Modified Hypocausts to Regulate Temperature?

I just read about hypocausts in Low<-Tech Magazine archives. Here are details on wikipedia:

https://en.wikipedia.org/wiki/Hypocaust

TL;DR: Primitive radiant floor and/or un-forced-air heating. It's a kind of basement level where air is heated and the heat is either absorbed directly by the thick stone floor above it, or delivered through vent channels between the two chambers.

...And according to LTM, later uses of the hypocaust (as in, the Middle Ages, not in Ancient Rome) included large slabs of rock that would absorb the heat and then provide heat for large upper chambers for as much as a week after only a single firing. Maybe combining this tech in some way with a rocket mass heater you could warm in the winter, and then cool things down in the summer? Attach a solar-powered fan to draw the warm air into the hypocaust chamber, cool it down, and then force it through wall pipes to the ceiling, perhaps...? I suspect that a well-made RMH would be sufficient for this purpose, and the underground chamber would serve better as a root cellar. But I wonder.

I originally read someone's post about regulating temperature in a building by cooling/warming air drawn through a subterranean chamber and didn't want to gum up their thread with this. But it's an idea that percolated in my head and I wanted to share it and see if anyone had ever attempted this.

Good idea, though a pretty expensive way to achieve radiant floor heating Traditional Korean houses used a version of this called an ondol (plenty of info on permies if you search for the term.)

A few people have done similar things with multiple ducts buried beneath a floor.

Using the hypocaust for summer cooling could work, though there is always the potential in humid climates for condensation and mold buildup in the underground passages.

Glenn Herbert wrote:Using the hypocaust for summer cooling could work, though there is always the potential in humid climates for condensation and mold buildup in the underground passages.

Thanks for this info, Glenn! The amount of time the basic design and concept have been around makes me think that some of these issues have been addressed. So I have a couple more questions, if you don't mind.

Depending on the design, do you think using the same duct-work for both heating and cooling can minimize/mitigate mold and mildew growth? Could someone maybe fire-up the hearth maybe one day in the summer, for example, and "flush" the growth out of the ducts?

Could keeping the heated footprint a small amount of square footage (instead of a Middle Ages-sized stone chamber, for example) help prevent the mold and mildew issues?

The concept has  been used for millennia as a heating method, but I don't know how much it has been used for cooling. Recent versions such as earth tubes have had mold issues when used for cooling in humid environments. I am not familiar with what has worked to mitigate the issue.