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'm pretty sure stls/regen.stl is the recovery core you're taking about tho I can't open it in a online stl viewer: https://drive.google.com/drive/folders/1py2YwmwBEcvmdw18SKwx...
In the photos it seems to be a bunch of nested single-perimeter cylinders that are joined at a few points to maintain spacing. Easy enough to model, but I agree the documentation is horrible and there's no way to contribute.
Commercial units are not comparable because they're way more expensive despite being so simple
Prusaslicer opens it, and it is the right size and shape to be the core, but there's no internal geometry in that STL, at least not how Prusaslicer renders it.
I'd be interested in seeing a diagram of how the air flows through it, if such a thing is available.
Edited to add: There are instructions in the WM12 manual to use your infill settings to make the old version of the core. Page 15 of the manual states there is a python script in the source files to generate the new core, but it only works for their particular printer. I wasn't able to find the script.
Thanks for mentioning that. It seems the PDF and the google docs "manual" have diverged a bit. (at least in page numbers).
I was curious about materials for the core. I know that they're supposed to exchange humidity as well as heat. I know PLA will absorb and release water but I would guess it wouldn't transfer enough to be very efficient. Though I would be happy to be wrong.
I assume the Core in my Panasonic whisper comfort was made out of something more permeable than "simply" extruded plastic. (would love to know more if someone has details).
There is the tw4, which is made to be put in a wall, and there is the WM12, which goes in the window. The main focus is the TW4. There are instructions in the manual for making an ERV core. It is not trivial.
I understand that the addition of desiccant material is the core aspect of what makes this an ERV. I don't actually see any clear explanation of how the desiccant material is added to the printed part. While the creator (open_erv2) mentions that sorbent/desiccant can be used to handle moisture ("If you have sorbent, it gets grabbed out of the air before it can condense"), they don't specify how it's incorporated into the design.
Is it added mid-print? After printing? Is it difficult to add?
Interesting. I'll paste it below.
Note on printing the regenerator/heat exchanger:
The latest and greatest heat exchanger is produced directly with python script generated gcode specific to the printer I use and cannot be practically produced diy, unfortunately. However the old model can be, and the STL is included for that, in the source repository. To do this, simply use Cura, load th STL in, put it in the center of the build plate, and set it to do “lines” infill with about 2.5 mm on center (between centers of the lines) spacing and 0.45 mm width, no top layer and no bottom layer (set them to zero). Check the preview and it should show you a structure which is much like grid infill, parallel channels which are square in cross section, with the outer wall. Tape can be applied over the nubs on the side to fit in an oversized pipe, or they can be sanded if the pipe is too small. You could also use grid infill, but the roads tend to have problems where they intersect. When the nozzle goes over one road, it wipes the plastic off, and not enough is deposited on the lee side. I don’t know how to solve this in Cura without using lines infill. If you could make it so the nozzle went in alternate directions each layer that would probably solve it well enough.
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.
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.
just saw this video https://www.youtube.com/watch?v=U-hVUczzlL4 and you get a very smart solution for a fair price, that does coordination etc.. and it's even esp32 based should the need arise. see https://www.bpcventilation.com/bsk-zephyr-single-room-heat-r...
I also have this DIY bookmarked: https://www.youtube.com/watch?v=wJB3dyHDa-8
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.
>that they are very expensive niche products
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 :)
I wish this was as common as having a fridge in the house. The productivity gains from people not being sleepy and tired from shit air would be insane.
When having my mini splits installed I pushed for an erv system in the bedroom. The installer had only ever done them in commercial units, and he hemmed and hawed about it, but I had two c02 monitors in my room showing it getting to above 2000 whilst sleeping. I've noticed a big improvement in how groggy I feel in the morning.
If there were good enough ERVs that could be installed by the DIY'er for about the cost of a cheap refrigerator (~$600 or so) then they would be more common.
I get that manufacturing the transfer plates isn't simple or cheap, but other than that one thing they're basically fans, they shouldn't cost that much.
