running the ducts. YMMV
It's just awesome. Every single room has fresh-smelling air and after fine tuning all my heating systems with algos implemented in Home Assistant - I'm getting ~60-100ppm over outdoor CO2, perfectly clean air, temperature within 1C of the set value, on-demand humidity extraction after showers etc. All it needs to be properly overengineered now is a bunch of dampers and per-room CO2/humidity feedback :)
These units are ubiquitus in northernish Europe, as any new/renovated building needs them to reach A/A++ energy effiency. Brands like Komfovent, SystemAir, offering 200 m³/h ducted units for 2000 Euros, with efficiency like:
Outdoors °C -23 -15 -10 -5 0 25 30 35
After unit, °C 12,9 14,5 15,5 16,5 17,5 22,6 23,6 24,6
You have it backwards. Counter flow units have lower efficiency than these "regenerative" type ERVs.
The downside of this is that the high efficiency is limited to small spaces (based on the mass of your core), where counter flow units are great for entire homes.
One point often overlooked with counter flow units, is that you can place exhaust ducts in spaces that you want to purposefully remove air, like bathrooms and kitchens, while providing fresh air to places with little air movement, like closets, basements.
Regenerative core ERVs do little for fresh air circulation.
What makes outdoor air "fresh" compared to indoor air? You said that the temperature and humidity of indoor air are preserved. So is it just CO2 concentration? Would installing a chemical CO2 scrubber have an effect similar to an ERV system then?
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. 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.
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.
Good project. I've added links from my MHRV pages which have quite good traction on search.
Small note: the older single-room unit we have with the fan on the outside can ice up and make horrible noises then stall at a few degrees below zero (here in London UK)... B^>
Also: as the creator of a project called OpenTRV, I cannot but help admire your taste in naming! B^> B^>
This is neat! I had some issues with ventilation in a foamed house and the only product that’s not a whole home ERV (which, I didn’t have space or ducting) was the Panasonic whispercomfort which actually has some requirements that were hard to meet (minimum duct length) and the overall efficiency isn’t that great. We put in two and have fresh air intake on our HVAC units. Still we’ve taken to running at least one bathroom or laundry fan non-stop.
I’m excited for more competition in this space. Beyond the hardware I’ve found that HVAC installers are way behind the curve on air quality. I hope education and awareness increases in the industry.
The ductless design seems great for smaller units or open spaces. Although for smaller units you want to get building owners to install these. Have you seen interest from them or are you expecting a company to take up this design and sell it to them?
I would consider installing this in my open finished attic even though I already have a whole house ERV. The problem with a whole house ERV, particularly in a multi story house is that it doesn’t necessarily produce a lot of fresh air where you are in the house.
Fyi the mobile image swipe mechanic on the linked page is inverted. Swiping left takes you to the image on the left, instead of the image on the right and vice versa.
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!
Unfortunately the recovery core, which is the interesting part of an ERV, is not included in the 3d stl's.
IMO, this feels like a more marketing project than anything open. ERVs are already very simple (a recovery core + blowers/fans). Commercial units last an extremely long time (some with 10 year warranties) and have comprehensive parts availability.
Also a long term window install is a bit janky and is likely to lose out on efficiency due to glass being a poor insulator.
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.
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 , would suggest not, as it talks about saving the energy needed for cooling or heating. Is there another clever trick?
What you describe is kind of like a theoretical heat exchanger that only averages temperature at a single point.
You can improve this by exchanging heat across a continuous length along opposing flows. Imagine two parallel pipes thermally bonded where fluids flow in opposite directions. Each point still averages the temperatures, but the average temperature varies across the length and approaches the interior temperature on the interior side and the exterior temperature on the exterior side.
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.
I find the idea of reversing the air flow direction every 30s simpler to understand than two counter-flowing pipe side by side.
Imagine a pipe filled with 3 metallic grid sections (such that the air temperature in the section will equalize with the metal temperature) separated by plastic grids (such that the heat isn't conducted through the metal), and you push air alternatively from one hot side at 20°C to a cold side at 0°C for 30s and in the other direction for 30s.
For symmetry reason, the pipe will passively (we don't count the energy required to move the air) have a gradient of temperature from the hot side to the cold side. The first section will be ~15°C, the second ~ 10°C, the third ~5°C. (Each section temperature is the temporal average of the temperature of the air flowing from previous sections : so because air switch direction, it means it's the average of left and right sections.)
