Let me warm up this interesting thread once again.
For me, "concrete core activation" means that the concrete is insulated downward so that the heating energy can be slowly absorbed and released again from above by the concrete core through underfloor heating.
Instead of the term "activation," one could also say "charging." Because nothing comes from nothing, as is well known. The better the thermal insulation downward, the fewer heat losses.
I myself do not like the inertia of this system at all. Even at temperatures of -20 degrees in winter, a very well-insulated and "tight" wooden house in Germany should not cool down too quickly even without concrete core activation. The combination "thermal floor slab with integrated underfloor heating and heat pump" may have proven itself in Sweden, where winter temperatures reach down to -60 degrees.
I have given a lot of thought to this topic over the past few years. For me too, the latter combination (underfloor heating with heat pump) in conjunction with solar thermal or photovoltaics with a power storage system was my favorite for some time. But then I did the math. And thought that only THAT cannot break down which you DO NOT have. It also cannot wear out or age and requires no maintenance.
My idea is a single-story wooden house (bungalow) built to the passive house standard with generous insulation below and above the concrete slab, without underfloor heating; wooden floors and wooden walls everywhere. No tile that can radiate cold...
The required heat is predominantly supplied by solar radiation using a south-facing orientation and generous window areas, supplemented if necessary by mobile radiators/convectors, as well as a log wood stove for all cases. The only disadvantage I see with this is the increased effort for shading in high summer.
By the way, I want to produce hot water decentrally via instantaneous water heaters directly at the four points of use (two bathrooms, kitchen, utility room). The hot water storage tank with extreme insulation is thus eliminated.
Oh yes, then I am dependent on electricity ... Who among you isn’t?
Best regards, Tom