How is the noise of these systems? And how often/long need they run to give you clean air and humidity extraction. Is there extra noise when it is windy outside? Is it installed inside the windows somehow or do I need to drill through the wall?
Typically 2 holes, one for air intake and one for air outtake are drilled through the wall. They’re often installed when a home is being built or heavily remodeled. They can be installed after the fact (especially if you have an accessible basement or attic) but it might be a bit invasive running ducts where you need them.
Alternatively, we got one piped into the HVAC ductwork. It's not as optimal as its own ducting, but it's much easier/cheaper than running a bunch of new ductwork.
That's what we did. Our house was built in 1916, but the weather sealing we've done combined with six people breathing in it led to quite high CO2 levels. We have a traditional ducted air conditioning system in the attic (heat is hot water radiant), and added the ERV there. It made a massive difference.
> after fine tuning all my heating systems with algos implemented in Home Assistant
I'd be very interested in hearing the details of this.
I'll definitely prepare a longer write-up when I have everything figure out, but here's a summary:
I have 4 systems:
- Komfovent HRV for ventilation
- NIBE F-series heat pump for floor and water heating
- Vaillant gas boiler that "supports" the heat pump
- Samsung multi-split AC units
HRV - Komfovent uses the same controllers in all of their units, so you get all the communication goodies you'd want - though it took me a long while to figure out that basic features need to be toggled on :) There are existing YAML presets for their C6/C6M controllers on HA forums. The only caveat is that if you want to feed it a virtual thermostat, you need a stuff a device simulating a 10k NTC inside of the ventilator. Otherwise it's just a single Ethernet cable.
Heat pump - I'm not exactly sure if I'm happy with NIBE, but thanks to the community the integration ended up being quite easy. I wasted a bunch of money on their MODBUS40 just to learn that you need to use a certain MODBUS address in the internal bus to make certain registries writeable (eg. thermostat values) - so I took an ESP32 with Ethernet, a galvanically isolated RS485 dongle, a 12V to 5V converter and used https://github.com/elupus/esphome-nibe. The firmware extracts my templated HA sensor's value and feeds it to the heat pump as a virtual thermostat.
Vaillant uses this weird "eBUS" protocol, there's a bunch of cheap PCBs that you can use to connect to it - I'm using https://github.com/danielkucera/esp-arduino-ebus. That's the last system that I haven't touched :)
Samsung ACs use their MIM-B19N modules installed in the outdoor units. There's some magic around enabling remote control, but once you plug their diagnostics device into their indoor units, you can flash all of them at once. I had to mess around with internal NASA addresses to have all the units appear at once.
For indoor sensors I have 3 types:
- AirGradient units measure CO2, tempeature, humidity, PMx etc. - these are mounted at ~150cm and feed the "current house temperature" template.
- I have like 8 Everything Presence One devices, powered by a custom PCB that converts 12V/24V sent over wired alarm cables to the device. They have built-in temperature, humidity and motion sensors. These are mostly installed for motion sensing and their height makes the temperature measurements quite useless.
- Everything else (and most importantly bathrooms) is done using custom ESP32-C3 devices that use SHT31 sensors to measure humidity and LD2412 for movement sensing. Also using the same adapter PCB for powering.
Thermostats are synchronized across all the devices with HA scripts. The HRV specifically uses its own wired temperature sensor to determine if it should enable heat recovery ("free cooling mode"), since its extracted air temp is always a bit lower than room temp (laziness :-)). "Current temperature" template fed to other heaters is derived from multiple room temperatures (currently using an average), with rooms "ignored" if AC is heating there (or was turned on recently). Ventilation has 2 modes set up - 20% and 80% - with the latter toggled by a bathroom humidity threshold.
