I'm exporting from domoticz into InfluxDB, which can be read by Grafana - great for graphing.
Yes, I can set flow temps via the interface - that was another reason for getting it. Although, I haven't pursued this yet - I'm not entirely sure what algorithm to use, and wasn't sure whether it would conflict with Evohome's TPI. It's on the list though!Originally Posted by bruce_miranda
Infact to start with an extremely simple algorithm would do too. The the TPI can just control the boiler on/off. All you need to do is sense when there is HW demand and make the target flow over 65C, everytime else it can be in the 50s. Or maybe track the return temp and make sure the flow allows for maximum condensation.
Flow temp is important. If it's too low and you divert it to the HW tank it'll actually EXTRACT heat!
Hence why I said the key thing is to sense HW demand and then raise the flow temperature to above 65C, rest of the time it can stay in the 50s.
DHW is easy to sense - CH %age seems a bit trickier based on what sensors I currently have in Domoticz - I'm sure there was a CH aggregated value somewhere, maybe it's dropped off.
Still a bit fuzzy in my head how I would translate CH heat demand into flow temperature though, guess it would need to learn somehow (outside temperature would be an factor) rather than use arbitrary values
I also have UFH in some rooms which would need to be factored in
Within Domoticz if you check the values of the devices "DHW Valve" and "CH Valve", it appears to show you the aggregated heat demand of both. Based on that just simply change the Target Flow temperature with DHW Valve taking priority. I think this will give you a better Opentherm implementation especially if the boiler switch on is still being controlled by the BDR91 Boiler relay.
You don't need to bother about outside temperature actually. It's the temperature inside the house that is of more importance.
Last edited by bruce_miranda; 17th November 2016 at 10:48 AM.
The more I look at the data, the more I am convinced that a better OpenTherm algorithm could be written especially if you have the ability to read the CH Valve and DHW Valve devices in Domoticz. I bet the OT bridge is simply using these aggregated values to determine what Target Flow to set for the boiler. So if I was doing this again, I probably wouldn't spend money on the OT bridge or the VR33 and would simply buy an eUSB interface and get that hooked up to Domoticz. It appears dead easy and no complex calculations are needed because all that is already being done by the controller and sending that information. If you have the Boiler relay then On/Off is sorted too. Ofcourse if my Domoticz went pop, then things would still work because the Boiler Relay is being controlled by evohome, except that I would lose the ability to vary the Flow temperature and that would mean I go back to a traditional setup.
The only thing is BDR91 boiler controller will do TPI won't it? Does it still do TPI when connected via Opentherm?
That's true. You could go the whole way and get your ebus interface to fire the boiler up too based on a Domoticz trigger/condition. That way you get maximum return for your investment in the ebus interface. You just have to mimic the ebus commands fired by the VR33 but with your own target temperature and on/off time.
I've set up some Domoticz logging to track the percentage demand on each 'circuit' to see how they correlate with the boiler flow/return and gas consumption
It looks like the boiler does a pretty good of modulating down once the flow/return temperatures start to equalise. I'm not sure without a bit more analysis on how I could improve on that.
Although, it has been quite cold today, maybe there would be more of difference on a day where the outside temperature was in the 10s.
Will continue to monitor..
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