This diagram on Wikipedia, which illustrates the “Solar chimney” article, is really pretty intuitive. And it takes into account something I’ve thought for a long time: if the earth, once you go down 5 or 10 feet, stays at a constant temperature, why aren’t we exploiting that?

It apparently works pretty well, too. There’s a German standard called Passivhaus which apparently permits something like 90% reductions in energy use (!), and which, in the dead of winter, lose something like 1 degree a day if no heating is used. A big part is the ground-coupled heat exchangers, the big pipes underground that allow air to be passed through and be cooled (or warmed, in the winter) to the earth’s ‘native’ temperature around 60. Simple systems just use the solar chimney (in the diagram), using the fact that hot air rises (and thus ‘pulls’ air in via draft) to bring in outside air, run it through lots of underground tubing, cool the house, and then get vented out. It seems you can enhance the effects, especially in extreme weather, by closing the paths to the outside and making a circular system: take the air that you’d be venting out and pipe it back through the underground tubes, so that it will re-cool the already kind-of-cool air being expelled.

What I like is that it’s so deceptively simple.