Proper way to control the central boiler with big inertia

[mszwajdo]

Hi,

I'm using VTherm for some time already in following configuration:

• 3 rooms, 3 on a climate VTherms
• TRVs are AVATTO TRV06_1 (https://www.zigbee2mqtt.io/devices/TRV06_1.html#avatto-trv06-1) - no direct valve control so I'm curently using Self-regulation/No auto-regulation
• each room has independend external temperature sensor (updated every 5 minutes)
• my heating source is a solid fuel (wood pellets) boiler, so it has quite big inertia
• boiler is controlled via on/off switch triggering heating mode

Curently I'm separately controlling boiler via HA Generic Thermostat (min of the 3 thermometers set to 20.5degC
+0.5/-0.2), and separately TRVs with VTherms (set e.g. to 20.5deg) to not to overheat rooms. In general it works fine (with some disadvantages) but I though that controlling central boiler by VTherm might work better than this combo I'm using right now.
So I have enabled VTherm's Control the central boiler feature to check (on some dummy switch for the moment) how it works.
What I see is that even if I set Cycle duration to 60 min and Regulation minimum period to 10 minutes on each VTherm, boiler switch is toggled even for 1 minute. This is unacceptable for solid fuel heaters (my boiler needs ab 15minutes just for kindling and stabilization and after that heating is started so it takes let say 30 minutes to start warming radiators). Could you advise what I'm doing wrong and how to use this feature?

[caiusseverus]

Do you have other rooms without smart TRVs as well, or does the whole system consist of just 3 radiators?

How does the boiler regulate its fuel use? Is it able to control the fuel consumption based on heat demand, or is it effectively just on and off? How long does it continue to provide heat for after the demand is satisfied - does it actively extinguish the flame, or just stop introducing fuel and allow the fire to burn out naturally?

If the boiler doesn't have much in the way of fuel regulation, it will probably be inefficient to have it controlled from the individual radiators - if they are somehow out of sync, you could end up with the boiler burning for longer than it needs to, first heating one room then another and so on - it will depend how well isolated the rooms are from each other.

I think it's quite normal to have a heat store or buffer to help even out demand to the boiler for solid fuel stoves because they are inherently harder to control - do you have anything like that, or does it just directly feed the radiators?

If you have other radiators as well as the three with smart TRVs, I would suggest decoupling the smart TRVs from the boiler control. Use them to stop rooms from overheating, but not control when the boiler fires.

Instead, set up a VTherm over switch to control the boiler directly and not with the central settings. Set the cycle time to quite long, 30 minutes to an hour but you might have to experiment to see what works best. Then set the minimum activation time to the shortest period you are happy for the boiler to fire for.

It's also an idea to set the minimum deactivation time to the shortest period you want between cycles - you probably don't want the boiler to fire for 28 minutes out of 30, switch off for two minutes only to fire up again 2 minutes later. That's a bit pointless and it would be better for it to carry on for the next cycle.

Then for the temperature sensor to control the boiler, set up a helper entity that gives the median temperature of your sensors - if you have other rooms being heated than the 3 with smart TRVs, it would be worth putting sensors there as well and including them.

If you only have the three radiators with smart TRVs, then you could also use them to trigger the boiler, but it would again be sensible to set longer cycle times and also require more than one be calling for heat before the boiler fires up. You could either do that via just counting the radiators, or by setting power levels for each radiator and then setting a power threshold for the boiler.