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A project log for OpenTherm interface

Hardware to interface with an OpenTherm enabled boiler

ivan-stepaniukIvan Stepaniuk 11/24/2020 at 11:084 Comments

So, cold temperatures are already here. I had not really touched the Node-RED PID controller after I lowered the derivative factor. It seems to be working properly. There is some overshot when adjusting the setpoint that could be corrected for, but the boiler clearly has it's own PID.


This is the current grafana output, including the gas consumption, but that is not very useful in this case because it also counts the shower (on for around 10 minutes at 9:45). The gas consumption is a rolling average and has some delay.

Note that both graphs have two Y axis. "ouside" and the gas m³/h are on the right side. The green spiky plot on the bottom is the heating circuit water temperature. It's LOW, which is the whole point; running it low to maximize the condensation boiler efficiency.

Discussions

Adrian N. wrote 12/20/2022 at 13:44 point

My gas meter uses an old mechanical counter and does not have any sort of digital interface. Not even a blinking led.  Opentherm standard does not have indeed anything for metering gas consumption but my Viessmann Vitodens 111 surely is capable of metering gas consumption. I've see reports and screenshots from users of this boiler type and thr ViCare app that is used to remotely manage these boiler that includes gas consumption when the boiler is connected to a Vitoconnect (OpenTherm + wifi) box. I do not have Vitoconnect so I cannot spy the communication to see what custom OEM IDs it is using and have not found anybody on the internet that did. I tried to do a scan to see if the boiler responds to any undocumented Id but so far I had no luck. I did find some undocumented ones but the values do not seem to match what I'm hoping to find and could not make sense what they are.

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Ivan Stepaniuk wrote 12/20/2022 at 13:56 point

Good luck and happy hacking! If you don't manage to get the boiler to speak, some mechanical gas integrators have an alternating black/reflective portion on the fastest counter digit wheel or elsewhere. You can use that feature to detect the wheel rotation using a led and a photodiode through the window. That's how I track my water consumption.

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Adrian N. wrote 12/20/2022 at 07:32 point

This is a very interesting projects. I'm especially interested on the gas consumption chart . Were you able to obtain gas consumption data from your boiler's OpenTherm interface? I'm trying to do the same but could not find the OpenTherm IDs for that .

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Ivan Stepaniuk wrote 12/20/2022 at 11:47 point

Unfortunately, I don't recall seeing anything related gas metering in the standard OpenTherm IDs. I get the meter readings directly from my smart meter. My tandem eletricity + gas smart meters have a DSMR/NTA 8130 port to connect to, perhaps yours has something similar?

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