Air-to-water heat pump sizing in new construction

here as JPGs

The only thing I can find about the outside temperature there is this:

What do you want to know about the house? It has no basement and is apparently "better" than KFW 55. Location Baden-Württemberg near Heilbronn. Timber frame construction with wooden facade.

I have never understood these energy saving ordinance calculations. They are of no use to you either. You need the heat load calculation according to DIN 12831 or something like that. Then you select the heat pump capacity based on that, not according to some energy saving ordinance calculations. If you know the following data, you can estimate it quite accurately. Transmission heat transfer coefficient=Ht-value Building envelope area NAT Desired temperature in the house Heated gross volume Number of occupants Type of ventilation

I never understood these energy saving ordinance calculations. They are useless to you. You need the heating load calculation according to DIN 12831 or something like that. Based on that, you select the heat pump capacity, not according to any energy saving ordinance calculations.
If you know the following data, you can estimate it quite accurately.
Transmission heat transfer coefficient = Ht value
Building envelope area
NAT
Desired indoor temperature
Heated gross volume
Number of occupants
Type of ventilation

Building envelope area: 559.65 m2
Building volume: 726.44 m3
Heated air volume: 552.09 m3
Useful building area: 232.46 m2
A/V0 ratio: 0.77 1/m
Window area: 30.41 m2

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

I don't know where to get the Ht value and NAT from?

I will try to request the heating load calculation. I find a 10 kW air-water heat pump for a new building quite extreme... that's why I got suspicious.

Regards

NAT is the standard outside temperature HT stood for me in the KfW certificate

NAT is the standard outside temperature HT was stated in my KfW certificate

NAT: -14W Unfortunately, I do not have the KfW certificate because we waived the subsidy.