Green energy from Lake Zurich

Already in the 1980s, the Zurich Convention Center was first connected to the lake water supply, but had to be shut down again in the late 1990s. With the reopening in summer 2021, the congress center will obtain its cooling and heating requirements from the now completely renovated and far more efficient system. This will help to achieve the climate goals of the city of Zurich.

The operator of the lake water network is the ewz. Several facilities around the lake basin supply the surrounding properties with renewable energy from the lake. Others are being planned. But how can lake water heat or cool large building complexes like the Zurich Convention Center?

A heat exchanger extracts heat from the water, which can be used by a heat pump for heating as well as for hot water preparation in the connected buildings. «Even in winter, the temperature of the lake water is sufficient to supply the installed heat pump with energy», explains Rainer Schellenberg, project manager at ewz, in a simplified manner, as he inspects the system with Roger Büchel, CEO of the Zurich Convention Center. In summer, the system simply works in reverse and the lake water is used for cooling. In both cases, the lake water flows back into the lake unchanged - and the circulation starts all over again.

The lake is proving to be an attractive energy reservoir right on the doorstep. The locally generated energy is CO₂-free, requires no transport routes and enables efficient use. Therefore the congress center heats mainly emission-free, locally and sustainably. But doesn't the lake gradually cool down due to the heat exchange process? Rainer Schellenberg, project manager at ewz, explains: «The heat extraction is so small in relation to the volume of the entire lake that there is no measurable effect!»