2 general questions on Homematic IP in openHAB

Hello all,

I have two general questions on OpenHAB and Homematic IP.
Currently I use my OpenHAB Installation to control 14 IKEA Trädfri lamps, 4 Smart Plugs (TP Link) and my Xiaomi Mi Robot.

The next planned step is to make the heating (floor Heating) smart. The only option I found, without modifying the whole installation, is to replace the existing thermostats with Homematic IP thermostats (HmIP-BWTH).

My two questions:

  • Should I define the rules for the heating in the CCU2 or within openHAB? How do you handle it?
  • Do you rather recommend using a CCU2 or Homegear with a CUL on the same machine where openHAB is installed (see config below).

Thanks for your recommendations.

  • Platform information:
    • Hardware: Intel Atom Mini PC / RAM: 2 GB / 32 GB eMMC
    • OS: Ubuntu 18.04 Server
    • Java Runtime Environment: OpenJDK Runtime (Zulu
  • openHAB version: 2.3

Heating is a complex topic and you should well be aware of the dependencies (also in terms of thermodynamics) and implications of changing components, and to speak frankly, it doesn’t really sound you are …
If you want to replace the loop control in underfloor heating, you either deploy a classic autonomous system to have inputs for temperature sensors or room thermostats, or you make OH take its place.
You need a smart plug (to power an electrically powered valve like these) and a OH temperature sensor per room. Then you need to program the valves to open/close in OH rules based on the temperature sensor’s input. Check out this post for a software framework.
But be aware that your heating will fail when OH fails, so ensure you have spare server HW and backups in place.


I’m aware that can be complex. But on the other hand:
The current situation is that there are only analog room thermostats (5 of them) measureing the current temperature and turning the valves off or on (according to a more or less estimated value, 1 -6).
There is no measurement of outside temp or other values considered for heating control. And currently thhere is no automatic night setback for example.

So it shouldn’t be too complex replacing the thermostats by digital ones, doing the same jpb in the first step.

The thermostats I referred to are programmable and also work autonomous (in case the CCU or openHAB should fail). Of course you loose comfort in this case.

So I’m not really afraid in matters of redundancy or complexity.

The electrical valves are still there, connected via 230V to the analog thermostats. The valves are NC.

Are you still sceptical?

I use almost the same set-up. I have the same valves (normally closed). and I attached them to sonoffs.
My temperatures sensors are MySensors home made sensors

The heating rules are not that complex but the scheduling is. Was. Until I passed the scheduling to node-red with the use of the ramp-thermostat.
The actual temperatures and time of heating in the thermostat nodes was a long process of learning the different thermal properties of each room.

Ok so at least you have spent a couple of thoughts on this.
Well there are not really any (autonomous) valves for underfloor because you need to have valves and temp sensors be located in different rooms, that’s why the 2 choices I mentioned.
To deploy Homematic is a bad move IMHO. It’s a proprietary system meant to control itself, leading to a number of problems as you already found out yourself (e.g. where to put rules).

Moving to OH means to lose ability to run without the server, then again autonomous controller devices can break as well.
If your OH server resilience concept is well designed so you would be able to replace that at least as fast as it would take to replace an electrical controller device in case of an outage, too.


rule creation was one reason why I asked for Homegear instead of a CCU since it comes with Node-blue.

And since you said that you have more or less the same setup: did you experience some savings or just more comfort?



Using Homegear instead of the CCU would make the Homematic system more “open” isn’t it?

Regarding the resilience of the OH Server: it depends… If the Hardwarre fails I have to buy a replacement - two days with Amazon.

In case of software issue it would take me 30 minutes to set it up again. The OH config itself is backed up regularly (after every major change) and copied to my NAS…

One reason why I considered the Homematic thermostats instead of a DIY soution was that I don’t want to have a “useless” hole in each wall where the old thermostats are mounted now. And it’s relatively cheap compared to other sstems I found.

And of course the valves are not autonomous but the thermostats should be - means the basic functionality should be there without a central control unit (independent if it is OH,CCU or anything else).

Nameable saving? Maybe I calculate the ROI for this step :thinking::yum:

Some say it can be 6 percent per degree room temp. The result would be a ROI of 10 years… So finally it’s just for fun and comfort

Currently I pay 60 € per month for heating + warm water and every year I get 300 € back…

I used to pay £50 a month for gas and now I pay £30. %40 saving!

Wow. This would be a strong argument to give it a try… Especially since some say that it makes no sense for a floor heating at all… Maybe they are wrong

I have radiators, not floor heating. The valves above are simple swap with the previous TRVs.

I installed one of the thermostats for testing, configured the CCU2 and intergrated it in OH.
Let’s see what happens when it gets colder. But in general everything seems to work…

Regardings my initial question: I defined some basic rules within the CCU, configured some virtual switches in the CCU to trigger those rules and I use those switches to trigger them from openhab. Sounds complicated but in fact it is not and the advantage is thet the heating control continues to work even if the openHAB server is down.


If it is still valid: try the Homematic IP Floor Heating Component ( HmIP-FAL230-C6 / C10 )

The wall thermostats replace your current analog thermostats, they communicate directly with the FAL. So basically, the logic of the control is in the HmIP components (when to open, when to close etc), you use openhab only to check the actual values or change the set point.

While the system is not perfect, it has a couple of advantages:

  • the logic of when to open / close is not trivial, especially with the slow reaction times of floor heating. The thermostats do that for you - they also (up to a point) adjust to the actual environment of your room
  • The FAL knows all valves, so it can load balance their openings (standard behaviour is only one valve open at a time - this prevents only cooled water to reach the last rooms in the chain)
  • Since the room thermostats and the FAL communicate using direct links, it also works if openhab / homegear / ccu fail
  • it has sensible default settings
  • it addionally allows some nifty features (which you COULD realize with node-* or openhab) like controlling the central heater depending on the state of all rooms (if no room needs heat right now, stop / lower the burner, stop the circulation pump)

I recently implemented this solution and I am really happy with it - I have no cost comparison, since this is the first winter im am spending in this house - but before the changes, the temperatur in the floor heating controlled rooms was always either too low or too high - now it works)

I like playing with home automation, and I like tweaking an tuning with lots of rules - but in the case of central heating, the WAF wins. And I doubt that I can reach a much better solution using homemade rules.



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meanwhile I replaced all analog thermostats with the HmIP-BWTH’s and im quite happy with that solution. Temperature regulation is much more precise than with the analog thermostats and the cycle time of 15 min. (which is the basis of the PDM regulation of tose devices) seems to be appropriate.

You might be rigt that the FAL might provide a more sophisticated logic. But on the other hand in my case most likely I wouldn’t benefit fom that since it is an appartment house and I can’t control some components of the heating, e.g. the pump or the inlet temperature.

I use openHAB only to make the values visible and to adjust some things like setpoint tempereture in case of need. The rest is controlled by the CCU. If the CCU fails, the thermostats work autonomous - of course without the ablity to reconfigure them.

I persist amongst others the state of each relay and I can see that in some rooms the valves are only open for approx. 1 hour wthin 48 hours. Overall this may be effecient and cost saving enough…



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