The system I was talking about used fans to pull hot air from up by the peak through perforated culvert a few feet deep under the greenhouse. It stores the best in the ground and the cooling of the air fries it out by condensing the moisture. The perforations let it drain. Later when the greenhouse is colder the cool air pulls the best back out of the ground. It's also good for bringing up your average soil temp in the cool season but takes a couple of seasons because of how much thermal mass is there and because the heat is being cycled in and out of the ground.
You could also use a water cooled co2 generator or even just an inline water heater hooked up to a co2 regulator for the hydronic floor heating. There's also cogeneration. It has to be done at a minimum scale to be efficient but a propane generator can be fitted with heat exchangers and catalytic converters to power the equipment and provide heat and co2 from the exhaust. There are alson insulated heat storage tanks that are basically just huge water tanks that let store that heat for when you need it.
Most of these things are at least fairly expensive to set up and only so efficient on their own but if a complete system were built using these features it would be untouchable. One of my favorites was the guy who daisy chained a few new car radiators together and built his compost pile on top. It was basically an on demand water heater that didn't use gas or electricity. A farm with enough turn over and scraps could potentially just use composting to power their hydronic floor heat.
Heat always flows from the warmest to the coldest ,
Water although is a great heat transfer material it is also one of the worst at storing heat.
It always amazes me the things people think of to come up with.
Ingenious
Sometimes these ideas are valid sometimes only good on paper.
The perfect example of this is geothermal. Great in theory just to expensive to purchase and maintain in reality.
If the government was not handing out free welfare checks to the rich( this is what it is) you would see very few geothermal systems.
The ideas are endless of heating and cooling methods that are available.
I like the idea, but from a installer or maintenance point of view a system must be reasonable to install have easy access to parts for repair, easy and inexpensive to maintain and reasonably efficient.
I talked piles of peke out of installing higher efficiency equipment because of the initial cost and maintenance of the equipment is more expensive than any realized cost savings .
Everything is a factor and it all boils down to money.
Not many people if they understand the whole picture will spend 10 thousand to save a couple of hundred dollars, there are some who will though .
I will try to look up the system you mentioned and do a little more research on the cost benefit of it.
I bet that makes for some crazy people.