Water-cooled mainframe computers are a technology widely associated with a dinosaur-like approach to computing. In the eighties and nineties of the past century, such data centers dominated corporate IT, and neither their vendors nor their operators cared much about ecological aspects; all they were considering was how to get the heat off their computers. When in the mid-nineties IBM as one of the last manufacturers switched from ECL to CMOS technology, the worst heat generators in the mainframe computers already was eliminated. The triumph of the client/server approach and blade servers using air-cooled standard high-volume CPUs finally sounded the death knell for water as a coolant for server farms, despite the fact that water offers much better cooling properties in terms of thermal conductivity and volumetric heat capacity than air.

If IBM researchers are on the right track, the water-cooled computer could be back soon. The company has developed a water-based cooling technology that enables operators to reuse or even resell the heat generated by the CPU chips.

The trick sounds extremely simple: While in earlier approaches the water used to cool down the sensitive electronic parts had a rather low temperature and the design target was to keep that temperature as low as possible, the IBM researchers work with water at a temperature in the range of 60 to 70 degrees Celsius. This is enough to use it for heating purposes and other energy-reuse concepts. "With the water temperature as low as about 25 to 35 degrees Celsius when it left the computer in earlier times, the only thing you could do is to pump it through a chiller and waste it," a researcher explained.

No chiller is necessary anymore in IBM's concept. Water-cooled data centers using this "high-grade heat" can achieve an even better power efficiency than conventional data centers with "medium grade" heat reuse, claims Bruno Michel, Manager Advanced Thermal Packaging at the IBM Zurich research center. The heat reuse helps to reduce or avoid CO2 generation associated with applications such as room heating, which leads to a drastically reduced overall carbon footprint. The company even talks about zero emission data centers.

At a press meeting in the Zurich research center, the company demonstrated the prototype of a water-cooled server blade equipped with two Intel processors. The standard heat sinks and blowers were replaced by a copper heat collector with water conducts in it. The water then was pumped through a system with a cooler which in normal operation would be replaced by a kind of heat reusing system. "Sell or reuse the heat, eliminate the CO2 footprint of data centers," Michel said.

The company said commercial availability of the technology is "very near". In a first step, standard server blades with readily available third-party CPU chips will be subject to the liquid cooling approach. However, IBM researchers are already working on 3D chip technologies where micro cooling conducts, much like vascular systems, are used to pump the water through the chips instead through a copper heat sink. This will further reduce the heat resistance between chip and cooling system and thus increase the effectiveness; IBM claims a cooling effect of up to 350 W/cm². The company however did not specify when this chip-scale liquid cooling will be commercially available.