Running a Vaillant VWL55 with OEM and checking on the figures through the installer portal and OEM has shocked me. First of all, their installer portal is very very poor.
Second, the difference between OEM and Vaillant is staggering, I get differences of over 50%. Rubbish, how can I sell that to any of my customers?
My observation is that it is likely caused by underreporting the supply temperature to the house, leading to underreporting of the amount of heat produced.
Could you elaborate on this?
How exactly do the OEM and Vaillant portal figures differ?
I’ve been manually monitoring the reported flow and return temps on my 7kW Arotherm Plus during compressor-off states.
It turns out that the return temp is reported 0.7K lower than flow, after a while of compressor-off.
If this 0.7K error is consistent, what would it mean for the CoP as calculated by the app?
COP is overstated.
But how anybody ever knows whether the difference is there when at normal operating temperatures I never understand.
These sensors are poorly calibrated on one hand, but on the other good enough that the poor calibration is consistent over their entire operating range?
This would cause myVaillant to overestimate the amount of heat being generated, and report a COP that’s higher than reality. My Dad’s Vaillant claims it’s achieving an amazing SCOP of 6.0 since install, whereas Carnot gives a more realistic 4.45.
I compared to my own calibrated PT1000 sensors and the delta sticks.
Immediately after the compressor is off, the system is still at normal operating temperature (=normal return temperature). Any delta you see there also appears at the +5K situation when the compressor is on.
That’s good.
But you measured it to make sure, which is what I would do too.
Thanks. I guess I’ll have to replace the internal sensors in the summer a-la @Andre_K …
What is the best method for calculating impact on CoP readings that this 0.7K delta is causing?
Calculate dT = T_flow-T_return during compressor-on and -off periods. Note that this can also be negative during the compressor-off phase depending on which direction the offset goes. Then
COP_True = COP_Measured * (dT_On - dT_Off) / (dT_On)
I’m currently trying to connect an ebus reader with emoncms.
It looks like my return temp only reads 0.1K below the flow but in this case I assume the recommended approach is to just add 0.1 to the return temperature with the calibration process option when creating the feed from the input?
Yes that would work. Congratulations on the well-calibrated sensors 
.
Thanks. I got lucky!