Something is awry with either my setup, or the accepted wisdom of how this stuff works. (Or maybe we just haven't reverse-engineered the protocol quite well enough yet and captured that knowledge correctly in Domoticz...)
General wisdom is that when Evohome is controlling the boiler via a BDR and TPI, it tells the BRD what heat load it wants (say, 73%) and then the BDR is responsible for cycling the boiler on and off within the various cycling parameters set to meet that heat load.
However, when I look at the boiler switch device in Domoticz, I see the following:
boiler.jpg
Since this is in Domoticz and I'm using an HGI80, this data must be coming from radio messages.
You can see that at 00:02 the line steps down to 35% where it stays until 00:10 when it steps down to 0% until 00:22. I have 3 cycles an hour, so I'm guessing that 00:02 to 00:22 is one cycle. During which, the boiler appears to be on for 8 minutes, or 40% of the time. This seems like it's reasonably close to 35% (although 7 minutes would be closer!)
However, at 00:56, the line steps up to 45%, where it stays until 01:11. That's 15 minutes out of a 20 minute cycle, or 75%. Nowhere close to 45%.
So it seems as though the controller is managing the duty cycle itself by turning the boiler on and off (if the radio messages have been interpreted correctly), but that that duty cycle doesn't necessarily seem to represent the heat demand contained within the control messages.
Thoughts?
General wisdom is that when Evohome is controlling the boiler via a BDR and TPI, it tells the BRD what heat load it wants (say, 73%) and then the BDR is responsible for cycling the boiler on and off within the various cycling parameters set to meet that heat load.
However, when I look at the boiler switch device in Domoticz, I see the following:
boiler.jpg
Since this is in Domoticz and I'm using an HGI80, this data must be coming from radio messages.
You can see that at 00:02 the line steps down to 35% where it stays until 00:10 when it steps down to 0% until 00:22. I have 3 cycles an hour, so I'm guessing that 00:02 to 00:22 is one cycle. During which, the boiler appears to be on for 8 minutes, or 40% of the time. This seems like it's reasonably close to 35% (although 7 minutes would be closer!)
However, at 00:56, the line steps up to 45%, where it stays until 01:11. That's 15 minutes out of a 20 minute cycle, or 75%. Nowhere close to 45%.
So it seems as though the controller is managing the duty cycle itself by turning the boiler on and off (if the radio messages have been interpreted correctly), but that that duty cycle doesn't necessarily seem to represent the heat demand contained within the control messages.
Thoughts?
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