From your knowledge: is there reliable and economic Thermostat that can be controlled by KNX. I mean not to go with the way of connecting the fan and valve to knx relays module and then get the room temperature from the room controller?
So, the thermostat will be replaced with traditional thermostat plus has ability to talk knx.
How about using Z-Wave thermostats with OH as a bridge to knx using a “virtual” knx thing having channels linked via the item definition ?
E.g. the devolo thermostats (with readable room temperature ) or the Danfoss LC13 (without).
Those don´t cost a fortune and you can use the Z-Wave network to connect e.g. window sensors where you need them.
Buy cheap a used one plus a Z-Wave stick (e.g. Aeontec) and simply give it a try.
KNX thermostats are expensive and require wiring and power supply (which may not be in place).
Thanks, but why even I connect to Z-Wave?
By the way are these Devolo and Danfoss are standalone thermostat with Z-wave interface?
They work as fully standalone products, KNX is not needed for operation!
You can set them up as you wish: stand-alone and/or communication enabled thermostats.
Stand-alone these two are a bit dumb: No timer programs, only setting your desired temperature.
The intelligence lies within the ZWave controller or the linked system (Either e.g. openHAB or e.g. from Devolo there ist on available that can be used for their ZWave components by smartphone).
Advantage openHAB: Bridges to other bus systems / protocol can easily be established.
Creating schedules and rule based heating is somehow a weak point in OH - there is no such concept of a “Schedule” object, neither in UI nor code (besides cron expressions and timers) - you need to code everything within rules and scripts.
Another option is the MAX!-System - they are programmed centrally but operate stand alone in case the central connection is not available. But many users are struggling with loosing their settings - the binding author is working on it, but it seems to be some restriction in the MAX!-firmware.
As for knx:
I have a knx system but do not use knx valves / thermostats because they have a very high price tag and / or need wiring.
Used MAX! up to now, but currently switching to ZWave as I prefer stability and standard interoperability.
In case you want to control a non-knx device with a knx device there is always the option to use OH as a bridge. Done that, works fine for me in both directions.
So what exactly is the plan you have, what are you trying to build/install ? With a bit more information we may be able to give more detailed advice.