Further Underground

The assumption that cooling underground means you're still dependent on outside air is still just an assumption. Here's some facts...

http://www.techworld.com/green-it/news/index.cfm?newsID=10667

"The coolant will be ground water and the site's temperature is a constant 15 degrees Celsius (59 degrees Fahrenheit) all year, meaning no air-conditioning will be needed outside the containers. This reduces the energy required for the water chillers, used with surface-level Blackbox containers."

Note in particular, not just the water cooling but the relevant fact that a static temperature of 15 degrees in a very large open space reduces the need for cooling anyway.

Above ground buildings are not only struggling with cooling because of the outside air, but because the buildings act like greenhouses. By locating underground, even if your cooling plant was above ground, your building is not being heated like a greenhouse. Of course there's a downside in that the temperature will not drop off in the night, but at least it's consistent.

It's a fact that places like disused mines (especially salt mines which have vast caverns), and disused bunkers, are being used by datacenter companies. Maybe they're stupid, but I suspect they've worked out the sense of it.

Though in part they're doing it to sell on security as well. Being underground is supposedly more "secure", but of course that wire sticking out of the ground is an open invitation to Mr Hacker ;)