in Altstetten
Another milestone is the connection of Altstetten West and East with district heating and cooling. To this end, the future energy centres in Herrlig and Rautistrasse will be connected via underground anergy pipes installed by way of a microtunnel. In addition to the anergy pipelines, the tunnel will also be used to strengthen the city of Zurich’s electrical supply.
1. What does anergy mean?
Anergy refers to the part of the thermal energy that cannot perform any work in a process. It can be explained a little more simply for use in our heating systems: heat whose temperature is too low for direct use. However, it is very valuable when the heat is raised to a higher temperature level with the help of heat pumps. Heat pumps require electrical energy for this purpose; depending on the temperature of the anergy, the input of one kilowatt-hour (kWh) of electricity leads to a usable heat of three to five kWh. The remaining two to four kWh are anergy that can be used. In the simplest case, anergy is extracted from the environment: this may be in the form of air, soil or groundwater or, as in the case of Altstetten, from the Werdhölzli wastewater treatment plant.
2. How does microtunneling work and which energy source is used for it?
This network component uses waste heat from the Werdhölzli wastewater treatment plant as its energy source. Anergy development is a key project in the new network. For the construction of the anergy pipeline that connects the energy source in the Werdhölzli wastewater treatment plant with the supply area in Altstetten south of the SBB tracks, conventional trench construction on public property is not possible due to time and space constraints. For this reason, construction of the microtunnel, which will run at a depth of 8 to a maximum of 20 metres, will begin in winter 2025. The tunnel has an outer diameter of 3 metres and an inner diameter of 2.6 metres and is walkable.
3. What are the advantages of microtunneling?
Although microtunneling is associated with higher costs, it offers many advantages. Important arguments include the space required, the time benefits and, in the case of walkable tunnels, accessibility to the infrastructure. The city is growing and the street spaces are already heavily occupied. It’s not easy to build the infrastructure for a thermal grid. In addition, obstruction of traffic flows due to working on the surface should be avoided to the extent possible. Where roads still have to be torn up, there needs to be good coordination between the parties involved. Coordinated planning and construction is required in order to reconcile the needs of the various stakeholder groups and minimise the impact on residents from construction sites. Due to frequent objections, the timing of surface changes is out of our control.
4. When will residents be able to draw heating and cooling from this network?
Work on the anergy connection to the new energy centre on Rautistrasse in Altstetten East is expected to be completed by the end of the first quarter of 2026. From mid-2026, the first users there will be able to benefit from climate-friendly heating and cooling while also helping to reach the city of Zurich’s ambitious net-zero target by 2040. Connection to a thermal grid is convenient for property owners. All that is needed in the basement is space for a heat exchanger, which transfers the heat from the transmission line of the thermal grid to the heating distribution system. In addition, maintenance costs are low and the subscribed capacity can be reduced again at a later date in future building renovations.
