Basement underfloor heating or low-temperature radiators

I understand that the return temperature must always be below 50 degrees. The system has to be efficiently designed if it receives the KFW 55 certification.

The system basically has to be planned efficiently if it gets the kfw 55 approval

District heating/remote heating already has a calculated advantage per se, which does not necessarily result in an efficient heating system or low heating costs.

Can the underfloor heating also be used for passive cooling in the summer?

Can the underfloor heating also be used for passive cooling in the summer?

With a supply temperature of 60 degrees mixed down to 30-40 degrees? Cooling probably only works at 50 degrees outside temperature ;-)

I definitely want to keep the option open to exit the [Nahwärme vertrag] later after 15 years

Which heating technology will be available to me then?

Actually only the air-to-water heat pump, right?

I do not have a gas connection

If I switch to a heat pump, it is definitely an advantage to have underfloor heating in the basement as well, right?

Does anyone have an idea how the underfloor heating works with [Nah bzw Fernwärme]?

Does the water stay in the house in a closed loop and only a little hot water is added as needed to maintain the temperature?