Many thanks for your reply. I suspect I might waffle a bit here as I share my experience to date and answer the question raised, so apologies.
As yet I haven’t approached my installer about poor performance / over rated unit. I had a few issues with the install which have been dealt with now, but before I go back with something else I want to collate evidence and present it in a way that ensures they either take action or I can approach MCS with it to mediate if they say no.
The heat pump was installed in July last year, I wanted to use a heat geek installer but none were available in my area at the time, so I approached Daikin directly and they sent me the details of my nearest ‘Certified installer’, which wasn’t actually that near at all. I live in Swindon and they are based out of Poole!
They came and completed a heat loss ‘survey’, he was here less than half an hour which I have later discovered probably indicates its not been completed that well. The survey itself I didn’t get until post installation, it estimates my heat loss around 5300w. I guess even with it I probably wasn’t that clued in at the time that a much larger unit would cause efficiency issues.
I recently used HeatPunk website to complete a survey myself and its suggests 5200w, so I suspect it’s probably in the right ball park. The house is detached, four double beds and is around 170sqm / 1800sq ft in size, built in 2016 with very good insulation and glazing etc.
The major issue with the installation which has now been fixed was in the 0c and below weather the RCBO for the heat pump kept tripping. The issue: they had installed a 16amp rated cable and 16amp fuse for a 32amp unit…… the back up heater circuit was fine…. For a certified installer I found this error surprising.
Anyway monitoring wise I used the amazing guide which I believe you put together (thank you) to connect a M5stack to the serial port and send data to my Home Assistant. This was suggesting as was the Daikin MMI display that my COP was around 3.0, much lower than the survey said it would be. The other thing it showed me was cycling, lots of cycling. The only outside temperature it appears not to cycle at is below 0c.
Recently I bought some power usage monitoring (EmonPi2) kit from Open Energy Monitoring to monitor the electric consumption. As we have solar and batteries with usage monitoring I suspected that the Daikin energy data was incorrect. I am now seeing the data varies quite a bit, for example the base watt draw reported by Daikin unit is 780w vs 940w monitoring the cable direct, which is more inline with what is suggested is the minimum watt draw of the unit by others in the forum. I monitor the BUH separately and this has not been used at all. I do wonder what the point of it is.
The COP now with the cable monitored sits around 2.6. The COP for heating is worse than the COP I get for heating the water which is around 2.8.
I suspect the heat produced is also reported incorrectly via the Daikin unit, so I have recently purchase and waiting for installation of the heat meter which I am getting installed by a local plumber who is training with heat geeks at the moment. I am going to work with him on a few tweaks to see if anything can be done to improve performance.
For instance the system has a buffer unit within a Daikin Preplumbed R32 tank. It has its own circulation pump, which is oddly triggered by some temperature monitoring on the tank itself. (This was the other issue I experienced as the installer couldn’t understand how to set it up correctly…. Again a surprise seeing they are meant to be Daikin certified.) The buffer was installed because I was told that our modern microbore piping wouldn’t be compatible.
It turns out that the microbore itself connects to a 22mm main artery which runs through the property from the tank location, and the microbore connection is limited. The ‘heat geek in training’ plumber I am using suggested that I dont need the buffer, and he can replumb the tank to be a volumiser instead, removing the additional pump as the heat pump circulation pump is more than capable, which may improve efficiency of heat delivery, but still wouldn’t deal with a unit being too big.
So I see my journey as being in stages as we make some tweaks and finally have enough evidence to prove what is at fault… It may be the tweaks get me to a place / compromise I am happy to live with, if not I suspect I will end up where you are and need the unit swapping for the 8kw unit which can modulate down.
My EmonPI is only collecting data locally at the moment, once I have the heat monitor installed I plan to push this to the shareable site, which I can then share with this forum.
As I said I see this as a journey and will be happy to share so others can learn as well.
Kind Regards
Matthew