When it comes to supercomputers, it’s not all about raw horsepower. Keeping a lid on energy consumption has become one of the biggest technical challenges for making beefier and faster supercomputers.

The Leibniz Supercomputing Centre today announced that its “SuperMUC” supercomputer (MUC is the airport code for the nearby Munich airport), built in conjunction with IBM, consumes 40 percent less energy than a comparable machine. The trick to dramatically lowering energy consumption is water cooling, an approach IBM continues to pursue to pack more computing power into smaller packages.

Computer water cooling systems circulate water over active components, such as processors and memory, to wick away heat. Often, these cooling systems have to lower the temperature of incoming water before it’s circulated, according to the Leibniz Supercomputing Centre. But the SuperMUC can operate with hot water up to 40°C (over 100°F). That means the outgoing hot water can be cooled by ambient air or through a heat exchange, rather than compressor cooling equipment.

In the Leibniz installation, water heated by the supercomputer will be circulated to a heat exchanger and then used to keep the building warm during the winter time. The Centre estimates it will save about one million Euros each year this way. For all its energy efficiency though, SuperMAC is no slouch in the computing department: equipped with more than 150,000 processor cores in 9,400 compute nodes and more than 300 terabytes of RAM, it’s the fastest supercomputer in Europe with a peak performance of three petaflops, or 10,000,000,000,000,000 Floating Point Operations per second.

The basic computer cooling technology, called Aquasar, stems from IBM Research’s Zurich lab. Small pipes, called microchannels, carry water directly to the surface of server processors. Once water is cooled off, it can be recirculated to remove heat again.

Work on water cooling has been going on for years but in a typical data center or supercomputer, the temperatures of servers and other equipment are controlled by passing cool air over racks. Cooling represents roughly half of the energy consumption from these large computing centers.

An energy-efficient computing architecture is important for environmentally-conscious Germany, says Herbert Huber from the Leibniz Supercomputing Centre. “Germany is very greenish so energy and power awareness is a crucial aspect,” he said.

In general, techniques for managing energy consumption and peak power are becoming more important as designers seek to pack more powerful computers into smaller spaces. Because of its energy-efficient design, SuperMAC is ten times more compact and has better peak performance than a comparable air-cooled machine, according to the Leibniz Supercomputing Centre.

IBM expects hot water cooling to be central to future supercomputers, including three-dimensional chip architectures where multiple processors are stacked on top of each other. Researchers are working on tiny tubes only 50 microns across embedded between the processor stacks, according to IBM Research. With water cooling, IBM predicts that by 2025 a supercomputer could fit into the casing of a 2012 desktop computer.