That sounds really interesting but isn't that useless because at that point you may as well use geothermal. Doesn't the exchanger need air to flow over it hence the fins for it to work? I think geothermal is the biggest win environmentally however so there is that.

In most places, "geothermal" is just a "ground sourced heat pump". Circulate a liquid underground so that it keeps that 50-degree temperature, run a heat exchange with that as the source instead of the air.

(In other places and to a larger extent pop culture, "geothermal" refers to tapping into actual heat sources underground.)