walipini greenhouses are interesting. They're greenhouses that are partially subterranean.
The average temperature one meter below ground is about a constant 55F, ~12C.
In hot climates, this means your greenhouse *starts* at a cooler temperature, and even when heated a good 40 degrees above that is not too hot to kill off the plants. Your greenhouse is temperature controlled.
In cold climates, your greenhouse again starts at about 55 degrees, above freezing, even without adding heat or the heating from the sun.
With basically zero effort, you get a year-round near ideal growing environment.
A lot of people will, when building a walipini, extend the trench in a big loop and put a duct there.
The air inside this duct will stay at a constant 55 degrees. Pumping this air into their home provides cooling in summer, heating in winter, with almost no effort.
A small fan on either end is basically enough to move this column of constant temperature air where and when you want.
In winter, you can easily heat your living area to 55 degrees baseline with little effort, and then only have to heat a bit above that for comfort. Not from ambient.
Many walipini designs include a heat sink such as a wall of rocks or barrels of water, this mass absorbs plenty of heat during the day and then slowly releases it at night.
Use the right heat sink, and you can keep the temperature right for such as tropical plants year round, with low effort.
Similarly, many people will bury a loop of pipe and flow water into it to cool it down to that constant year-round temperature.
Let it cool overnight, pump it back indoors to absorb the day's heat, rinse and repeat etc.
You can also bolt this onto a central heating system with little effort, since you have all the ducting in place. You just need a sufficiently long geotherm loop with the impellers on the HVAC's intake and return vents.
You could, potentially, even run these systems for entire neighborhoods, since you know how many cubic feet you need to service per install. Trench in your loops along with other subterranean infrastructure and then hook it up to existing housing like you would cable or anything else.
Of course, since I always advocate to include the worst person you know in your design phase: You need to harden this against attack with good filtration, ventilation, and early detection systems. But it shouldn't be too susceptible due to the sheer volume of air that would need to be compromised.
Every big city is standing atop a massive subterranean tunnel system with parts long since totally forgotten and unused, rotting there at a constant temperature in the dark and damp
Well for big cities I would, given complete control of all government and economic apparatuses, look to expand that into usable space.
I thought that was what The Boring Company was actually about, creating geofronts under existing metropolitan areas, but nope! Just a way to kill public transport!