There are 3 remaining things I want to set up:
- auto switching to gas heating if it's cheaper / the house is running on batteries - so far I've only imported electricity / gas prices into HA and quickly realized that I'm missing a power monitor on the heat pump circuit
- dampening of air ducts to reduce the temp drop when high humidity extraction boost gets triggered
- using more of the HRV range by auto-adjusting fan speed depending on real CO2 values - there's max 2 ppl at the house most of the time, so even at 20% the HRV is quite wasteful
Very cool! I think one of my biggest things is that I need my sensors to be able to manage things well.
Anyone know if there's a good way to control 0-10V dampers? I looked for a solution to control 5 dampers but I didn't find anything, so I started to design my own a couple years ago but never finished the project. I'm having a hard time imagining something so common doesn't have a common solution.
If you're OK with large controllers, the cheap Chinese RS485 stuff seems to work perfectly fine. For "digital inputs" I started out with Polish $150 devices, eventually ended up using the cheapest AliExpress listings for some expansions and so far they've been working exactly the same, with the only difference being the quality of the docs. I'd expect the 0-10V modules to be exactly the same.
Would you have a link/reference?
https://www.komfovent.com/en/products/domekt-r-400-f-c6m-573
I think this is the one I'm using for ~200-ish sqm.
Great thank you
ERVs are not expensive, 1500 USD will get you a decent whole house unit. The installation is the expensive part, which this project doesn't change.
These units are ubiquitus in northernish Europe, as any new/renovated building needs them to reach A/A++ energy effiency. Brands like Komfovent, SystemAir, offering 200 m³/h ducted units for 2000 Euros, with efficiency like:
with indoor conditions + 22 °C, 20 % RHOutdoors °C -23 -15 -10 -5 0 25 30 35 After unit, °C 12,9 14,5 15,5 16,5 17,5 22,6 23,6 24,6What makes outdoor air "fresh" compared to indoor air? You said that the temperature and humidity of indoor air are preserved. So is it just CO2 concentration? Would installing a chemical CO2 scrubber have an effect similar to an ERV system then?
> One problem with ERV/HRV systems right now is that they are very expensive niche products.
Most building codes in US/CA mandate them since about 2015, so I'm not sure how niche they are (at least in new construction).
Depending on the (air) volumes involved, ERVs can be had for under CA$ 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.
Installation is usually the most expensive part, and can easily send the total price into 5 digits of $, especially in a retrofit, depending on the market.
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?
The direction of flow is reversed every 30s. The cycle is short enough that due to the thermal mass there is thermal gradient within the heat-exchanger. So it effectively works as counter-flow heat exchanger. Same principle (but continuous flow) is used in rotor ERV: https://en.wikipedia.org/wiki/Heat_recovery_ventilation#Ther...
Heat exchanger there is usually an extruded ceramic grid (ERV) or rolled corrugated aluminum (functions closer to HRV than ERV)
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.
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.
Duh, thank you for reminding me air flows in a duct.
the intuition: if the 2 colums flow in the same direction, the final temp is the average. but if the 2 columns flow in the oposite directions it is posible to fully exchange the temperature
Planning a renovation of my 1947 rowhome in DC, and I’m really looking forward to adding an ERV.
You probably cannot do a renovation the tightens up your house enough to matter. Of course you have not specified what you are doing, it is certainly possible to do that, but it is a major effort that makes the house unlivable for a couple months and costs a lot of money. If you don't do that level of renovation your house will have enough leaks that a ERV will not make any difference in air quality (and even that level doesn't always make the house airtight enough to need an ERV). Making a house airtight is very hard - worth doing because of the energy savings, but not easy.
If you are doing that level of renovation is is probably better to just tear down the house and rebuild. The costs will be similar and there are a lot of other things people demand of a new house layout that cannot be retrofitted in the old shell. Often the law will not allow this and so you are forced to renovate just to keep some now illegal feature that is worth keeping, but otherwise a tear down would be better.
Anyone can do a renovation that "tightens up your house enough to matter".
Use a qualified professional. Get multiple inputs.
It will cost money, and more money as you approach perfection, but it is doable.
