Is an exterior masonry wall KS 17.5 + 16 mineral wool + facing bricks with KfW 70 realizable?

It is possible if you still have a corresponding heat source. However, the floor slab should/must definitely also be insulated.

Brine-water heat pump is planned. I have no concerns about qT - however, I look at HT with some frown... I do not quite understand the influence on HT by technology.

HT is also independent of the technology (at least I am pretty sure of that).

We calculated an HT of 0.3, which is not exactly impressive, but will still change.

Nevertheless, we have the equivalent of KFW56.

0.3 W/K*m²? So the construction described here has 0.2 W/K*m² - with aerated concrete it would be 0.15 W/K*m² - so 25% better. On Wiki it says 70% of the maximum value of the Energy Saving Ordinance 2009 - back then it was 0.24 W/K*m² - so theoretically 0.168 W/K*m² would be sufficient for KWF 55... if it were really that simple :D of course it's clear that the other exterior walls/windows have to be included in this.

Can someone please send me the link to the other forum? I'm interested in the other answers...

We have just received our KFW calculation: KFW55 with exactly your wall structure