TL;DR: How do I make the thermostat send a ‘heat’ request to the boiler without making the boiler use way too much gas?
Hi all,
I have a question about automating central heating. My current setup:
Ground floor:
- Main thermostat linked to boiler (Honeywell T6 on WiFi through Honeywell integration)
- One radiator with Sonoff TRV-ZB, zigbee
- Three radiators with non-smart knobs that are usually open
- The main room has a Sonoff Presence sensor
First floor:
- Three rooms that can be occupied with Sonoff TRV-ZBs.
- Two of three rooms have Sonoff Presence sensors
All rooms that can be heated smartly are controlled through a blueprint once shared here called ‘Advanced heating control V5’.
I have a helper called ‘Comfort Temp’ which is a slider that controls the setpoint on the main thermostat and the TRV of an occupied room.
So the obvious question is: is there any good way to get the main thermostat to send a heating request to the boiler?
I’ve seen something about a WiFi module that you can put in between the main thermostat and the boiler that offers more control (Nodo OpenTherm Gateway, OTGW). Does anyone have experience with this? Or do I solve this with more TRVs on my ground floor? I’ve heard about central heating systems not enjoying a fully thermostatic valved circuit. More TRVs also means I have to replace the valves on a couple of radiators.
Any advice would be greatly appreciated!
The issue I’m trying to solve is to heat a room upstairs whilst not having the boiler in a constant ‘on’ state (the main thermostat is modulating and uses OpenTherm to communicate but that’s beside the point).
A use case: say I’m going to work in my room upstairs. It’s currently 18°C. The living room, where my main thermostat is, is 18°C. I have my coffee in the living room, causing my automation to recognize I’m in the living room.
I move up to my room and set my comfort temp to 20°C. The thermostat in the living room adapts to that. So does the TRV in my office. Since the setpoint of the main is higher than the measured room temp, it sends a heating request to the boiler. One of the radiators in the living room is closed, since the presence detector don’t show occupation in the living room.
In this case, my office might not make it to 20°C before the living room does. The pump stops and no newly hot water gets sent to my office even though the valve is open.
Bottom line: with the current blueprint I mentioned, everything works moderately well. What I want to avoid is to have the boiler heating water if the only occupied room is already at its setpoint. What I want to achieve is more control over when the boiler should heat water (and also pump it around) so that I don’t have to heat the living room when heating, say, the bedroom.
Oh and as far as the time between presence sensing and heating goes: I’m fine being a little chilly for ten minutes. Like I said, I keep every room at a minimum of 18°C to make sure it never takes too long to heat if I want it.
Having seen this webpage https://www.draytoncontrols.co.uk/news/opentherm-explained , which kind of modulation do you have? Long boiler runs are not always bad.
Also, are you able to use the living room TRVs to restrict the livingroom radiators heat output while keeping what you have set as the main setpoint, in the use case you detailed. That would avoid having the main thermostat triggered off too soon.
There is only one TRV in the living room because the other valves are not thermostatic. I would need to replace those to achieve what you describe. But then I think that’s not the way to go because it could damage the pump from what I hear.
The boiler is a Remeha Tzerra Ace which supports Opentherm with modulation. It’s also wired on the opentherm contacts and the T6 supports it.
From the site: with opentherm modulation “the boiler will run for longer periods but it will be producing water at lower temperatures, resulting in less energy being used and maximising the time spent in the higher efficiency condensing mode.” So, longer running times should not be a problem in your setup.