My French relatives have some sort of ground source heat pump, having designed everything in their home to work on that basis, and it is everything you describe in terms of size - the pump unit is huge and impressively loud. It worked very well, when it worked. Unfortunately, the underground bit is also broken and the installers who broke it have refused to solve the problem. There is a fair amount of cowboy engineering going on in this domain, it turns out, a lack of reliable support for existing units/installs, and of course the usual attempts to extort money from people of a certain age. It makes me sick that they did everything right and were let down anyway. I’m not saying avoid this technology necessarily, but if you get a lemon and/or are unlucky and hire shysters there is practically no ceiling to the costs involved.