Controlled residential ventilation vs. exhaust air heat pump

We have something similar planned. Controlled residential ventilation is certain, but for us it will probably be a KFW55 house. A first estimate says 40kWh/m²a and 5kW heating load .. for 150m²

Estimates are usually a rather unreliable basis for a significant investment decision. This should be determined with sufficient accuracy. Energy Saving Ordinance or KfW data are unsuitable for this or it is even impermissible to use them.

... But space for geothermal collector is tight and drilling probably not approved. air heat pump ?

Forecasts are hardly possible without exact data. For KFW 55 a ground-source heat pump is probably a bit over the top. I would certainly include a fully modulating split air heat pump in the considerations.

Thank you. Then I will wait to see what the calculation turns out to be.

Yes. By the way, this does not always require a collector field or vertical drilling. Sometimes a cost-effective trench collector is also helpful. In this case, however, a KfW 55 would probably be over the top. EH 70 would be more suitable.