Roryb

@IcevergeUsing a very large thermal store meant I can plug lots of heat sources in and flexibility on what to use when - so a trailer load of free wood can go to good use. I'll do some pics but it's a mess at the moment on wiring and piping - I'll sort that out before I embarrass myself. Good point on the flow temp @JohnMo- I started out at 55C and found it was eating into the grid feed as well so have been dialling it back slowly to try and get it optimal - looks like high 40's will work. I have spare capacity on the solar inverter and panel prices have dropped so much in the last 18 months that adding another 5kw has become pretty affordable. The external unit is actually in an unheated outbuilding which has not dropped below freezing - hopefully the off cycles are long enough so it I never need to run defrosting.

Came across this thread when looking for advice on optimising my heat pump performance. If it's helpful, I am running a 1500l Thermal store (https://akvaterm.fi/en/product/akva-ek/#specifications) with a wood burner, gas boiler and 5kw 3 phase immersion (fed by PV excess) feeding into it. Added a Samsung heat pump last summer as well to provide base level heating more efficiently. DHW is done by putting the cold feed sequentially through bottom and top coils and into a separate DHW tank (which has an additional solar vacuum tube array feeding a coil) effectively pre heating the cold feed into the DHW. Heating is both underfloor and rads taking off the thermal store via a Viessman heat exchange (long sad story of a very bad Viessman boiler). The heat pump seems to be working as expected taking the store up to about 50C (mostly off the solar PV) usually taking <10KwH per day depending on weather. I have had to dial the ASHP circulating pump back as much as possible to preserve stratification in the thermal store though in order to keep the DHW consistent. It's very unlikely it's the most efficient setup out there as it's evolved over time (have not attempted to calculate the COP I am getting) but seems to work and the heating bills are minimal even though the house is ancient and badly insulated. Biggest mistake I think was not going for a significantly larger thermal store