AroTherm Plus 7kW – COP Drop During Short Cycles

Hardware Heatpump
22

I’ve been thinking about these dips and whether they could the be normal.

Here’s my thought process:
Heat output is calculated based on the dT and flow rate by the heat meter. When the heat pump gets up to its set point temperature and wants to back off a bit it would be expected that the flow temperature would stop rising or do so more slowly but there would be a lag on the return temperature reacting to this. This would mean until the return temp catches up there would be a reduction in dT for a bit and this would look like a reduction in output.
I guess this should then average out later as the return temperature catches up and after a cycle when the volume cools down.
The heat pump is still consuming electricity during this dT dip so COP will drop off at this point as well.

I guess if this is correct then systems with larger volumes will be worse?

Thoughts?

23

I don’t think these dips are due to lag in the system; the volume between the return and flow sensors is relatively small, and temperatures will equalise with a minute or two. You can see that at the end of reach cycle.

24

These so called hick ups are due to wrong setting of EEV after compressor modulation drop. I made a query in other thread to @Andre_K I think to monitor and log the EEV position at these points but didn`t recieve any feedback…

25

Interesting, this sounds very plausible.

Is there anything we can do to improve this behaviour? Or is it purely valiant firmware issue?

26

Sorry, I missed that. Can you point me to your reply?

27

It was in the Vaillant owners thread - few months ago…Can you log EEV positions in one of these cycles and link it here?