Peter Tobler: From 1942, ETH had a large heat pump at the Walheplatz in Zurich, which took heat from the Limmat for ETH. Then it was a pioneering achievement! How has this been further developed and what contribution does the system make today?
Joel Mesot: This is a question about a fascinating part of the history of ETH and technology – with an actual connection. The crises show how dependent Switzerland is on fuel imports. This is the case today, and this was the case before and during World War II, when fossil fuels became scarce. At the same time, Swiss companies such as Brown Boveri, Sulzer and Escher Wyss made huge strides in the development of heat engines during the interwar period. This is how Switzerland became a pioneer in the field of heat pumps.
As early as 1938, a 100 kW heat pump was installed in the Zurich City Hall to use the Limmat flowing under the house as a source of heat and cooling. The use of a heat pump to heat the city’s newly built indoor swimming pool in Zurich in 1941 was revolutionary. The positive experience and the ongoing uncertain situation with fuel supplies prompted then to build a third heat pump system in Zurich: the system you mentioned on the Walch, opposite the main railway station.
The cavern, created in 1942, originally contained three heat pumps with a total capacity of almost 6 MW. The university district was supplied with water at a temperature of about 70°C through a district heating network. The plant was shut down in 1972 as maintenance became unprofitable. However, in 1988, work resumed with two brand new heat pumps to supply the ETH building in the center, the cantonal administration in the Walch area and private customers in an environmentally friendly way. This plant worked until 2017.
The end came for various reasons. The immediate trigger was that for better protection against water, the coolant circuit had to be isolated from the Limmat by an intermediate circuit, which would have cost a lot of money. Times have also changed. The demand for heating ETH buildings is declining over time, and space cooling is becoming more and more important. Think of an IT infrastructure that needs constant cooling. And if you can temporarily lower the temperature in the room by a few degrees, then the failure of the cooling system in the server rooms is fraught with serious consequences.
ETH has implemented an innovative heating and cooling solution for its buildings on the Hönggerberg campus. Since 2013, we have been operating a dynamic underground storage facility that saves about 5,000 tons of CO annually.2 save on. In order to be able to respond to hotter summers, we have also started building a highly efficient cooling network. Here we also use our own campus as a kind of real laboratory for new technical solutions. Among other things, we aim for renewable water cooling from the depths of Lake Zurich. To this end, a water pipeline from the lake should be laid to the university territory, and then the water from the lake will return through the Walhe cave, which means that this infrastructure will remain important in the future.
Many thanks to Wolfgang Seifert, Director of Energy at ETH Zurich, for his valuable input.