The only problem is retrofitting older buildings. That is somewhat expensive, but entirely possible especially with ground source heat pumps.

But does it require big (or deep) fields for heat exchange?

I mean, lets take a 20-story building, the amount of heating energy it consumes is really high, especially during winters. So you probably would need a soccer-field size heat exchanger in order for the heat to be extracted from the ground.

I bet it will also use quite a lot of electricity to compress the transporting liquid.

With tall buildings an option is to drill to 300 meters or deeper, https://hvac.okstate.edu/sites/default/files/pubs/papers/201...

Thanks for the article!

As I understood, drilling deep is quite expensive and, comparing to centralized heating stations working with gas for instance, the thermal output does not allow building heat factories. In example they state that they needed 8 500-meter holes for 4 houses and only 64 apts. So they are talking about typical Scandinavian 4-floor buildings, which are as well A-class insulated.

It stands nowhere near to typical buildings of East Berlin for instance.

The article mentioned Akershus hospital in Norway. It is a big 6-floor building. For taller buildings deeper drilling is required, but still should possible. But I guess for really toll buildings one should focus on improving isolation as presently it may not be cost-effective just to install heat pumps.