A high-performance computing centre like CSCS uses as much electricity every day as a small town. About a third of this electricity is used for cooling. If supercomputers are not constantly cooled, they overheat and, in the worst case scenario, may be damaged.
In conventional computing centres, compressors generate cold water to cool the computers. To save energy, CSCS make use of a natural cooling source: water extracted from Lake Lugano at 45 meters depth at a temperature of 6 degrees Celsius. This will greatly reduce the amount of electricity used by CSCS for cooling.
To operate the cooling system, a pumping station has been built on the lake shore in Parco Ciani, in the centre of Lugano. Through a pipe, three pumps in the pumping station will pump up to 760 litres of water per second. 460 litres will go to CSCS for cooling purposes, while up to 300 litres will be available to AIL (Aziende Industriali Lugano) for its water reservoir. On its way to CSCS, the water will climb 30 metres and cover a distance of 2.8 kilometres.
The pipeline connecting CSCS to the pumping station is 80 centimetres in diameter. At the arrival point at CSCS, the lake water circuit and the internal cooling water circuit meet in heat exchangers. The internal water cooling circuit delivers the water, which has now reached 8-9 degrees Celsius, to the supercomputers for cooling.
Once the water has passed through this first cooling circuit, it has been heated up by eight degrees. The now 16 to 17 ℃ water is sent through a further heat exchanger, connected to a second cooling circuit. This mid-temperature circuit cools the air in the housing for the computers and hard drives of lesser energy density, which can therefore be cooled with water that is less cold. This means that with one pumping operation, cold water is supplied to two circuits to cool two types of systems.
Before the lake water returns to the lake, it passes through a stilling basin which can hold 120 cubic metres. The basin collects the water and makes sure that it flows freely down the return pipe back to the lake at a constant pressure and with no need for further power to be used.
So as not to affect the ecological balance of the lake, the water going back into the lake must never exceed 25 degrees Celsius. To ensure that this is always the case, a back-mixing funnel has been fitted, which will add cold water if necessary.