PUE may not be the best of instruments for handing out, let's say, world wide energy labels. But what PUE can offer is a view at how well you're operation is going, and it gives a quick answer to the question wheter there is any space for improvement.

Consequently, the data center space is locked in a friendly competition of 'who has the smallest', or more accurately: who comes closest to 1.

For example, a facility built by Keysource in the United Kingdom this month announced an annualised PUE of 1.17. The facility which is used by Petroleum Geo-Services has been awarded last year with a Data Center Leader's Award, and they apparently like the PR-boost because of that. They want more.

Now a figure like that is as low as you can get right now. But it is not the only facility by a long shot sporting figures like this. A new facility for Facebook is going for 1.15. Not bad, as Google's coming data centers will probably be hitting the 1.3's.

So what's the limit? Well, this chap reckons it would be 1.04 for his sites. Undoubtetly, someone will come with an even lower estimate at some point. It is the lowest reckoning I have come accross so far.

The arms race will be hotting up, even if PUE comparison says as much about your data center as your ranking in a game of pub golf says about your general drinking prowess.