Room Thermostats Heating/Cooling

Sorry, the other way around. When heating, cold air is drawn in and even colder air is blown out. When cooling, warm air is drawn in and even warmer air is blown out.

Exactly. An air conditioner is also a heat pump.

Yeah, but with different performance. The effect with an air-to-water heat pump is not even remotely comparable. Hence probably also the reference to the sales argumentation ...

The cooling capacity is usually hardly lower than the heating capacity in a heat pump with active cooling. The insulation to the outside works both in winter and summer. In winter, temperature differences of 32-36 degrees sometimes need to be achieved (20 degrees inside and up to -16 degrees outside). In summer, it is rather the case that only a few degrees of difference need to be created from the 30-35 degrees outside (around 23 degrees, a maximum difference of 12 degrees). The capacity should be sufficient. Of course, cooling solely via floors may not be optimal in terms of heat/cold distribution. But it should work.

The OP is only asking about the control - is it simply set at the heat pump and done? Apparently, he has installed "wrong" room thermostats, but I also don't think it should fail because of that. Can all room thermostats be turned to maximum and the heat pump then set to cooling instead of heating?

The difference is that in heating mode, "warm" outside air is drawn in as a heat source by a powerful fan, and the heat is then transferred to water via a compressor, which flows through the surface heating. How do you transfer the heat from the indoor air to the water of the surface heating in cooling mode so that the air-water heat pump can transfer the heat from the water to the outside air in reverse operation? Yes, it is possible, but the effect is rather ... well. With a brine-water heat pump or groundwater heat pump, it is different because in summer the brine or groundwater is cooler than the indoor air, the temperature of which you want to reduce. But then there are issues like dew point control, etc., so a bit more is involved. I'm dealing with that right now too :)

: I thought the same. The temperature should be adjustable via the flow temperature.

Alex, that works wonderfully with an air-to-water heat pump. It is called active cooling and provides more than just passive cooling through brine.