I plan to build using this technique.
Best part, no need for Sheetrock.
Yeah that is one of the ones I saw. I would still sheetrock and insulate between the studs though for even more resistance to heat exchange.
As far as heart pumps they stick below a certain temp but that is where the geo thermal ones are the best. The ground two states fairly stable so it's cool in summer and warm in winter. Not to mention that cooling well be a lot cheaper than a conventional system as instead of trying to force more heat into hot air you are just pushing it in to the ground which is only going to be 55 to 60 degrees.