With rank 51 in the Green500 list (as of 06/2019), CLAIX-2018 of RWTH Aachen University is already well positioned. In addition, the stability of the upstream electrical supply network (less than one failure event per year) allows to do without a cost- and energy-intensive uninterruptible power supply for the HPC computers. Storage, access systems and network technology, on the other hand, are designed to be highly available in order to exclude data loss or prevent long recovery times. The availability can be rated according to DIN/EN 50600 with availability class 3, i.e. "high".
But mainframe computers in particular have a high energy consumption, which is almost completely converted into heat and has to be dissipated. This is because the processors work around the clock, get very hot and, together with other components, fans and power supplies, convert all the electrical energy absorbed into heat. Without sufficient cooling, the processors would burn out in a very short time or switch themselves off beforehand for self-protection. In order to dissipate this heat via conventional room air cooling, even efficient systems require an additional energy input of up to 50 % of the energy consumption of the computer. At the current power consumption of about 700 kW, this would mean up to about 3 gigawatt hours of electrical energy or up to 1,300t CO2 per year - a huge cost and environmental factor.
For this reason (within the framework of Green IT), a lower effort for cooling is aimed for in relation to the power consumption of the computers. For this reason, the IT Center relies on a combination of hot water cooling and free recooling. This reduces the described energy consumption for cooling to less than 10 percent of the systems' energy consumption.