HELSINKI, FINLAND: In the chill of a massive cave beneath an orthodox Christian cathedral, a city power firm is preparing what it thinks will be the greenest data centre on the planet.

Excess heat from hundreds of computer servers to be located in the bedrock beneath Uspenski Cathedral, one of Helsinki's most popular tourist sites, will be captured and channelled into the district heating network, a system of water-heated pipes used to warm homes in the Finnish capital.

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"It is perfectly feasible that a quite considerable proportion of the heating in the capital city could be produced from thermal energy generated by computer halls," said Juha Sipila, project manager at Helsingin Energia.

Finland and other north European countries are using their water-powered networks as a conduit for renewable energy sources: capturing waste to heat the water that is pumped through the system.

Due online in January, the new data centre for local information technology services firm Academica is one way of addressing environmental concerns around the rise of the Internet as a central repository for the world's data and processing -- known as "cloud computing".

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Companies seeking large-scale, long-term cuts in information technology spending are concentrating on data centers, which account for up to 30 percent of many corporations' energy bills.

Data centers such as those run by Google already use around 1 percent of the world's energy, and their demand for power is rising fast with the trend to outsource computing.

One major problem is that in a typical data centre only 40-45 percent of energy use is for the actual computing -- the rest is used mostly for cooling down the servers.

"It is a pressing issue for IT vendors since the rise in energy costs to power and cool servers is estimated to be outpacing the demand for servers," said Steven Nathasingh, chief executive of research firm Vaxa Inc.

"But IT companies cannot solve the challenge by themselves and must create new partnerships with experts in energy management like the utility companies and others," he said.

Data centers' emissions of carbon dioxide have been running at around one third of those of airlines, but are growing 10 percent a year and now approach levels of entire countries such as Argentina or the Netherlands.

Energy Savings
Besides providing heat to homes in the Finnish capital, the new Uspenski computer hall will use half the energy of a typical datacenter, said Sipila.

Its input into the district heating network will be comparable to one large wind turbine, or enough to heat 500 large private houses.

"Green is a great sales point, but equally important are cost savings," said Pietari Paivanen, sales head at Academica: the center, when expanded as planned, will trim 375,000 euros ($561,000) a year from the company's annual power bill. Academica's revenue in 2008 was 15 million euros.

"It's a win-win thing. We are offering the client cheap cooling as we can use the excess heat," Sipila said.

The center's location in the bowels of the cathedral has an added bonus: security. It is taking over a former bomb shelter carved into the rock by the fire brigade in World War Two as a refuge for city officials from Russian air raids.