From the point of view of the house, you only lose energy from the first section of the pipe which will be more like 15°C rather than 0°C.
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.)
Co-current flow (both flows moving in the same direction) work the way you described.
Countercurrent-flow heat exchangers (where the two channels of the fluid/gas) move in opposite directions on both sides of the heat-transfer mechanism maintain a heat flow gradient over the entire length of the heat exchanger. This can result in an almost complete transfer of heat from one current to another.
High efficiency HRV/ERVs use counter-current flow heat exchangers.
I'm not 100% sure about this. But with ERV (opposed to HRVs), iirc, also the moist of the air is transferred to the incoming air. The moist contains a lot of the energy.
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.
> 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.
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.
Check out Komfovent units if you want a ready solution. My setup is Komfovent HRV (over MODBUS TCP), NIBE heatpump (over MODBUS UDP + esphome-nibe), Vaillant gas boiler (over eBUS-WiFi) + a bunch of AirGradients scattered around the house. Nothing has access to the internet, everything is glued together with HA. Works surprisingly well :)
37dba is practically nothing. Like a very soft whisper from a couple meters away. Remember the scale is logarithmic, 37 is almost 2 orders of magnitude below 52.
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.
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.
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!
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.
- 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.
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.
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.
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.
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.
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
I don't think it's FOSS at the moment. I actually would build two or three of these units on my own and could provide some feedback along the way. My definition of open source means that I should be able to do so.
Unfortunately, the gDrive files are not providing enough information for me to build one of these in a DIY manner. I didn't find enough information on the hardware side, no BOM, no hardware documentation. I think that, if the author would like to actually boost DIY adoption, it'd be worth having a step by step assembly guide. At the same time, when reading the page, I had a feeling like it's more supposed to be a way of advertising a future commercial product, not really focusing on the FOSS/DIY side.
The software is provided, but from my experience with such projects, it's maybe half of the minimum information needed to build a full fledged device.
I like the project and would love to build it in the near future though.
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).
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.
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.
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.
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 )
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).
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.
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.
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?
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.
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.
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.
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.
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.
Look up the price of a blauberg Vento or a Lunos e2. They are ~$1800 CAD, and they get a fraction of the airflow. Computers have a large ecosystem behind them and have been in development for a very long time. This is still at the start of the deployment curve.
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.
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.
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).
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.
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.
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.
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?)
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.
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.
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.
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
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...
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.
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.
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.
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.
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.
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?
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.
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.
danans|1 year ago
"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.
pzduniak|1 year ago
My entire "medium sized European suburban house" runs on a $2.5k 400m3/h unit with HEPA filters made in Lithuania - and that was the more expensive model that I can directly control over MODBUS / 0-10V signal (even turning it into a "dumb" unit). Most of the expenses were running the ducts. YMMV
It's just awesome. Every single room has fresh-smelling air and after fine tuning all my heating systems with algos implemented in Home Assistant - I'm getting ~60-100ppm over outdoor CO2, perfectly clean air, temperature within 1C of the set value, on-demand humidity extraction after showers etc. All it needs to be properly overengineered now is a bunch of dampers and per-room CO2/humidity feedback :)
throw0101b|1 year ago
Most building codes in US/CA mandate them since about 2015, so I'm not sure how niche they are (at least in new construction).
Depending on the (air) volumes involved, ERVs can be had for under CA$ 2000:
* https://gasexperts.ca/product-category/air-exchangers/lifebr...
* https://bphsales.ca/collections/high-quality-erv-air-exchang...
HRVs for less, but it's probably worth the extra few hundred for better humidity management.
batushka5|1 year ago
turtlebits|1 year ago
turtlebits|1 year ago
The downside of this is that the high efficiency is limited to small spaces (based on the mass of your core), where counter flow units are great for entire homes.
One point often overlooked with counter flow units, is that you can place exhaust ducts in spaces that you want to purposefully remove air, like bathrooms and kitchens, while providing fresh air to places with little air movement, like closets, basements.
Regenerative core ERVs do little for fresh air circulation.
llm_trw|1 year ago
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?
kccqzy|1 year ago
jonstewart|1 year ago
colordrops|1 year ago
zerr|1 year ago
littlestymaar|1 year ago
Getting rid of humidity in winter is the main reason why you want to bring fresh air in a house though!
open_erv2|1 year ago
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. 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|1 year ago
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.
