[cycomanic]

While that is in principle true, in practice there are quite a few issues. Many heatpumps here are made to heat the water for floor heating but don't transfer heat to air indoors. So you would cool using your floor which isn't very comfortable usually. More importantly because of the above the heat pumps are build for only one directional transfer. If one builds their own system it might make sense to plan for it, but even then it's unlikely that Sweden will become so hot that opening windows will not cool off the house enough. If it comes so far we likely have more pressing problems.

[patd]

The ground heat pumps are not used in the opposite direction, it doesn't cool down water to the floor but it flows water at 10-15C into your floor. According to the installers I've talked to here in Belgium, all the ground heat pumps devices are capable of doing that.

While this might not be needed in Sweden, it's more interesting further south. I live in Belgium and we had a long heatwave this summer and they predict more of those in the coming years. So cheap efficient cooling might turn out useful here (even if nobody had AC systems 20 years ago)

[vel0city]

It would be cool to have a valve to change between a floor heat loop and an air heat exchanger for the inside side of the system.

Of course this makes the system more complicated. More complicated means more chances for failure and higher costs for designing and installing.

[patd]

Some do wall heating or ceiling heating instead of floor heating. Wall heating/cooling would probably not require two systems.