Making computing systems and data centers energy-efficient is a staggering undertaking. Today, the IT industry accounts for 2 percent of the world’s total carbon emissions—as much as is released by global air traffic. Up to 50 percent of an average air-cooled data center’s energy consumption and carbon footprint is not caused by computing but by powering the necessary cooling systems to keep the processors from overheating. This situation is far from optimal if we look at energy efficiency from a holistic perspective.
The key for ratcheting down a data center’s energy consumption is to cool it with hot water. Hot water cooling has compelling advantages. It eliminates the need for today’s energy-hungry chillers in data centers. Moreover, high-grade heat at the output can be used, for example, to heat buildings (Figure 1).
IBM has built a first-of-a-kind hot water-cooled supercomputer for the Swiss Federal Institute of Technology Zurich (ETH Zurich), thus marking a new era in energy-aware computing (Figure 2). The innovative system, dubbed Aquasar, consumes up to 40 percent less energy than a comparable air-cooled machine. Through the direct use of waste heat, which provides warmth to the university buildings, it decreases the carbon footprint of the system by up to 85 percent.
The development of Aquasar was part of IBM's First-Of-A-Kind (FOAK) program, which brings IBM’s scientists together with clients to explore and pilot emerging technologies that address today’s business problems. The supercomputer consists of special water-cooled IBM BladeCenter Servers*, which were designed and manufactured by IBM scientists in Zurich and Böblingen, Germany (Figure 3). The servers comprise microchannel coolers, which are attached directly to the processors. Owing to this chip-level cooling, the thermal resistance between the processor and the water is reduced to the extent that even cooling water temperatures of up to 60°C ensure no overheating of the processors. This high input temperature of the water results in high-grade heat at the output, which in the case of Aquasar is up to 65°C.
For direct comparison with traditional systems, Aquasar also has air-cooled IBM BladeCenter servers. In total, the system achieves a performance of 6 Teraflops and has an energy efficiency of about 450 Megaflops per Watt. In addition, about 6 kilowatts of thermal power are fed into the ETH Zurich’s heating system. With its innovative water-cooling system and direct utilization of waste heat, Aquasar is now fully operational in the Department of Mechanical and Process Engineering at ETH Zurich.
Aquasar demonstrates that it is possible to reduce the energy consumption of data centers while restraining costs and curtailing carbon emissions. Liquid cooling and deploying waste heat appear to become instrumental in the drive to improve the energy efficiency of data centers.
* The IBM BladeCenter Cluster is comprised of 3 IBM BladeCenter H chassis with a total of 33 IBM BladeCenter QS22 servers (equipped with 2 IBM PowerXCell 8i processors each) and 9 IBM BladeCenter HS22 servers (equipped with 2 Intel Nehalem EP processors each). Water-cooled are 2 IBM BladeCenter H Chassis with a total of 22 IBM BladeCenter QS22 and 6 IBM BladeCenter HS22 servers.
 G. I. Meijer, Cooling Energy-Hungry Data Centers, Science 328, 316 (2010).
 T. Brunschwiler, B. Smith, E. Ruetsche, and B. Michel, Toward Zero-Emission Data Centers through Direct Reuse of Thermal Energy, IBM Journal of Research and Development 53, 476 (2009).
- Leibniz-Rechenzentrum entscheidet sich für neuen IBM Supercomputer mit Intel® Xeon® Prozessoren der nächsten Generation für anspruchsvolle Forschungsanwendungen, Garching/München/Stuttgart, 13 December 2010.
- Made in IBM Labs: IBM Hot Water-Cooled Supercomputer Goes Live at ETH Zurich, Zurich, 2 July 2010.