Air-to-water heat pump sizing in new construction

Hm, can you ask [beim Energieberater]?

I just read that it must apparently also be included in the [Energieeinsparverordnung] certificate.

And then google Trenchplaner Ringgrabenkollektor.

Building envelope area: 559.65 m2
Building volume: 726.44 m3
Heated air volume: 552.09 m3

Desired temperature: 20-21°C
Occupants: Currently: 2+1 child + possible granny flat (let's assume max. 5-6)
Ventilation: None

With the data, you get a rather conservative H,t-value of 0.3 W/m²K in Trenchplanner resulting in 7.2 kW without ventilation system and 6 kW with central controlled residential ventilation.

It is important that you find the H,T-value of the house (best to ask the energy consultant and get the H,t-values of the individual building parts as well as the overall H,t-value). An improvement of 0.05 W/m²K already accounts for almost 1 kW heating load. If you build without controlled residential ventilation, the H,t-value should be optimized as well as possible. Because as you can see, without controlled residential ventilation, you are basically heating out the window (around 1.3 kW per year with normative ventilation).

And an Ht value of 0.3 is really very conservatively assumed... Actually unworthy of a new building, it will certainly be better.

Even without a ventilation system, a 6 kW air-water heat pump should be able to keep a new building with 180 sqm warm at all times without a ventilation system. Also keep in mind that internal gains (from devices, from the occupants, etc.) are not taken into account at all in the calculations, meaning the real heating load is even lower than calculated.

In the end, only a proper heating load calculation will help you, without safety margins. You need it anyway for the correct dimensioning of the underfloor heating.

And as a tip: if you still have the chance, install a central ventilation system. Regardless of the heating load, there is nothing that provides such a high comfort gain in a new building. Fresh air after getting up, even in the deepest winter. No need to ventilate by opening windows,... I don't know anyone who regrets the decision for controlled residential ventilation, but many who later regret not having installed one. The only disadvantage: once you have lived in a house with controlled residential ventilation, you won’t want anything else.

If I have read that correctly, they assume 5566 KW on the ID.