Image: Empa

Buried heat storage tank

The new research campus “co-operate” in Dübendorf is itself an object of research. This is because an experimental seasonal energy storage facility is being built under the site, which will supply energy not only to the new buildings but also to the entire Empa site. In summer, for example, the waste heat from ventilation and laboratory equipment is stored – so that it can then be used in winter for heating or for the production of domestic hot water. The aim is to use around 90% of the waste heat generated either directly or to store it temporarily in the ground storage facility. In this way, Empa aims to reduce the CO2 emissions of its buildings to a minimum and thus lay an important milestone for a sustainable energy future.

Maximum temperatures up to 50 degrees
Empa will be able to use the heat storage facility primarily for research purposes for a period of ten years. The heat reservoir – a field of geothermal probes with a temperature gradient – comprises 144 geothermal probes extending up to 100 metres deep into the ground. At this depth, the storage tank works particularly effectively and loses only a small proportion of the stored heat to the environment. In the centre of the borehole heat exchanger field the maximum temperatures can be up to 50°C and at the edge the values are around 10°C. By means of a tube system it is possible to control each tube of the borehole heat exchanger individually or also defined areas and thus to achieve the optimum mix between temperature, efficiency and energy storage.

Although such an earth reservoir is very effective, it is also inert due to its large mass. The Empa researchers assume that the final operating temperature will be reached after about three to four years.