UFH to be connected to ASHP ?

[newtoallthis]

Sounds good.

The slab takes a lot of energy to heat it up, but then it takes a long time to cool down - this is going to provide a challenge for optimisation but I'll worry about that when the time comes.

With such a long time constant, as long as/to the extent that the loss is only 1/3 of the capability of the HP then you would be able to run it entirely in the 8 hrs of Cosy cheap periods £££ . Just need to match long term integral of heat input with overall heat loss. I would have thought Vaillant's WC algorithm would do quite a good job of this - even without the fancier options such as active, extended or adaptive.

I am hoping that you are correct.