Not really as the structrure of most houses leaks. It can be done but you are doing a lot of work that is easy to skip
That is true, and I guess technically you don't want a house with no leaks, only with leaks that you have complete control over.
Spray foam insulation can seal essentially any structure, and it doesn't require much more than a small hole drilled into the wall between the beams which is easily spackled over.
It can also be put on as insulation in attics and crawlspaces.
Combine that with a full ducting audit if any of your ducting pierces the envelope, a full intrusions audit for power boxes and the like, and new windows/house sheathing/ proper roofing, you can get very close to as good as a new built.
Most of these I would not suggest doing as a DIY, therefore I still say it is expensive, and even moreso if you have lathe and plaster instead of more modern drywall or encounter any of a myriad of issues likely to be uncovered when doing these things to a very old house.
To be fair, the temperature (coldness) of the outdoor air contributes to refreshing the room as well.
I don't think this is meant as a replacement for windows :D
In Finland, many people avoid opening windows altogether, and only rely on various devices for mechanical movement of air. I find it quite alarming actually, as many homes have stale air and subpar ventilation systems, always justified by "never let heat escape the house". The idea of opening windows to refresh the air in the house is basically alien to many Finns, while it's a normal thing to do in other countries; in German, there's a term Stoßlüften.
Stoßlüften isn’t merely a term, it’s a German religion
I can't find anyone to install one in Los Angeles. Is there a particular climate these are suited for?
Air exchange HRVs are quite common here in the Netherlands. Not exactly ubiquitous, but common enough that you can find them in most recently built apartments at the very least. If you're going to have mechanical ventilation installed, you may as well save a buck in the long run on the heat loss.
There's only so much temperature gradient these setups can handle economically, and it's quite possible that the hot LA summers combined with the cool AC air are too much for such an installation not to leak energy at an unacceptable rate.
Then again, just like with ACs that also serve as heat pumps, it could just be a matter of not enough people (or professionals) knowing about these installations to make it viable to build a business around them.
HVAC folk ought to know about ERVs.
Type in HRV system in to your preferred search provider and hit the shopping tab.
Here in Australia they range from about 1500 Antipodean Dineros for a single room through-wall mounted systems, and around 5500 upward for a centralised unit. Plus installation costs, but HVAC install is one of my paid activities, so I mostly don’t pay that part.
NB heat pump is a more accurate term for refrigeration type air conditioners, as in cooling mode they’re ‘pumping’ the heat out of the inside environment and rejecting it outside.
But have you heard about brown?
That's surprising. Doesn't CA require them in new construction? All CA HVAC contractors should be familiar with them now.
They have been required by code in all new houses in Minnesota for about 25 years. I'm sure CA requires them too. Though in older houses they are a waste of money as your house already leaks much air. These are a good thing if you have a well sealed house, but older houses universally are not sealed that well and so they won't give you anything.
> I can't find anyone to install one in Los Angeles.
If you call a random HVAC company, they may not want to deal with "fussy clients" that want something "fancy" like an HRV/ERV. Best to look at folks that perhaps try to adhere to building science more. A quick search for the LA area:
* https://www.jmsacandheating.com/indoor-air-quality/heat-ener...
* https://www.aircomfortexperts.com/additional-products/ervs/
* https://www.azaircond.com/indoor-air-quality/energy-recovery...
* https://www.socalclimatecontrol.com/ervs-and-hrvs-energy-eff...
Or do a dealer search from a manufacturer, e.g.,:
* https://broan-nutone.com/en-us/home/dealer-locator
> Is there a particular climate these are suited for?
Any climate. Modern ones can even handle IECC Zones 6 and 7:
> most of the heat/humidity would stay in during the winter
Getting rid of humidity in winter is the main reason why you want to bring fresh air in a house though!
Isn't it the other way around? 50% humidity means that air contains 50% as much moisture as it, at a given temperature. Raising the temperature means that the air can now hold much more moisture.
Bringing in cold air at 50% humidity, then warming it up to room temp makes the humidity fall, leading to dryer air indoors than comfortable.
