Hydrogeological Report - Geothermal Energy, Air-Water Heat Pump or Ice Storage?

What about: facade insulation, insulation of the basement ceiling / roof / upper floor ceiling, new windows, etc.? Just underfloor heating + heat pump does not automatically mean low heating costs. What does the room-by-room heating load calculation say? I find it more and more sensible, because then you can lay things more flexibly (different (larger) pipe sizes and spacing - a heat pump requires flow, flow, and flow) and you also don't really become more expensive. Remember, not only the pure heating system but also the associated work is subsidized. Both systems actually work very well. Assume that you will never recover the extra investment for geothermal energy in your lifetime (due to the drilling it easily gets tens of thousands of euros more expensive than the "simple" air-water heat pump. Far from "somewhat cheaper"). The increased efficiency means for a new building then €47 heating costs instead of €50 monthly with the air-water heat pump. Exotic, but it probably works. However, in over 20 years in the construction (financing) industry, I have never seen it live. By far the most expensive variant due to the combination of geothermal and ice storage (the ice storage alone probably costs five figures - additionally). As far as I know, suitable for houses with very high heating and cooling demands - i.e., commercial properties.

Yes, of course. The worse the house, the sooner you recoup the extra cost for geothermal energy. Accordingly, the current energy consumption as well as the planned consumption after renovation would be important.
It would also be relevant in which area the house is located and what temperatures can be expected in winter.

We are also building in the water protection area and planning a brine heat pump. Deep drilling is not allowed, but surface collectors are. I spoke with the lower water authority and it was basically no problem… there are a few requirements regarding installation depth (x meters above the groundwater), pressure monitoring of the brine circuit to detect leaks (easy) and requirements for the brine itself (easy). Connection must be done by a specialist company, that’s about it as far as I remember.

We are planning a trench collector, google it, there is a lot of information in the home technology forum.

A hydrogeological report apparently relates to the groundwater level, we don’t need it because the collector is only installed at a maximum depth of 2m and our groundwater is much deeper.

The current energy consumption (gas) is about 25,000 kwh per year.

I see it like k-man: With old, large houses, you often also have a decent garden. In that case, you should consider WWWP at NAT < -12°. Trench collectors can be laid quite easily yourself, which brings additional savings. Unless you live in the mountains, there is hardly any house that cannot be operated properly with a modern R290 heat pump. Of course, assuming the house is reasonably well maintained. If nothing has been done for 30 years, it simply has to be renovated. But that has nothing to do with the heating system, you have to do that anyway. And ideally BEFORE renewing the heating system, otherwise the heat pump will be too big for proper operation.