A data center in Sweden has cut its energy bills by a million dollars a year using seawater to cool its servers, though jellyfish are an occasional hazard.
Interxion, a collocation company in the Netherlands that rents data center space in 11 countries, uses water pumped from the Baltic Sea to cool the IT equipment at its facilities in Stockholm.
The energy used to cool IT equipment is one of the costliest areas of running a data center. Companies have traditionally used big, mechanical chillers, but some are turning to outside air and evaporative techniques as lower-cost alternatives.
Seawater is another option, and apparently an effective one. Interxion recouped its initial investment after about a year, with the "cost" of the seawater equivalent to US$0.03 per kWh, said Lex Coors, Interxion's chief engineering officer, at the Uptime Institute's data center conference in Santa Clara, California, this week.
Interxion benefited greatly from the fact that there was already a network of pipes around Stockholm that provides seawater for cooling. It worked with a local partner to connect its data center to that network, at a cost of about $1 million.
But other bodies of water might make sense for data centers where seawater isn't an option. A data center in Zurich is using water from a deep lake, and aquifers and mines are another option, Coors said.
Using seawater for cooling isn't unique. Several companies in the Nordic region are already doing it, including Google at a data center in Finland. What makes Interxion different, according to Coors, is that it reuses the same seawater in several data centers, effectively getting more for its money.
It can do that because it builds out its data centers in a modular fashion, Coors said. When it realized the seawater was cool enough to be reused after going through its first data center, it added more server halls until it had maxed out its usefulness.
The water enters the first facility at 42.8 degrees Fahrenheit (6 degrees Celsius) and exits at 53.6 F (12 C). It's pumped to a second site, which it leaves at 64.4 F (18 C), and a third, which it leaves at 75.2 F (24 C). It's then sent to a heat pump and used to heat local homes and offices.
Before Interxion started the project, its energy bills were about $2.6 million a year to cool 1 megawatt of IT load. Today, its energy bill is $5.4 million to cool 5.5 megawatts of IT load, meaning the system has saved it about $1 million a year.
It doesn't pump seawater directly through its cooling systems. Instead, the seawater goes to a heat exchanger where it's used to cool fresh water. It has to clean the exchanger fairly regularly, but Coors said it's a simple maintenance job.
Over the life of the project, Interxion has lowered its Power Usage Effectiveness ratio, a measure of how efficiently energy is used, from 1.95 to 1.09, which is an enviably low score.
Since Interxion relies on a third party for its seawater, it can't guarantee the supply will never be shut off. It therefore has chillers on site so that it can guarantee reliability levels to its hosting clients.
But it had to run the chillers only a few hours last year, Coors said, when the government ordered its partner to stop pumping seawater. Coors isn't certain why that was, but he believes it's for environmental reasons. "I think it's to protect the jellyfish," he said.
He'd like to use water from other rivers and lakes around Europe, but some regions are skittish about potential environmental impacts.
"London would be excellent if we could get access to the Thames, but they're kind of scared," he said.
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