Did some reading, so I can reply with some knowledge imparted from the read.
I'm wondering what kind of insulation this guy uses for his actual home. I don't doubt that moving large volumes of warmer air would heat a home, but I'm not sure the warm air would stay warm at night. Are the tubes buried? The pressure difference between the warm and cold air could move it through a home, but it sounds like he uses fans.
The tubes are buried, below grade, below the frostline / permafrost if you're REALLY far north or south on the planet. In around 8 feet deep, where you reach a near constant 50-65F for a ground tempurature. The greenhouse uses a very simple system of pulling air out of a drainage tile loop buried to that depth. The tempurature differential between the greenhouse air temp and the loop's air temp (which gets moderated to in around 52F in Russ Finch's greenhouse location). So, it can heat or cool the air in the entire greenhouse, just by air exchange, pulling it out of the loop, and drawing greenhouse air into the loop and dumping heat into the ground in summer, and pulling heat out of the ground in winter.
What he uses in his house and workshop, is a two stage setup -- which he set up first, the greenhouse came later, apparently.
The same simple ground air tube loop exists, and dumps into an 8x8x8 ft room in the house. Inside that room, the air temp is moderated to ... somewhat close to 50F, near the 52F the air temp is in the ground after it's been sitting in the tube, in the ground as it gets pulled through.
Also inside the room is a more conventional heat pump, which pumps refrigerant, and it has a loop that circulates in the house. And that heats/cools the house.
In a "normal" heat pump installation, it's mounted outside the house, in a climate like, Florida, where they don't have sub-freezing day/night air temperatures often. So you circulate the refrigerant/coolant loop in the house, and it dumps heat to the outside when it's hot inside, but the same loop also pulls heat from the outside and dumps it inside, when it's cold enough. So, there'll still be a bit of angry pixies, aka, electricity used to power the blower fan for the simple air loop, and to power the heat pump.
They'd both be thermostatically controlled, so you're not running them when they're not effective (when air temps are near the 50-55F mark for outside air temps). That would limit electricity use somewhat.
I didn't get a good feel about how insulated his home was, but he built it in the late 70s, using a few unconventional construction techniques, and the heating system too...
I can make educated guesses, because post-Arab Oil Crisis in the mid 70s, there were a lot of efficient house designs that cropped up.
Up here in Canada, they had an R-2000 House "design" of sorts (pointing to the future, the year 2000). My parents designed a house with energy conservation in mind -- longer roof eaves that shaded the windows in summer, but let in sunlight/heat in winter, and radically thicker exterior walls than the norm, and IIRC, they had 10" nominal walls - 2x4 and 2x6 alternating studs, which I do recall *perfectly* were a total pain in the arse to fit insulation batts into.
But, in summer, during the day, at my parents house, there was an easy 8-15F temperature drop versus outside temperatures. They don't have A/C, nor a heat pump, nor a air-heat exchanger. Just well insulated walls/roof and good doors and windows.
Earthships use material with high specific heat (and I presume diffusivity? I need some basic thermodynamics knowledge.) Specifically, they fill tires with dirt and let them heat up during the day and it keeps it warm at night. I'd expect this would make it relatively simple to keep it about the average year-round temperature of whatever location. An 'underground' greenhouse is probably going to have a similar effect, but with a bit more variance between night and day.
Earthships rely on thermal mass and passive solar. The low grade geothermal is an active system, and isn't effective when the daytime temps are near the constant below-frost-line stable ground temperature (in around 50-65F or 8-15C at 8ft and deeper), as described above. The passive ideas of an earthship work, but they work less well in colder climates.
My bias against that, other than living at around 52?N of the equator, knowing that I'd be fighting against extreme cold for part of the year, and possibly lacking tree cover at many building sites here... is permitting in my jurisdiction. I'd consider a go of it otherwise, though then I'd run into resistance from the wife-person over building a house from scratch, from apparently scrap materials. It's a plus in my books, but i'd have to go through legal hoops to make it happen.
On the other hand, putting a pipe in the ground, Albertans know all about that already! ;)