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!
How does one access the “test menu” to see the reported flow and return temperatures sensed inside the outdoor unit?
Edit; answering my own question it’s Menu → Installer level (17)→ Test menu →Sensor/actuator test
Has anyone looked at these values to assess the performance of the two temperature sensors?
Mine seem to read 0.9 to 1.0 K different, no matter how long the pump is left stopped. I would expect both to cool to ambient and eventually read the same.
This is very similar to what @Andre_K was seeing in post 40 Vaillant inbuilt monitoring vs MID meters - #40 by Andre_K
Ideally, the circulation pump should run but the compressor should be off. If the two sensors don’t equilibrate within a minute then you have the intrinsic offset I also saw. Looking at the temperature readings when the circulation pump is also off will not really equilibrate the temperatures as they are in different positions inside the outdoor unit and experience different heating due to external influences.
Yeah I’ve “pulsed” the circulation pump a couple of times (by putting room temp mod to inactive, then turning heating on for a few tens of seconds. The circulation pump spins up but the compressor doesn’t in that time). My IR thermometer does suggest that the top of the compartment is maybe 0.5-1.0° warmer than the bottom; the heat source being the electronics box that backs on to the hydraulic compartment.
However I’ve now removed the temperature sensors and taped them together so they should be measuring the same bit of air. Going to leave them an hour or two to stabilise.
Andre, you changed your temperature sensors didn’t you? How do you remove the wires from the sensors? I’d like to swap mine around, but can’t get the connectors undone. I don’t want to break anything through force…
Photos of said connectors in case anyone else knows:
I did - as far as I remember there is a simple 2-pin contact at the sensor that plugs into a socket on the cable. I just pulled them off - I don’t remember having any issues there but they might require some force.
Yep hanging in free air next to each other flow is 16.7° and return is 15.9°. Ambient is 15.5° but they’re still in the box by the house.
I’ve now swapped them around (levered the connectors off with a flat-blade screwdriver) and will now watch my COP plummet 
Edit: I should have powered the outdoor unit off before swapping the sensors (I’m not sure how to do that though; just turn the rotary isolator? Throw the circuit breaker?) because the compressor didn’t want to start up afterwards. There were two sensor faults in the fault list in the installer menu on the VWZ AI; deleting them cleared the problem.
Will be interesting to see how the VWZ AI reports the flow-return temperatures during compressor-off/pump-on now! Please do report back if you can.
Exactly, as far as I know that’s the only way. And you should never work on a live appliance while it is powered.
