I have a Riello 8kW ASHP which I’ve noticed often has behaviour which appears to be causing the heating cycle to be shorter than expected.
Here is a typical period with the compressor on and a fixed 32deg flow temp:
If you look closer at the end of the cycle the input power doubles when the compressor speed increases. The extra energy produced causes a spike in flow temperature causing the compressor to turn off when it reaches the flow temp limit of 36C (32C flow with 4C hysteresis).
My entire system is now running open loop with no buffer (although I do use one as a volumizer) and all TRVs are at max. It can be seen that the flow rate is steady until the power increase. The outside temp is also in a steady state so why would the compressor double its power?
This does not happen all the time and appears to be quite random.
I would like to understand why this is happening.
I’m not familiar with the Riello, but some heat pump controllers do a lot of housekeeping things in the background (e.g. exercising valves or starting/stopping pumps at intervals to ensure nothing is jammed). Could be that what you are seeing is your controller’s random check on compressor speed control (you’d only need a 30% speed increase to draw double the power).
The increased flow/LWT/heat output may have been the controller’s normal response to compressor shutdown - it wanted to shift heat to cool down the compressor casing (they can get quite hot without any throughput).
I wouldn’t lose too much sleep over 2 minutes @ 800W extra if it’s doing something helpful like minimising thermal shock in a fairly delicate circuit…
Thats an interesting idea. It has to be initiated by the heat pump controller as the external influences are in a steady state. I find it surprising that it could be performing self-checks up to 4 times a day but I don’t have a better explanation. Do you have any idea how frequently other manufactures perform such background checks?
Me too. I recall that someone on the forum reported apparent daily automatic checks by their controller, but can’t find the post, so don’t know which HP. I don’t monitor my Samsung HP (can’t afford @glyn.hudson’s prices… ) so can only speculate on your observations…
I have an update on this.
I was checking flow and return temps on the UFH which varied widely. After balancing the circuits, the run times are much longer and small spikes in compressor power can be observed every 6 hours.
I think this confirms your hypothesis
) so can only speculate on your observations…