Massive supercomputers that devour electricity to keep them humming are not exactly the poster children for green technology. But IBM hopes to change that with its plans to build a supercomputer that will use water to keep the system cool and even recycle some of the waste heat to help heat the university where it's housed.

The technology could lead to a reduction in overall energy consumption by at least 40 percent, when compared to similar air-cooled machines, says the company.

“Energy is arguably the number one challenge humanity will be facing in the 21st century," says Dimos Poulikakos, lead investigator of the project. "We cannot afford anymore to design computer systems based on the criterion of computational speed and performance alone."

Supercomputers are used in energy research labs such as Argonne National Laboratory, in space research by NASA and at universities for scientific research, all applications which have a nearly insatiable demand for processing power. The new supercomputer, called Aquasar, will be housed at the Swiss Federal Institute of Technology (ETH) Zurich and will have a top speed of 10 teraflops. (A teraflop is a trillion floating point operations per second, a measure of computing capacity.) While that's a lot of computing power – a Core 2 Duo processor is capable of about 20 gigaflops, or 1/500 the speed of Aquasar – it's a fraction of what some of the fastest supercomputers today. For instance, IBM's Blue Gene/L supercomputer, which ranks fourth on the top 100 list, has a peak speed of 596 teraflops. Meanwhile, IBM has moved on to create its first supercomputer in Europe capable of one petaflop, or one thousand trillion operations per second.

Keeping these massive machines running isn't as much a challenge as trying to maintain them in an optimal temperature band. Aquasar, however, hopes to offer more bang for the buck in terms of its energy consumption. Many of the chips used the supercomputing systems dissipate about ten times as much heat as a typical kitchen hotplate, says Thomas Brunschwiler, a researcher at IBM Zurich Research Lab. For optimal performance, the chips must be cooled below 185 degrees Fahrenheit (85 degrees Celsius).

Accomplishing that much cooling across a huge data center means a significant strain on electricity consumption. Researchers estimate that about 50 percent of an average air-cooled data center’s energy consumption stems from powering the cooling systems to keep the processors from overheating. Reducing that would be a big step towards energy efficiency.

The power consumption of one rack of the Aquasar will be around 10 KW, IBM officials say. By comparison, theBlue Gene L/P supercomputer consumes about 40 KW of power per rack, and the average power consumption of a supercomputer in the top 500 list is 257 KW. Aquasar, set to be commissioned in 2010, will have two IBM BladeCenter servers in each rack. Power consumption per teraflop for Aquasar will be known once the system is built, says IBM.

Aquasar's breakthrough lies in how it has successfully managed chip level water cooling, says Brunschwiler.

"One way to do it is to cool the air in a data center to 40 degrees Celsius (104 degrees Fahrenheit) , which means air conditioning units that take space and energy," he says. "Or you can use liquid cooling to get there."

In the Aquasar system, high performance micro-channel coolers are attached directly to the backside of the processor. In them, the cooler water is distributed through a fine network of capillaries that spread throughout the back.

It's different from the water-cooled modules used in other supercomputers, says Brunschwiler. Water cooling on a module level brings the liquid between the processors, but not right up against them via micro capillaries.

"The breakthrough in our special package design lies in how we can bring the water as close as possible to the chips without letting it affect the chips' performance," says Brunschwiler.

The water-cooled supercomputer will require a small amount, just about 2.64 gallons of water for cooling. A pump ensures the water flows through at the rate of roughly 7.9 gallons per minute.

For overall efficiency, the entire cooling system is a closed circuit. The heated water from the chips is cooled as it passes through a passive heat exchanger and the removed heat is recycled. In this case, it is channeled into the University's heating system.

“Heat is a valuable commodity that we rely on in our everyday lives," says Bruno Michel, manager at IBM’s Zurich Research Laboratory. "If we capture and transport the waste heat from the active components in a computer system as efficiently as possible, we can reuse it as a resource."

Photo: Aquasar/IBM Research