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.