Cooling systems at the IT center

  Photo of the recoolers with optional "adiabatic" pre-cooling Copyright: © IT Center

Recooler with optional "adiabatic" pre-cooling. The visible filter mats are moistened with water if required.


The core piece is the free cooling system with three water/air heat exchangers with 800 kW each (a total of 2,400 KW) output, which can be operated all year round and requires up to 90% less energy than, for example, compression refrigeration. The hot water cooling circuit is designed to directly cool the computers with a minimum temperature of 30°C (Direct-Liquid-Cooling, DLC). These high temperatures are on the one hand the prerequisite for year-round free cooling and on the other hand provide the possibility to use the waste heat for heating purposes. Corresponding possibilities for heat extraction are also planned for the IT center and are to be used in the future.

If required, the cooling air can be pre-cooled by humidification, i.e. "adiabatic", to ensure the cooling capacity even on warm days. The system manages without circulating water, so that no chemical treatment of the water is necessary in an environmentally friendly manner.

However, it is currently not yet possible to dissipate the entire heat of the systems via the hot water cooling system. Therefore, conventional air cooling is provided for about 10% of the connected load, which is supplied by central district cooling from the university's own combined heat, power and cooling system. The district cooling also serves as a fallback option in the hot water cooling circuit and can take over up to 100 kW cooling load. This meant that the design of the heat exchangers could be dispensed with to cope with extreme outside temperatures without any operating restrictions, thus saving considerable costs. In addition, this coupling in the opposite direction ensures that the combined heat, power and cooling (CHCP) of the cogeneration unit always has sufficient cooling demand for safe and energy-efficient operation.

  Diagram of the cooling circuits  

Diagram of the cooling circuits for the server rooms Seffenter Weg and Kopernikusstraße.

Cooling means "heat transport". This takes place with the medium water, i.e. by orders of magnitude more efficient and energy-saving than with air.

Nevertheless, in parallel to pure water cooling in server rooms, classical air cooling is also provided for a small part of the power. For example, for devices that cannot yet be economically equipped with direct water cooling (e.g. hard disk storage systems). The air cooling is still operated with the central district cooling from the CHP power plant.

At the same time, however, there is a requirement on the current HPC computer system that at least 90% of the waste heat must be discharged directly into the hot water cooling circuit.