At least here in Finland, it’s becoming more and more common for houses to use this kind of energy. I’ve even noticed a few isolated apartment blocks using it. Finland obviously requires a lot of heat, and it seems that everyone I know who uses it is happy, so it’s certainly interesting technology.
I think the Otaniemi project didn't pan out too great and that was proper geothermal. Ground source heatpumps are great. But those are often just capturing heat that comes from sunlight and get stored if I have understood right.
Is that really geothermal, or is it a heat pump? A heat pump just uses the thermal mass of the earth to provide more efficient electric heating and cooling, it doesn't heat using geothermal power.
You're not wrong; however that is an unfortunate misnomer since ground source bore holes (along with horizontal soil collectors and lakebed collectors) on the order of 100-300 m deep are still utilizing heat from the sun stored in the ground, and not heat produced from Earth's core.
I'd say it's a pretty good idea to not conflate the two by using more precise language, even if not doing so might be "technically correct".
I installed a ground sourced heat pump a couple of years ago, and my heat pump manufacturer refers to it as geothermal: https://www.waterfurnace.com/switch . Most people don't think of this as 'geothermal' however so I avoid using the term.
It's a mix of geothermal energy (extra heat), and insulation/thermal mass abitrage. Several hundred tons of rock/stone/soil are a great insulator, and are going to be consistently above freezing, which means you get a munch higher starting temperature for heatpumps if the alternative is freezing air.