Yep. Humidity will tank to 25% here in winter. I have two humidifiers fighting the HRV continuously when it gets cold. As I understand it an ERV controls moisture as well, but such a module for my system costs over $4000.
I think you are agreeing with the parent comment with a tone of disagreement.
They say they let cold air in during the winter because they want to lower the humidity.
Then you say that, if you let cold air in (and then let it heat back up again) then you end up with lower humidity.
The only thing you might disagree on is exactly what humidity you would like inside your house. But that's subjective. (As it happens, I agree with them: I often find it too humid inside during the winter, because I've restricted airflow to keep the heat in.)
But household activities like cooking, showering, drying laundry, or even just washing the dishes etc. generate tons of moisture, and this moisture is the reason why your home has ventilation in the first place: to get it out and avoid mold!
There's a problem with “dumb” ventilation systems though: they can't really adapt to big variations in outdoor conditions, and as such they tend to such way too much air out of your house than needed during the cold days (and it also tend to be designed to suck cold air into dry room first, and get out from wet rooms, when you want it the other way round when it's very cold).
Not in the winter though!
In the hot and humid summer you're definitely trying to reduce indoor humidity.
But in the winter when it's bone-dry? A hot shower barely makes a difference.
I keep two humidifiers running all winter long just to bring indoor humidity up to 35% or 40% where it's healthy.
Otherwise it often goes down to 15% or even 10% on cold winter days, which is terribly unhealthy.
> Not in the winter though!
> In the hot and humid summer you're definitely trying to reduce indoor humidity.
No, you can't do that with ventilation when it's hotter outside than inside actually, that's not how thermodynamics works! But we don't care about that, because in the summer you don't have cold walls or window where water vapor can condense and let mold grow.
> But in the winter when it's bone-dry? A hot shower barely makes a difference.
The reason why it doesn't make a difference is because all the moisture is vented away by your ventilation system! And that's because that's what it's designed to do! Stop it and see how it goes! For the record a single wet sponge drying up in your kitchen is enough to raise humidity by 10%! You barely need 2cL of water per cubic meter to have 50% humidity at 20°C.
As I said the problem is that in winter, ventilation system often ventilate way too much.
Also, they are often designed so the cold and dry air enters in the bedrooms/living room and the warm/moist air is extracted in the kitchen and the bathroom, and because of that the rest of the house doesn't get any of the excess moisture of these places. This is done because the designers wanted to make sure that the humidity level never raise too much in the room, because again humidity will ruin your house and health pretty quick (having air that's too dry isn't very good for your lungs, but having fungi spores in the air is much worse!)
Not in cold climates where in winter the air outdoors is very dry. Heating systems in such climates often have integrated humidifiers.
Then it just means that you're overventilating! We emit much more steam (through cooking and showering for instance) than we consume oxygen/emit CO2 so controlling the humidity is the main purpose of ventilation, air renewal comes for free as a byproduct of that.
My system doesn’t over ventilate - we sometimes have too high CO2 in the bed rooms, but humidity is way too low in winters, sometimes below 30%. That means getting sick more often and having irritated airways at times.
For reference, it is currently 84% relative humidity and -20°C outside where I live. This is about the same absolute humidity as 5% relative humidity at 22°C (i.e., inside).
An all you need to bring that up to above 50% is 2cl/cubic meter of water!
A sponge drying up in your kitchen sink is enough to raise your kitchen's air humidity by 10%. Shut down your ventilation and you'll see, you won't suffocate but instead you'll get mold starting to pop-up. Moisture is the reason why houses have ventilation system in the first place.
As I said elsewhere in this thread, though, there's a problem with “dumb” ventilation systems though: they can't really adapt to big variations in outdoor conditions, and as such they tend to suck way too much air out of your house than needed during the cold days.
> A sponge drying up in your kitchen sink is enough to raise your kitchen's air humidity by 10%.
That's simply not correct.
