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].