John
28 February 2024 10:24
107
John:
Following my own experiences with ESPAltherma and the use of R1T & R2T (Before and After BackUp Heater respectively), I would suggest that users would be wise to “calibrate” the temperature sensors in the HP prior to using their data for meaningful measurements. These are NOT certified or calibrated sensors, intended for accurate billing measurements, merely devices intended to allow the HP to function.
Simply, by allowing the heating circuit water temperature to even out, one can compare the readings of R1T, R2T and R4T (return flow temperature) directly, and make adjustments to the values received to compensate for variations in thermistor performance. This is probably best done when the heating system is not in use! In my case, given I wanted some reasonable data now (in December), I
manually set the LWT to -10C offset i.e. stopped the compressor working
using Installer mode in the MMI, set [F-0D] to 0 i.e. circulation pump always on
allowed the flow water temperature to drop for an hour or so, at which point it levelled out
took the readings of the three sensors
returned the settings to the normal running state
The observed sensor values were:
R1T - 26C
R2T - 24.1C
R4T - 25.5C
In addition, I have two other independent sensors on the exterior of flow/return pipes in the house, which read the same values within their level of accuracy. I thus had a reasonable degree of confidence that the flow water was at the same temperature throughout the system.
I have adjusted the values received by EmonHub/CMS to account for the difference. As a BUH installation, I’m using R2T and R4T, so I bumped up my received R2T value by 1.4C, using the Process “Add a constant” operation in Inputs. Arguably, I should have adjusted R2T by 1.9 and R4T by 0.5, but I’m not too concerned about R1T-relative values.
I will of course do this again when the heating goes off and it’s not generating DHW, but for now this at least provides some measure of confidence in the critical Flow dT I’m measuring.
You can see the effect of the cooling off, the very parallel lines and the effect of the new offset following about 10:18.
Thanks to the efforts of @squarepeg77 and Dan from Daikin (thanks!), the cause of the R1T/R2T/R4T thermistor value differences has been traced to the tape heaters around the plate heat exchanger being activated as part of what seems to be a “belt and braces” anti-freezing policy by Daikin. Your friendly engineer can remove said link (5-7 on X7M) which is described in a Daikin technical bulletin for exactly this situation i.e. using 3rd party monitoring which relies on these sensors, which in my case got them to within 0.1C of each other.
So now I don’t need the offset! And I’m saving 66W while the circulation pump is running. Hurrah.
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