I go through liters of water a day with my two humidifiers just to try to raise humidity by around 20 percentage points. In a small urban apartment that isn't much bigger than some people's whole suburban kitchens.
A damp sponge isn't going to do a thing, and I can't imagine where you would ever have gotten the idea that it would.
Moisture is not the primary reason for ventilation, except above showers -- it's to prevent CO2 buildup along with other toxic gases like CO and VOC's.
I have not observed this to be true. Ventilating enough to keep CO2 low means sub 20% winter humidity in multiple places I’ve lived.
Even with our cross counterflow enthalpy exchanger it can get somewhat dry in the bedroom in winter. The device in the OP would probably require an additional humidifier.
The less co2 you have the less effect of air exchange does have. Also more co2 in air also decreases this over the decades.
My house currently is sitting at 35% humidity while being very poorly ventilated (~900ppm CO2). In the summer, it’s around 50% with the same level of ventilation. This generally has been the case everywhere I’ve lived; in the summer, you’re cooling air, which (all else equal) increases the relative humidity of that air. In the winter, you’re heating air, which decreases the relative humidity of that air.
> while being very poorly ventilated (~900ppm CO2)
Aren't you missing a zero of something? Because 900ppm isn't “very poorly ventilated”.
It absolutely is poorly ventilated.
I notice I'm not as mentally focused once it gets to 800 or so.
I have a CO2 monitor to keep it below 600 for productivity and concentration.
Remember, fresh air is around 420.
ERV is apparently the term used for HRVs that also exchange humidity and keep it in/out as required, though I'm not sure that makes much logical sense since E is for Energy and H is for Heat, no mention of humidity.
Possibly just different terms used in different countries where the humidity is a bigger problem (very hot and/or very cold outside air).
This current OpenERV product appears to use dessicants for this purpose but might be an optional add-on?
A perfect ERV will recover the heat (occurs naturally by a temperature difference) and the latent heat (associated with condensation/evaporation). i.e. water vapour in the outbound flow should be transferred the inbound flow.
This is to avoid energy loss that would occur when moisture condenses (i.e. the latent heat) by using an adsorbant material to capture moisture before it escapes, or a membrane that allows moisture in the outbound flow to pass to the inbound flow.
Does very much depend on your location. In the UK a dehumidifier is still often a good idea in the winter because although our humidity drops, its nowhere near enough. Inside can still be high 50's, in older properties it'll never really go below 60%.
Really a lot of our older homes shoud be retrofitted with a MVHR unit to help things as ventelation is awful in most houses. I'm actually quite surprised a lot of landlords in the UK don't do it as theres always a fight between them and their tenants who don't necesserily want to leave a window open all day in the winter to stop mold.
Positive Input Ventilation (PIV) units seem to be a new thing for landlords to battle this problem.
I think it basically trickles in cold (and therefore drier) air into a central space to reduce humidity, like an (slower, quieter) extractor fan in reverse.
Seems a bit of a conflict of interest still, especially if the tenant is paying for heating.
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.
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.
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^>
That's an amazing project! I'm blessed to be in such company. Seriously, I use open source stuff and I prefer to do business with such relatively wise people. If you want a beta unit, email me and I'll put you at the top of the list!
That's very kind, but I have all the (SR)MHRV units that I can reasonably fit!
FWIW the email address on your site page is bouncing for me.
Please do add my email (in my profile here) to a low-volume mailing/updates list if you have one.
And if my limited experience of bringing an open hardware project to market might be of help, let me know!
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.
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.
I'm planning to just putter along selling units, making about 50% of my living like that, and if a company comes along and wants to buy the design/company that's good. If not, I get some stuff done, earn a living. This isn't a get rich quick scheme, it's an honest living type stuff.
Is there a link to the big quiet fan project?
>To clarify some of the discussion, it is not a counterflow heat exchanger, it is a regenerative type.
