Domoticz

Hello,

I have an evohome system and due to interface complications I am not able to directly interface to the boiler. I just have the TRV's which are working fine, but I wonder whether I could get more efficiency if I could use the Evohome data through Domoticz as a basis to set my boiler.

Currently an indoor desired temperature can be set on my boiler, and the only data it seems to get is the outside temperature.

It is an Buderus boiler and I have just purchased and EMS controller from https://bbqkees-electronics.nl/

I'm still waiting for the unit but theoretically i should be able to control the setpoint of the boiler through Domoticz with this.

I am wondering if there is any documentation or whether anybody knows how the Evohome would set the boiler's set point based on the data of the multiple TRV's and also the water heater? ... then it could possibly be emulated with a script?

Could you not use a basic "On/Off Room Thermostat", disconnect the rotary thermostat and connect a BDR91 in it's place?
Without a wiring diagram for the boiler and knowing how Buderus control the boilers it's difficult to comment.

Well, i thought of something similar actually.
The interface to the boiler is already sorted with the EMS Interface from BBQKees. This is no problem.
I was thinking of connecting a BDR91 to the GPIO pins on Domoticz (of course with the appropriate resistors etc.. ) so as to detect when Evohome is sending requests to the boiler.

However this approach has one problem : The EMS interface can only set a Setpoint on the boiler - it does not control whether the boiler goes on and off - which is anyway to be avoided because the boiler has it's own management (I also have a solar module etc.. so i'm pretty sure it will not do much help to override when the boiler switches on and off, but understanding ultimately what triggers Evohome to request that single on-off request based on the status of multiple TRV's would go a long way in understanding how to set that set point.

So far I am trying this approach, but time will tell whether it will work :

- Calculate an average temperature based on all the TRV's in the house. (potentially fine tuning this to the size of the rooms.. I don't know)
- Calculate a temperature differential between he outside and the inside - and store this in a counter. I call it "Degree Hours"
- Store the amount of time the boiler is on into a similar counter - "Boiler Hours"
- Efficiency would then be Degree Hours/Boiler Hours
- Attempt to set the set point on the boiler through the EMS interface in such a way that that efficiency is increased

I know it's not very scientific but currently i am searching for a rule of thumb. Then i can play with an algorithm to increase that efficiency through trial and error. I also have no idea whether this will fall apart once it starts getting gradually warmer and that temperature differential starts going down. It's probably not a linear relationship, but one has to start somewhere.

Probably by the time i get somewhere it's going to be summer and it will be time to turn everything off

...and another approach I am looking at is to invest in whatever module exists that allows you to control the TRV's directly (HRsomething?) - in which case perhaps, if one can obtain a % valve open value - this would generate a more direct relationship to the boiler than determining this from the average temperature.