DamonHD|1 year ago
Small note: the older single-room unit we have with the fan on the outside can ice up and make horrible noises then stall at a few degrees below zero (here in London UK)... B^>
Also: as the creator of a project called OpenTRV, I cannot but help admire your taste in naming! B^> B^>
schneems|1 year ago
I’m excited for more competition in this space. Beyond the hardware I’ve found that HVAC installers are way behind the curve on air quality. I hope education and awareness increases in the industry.
benj111|1 year ago
Can someone expand of this?
intuition tells me that a regenerative design can be no better than 50% efficient, and would be worse at recovering latent heat
gregwebs|1 year ago
I would consider installing this in my open finished attic even though I already have a whole house ERV. The problem with a whole house ERV, particularly in a multi story house is that it doesn’t necessarily produce a lot of fresh air where you are in the house.
nabakin|1 year ago
Abekkus|1 year ago
wakeforce|1 year ago
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!
turtlebits|1 year ago
IMO, this feels like a more marketing project than anything open. ERVs are already very simple (a recovery core + blowers/fans). Commercial units last an extremely long time (some with 10 year warranties) and have comprehensive parts availability.
Also a long term window install is a bit janky and is likely to lose out on efficiency due to glass being a poor insulator.
Aurornis|1 year ago
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.
outlog|1 year ago
I also have this DIY bookmarked: https://www.youtube.com/watch?v=wJB3dyHDa-8
ilyagr|1 year ago
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 , would suggest not, as it talks about saving the energy needed for cooling or heating. Is there another clever trick?
singron|1 year ago
You can improve this by exchanging heat across a continuous length along opposing flows. Imagine two parallel pipes thermally bonded where fluids flow in opposite directions. Each point still averages the temperatures, but the average temperature varies across the length and approaches the interior temperature on the interior side and the exterior temperature on the exterior side.
snewman|1 year ago
GistNoesis|1 year ago
Imagine a pipe filled with 3 metallic grid sections (such that the air temperature in the section will equalize with the metal temperature) separated by plastic grids (such that the heat isn't conducted through the metal), and you push air alternatively from one hot side at 20°C to a cold side at 0°C for 30s and in the other direction for 30s.
For symmetry reason, the pipe will passively (we don't count the energy required to move the air) have a gradient of temperature from the hot side to the cold side. The first section will be ~15°C, the second ~ 10°C, the third ~5°C. (Each section temperature is the temporal average of the temperature of the air flowing from previous sections : so because air switch direction, it means it's the average of left and right sections.)
From the point of view of the house, you only lose energy from the first section of the pipe which will be more like 15°C rather than 0°C.
LukeShu|1 year ago
(I've seen ERVs with heaters attached; but for the purpose of avoiding frost buildup when it's below freezing outside.)
cyberax|1 year ago
Imagine two air streams counter-flowing. They "swap places" within your heat exchanger, so you can (theoretically) get 100% heat recovery.
This principle is used by animals to minimize the heat waste, by counter-flowing warm and cold blood: https://en.wikipedia.org/wiki/Rete_mirabile
danans|1 year ago
Countercurrent-flow heat exchangers (where the two channels of the fluid/gas) move in opposite directions on both sides of the heat-transfer mechanism maintain a heat flow gradient over the entire length of the heat exchanger. This can result in an almost complete transfer of heat from one current to another.
High efficiency HRV/ERVs use counter-current flow heat exchangers.
cies|1 year ago
ailawyer|1 year ago
[deleted]
teekert|1 year ago
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...
[1] https://www.filterfabriek.nl/ventilatoren/badkamerventilator...
[2] https://www.hornbach.nl/p/rotheigner-toilet-badkamerventilat...
Y_Y|1 year ago
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/79/1/74/10418...
