The bank outlined plans back in August 2007 to spend EUR170 million to build one of the "greenest" data centres in the world in the German city, which provides IT services for Emea operations.

The 230,000 square foot building, opened last year, is the first data centre to receive platinum accreditation. Citi says it cost no more than conventional data centres and does not affect the reliability and resilience of the systems it houses.

The new building uses 30% of the power required for a conventional data centre and cuts carbon dioxide emissions by around 11,750 tons per annum.

An "optimised cooling design", means it enjoys an enhanced free cooling rate of 63% and reverse osmosis water treatment for cooling saves 50 million litres a year. Around 250 kilometres of cabling has been saved by using virtualised technology, deployed in a modular design which also optimises energy usage.

Nearly three quarters of the roof is vegetated and the building has a full green wall, irrigated from harvested rainwater.

Photo: Christian Richterus

Stephen Ellis, head, technology infrastructure, Emea, says: "The energy efficient design of the data centre, coupled with extensive use of new, energy efficient virtualised technology, housed in innovative modular cabinets has optimized energy use and reduced the data cabling needs."

In November the bank opened an environmentally friendly data centre in Georgetown, Texas, although that only received Leed gold certification.

Meanwhile, Swiss bank PostFinance has begun using water from the Aare river to cool its computer centre at Engehaldenstrasse in Berne. The bank commissioned a pump station on the banks of the river with the water - which has a temperature of 10°C - channelled into the refrigeration plant and used to cool the IT systems rooms.

PostFinance uses this climate-neutral measure to save the equivalent in electricity consumption of 300 Swiss households.