Optimising the energy consumption of a metro line's de-icing system

Less noise disturbances, fewer vibrations. Opting for a metro running on concrete tracks provides better traction, thus optimizing travel times, especially on demanding track routes. However, a slight drawback arises: during winter months, frost reduces tire grip on the outer portions of the track. Thus, there is a need to be able to heat the track at certain times while minimizing electricity consumption. This requires a deep understanding of the thermal response of the structure.

To explore these characteristics, the industrial giant Siemens sought to benefit from scientific expertise well before the start of construction. "I was approached as early as 2012, long before the formation of the joint I4S team with Inria," says Jean Dumoulin, a researcher at Gustave Eiffel University.

The collaboration with the industrial partner unfolds in several stages. The first, modeling, is essential. "It's crucial to fully understand the system's behavior in its environment. We face two distinct situations. Part of the track is at ground level, while another part crosses a viaduct. So, we must take into account a variety of phenomena."

This study phase raises many questions, especially regarding thermal dissipation, the number and placement of heating sources, and a crucial element: the heating cycle. "It's necessary to consider the material's inertia and diffusion through the mass. Simply quickly activating and deactivating heating, as practiced in other fields, has little advantage. Although it may seem interesting from an electricity consumption perspective, thermally, it has little impact on the track's surface," he adds.

In 2013, the research team made an initial presentation of their work to Siemens. "We used a simplified model that allowed us to deepen our knowledge and identify potential research problems. For the company, this presentation also represented an opportunity to build relationships, start collaborating with a scientific team, assess our skills, and our added value to their project."

At the same time, the I4S team was thriving and beginning to explore various research avenues. "In 2014, we launched the Cloud2IR project, focused on building monitoring through infrared thermography. Our goal was to advance in the design of generic surveillance systems for outdoor structures by combining environmental sensors and thermography. We felt the need to deepen our tools to obtain more precise data." The following year, Siemens decided to build a 100-meter experimental track at the Nantes campus reference track site.

In 2015, I4S also initiated a thesis on the concept of solar roads, where photovoltaic cells power pumps for heat exchange through water circulation.

In early 2019, a new step was taken: "Siemens asked us to design a research proof of concept to implement it in the Rennes metro. The goal is to develop software capable of aggregating temperature measurements taken on the track and then querying data from Météo France's Arôme model to calculate a prediction of heating needs for the ground-level and viaduct tracks over several hours."

With these results displayed on a screen in the control room, the operator can then decide the optimal time to activate the heating system. Transitioning from a laboratory prototype to a proof of concept on an operational metro line represents a significant scale change. All the development work aiming to transition from a research prototype to industrial-quality software, achieving a technological maturity level of TRL6/TRL7, was carried out thanks to the field expertise of Gustave Eiffel University, inherited from the former Central Laboratory of Bridges and Highways, as well as with the support of Inria Tech, and then the SED (Experimentation and Development Service) of Inria.