The (hopefully) final episode in my epic quest for accurate measurements: I added some additional insulation around the temperature sensors. This got my compressor-off-delta down to around 0.1-0.2K. Today’s DHW run measured 6.3 kWh generated hot water inside Vaillan’s app; my own sensors yield 6.05 kWh. This is a < 5% error and totally acceptable for me.
I also turned the heating on despite having 25°C outside. Vaillant’s app shows 3 kWh generated heat, my own measurements show 2.945 kWh - a < 2% error.
Of course the true test will be monitoring over a longer period and looking at the next heating period, but this is looking pretty good. Much, much better than the 40% I had at the beginning of this journey.
Interestingly, the measured temperature of the flow temp sensor still shoots up like in my previous post. This leads me to conclude that this is rather conducted heat along the copper pipe than a direct environmental effect.
To summarize:
- Get matching 10k NTCs (the hard part)
- Make sure the insulation is not trapped between sensor and pipe
- Use thermal grease at their contact point
- Apply additional external insulation
