Which combination of heat pump and auxiliary supply?

Hello everyone,

the floor plan planning is almost finished and there is already a proposal from the general contractor regarding the heating system. Now I am trying to deal with the topic myself a bit, to critically question it, or I suspect that the general contractor wants to sell his “favorite.”

The house will be built to Kfw70 standard with underfloor heating on about 179m² of living space without room ventilation. The plot is planted only along the property boundaries with tall conifer trees and is a total of 1100m² in size, with about 40% built up by house/garage/terrace. The roof facing south at an angle of 22° offers space for photovoltaics with about 5kWp capacity.

Gas boiler is completely out of the question!

The general contractor’s proposal includes an air-water heat pump with solar thermal (4m² vacuum tube collector). The outdoor unit of the heat pump is located facing the street (neighbor >15m away) and about 7m in clear distance from my own bedroom.

Now my questions:
Does it make more sense to combine a heat pump with photovoltaics instead of solar thermal? How do you roughly estimate the costs for photovoltaics? (my rough calculation: €1,700/kWp = €9,000)

Would you prefer a brine-water heat pump instead of the air-water heat pump? I have already read quite a bit about trench collectors, as the costs are manageable here and I don’t have to dig up the entire property, but the experiences and explanations are more based on anecdotal evidence...?

I am grateful for any suggestions.

As far as I know, a heat pump combined with solar thermal actually doesn’t make much sense. With heat pumps, you no longer need a large buffer tank because the pumps are designed to heat the tank intermittently. If the tank is too large, you only lose energy due to constant reheating.

With solar thermal, it makes a lot of sense to install the largest possible buffer tank (in relation to the number of solar panels, of course) so that as much water as possible is heated during all-day sunshine, thereby extracting as much solar energy as possible.

A gas boiler is currently one of the cheapest heating systems to purchase. An air heat pump is roughly comparable. However, both have somewhat higher ongoing energy costs in comparison.

A geothermal heat pump, or brine heat pump, has a higher efficiency and thus the monthly electricity bill for heating decreases. If your property allows it, I would consider going in this direction. We also originally wanted this heating system, but it was not possible with our property. Especially the large trees could be a problem... However, I only know this "trench collector" from the pink forum as a "DIY solution," which personally seems too uncertain to me. But there are other providers of geothermal heating who, for example, bury cylindrical baskets in the ground. (So the entire property does not have to be dug up)

Would you prefer a brine-water heat pump instead of an air-water heat pump? I've already read quite a bit about trench collectors, since the costs are kept within limits here and I don't have to dig up the entire property, but the experiences and explanations are more based on empirical values...?

Definitely, as long as the property allows it.

The calculations made in the pink forum are certainly more sound than the rough rule of thumb (doubling the living area) used by the average heating company when designing an area collector.