[mreiner]

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.

[open_erv2]

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.