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
I think it means that it's like [Lunos](https://www.lunos.de/en/for-heat-recovery). The unit alternates between exhaust and intake every couple of minutes. The air being exhausted heats up a core, which in the next cycle warms the air from the outside. Lunos e2 is advertised to recover 90% of heat and 20–30% of humidity.
yes i get that, but say you have an indoor temp of 30c and an outdoor temp of 0c. the average of this heat exchanger is going to be 15c. so on average youre only cooling the exhaust down to 15, and heating up the intake to 15c.
a counter flow heat exchanger can get the temperature higher than the average because 30c exhaust is meeting partially warmed intake, and 0c intake is meeting partially cooled exhaust.
Unless theres a phase change???
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.
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 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.
Yeah, I think this makes sense. If you connect many of my heat exchangers in series, the temperature gradient increases; only the middle one will work at the average of the inside and outside temperature (the example of 3 in a row makes sense to me). At the limit, it becomes what you described.
Thanks!
The mechanism described is called a countercurrent exchange. One fun detail is that it's quite commonly found in biological systems in nature too!
It's actually a regenerative heat exchanger: https://en.wikipedia.org/wiki/Regenerative_heat_exchanger.
The person you are replying to was discussing "exchanging heat across a continuous length along opposing flows", which is countercurrent exchange. Regenerative exchange is, at least to my understanding, more of a cyclical store and release process.
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.)
In my experience 80% plus is quite common in the models sold for colder environments. E.g. Mitsubishi electric Lossnay advertises 86%.
Commercial HRVs often use rotating disks, not counterflow heat exchangers. Disks are freeze-proof, but they need to be powered.
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 confused how the heat retention could be around 80-90% without expending a ton of energy.
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
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 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:
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.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 rThe 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.
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 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...
[1] https://www.filterfabriek.nl/ventilatoren/badkamerventilator...
[2] https://www.hornbach.nl/p/rotheigner-toilet-badkamerventilat...
> 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/79/1/74/10418...
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.
Don't get me started on the idea that you can cool a closed room by running a fan or opening a fridge.
Oh man I had this discussion with my wife yesterday, we have a small electric heater in a room where a pipe burst and I still need to fix that (no heating means instant fungus problems). It keeps its fan rotating always, that way it determines the input temp for its thermostat more accurately. But wife insists it is sometimes blowing cold air and thus very very bad... I explain what a thermostat is (bimetals and all) and that she experiences "coldness" because a layer of warm air is blown from her skin, it's not blowing cold air... she doesn't follow... I even measure the energy usage and the thing only uses 20 W or so when just blowing, not heating. Even when just blowing it's moving cold moist air from the walls so overall good. It's difficult dealing with her like this.
I'll pay someone to tell me how to deal with someone like this and maintain a positive atmosphere. The thing is, I also do it for things that really are probably not worth discussing... I should pick my battles better, is there ever a good time for some mansplaining? Or should I say... Nerdsplaining?
The problem as it stands now is that she is experiencing something (“it is blowing cold air”) and your claims (“no it’s not”) run counter to that direct experience.
Place and leave a thermometer in front of it and give her the information that you are using to make your own claims.
You went through a process to learn that moving air feels colder than still air at the same temperature. It seems that perhaps she has not. Surfacing the ground truth of the air temperature may help the situation.
Full of enthusiasm I did this whole thing as they did in Veratasium [0]. Didn't impress anybody in my family. Although my son is getting there I think... Maybe I'm just too bad and lengthy at nerdsplaining.
Actually, I didn't put an ice cube on the metal, that is the trick. of course.
> Don't get me started on the idea that you can cool a closed room by running a fan or opening a fridge.
On that note, I'm curious if hybrid heating/cooling solutions will ever take off. Other than this OpenERV product I mean, which I guess technically counts!
Low Tech Magazine mentioned some experiments in their article on compressed air energy storage (CAES). Instead of trying to make that form of energy storage an adiabatic process, the idea is to use the heat produced/required in the compression/decompression steps in the household to improve the energy efficiency (e.g. use heat produced during compression to heat water; do the decompression in a space that should be cold anyway like a basement used for food storage).
