East Boston gets a geothermally heated greenhouse

"Geothermal" gets used to talk about a lot of things, from true geothermal seen in volcanically-active areas (Iceland, California) to ground source heat pumps to so-called "climate battery" greenhouse systems which is a sort of very simplified and low cost ground-source system.

I spent a decent chunk of time looking into the latter for a greenhouse out in western Mass and concluded that they're either vastly oversold or only work on a very small scale. Youtube is full of people showing their designs and building projects, but very few showing them working a year or two later.

More broadly, while I know of ground-source heat pump installations going back a few decades, air-source systems seem to be winning these days. While ground-source systems are theoretically more efficient, these comparisons tend to leave out little things like the electricity used for circulating the water. And there have also been pretty big efficiency gains in recent years in air-source systems versus what was available ten years ago, so the real-world COP advantage of ground-source systems is a lot smaller than it used to be.

Meanwhile the installation and maintenance costs for ground-source systems remains higher. The HEET thing you linked is interesting, but my gut says that you could take the money spent on that and spend it on more PV panels, batteries, and a better grid instead, and be ahead. But sure, give it a try in the real world.