Hi, and welcome to the forum.

I cant quite understand whats going on in the charts because the labels arent obvious. 

Cn you clarify which of the lines shows:

Temperature of the water exiting the heat pump flowing to the buffer

Temperature of the water exiting the buffer flowing to the emitters

Temperature of the water returning to the buffer from the emitters

It looks like with an outside temp of ~7 you are running at a flow temp (I cant tell whether measured at the heat pump or at the output of the buffer) of ~40.  Is that a correct interpretation?  Can you tell me what your weather compensation parameters are please?  

@jamespa Sorry for the late reply, I apologize for the graphs not clear. you are correct, so for example for the past 12hrs or so exterior temperature was between 5 and 7 C, the heatpump maintains a constant delta 5 between what it prduces and the return, and it never stops, it runs at the minimum of 25hz which is 28% of the compressor, and it delivers 4.3 KW of thermal energy (according to the data it spits out), it produces water around 40C and I will say that it can't run any better. I have a shelly that measures the electric consumption of heatpump with all the pumps, including 2 wilo pumps that serve 2 circuits at the same temperature (radiators+fancoils), IF I calculate the COP using this data en the heat generated (data from hetpump), I average a cop of 3.4. The heatpump itself says 4.3 because it doesn't count any pump but only the compressor (that's what veissman says). I'm planning to replace some radiators next year so I can reduce the supply temperature, I'll probably have more on/off but I don't see anything else I can try. my next step is to measure the delta after the buffer to see if I can improve on that side, right now both pumps run at minimum speed. you can see from the new graphs the behaviour. The big "bumps" in the graphs are Hot water preparation, not sure about the small bumps but I don't think it's defrost. to read the charts, blue line in the first graph is power consumption for the whole system (shelly em ), red is supply temperature, yellow return temperature, green buffer temperature, blue in second graph is outside air temperature

Just an update, I was able to impreove a bit the COP with some more monitoring, I realized that the Delta T after the buffer was too low so the additional pumps were sucking colder return water. So I went to each radiator starting from the one closest to the HP and closed off the return valve little by little to obtain around 4-5 C delta in each radiator, after that I reduced the delta between HP and buffer to 4, now it heats the house better with lower supply temperature. I honestly had no idea about balancing and I've never seen it mentioned in Italian groups, but I think it's very important, I just wish the installers did their job to begin with. 

@materox345 It would seem that some installers regard the commissioning stage as an ‘optional extra’ and only do that which enables them to ‘sort of comply’ with MCS requirements in the UK (perhaps something similar happens in Italy). Balancing the system does seem to be very optional when it comes to some installers. ☹️ Toodles.

Well in Italy there is nothing controlling the quality of the work in any capacity. There are very few competent installers as far as I know, and a lot of costumers with nightmare installations. To give an example I have a friend that recently remodeled his house, it's a single building but pretty small, 2 floors with about 75 sq meters total area with brand new underfloor heating (low thickness) and very good new double glazed windows. few months ago he got 2 different quotes from installers recommended by the construction company. One told him he needed 16kw heatpump. and the other told hime he needed 2, the first of 12kw for heating and another 4kw to do hot water only, both quotes were astronomical in price and comical. Note that neither company did any sort of heatloss calculation in person, nothing at all, but gave him final quotes based on paper plans. In the end I convinced him to go with a reputable installer that put a 5kw panasonic K and he is very happy with it, low consumption, optimal comfort. This is just an example but there are many many horror stories around. Most boiler installers here keep going with the same : it doesn't work when it's cold etc etc and if they install anything is very very oversized like Italy is the new Siberia when last year in my area we went below 0 just 2 nights total