[CyberDildonics]

In the context of a heat pump yes, but what I'm saying is why not cycle the air of a building underground directly? I would think lots of air would be moved for very little energy and could be put through an underground radiator with lots of surface area.

Even with a heat pump, air has to be passed over the evaporation coils anyway.

[JshWright]

If you're trying to cool a building, the goal isn't moving air, it's moving heat. Pushing air around is a convenient way of moving that heat around inside a structure, but it's a lousy way of changing the total amount of heat inside the structure.

[CyberDildonics]

But again a heat pump is still running air over the evaporation coils so how does that end up better than having a radiator underground?

[JshWright]

The amount of surface area you would need to have underground to expose the air to would be tremendous. The reason heat exchangers work is because they substantially concentrate the heat (or the 'cold'), reducing the surface area needed.