Since I am also interested, what about the difference in acquisition costs? Do the systems cost roughly the same, with only the ground drilling, as I have read, adding about €10,000? These would then also be eligible for subsidies...? I am also facing a new build and in the consultation we were planned a Viessmann (VitoCal 200-S) air-to-water split heat pump. I am also considering changing this and switching to a brine heat pump?!
It is hard to say so generally. In theory, a brine heat pump should be slightly cheaper, if only because the outdoor unit is omitted. In practice, especially with a general contractor, you usually pay slightly more "because of XY". It naturally also depends on the brand and the previous contract standard. For us, a difficult connection was charged as an extra cost, about €3,000. We also took the opportunity to include passive cooling, about €2,500. Then there is the drilling, depending on location, geology and heat demand about €10,000–13,000. All these costs are easily eligible for subsidies. The general contractor knows this and naturally wants a piece of the pie. Since 12 months ago we already obtained several offers for the drilling, it can also be seen that prices have generally risen by about 20% since January. This can be increased demand or just company strategy like with any other subsidy.