Add support for Opentherm?

[GravitySandwichh]

I've noticed that this plugin has everything i would want for automated heating per room. The only thing however that is sadly missing is the possibility to use an opentherm based thermostat central heater instead of a on/off central heater. Would it be possible to implement something like this? I am currently running an DIYLess Opentherm gateway on ESPHome and would love this to interact with it.

Kind Regards,
Paul

[jmcollin78]

Hello, I don't know OPentherm and you are the first one to claim this. Can you tell me more ?

[tbrasser]

Same here, opentherm component just now got added to esphome.

Opentherm is a commonly used protocol for modulating boilers. Basically it allows you to set a desired water temperature and it will modulate the power based on actual and return water temperature:

• https://esphome.io/components/opentherm.html
• https://github.com/olegtarasov/esphome-opentherm

Some screenshots of my Remeha 35kW boiler (it's showing as 10kW but either that's wrong, or it's reflecting the fact that I lowered the max fan speed on the boiler itself (not exposed over opentherm)

As you can see in screenshots I have the heating water setpoint exposed as a number. A more standard configuration would be to implement a pid climate on the same esphome devices with that heating water temperature setpoint as its output and livingroom temperature as ambient, and exposed to HA as a climate device.

[tbrasser]

I was also thinking on how to drive my opentherm boiler best using versatile thermostat.

Current ideas (not yet concrete enough):

• filter a dummy switch a bit so even when vtherms have no demand the boiler doesnt flip on/off that often.
• derive some control loop based on behaviour of return temperature wrt behaviour of feed temperature (and how they behave wrt the current setpoint)

I think it's common to involve the actual heat demand into this equation (based on outside temperature and valve positions of trvs etc) but I was hoping that versatile thermostat would be concerned with that and that an algorithm can be used that only needs the 3 opentherm variables over time (setpoint, actual, return)

Btw my original setup was having pid climate and set the current and measured temperature the same as the vtherm with the biggest demand. But the fact that we have now a central pid before all the versatile thermostat pids seems too many cooks.

[jmcollin78]

VTherm is for controlling heaters and not boiler (with temperature water target). Not sure this is in the targeet feature

[GravitySandwichh]

VTherm is for controlling heaters and not boiler (with temperature water target). Not sure this is in the targeet feature

Keep in mind that it's also used for heaters. One central heating unit and seperate valve controlled radiators. OpenTherm makes it possible to modulate based on the requirement amount of heating.

[tbrasser]

Maybe the esphome opentherm devs can help us out understand how to best connect versatile central boiler features onto opentherm.

For now I created automations to turn off CH if nb_devices is 0 for more than 15 minutes, and turn on CH when nb_devices is above 0 for more than 5 minutes. (something similar with DHW enable/disable based on motion detected in kitchen & bathroom)

Still debating myself which inputs to use to drive the CH setpoint, maybe info from vtherm, or maybe try to keep it internal to the boiler.