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Hello forum friends,

I have been reading a lot about OpenTherm, the opentherm gateway at http://otgw.tclcode.com/, this forum and many other sources. I have found the different the products at the nodo-shop. Still I can use some advices : Am I thinking in the right direction? Does my solution make any sense?

I have a chalet with about 5 rooms, 7 radiators. 1 thermostat (Remeha Celsia 20), 1 boiler (Remeha Avanti). The radiators are equipped with just simple (and very old) cranes. The radiators are more or less balanced with a "voetventiel".

I have a complete zigbee installation for the lighting and now I want to incorporate the heating as well. So here is my thought:

I need 7 Danfoss Ally thermostatic cranes on the radiators. The reduction vales will be fully opened. The Danfoss cranes will speak zigbee to me and tell me when they want heat or if they reached the setpoint. I then need a OpenTherm GateWay to interact with the boiler in order to supply the heat or turn down the flames. The otgw basically talks RS232, but with an simple raspberry I can easily connect it to a MQTT message broker.

Would this survive or is this thought ridiculous?

My zigbee automation basically exists of an MQTT and zigbee2mqtt running on a raspberry. I wrote my own automation program to deal with events, sensors etc. I really don´t have found any clue on what to speak to the Wifi solution that is offered by nodo-shop. But in the worst case I can talk RS232 from an additional raspberry which can hold a wifi interface to the RS232 level.

For short : I feel insecure about how to bring the otgw in contact with the MQTT or zigbee on my raspberry.
And : I hope this solution can regulate the temperature in different place on different set points.

kind regards, Vonkentrekker.

The OTGW can adjust the room setpoint on the Celcia 20. So the most simple solution would be to just keep the existing radiator valves and control the Celcia 20 from your home automation system.

For finer grained control, I suspect you intend to control the heater directly, rather than the thermostat, which in turn controls the heater. To control the heater, you not only have to tell it when to heat, but also what water temperature (control setpoint) you want and what modulation level it may use to achieve that.

Looking at the zigbee parameters the Ally radiator thermostat exposes, it seems the heat_required property just says true or false. It doesn't indicate how much heat it requires. This makes it difficult to come up with an appropriate control setpoint and modulation level. Just switching on the heater at full blast whenever any valve indicates a heat demand isn't going to be the most economical method.

I guess you could look at the difference between the occupied_heating_setpoint and local_temperature. If the difference is small you can use a low control setpoint and maybe minimal power. But you may also have to take into account how many valves simultaneously have a heat demand. Coming up with a good algorithm for that can be challenging.

In your studies, did you come across my page with background information? It is not (yet) mentioned in the menu, but it may contain some information that could be useful for you.


The nodo shop offers 4 interface options for the OGTW: Serial, USB, Ethernet, and WiFi. The first two provide a connection as a serial port. The last two implement a serial to TCP convertor. All four give you access to the same information. As the WiFi option is implemented using a Wemos D1 mini, it is also possible to add some more post-processing of the data in the ESP8266 of that device. In your case I suggest the ESP8266 firmware by rvdbreemen. It has the possibility to communicate via MQTT. No Raspberry pi required.

Thanks so much for the advise.

Again I have been reading and thinking about the information available. I decided to
a) First build the OTGW and start monitoring whats going on in the system
b) Place an additional PI with some kind of an interface (wifi) with my automation (zigbee) PI.
c) Find/build an algorithm that suites my needs for heating curves, minimize on gas usage and keep comfort at an acceptable level.

Point c will not be easy but that makes the fun.

again, many thanks for the quick response.