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.
pzduniak|1 year ago
salomonk_mur|1 year ago
gcormier|1 year ago
boomskats|1 year ago
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:
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|1 year ago
turtlebits|1 year ago
They should be made of high thermal conductivity material like resin or ceramic.
elric|1 year ago
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.
mreiner|1 year ago
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|1 year ago
snickerer|1 year ago
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.
jsiepkes|1 year ago
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/ve...
jacobgorm|1 year ago
The old-and-trusted brand here is https://www.genvex.com/en (ours was supplied by Ecovent though https://ecovent.dk/?lang=en )
moooo99|1 year ago
open_erv2|1 year ago
ra|1 year ago
toboche|1 year ago
Unfortunately, the gDrive files are not providing enough information for me to build one of these in a DIY manner. I didn't find enough information on the hardware side, no BOM, no hardware documentation. I think that, if the author would like to actually boost DIY adoption, it'd be worth having a step by step assembly guide. At the same time, when reading the page, I had a feeling like it's more supposed to be a way of advertising a future commercial product, not really focusing on the FOSS/DIY side.
The software is provided, but from my experience with such projects, it's maybe half of the minimum information needed to build a full fledged device.
I like the project and would love to build it in the near future though.
jeroenhd|1 year ago
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).
thanzex|1 year ago
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
M2Ys4U|1 year ago
MichaelRazum|1 year ago
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|1 year ago
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.
unknown|1 year ago
[deleted]
GistNoesis|1 year ago
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 )
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).
wtcactus|1 year ago
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|1 year ago
londons_explore|1 year ago
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
funsi|1 year ago
Prices there start at $150 + shipping.
Has anyone tested these?
dzhiurgis|1 year ago
ZeroGravitas|1 year ago
> 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|1 year 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.
fudged71|1 year ago
woolion|1 year ago
open_erv2|1 year ago
littlestymaar|1 year ago
open_erv2|1 year ago
4gotunameagain|1 year ago
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|1 year ago
The whole thing, designed and made in China could probably come to a BOM under $4, and retail in the USA for $12.
funsi|1 year ago
open_erv2|1 year ago
xnx|1 year ago
londons_explore|1 year ago
sesm|1 year ago
alextingle|1 year ago
There's lots of text on that web-site, but details of the actual design of the thing are pretty scant.
UniverseHacker|1 year ago
The worst scenario is during high wildfire smoke events... trying to keep the house sealed enough to keep the smoke out often requires taping door seams, etc. and the CO2 skyrockets.
willlma|1 year ago
jtbayly|1 year ago
We have a fireplace, which is not efficient at all, in part because it sucks cold air in from the outside. I was thinking it would be great it we could use an ERV to condition the air that gets brought in.
However, as far as I can tell, the moment you exhaust air from your house in any way except through the ERV itself, the ERV cannot help you with the replacement air that comes in.
Is that correct?
open_erv2|1 year ago
tempestn|1 year ago
turtlebits|1 year ago
kennethh|1 year ago
This product cost around 500$ and also has heat exchange. A friend of mine has installed it and is very happy with it.
open_erv2|1 year ago
vizzah|1 year ago
This model is available in Europe for about 900 EUR: https://www.international.zehnder-systems.com/en/comfortable...
brunoqc|1 year ago
danans|1 year ago
KETpXDDzR|1 year ago
aojdwhsd|1 year ago
xnx|1 year ago
torginus|1 year ago
Unfortunately, due to cars and dirty heating systems around where I live, outdoor air tends to be not great.
madduci|1 year ago
m12k|1 year ago
coryfklein|1 year ago
NavinF|1 year ago
gardenhedge|1 year ago
ggeorg|1 year ago
ensignavenger|1 year ago
NavinF|1 year ago
How did you get the fans to run backwards? They look like standard PC fans
farawayea|1 year ago
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.
20after4|1 year ago
ltbarcly3|1 year ago
ucefkh|1 year ago
nubinetwork|1 year ago
stackghost|1 year ago
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.
numpad0|1 year ago
margalabargala|1 year ago
jmb99|1 year ago
PittleyDunkin|1 year ago
Is the air outdoor or clean? It can't be both!
Marketing bullshit aside, this looks great!
LukeShu|1 year ago
Low-CO2 outdoor air vs high-CO2 indoor air, if you prefer. Important for how air-tight modern energy-efficient construction is.
20after4|1 year ago
throw4321|1 year ago
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.
tantalor|1 year ago
But this is actually treating indoor air, that's very confusing.
Fresh outdoor air is easy to find: just go outside!
brodouevencode|1 year ago
Hippocrates|1 year ago
reubenmorais|1 year ago
ghosty141|1 year ago
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.
Slurpee99|1 year ago