Solar heat pump / what to watch for in the offer (single-family house, new construction, KFW70)

Hello everyone,

we want to build with a general contractor (single-family house, approx. 136 sqm, gable roof, <=KFW70) and would like to enter final negotiations with the last 2-3. The construction descriptions each list the ground source heat pumps (brand name + buffer tank), but not in much detail. Here I would like to inquire what you would recommend in this regard.

Since brand names probably cannot be mentioned here: Set is a brine-water heat pump with a COP of 4.7 (integrated hot water storage tank of 185L). Additionally, a buffer tank, probably between 200 - 300 L, is to be used.

1. Is this combination reasonable? 2. What should generally be considered with heat pumps? I would definitely have a heat meter and a separate electricity meter installed. What else should be considered? 3. What combination would be the most sensible from your point of view (i.e., size of the buffer tank, etc.) assuming a 2-person household (both employed, possibly a child in a few years)?

Thanks a lot in advance, Lacos

First of all, the question arises as to how high the heat demand is and whether it can be reasonably met with a heat pump...

If it cannot, then you are building a money pit... even if the glossy brochures promise a lot... not everything is true as it is stated there...

I would doubt the usefulness of a buffer tank. Otherwise, I am convinced of brine heat pumps, as they probably represent a sensible investment given rising energy prices.

With a heat pump, I would rather rely on two storage tanks... one for domestic hot water and one for heating... otherwise, it runs continuously at full load...

Why should it continuously run at full load? At most if it was incorrectly sized... My brine heat pump is currently still operated purely electrically with a 9kW heating rod to drive out the residual moisture from the screed. With the 9kW heating cartridge, we achieve room temperatures of over 30°C. If it then runs at full load in everyday use, something is planned wrong.

Quote from another forum: ...no matter how you do it afterwards, definitely make sure that the domestic hot water storage tank is separate from the heating storage tank. I made a belly flop with this, as the different temperature zones in the stratified storage tank kept mixing, and the heat pump always had to run at a high performance level. Only since I properly separated the tanks from each other has there been peace.