Using the right glass is key, I think, to allowing visible light and uv in but reducing IR. I have a thread on glass and surface treatment options
http://www.reefcentral.com/forums/sh...2537919&page=2
My inspiration was the Berlin greenhouse renovation a few years ago.
Geothermal or at least earth-mass cooling (like a concrete in ground pond) would help but I can usually manage with chillers and evaporative cooling, as long as the humidity is low enough.
I did run geothermal tubes but never finished the project... But definitely a good consideration when giving the sun easy access to the system.