Top 10 greenest data centres
Citigroup's data centre makes the list after enormous progress. Its giant data centre in Frankfurt started at 2.8 PUE and has been brought down by nearly half to 1.5, and the company is still on a mission to get it to 1.0. Awarded with a platinum rating from LEED in 2009, this building is covered in vegetation. Climbing greenery covers each wall of the 230,000 sq-ft building, which also features a roof garden. The plants absorb the heat to lower energy use and purify the air both in and around the buildings.