Detached property, hosted by Huw

This was something we always wanted to do. The cottage was converted in 2010 - a near total rebuild other than the original solid stone walls - to fairly exacting standards including UFH and PV on the roof (even space and piping for thermal solar is every we extended to a utility room. But space being extremely limited we could not fit a big buffer tank and so the big compromise was to have gas for HTG and HW.
After completing the build, we then thought to may be hire it out as a holiday cottage and it has been successful ever since.
When we had the money to consider a HP (Air or Ground), the issue was still needing a big buffer tank. We started by getting a detailed engineering survey and suggestion - for both our big old house and the cottage. The cottage (unsurprisingly) looked the best fit for HP. And now our consulting engineers first advised against a ground-source solution due to cost and location/geology. They also alerted us to the new Sunamp heat store using phase change materials to make them small. We could just fit one under our stairs (leaving critical room for other storage).
Trouble was Sunamp did not (yet) work with STIEBEL ELTRON, so all three parties (Stiebel, Sunamp and Map Renewables)worked together over some months to ensure they would work well.
Work done the installation and commissioning took just over a week. Then a week for us to understand it, test it and tune in the settings.

Ours is a slightly odd application: it is not for a house we live in and can tune in to a main heat level, day in day out all year. Instead we have a cottage that is often booked but equally can have days and weeks of being empty.
Also some like it at different temperatures. And some (a few) like windows open even in cold weather (sigh).
But now it is working well. Guests (one not very well) at Christmas wanted it at 23C! And windows open. That pushed it to the limit (and they used the wood burning stove to hit the high temps). Another pair liked it cold 14C! (and windows always open in February), so that was OK because the heating was largely off. I these cases rather than have them fiddle with the controls, we ask them to message us and we remotely tweak settings.
The vast majority of guests so far have been very happy with a base 20C.
The Sunamp (after some teething problems) now supplies plenty of HW on demand.
So it all seems to be good. And running costs are so far looking to be broadly equivalent to when we used gas.
When we have no guests we back off the system to 12C, and just need to wind it up about 24-48 hours before the next guests come, to give the cottage time to build up warmth. We could also put the entire system in to Standby and may well do this in summer when the outside temperature is not too cold.