[0] https://solar.lowtechmagazine.com/2018/05/ditch-the-batterie...
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.
Thank you, this is correct. Using my class 2 sound meter, if I stand in my house in nowhereland cornwall with power shut off to the whole house, it's 38 dBa. 37 dBa is audible in that environment but nearly inaudible in a normal environment where your computer cooling fan is making 45 dBa at 1 meter, etc. 42 dBa is pretty quiet too, my furnace makes 43 dBa at 1 meter from the duct when it turns on. And that 42 dBa is a full 60 cfm, full blast. That's more than twice the airflow of competing units like the blauberg vento. You don't turn it up that high when you are sleeping.
Ok, so that 25 dB fan is a lie then because it can very easily be heard over other noise.
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
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.
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 use similar decentralized (single-room) ventilation units here in Northern Germany: 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.
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.
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/ve...
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 (ours was supplied by Ecovent though https://ecovent.dk/?lang=en )
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
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.
I'm confused if this is true open source hardware and software or not?
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.
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
No, it's not. Files are available under the CC BY-NC-SA licence which, because it does not allow commercial usage, is not open source.
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).
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.
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...
Prices there start at $150 + shipping.
Has anyone tested these?
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.
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.
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
This is amazing but needs much clearer docs rbh
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.
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
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.
The CO2 levels outside are definitely lower than inside. Often by 4x. Fixing that without freezing is the main use case for an ERV
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.
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.
The file limit sizes on github are a problem, there is some workaround but I haven't gotten around to dealing with it yet.
Try Oxen.ai
Try git lfs
This looks great. How well does the WM12 circulate the air, with the intake and exhaust being so close?
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...
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).
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.
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).
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
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.
What would be the advantage compared to commercial products like: 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.
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.
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.
Nice idea, but why do they use Google Drive for sharing their code?
Poor man's CDN?
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.
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...
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.
What happens to the humidity in the outflow air when it cools down and condense?
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.
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 :)
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.
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.
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.
Got any links for the $250 moulds and companies ?
Maybe I could use them in my own project :)
Send these guys a message:
https://zhongshengmould.en.alibaba.com/
Never pay for a mould to be made with plans to ship the mould itself to another manufacturer - it's a common scam. Always make mould+make parts as a single transaction.
thanks !
You get similar ones from alibaba from around $175 : https://www.alibaba.com/product-detail/Fresh-Air-Ventilation...
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.
This has not answered my question. I can also come up with many examples of things that are expensive.
What does really inflate the BOM ?
And this is in no way to discount your effort or your results, I'm genuinely curious.
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.
it appears the air filter is an optional extra, but incompatible with the storm vent.
The filter is a bit messed up right now, you can put one on the TW4 but not the WM12.
This looks really cool! I started to build something like this using thin square aluminum tubing but I never finished the project.
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.
Is it safe? I think I heard that home made heat exchangers cause listeria or something like that. Something about condensation.
IINM, listeria is usually spread by contaminated food, not air.
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-legi...
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.
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 is so cool!
> clean outdoor air
Is the air outdoor or clean? It can't be both!
Marketing bullshit aside, this looks great!
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.
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.
That kind of depends on where you live. And this can be combined with air filtration.
Definitely in some places, but is there a region where outdoor air is so clean you don't need this device?
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.
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.
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.
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.
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.
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.
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.
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.
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).
(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)
- 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
> hard to come by
They are $200-300 online. Not Toto quality, but plenty good enough.
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.
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.
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.
Why can't I just glue a fan to an air filter?
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.
That won't decrease CO2 or VOC levels.
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.
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.
Possibly could help with radon poisoning
> Fresh outdoor air
But this is actually treating indoor air, that's very confusing.
Fresh outdoor air is easy to find: just go outside!
You're also only going to get clean outdoor air in rural places where there is no/minimal farming and construction.