larsalmen

No it's not. The bore-hole is lined with a outer steel pipe until the drill hits bedrock, keeping it very much insulated from the ground. And the upper-most part of the energy-well that's lined is considered inactive, and is not counted in the "150 m deep energy well".

Right, I stand corrected. I had never seen such a heatpump (based in the nordics, that concept would never fly), and I'll agree with you that in homes heated by "regular means" (resistive/electrical, fossil fuels) they add little to no value, simply adding complexity. In heating season they would just siphon heat energy from the rest of the house...

(They would however de-humudify the space they are in, but that's another thing...)

I'd argue that every house that has any sort of ventilation, even naturally aspirated ones, have excess heat in that any amount of air leaving the house "unreclaimed" while there is any heating need contains wasted energy.

Heatpumps using that energy are very prevalent in the Nordics and Scandinavia, even with a majority of the time being heating season here.

Who has that, a "indoor heat pump"? That's just stupid. Sure, exhaust air heatpumps "use" the (excess) heat from indoors, but that would just get expelled anyways.

Nah. It does not necessarily have to be an air-water heatpump either, colder climates more often use geo-thermal or ground-water loops as the energy-well. Then the surrounding climate have much less of an impact.

Refrigerant leaks are still an issue though, but moving to hydrocarbons and CO2 will mitigate that. Even R32 is a step up in that regard.

Mass ≠ insulation. You can have mass as a buffer and regulator, but normally stone or brick and mortar houses simply shift the issues to later in the hot season. It is usually a more even temperature over any given timespan though, as you say.

I'd think barns would have very low mass in comparison to their size, but would stay close to surrounding temp by way of having very little insulation and being very "drafty"