Smart radiator valves + opentherm or on/off

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Moderator: hvxl

Smart radiator valves + opentherm or on/off

Postby » Fri Sep 13, 2019 8:55 am

Hi everyone,

I'm new here, so I'll briefly introduce my setup:
I have a rapsberry pi, running domoticz.
My central heating system currently is a 40 year old oil burner, with on/off control.
To make life better, I've installed ELV/EQ-3 MAX! smart radiator valves on all of our 12 radiators.
I use this python domoticz plugin to read-out the smart radiator valves:
In case one of the radiator valves is open for >10%, a ESP8266 module switches a relay on (connected to my oil burner) to swith on the oil burner (on/off control).
This actualy works great, and allows me to control the temperature in each room seperately. Especialy at night, when I like to keep the room of my little son at >18°C, I no longer have to heat the living room where a fixed thermostat would be.

So, now I want to go for a more modern gas burner (condensation). Probably a remeha (opentherm) of bulex (ebus) system.
What I could do is have an opentherm thermostat in the living room.
A) in case there is heat demand from the smart radiator valves in the living room, the opentherm gateway can increase the temperature setpoint of the opentherm thermostat. Which starts up the heat demand from the boiler. As soon as the radiator valves close because the set temperature is achieved, the setpoint on the opentherm thermostat is lowered again.
B) in case there is heat temand from a smart radiator in the bathroom, the opentherm gateway increases the temperature setpoint of the opentherm thermostat in the living room. This starts up the heat demand from the boiler, which starts to heat up the bathroom. However, since the radiator valves in the living room are closed, the living room is not heating. In this case, the PID control of the opentherm thermostat notices that although the heat demand is increased, no temperature increase is noticed, so it will force the heat demand gradually all the way up to 100%. Until suddenly the temperature in the bathroom is achieved, radiator valve closes, no more heat demand in bathroom so setpoint of opentherm thermostat in living room is lowered, and heat demand goes back all the way to 0%.

I' afraid that in the case of an opentherm thermostat, situation B will completely destrol the teach-in of the PID control. Since the action (increase heat demand) will have no effect at all on the result (temperature in living room), while in option A it will have. So it will never dial in properly.

Is this correct? In this case, am I better of sticking to on/off control in combination with the smart radiator valves? Any other options?

Thanks for your suggestions
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Re: Smart radiator valves + opentherm or on/off

Postby hvxl » Mon Sep 16, 2019 9:13 pm

In a situation like this, I would not mess with the room setpoint, but rather manipulate the control setpoint. That is less likely to confuse the thermostat. It also doesn't require a thermostat that supports remotely changing its setpoint.

You appear to be able to determine the setting of the valves. You could use that as a base for coming up with a control setpoint value. If only a single valve is open at a low level, you could pick a low control setpoint, like 30°C. When multiple valves are open wider, you could raise the control setpoint to 50°C, or even higher.
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