Water and electricity mixed to cool servers

In response to the growing demand for more powerful servers, a water-cooled server rack system has been developed that’s attracting huge interest from several major IT hardware manufacturers. Dean Palmer reports UK-based enclosure and control cabinet manufacturer Rittal has developed a unique liquid-cooled enclosure for computer servers. The firm, which has recently branched out into industrial touch-screen terminals and thermal management software, started developing the new technology back in 2001, in response to the growing demand for larger, more powerful servers that require more sophisticated cooling methods to cope with the higher heat dissipation levels. The systems are still under test and are being ‘observed’ by several large IT hardware manufacturers, including Dell, Compaq, Sun Microsystems and IBM. The new technology was first installed at the end of last year at the Max-Planck Institute (MPI) in Germany, on its 3D Kryo-electron microscope which examines the structures of biological macromolecules. The 3D structure was calculated from 10,000 to 40,000 images and in order to be able to produce even more precise results, up to 50,000 images per molecule were required, which in turn meant more computing power was needed. Dr Henry Stark, head of the working group at MPI, explained: “Adding more conventional [air cooled] systems would be very expensive and pushed us to our financial limits as well as taking up valuable space. Liquid cooling appeared to be the most suitable way out of this dilemma.” In late 2002, Rittal installed a server rack which included 34 dual Athlon mainboards and 68 Athlon MP2000+ computers, their combined computing power greatly increasing MPI’s image processing capacity. The central processing unit (CPU) dissipation level was 4488W. Rittal’s solution includes heat sinks fitted on the CPU which are responsible for the immediate heat dissipation at the precise point where it occurs. Heat is removed directly above the CPU with a small heat exchanger. Water is distributed by stainless steel manifolds in the back area of the rack. The system is controlled by temperature and a CMC magnetic valve will open and close the second side of the heat exchanger to cool down the server circuit with ‘house water’ (7 deg C cold). Incoming and outgoing pipelines have been integrated into the enclosure, and in order to ensure a specific supply of liquid, are interconnected with an external, central re-cooling unit. The Rittal CMC Module provides additional safety by monitoring the incoming and outgoing actual water temperatures as well as the flow rate. The new cooling technology has meant that MPI can now perform the same calculations in four days rather than 60 days. The system also has low noise levels, saves energy when the re-cooling unit operates in free-cooling mode. John Wilkins, marketing manager at Rittal UK, said of the new technology: “Air alone can no longer cope with the cooling requirements for the chips. The heat dissipated increases proportionately with the size and density of the chip technology. Intel and AMD chips today require 70W/cm2 cooling, so water is the better and more cost effective solution.” He added that the cost of cooling (via air conditioning) large rooms full of servers was becoming a problem for many companies and that water cooling would relieve some of this burden. “Once you get heat dissipation levels on racks of 5kW and above, you really need to start thinking of a water cooling system,” said Wilkins. The technology could also be adapted to other areas where high heat loads and subsequent cooling are critical to performance. Telecommunications is an obvious example.