I can help get you going in the right direction here. The key place to look is in the OpenHAB Rules. I don’t have a thermostat set up right now that I can play with, but I made a post about it for another community member a few months ago here:
Looking at that particular .json file is something even I avoid any time I can, but the web UI is reasonable. Once you make the changes, you’ll want to back up /var/lib/openhab2/jsondb/automation_rules.json so it’s easy to restore if you ever need to re-image your SD card.
In the rules, you’ll see this variable called “SystemType” in a few places. These control whether the relays Heating, Cooling, Hot Water, [de]humidification, and so on. The values are either “US” or “EU” which line up with the wiring diagrams on the wiki. The values are not ideal since there are systems in the EU which have cooling, and systems in the US which have [de]humidification, but they work well enough that I’m not too motivated to change them.
I would suggest you create a third option for SystemType which is something like “HeatPump”. Then, look for all the rules that use SystemType. This is where the code will turn on a certain relay (or set of relays) when the heat or cooling is turned on, or turn off a relay when those features are turned off. Your system will be more similar to the US mode than the EU one, as you have the exact same functionality (heating, cooling, fan, and stage 2 heating).
You can find the relay mappings on thei wiki. You’ll have to pick which relays you want to use for which features. I’d suggest trying to make them match existing hardware wiring where possible. For example, connect the fan to G, the compressor to Y (since it’s most similar to “cooling”), and the emergency heat to W2.
If you have any questions about the code, post them here. I didn’t write the code, but I’ve read it a fair number of times and had to make some custom modifications for my home system in the past (we have radiators and didn’t want the fan to turn on when the heat came on, for example). There are other people who have experience in this department lurking on this forum too.
If you implement it as a third SystemType, we should eventually be able pull your changes into the official HestiaPi SD card image. It’s just important that everything works exactly the same as the current software works now when it’s in US or EU mode.
Once you have changes ready, I’ll review and test your changes, and it’ll be up to @HestiaPi to do the official merge into the git repo.