Thanks, Rob
I've been thinking 'bout your greenhouse. I visited an amazing greenhouse not long ago, one that vented the hot air at the top down into the ground using a series of buried ducts (black flexible 4" drainage pipe.) This uses the ground as thermal mass. I used to have some links to this, or a pdf, but I'm still looking for it. When I find it, I'll post it.
The greenhouse was at 8000 feet and had the biggest fig tree I've ever seen inside a structure, so obviously the system works.