Sweden : how to cool down a data centre using the surrounding air ? The example of Facebook

data centers, energy efficiency, free cooling A data centre’s cooling system is essential for the servers to work, but it uses up a lot of power, up to 40% of the facility’s total energy consumption. For the sake of energy efficiency, the European Commission created a Code of conduct for data centres that promotes the use of new cooling technologies.

A vital but expensive system

A data centre is home to all of a company’s servers, processing and saving its computer data. One single centre can host several thousands of servers working 24/7. Because servers are permanently turned on, the heat goes up and they need to be cooled down to an ambient temperature no more than 24°C. That’s why the cooling system is crucial.

Such a system traditionally rests on the use of refrigerators, freezers or air-conditioning which produce coolness quickly but in return use up a significant amount of energy. Today more economical cooling systems can keep servers at an adequate temperature for less money, while causing a limited harm to the environment.

Optimizing energy efficiency thanks to “free cooling”

Free cooling consists in using natural sources of coolness. For instance, the system can be fuelled by a fresh water source: water runs directly through the centre’s circuit and then flows into the nearby river or sea. Google resorts to this method in the centre it opened in 2011 in Hamina, Finland.

A less known technique consists in using the outside air. Facebook chose this method for its new data centre in Lulea, Sweden. The location is no accident: the city is positioned near the Arctic Circle and its climate is particularly cold (1°C in winter and 20°C in summer on average). The data centre will thus use the cold from the outside air to cool down the 10,000 servers it will host in 2014 and will significantly limit its air-conditioning and electricity costs. Furthermore, this centre will be powered by the hydroelectric dam on the nearby Lule River. Thanks to free air cooling, this data centre will only require 120 megawatts to function – which is still tantamount to the overall consumption of a city of 16,000 inhabitants – instead of the 260 megawatts used up by the least energy-efficient centres.

Professionals are aware of the importance of optimizing their centres’ energy efficiency. An example of that is The Green Grid organization, comprised of computer giants such as HP, IBM or Intel, which offers a range of tools and advice to companies willing to resort to free cooling.

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