How can hot water cool a supercomputer?

SuperMUC uses 40 percent less energy than would be required by an equivalent air-cooled system.
SuperMUC uses 40 percent less energy than would be required by an equivalent air-cooled system.
Courtesy of IBM Research - Zurich

If you think about it, computer engineering has always focused on decreasing size and heat concerns just as much as it has on increasing computing power. That's true whether you're talking about a laptop, massive mainframe or even your tablet, but real jumps in utility, green technology and size constraints are even more important on the supercomputing scale than with the things we use every day.

In July 2012, engineers at the Leibniz Supercomputing Centre (Leibniz-Rechenzentrum, or LRZ, in German) debuted their new SuperMUC supercomputer, which uses water-cooled servers to approach performance levels of up to three petaflops, or basically the work of more than 110,000 personal computers. While SuperMUC's heat management system -- which sits on top of the mainframe, carrying water though microchannels on the hardware itself -- is called "hot water" cooling, it's kind of a misnomer.


The system was inspired by the way blood and water move through our bodies, and keeps the machine at about 45 degrees Celsius (113 degrees Fahrenheit). The reason engineers stress the hot water aspect of this system -- which improves performance while shrinking the system by 10 times and using 40 percent less energy -- is to emphasize the difference from standard air-cooling and the way we usually think of fluid coolants [sources: Clancy, IBM Labs].

But what exactly is that water doing, and why is the design so groundbreaking?

How the Water Makes Its Rounds

SuperMUC is more colorful than most other supercomputers. And while the color isn't present in the visual design, this impressive system is also green.
SuperMUC is more colorful than most other supercomputers. And while the color isn't present in the visual design, this impressive system is also green.
Courtesy of IBM Research - Zurich

Most personal and business computers use fans and open slots to circulate room-temperature air through the machine, keeping its circuitry and moving parts cool. Supercooled air and low-temp refrigeration is a common way of keeping larger mainframes from overheating, but those methods use up a ton of energy. (Typically, about half the energy we use running computers is actually used to cool them.) The next level, water cooling, takes its cue from centuries of the combustion-engine paradigm: Moving parts create kinetic energy and cold water takes away the excess temperature.

But the "hot water" cooling system that's enabled the SuperMUC to break supercomputing barriers is something completely different. The German-based LRZ lab is very eco-conscious, and has incorporated green solutions into their designs for years. The water that cools the technology in the cooling system's proprietary "microchannels" is conducted away from the machines, carrying heat with it to an exchange in which it's used in heating the human-occupied areas of the building. (Incidentally, this saves more than 1 million Euros -- about $1.27 million -- each year in heating costs.)


The water, having dropped some of its heat, is then pumped back to the processors, making direct contact with them and drawing heat away as it passes through on its next round. The LRZ's Herbert Huber calls it "a completely different cooling technology" which allows them to use their supercomputers all year "... without any chiller, without any compressor" [source: IBM Labs]. How much better is this new concept? It's 4 thousand times more efficient than air cooling.

But this is just the start. IBM, which pioneered the technology used by the SuperMUC, says that it'll only take five years for a size-reduction by another factor of 10, and five years after that for the next, and so on, towards a million-fold reduction of SuperMUC's size -- small enough for use in a personal PC [source: IBM Labs].

Author's Note

For me, the most interesting part of learning about the here and now of supercomputing was seeing how scientists are addressing green issues -- cooling, mainframe footprint, etc. -- while continuing to raise the bar on what our computers and networks can do. It was exciting to hear about this latest development along those lines. There's something about the intersection of low- and high-tech solutions that really gets my heart racing. I suppose because I see no reason we shouldn't be developing an outlook that incorporates them both -- a view of "nature" and what's "natural" that includes iPods and homeopathic medicines as well as California redwoods and urban green spaces. We are only as divided from nature and from one another as our language and heritage allow us to be. And I look forward to a time when that distinction between lo- and hi-tech means as little as the low-culture/high-culture divide has come to mean today.

Related Articles


  • Borghino, Dario. "Europe's fastest supercomputer uses warm water cooling to conserve energy and heat buildings." June 26, 2012. (Oct. 22, 2012)
  • Clancy, Heather. "IBM cools supercomputer with hot water." ZDNet: GreenTech Pastures. June 19, 2012. (Oct. 22, 2012)
  • Cooper, Daniel. "IBM's water-cooled supercomputer saves energy and helps with your heating bill." Engadget. June 19,2012. (Oct. 22, 2012)
  • Hruska, Joel. "IBM deploys hot-water cooled supercomputer." Extreme Tech. June 18, 2012. (Oct. 22, 2012)
  • IBMLabs. "SuperMUC: First Commercial Hot-Water Cooled Supercomputer to Consume 40 Percent Less Energy." IBMLabs Youtube Channel. June 18, 2012. (Oct. 22, 2012)
  • IBM. "First Commercial IBM Hot-Water Cooled Supercomputer to Consume 40 Percent Less Energy." IBM. June 18, 2012. (Oct. 22, 2012)
  • LaMonica, Martin. "Hot Water Helps a Super-efficient Supercomputer Keep its Cool." MIT Technology Review. June 18, 2012. (Oct. 22, 2012)
  • Mick, Jason. "Europe's Strongest Supercomputer Gets Hot Water Cooling, Cuts Power 40 Percent." June 19, 2012. (Oct. 22, 2012)