TempTrim: A tool to increase our understanding of potential energy savings in public transport heating

Switzerland’s domestic energy supply has consistently failed to keep up with winter demand. From 2003-2019, the average winter energy deficit was 4.4 TWh (around 12.6%), but this number has surged in recent years due to the decommissioning of nuclear power plants and an overall rise in electricity demand. In the winter of 2022, people were increasingly worried about a looming energy crisis associated with disrupted supply after Russia’s invasion of Ukraine and the resulting EU sanctions. Although a major energy shortage was successfully avoided, the Swiss government still urged the population to limit their winter energy consumption through various energy saving measures amidst rising prices, reduced capacities, and growing concern over climate change.

The Zurich public transport service, Verkehrsbetriebe Zürich (VBZ), has acknowledged that during wintertime, a considerable amount of energy is used by their trams and buses to ensure the thermal comfort of their passengers. They estimate that on the coldest days, the energy demand for heating the trams is even comparable to the energy demand for driving them. However, when deciding on the temperature set-point to fix on all their trams, public transport operators like VBZ are generally unaware of the savings that could be achieved simply by lowering vehicle temperatures.

TempTrim as a solution

As one of the industry partners of the Energy Science Center’s EnergyNow! 2.0 Impact Accelerator Program, the VBZ proposed the development of a web-based tool that would allow public transport operators to assess and optimize energy consumption within their fleets, with a particular focus on their heating systems. Our team – consisting of ETH students Florian Schubert, Clara Tillous Oliva, Yash Dubey, Oleksandr Halipchak, and myself – responded to this call by developing the TempTrim app.

TempTrim was designed to quantify the potential energy savings that could be achieved by adjusting the heat settings in trams. This was based on a thermodynamic model that estimates the electric energy consumed by the heating system of a tram fleet. Validation was done using experimental data from the Cobra fleet, which was collected by VBZ for a preliminary analysis.

Users can input their fleet specifications, operating schedule, heating system characteristics, and cost of electricity into the TempTrim dashboard. Geographic location is also needed to determine the ambient temperature based on climate data from the EU Photovoltaic Geographical Information System. It will then calculate the amount of heat needed to achieve the desired temperature, the electricity required to generate this heat, and the associated electricity costs. Several temperature set-points can be compared to determine the difference in potential savings.