Direct use of waste heat to minimize carbon-dioxide emissions
Making computing systems and data centers energy-efficient is a staggering undertaking. Today, the IT industry accounts for 2% of the world’s total carbon emissions—more than the amount generated by global air traffic.
“Hot-water cooling has compelling advantages.”
—IBM scientist Bruno Michel
Up to 50% 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 to reducing a data center's energy consumption is to cool it with hot water. This eliminates the need for today’s energy-hungry chillers in data centers. Moreover, high-grade heat at the output can be used for such needs as heating building spaces.
Schematic concept of a zero-emission data center. Hot water collects heat from electronic components and is then transferred to a district heating system to heat buildings.
In 2010, IBM built a hot-water-cooled supercomputer for the Swiss Federal Institute of Technology (ETH) in Zurich as part of IBM’s First-Of-A-Kind (FOAK) program. Marking a new era in energy-aware computing, this innovative system, dubbed Aquasar, consumed up to 40% less energy than a comparable air-cooled machine. Direct use of waste heating in the hot-water grid of ETH decreased the carbon footprint of the system by up to 85%. The Aquasar supercomputer consisted of special water-cooled IBM BladeCenter Servers, which were designed and manufactured by IBM scientists in Zurich and Böblingen, Germany.
The servers comprised microchannel coolers attached directly to the processors. Thanks to this chip-level cooling, the thermal resistance between the processor and the water was reduced to the extent that even cooling water temperatures of up to 60°C ensured that the processors did not overheat. This high input temperature of the water resulted in high-grade heat at the output, which in the case of Aquasar is up to 65°C.
Aquasar demonstrated 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 are becoming instrumental in the drive to improve the energy efficiency of data centers.
Building on the experience gained from the Aquasar system, the IBM iDataPlex DWC dx360 M4 and IBM / Lenovo NeXtScale DWC nx360 M5 servers were designed. These servers are deployed in warm-water-cooled, high-performance computing (HPC) systems at Leibniz Rechenzentrum (LRZ), Garching, Germany: SuperMUC Phase 1 (2012) and Phase 2 (2015).
Lenovo NeXtScale DWC nx360 M5 hardware was additionally implemented in CoolMUC-2, an HPC cluster from which waste heat is used to drive adsorption chillers, which in turn provide cooling for storage servers.
Aquasar system and direct water-cooled IBM BladeCenter QS22 and HS22.
Processors and numerous other components are water-cooled, and the server heat is utilized in the hot-water grid.
Warm-water cooled HPC Systems SuperMUC Phase 1 and Phase 2 at Leibniz Rechenzentrum (LRZ), Garching, Germany.
IBM iDataPlex DWC dx360 M4.
IBM / Lenovo NeXtScale DWC nx360 M5.
 M. Cossale, S. Paredes, R.P. Luijten, and B. Michel,
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 W. Escher, B. Michel, and D. Poulikakos,
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