Heat pump Knv or IDM air heat pump

All right, thanks. I will look around with the manufacturers.

How can I improve this bivalence temperature or the bivalence point?

Select the appropriate heat pump. It must have enough capacity at low outdoor temperatures to operate without an electric heating element. And/or better thermal insulation. The bivalence point depends on the heating load/insulation of the house, the desired temperatures, the design of the underfloor heating (flow temperature), and the characteristic curve (compressor capacity at outdoor temperature) of the heat pump.

More thermal insulation is hardly possible anymore, construction is done with 38cm filled bricks. Now every heat pump salesman will tell me again that theirs can do that and is the best. My installer lays pipes with a 10cm spacing in every room and a small piece of wall heating in the bathroom. The room temperature is then controlled via the supply temperature, that's how I understand it.

Most heat pumps regulate via the return temperature. The supply temperature then results from the supply-return spread. This depends on the energy provided and the volume flow. The optimal spread depends on the refrigerant. It's all a science... Make sure that the heat pump is not too weak for the really cold days. Although it does not necessarily have to provide the required heat at [NAT] only via the compressor. You rarely have [NAT]. Equally important is that the heat pump can modulate the output down significantly. Otherwise, you will have a cycling heat pump at milder temperatures.

I have not yet found a 7-8kw pump that is under 3kw.