[wakeforce]

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!

[turtlebits]

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.

[NavinF]

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

[bittercynic]

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.

[schneems]

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).

[open_erv2]

The MPLA (not pla) does not absorb the water vapor, but it condenses on the plastic and then evaporates. There is also the option of sorbent, which grabs the water vapor and then releases it with each cycle, before condensation occurs, getting higher efficiency.

The material in the whispercomfort is IIRC a fiberglass paper. It can only transfer liquid water, not solid water, and not vapor, effectively. The water condenses, whets the paper, then evaporates out the other side. It's a reasonable approach but does not work well in very low temperatures, and also the condensation process implies certain limits to efficiency, same as a non sorbent coated regenerative heat exchanger. The water doesn't start to condense until 100% RH, so it is 100% when it leaves the exchanger, while the air coming in is lower than that, usually. Thus water is lost.

[NavinF]

Very interesting! Do you have a method of adding sorbent to a 3d print?

I wonder if it'd be worth having three TW4 modules with sorbent on only one of them. That way you can control humidity better by choosing 2 of the 3 to use at a time. Eg after a long shower you might wanna discard water vapor for an hour

What's the significance of the model numbers 4 and 12?

[turtlebits]

You can get a commercial unit for under $400 USD. Search for "Pioneer 50 ERV", which claims 97% efficiency or look on aliexpress for units under $200.

That said, I find these "regenerative" heat exchangers too limiting as they generally only work for a single room/space.

[open_erv2]

My price is for a pair, remember, not one. And those pioneer things don't work very well, poor flow and efficiency unfortunately. They claim high efficiency but it's only at the lowest flow rates and not the average for the cycle, only at the beginning of the cycle. There is one company that keeps emailing me trying to sell me units wholesale, I keep telling them to send me actual test data and then I might buy some (for testing), and they never do.

[open_erv2]

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.

[fudged71]

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?

[open_erv2]

I invented a process using some environmentally friendly solvents, grinding the sorbent and so on. It is not diy friendly unfortunately so there is little point in sharing the recipe.

[NavinF]

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.

[Aurornis]

I expected a community open source project from the title, but reading the docs led me to the same conclusion: The website is about convincing you to buy one while discouraging you from attempting to build one.

It looks like a fun project. I don’t want to discount what has been designed and built. It is confusing to start reading about the project and discover that it’s more of a business than a community project while simultaneously being unavailable for purchase. The person who built it commented on HN that they’re focused on a 3rd different fan project right now, which brings the future of this project into question.

It would be great if a community effort could fork this project and work on making it easier to DIY so the community could push it forward.

EDIT: After exploring the files I’m not sure I’d even call this open source. I either can’t find some key files or they’re deliberately excluded. True open source projects would also include the CAD source, not only .STLs so others could adapt and modify the source. I think the open angle on this project is more marketing than substance.

[open_erv2]

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.

[zajio1am]

It is not open source (per OSI definition), as it is under CC BY-NC-SA.

[outlog]

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