Tunnels: cutting-edge engineering, particularly in terms of ventilation
Interview with Damien Buffet, Project Manager at Axima Tunnels, an Equans subsidiary specializing in ventilation for underground spaces.
Why is ventilation so important in a tunnel?
A ventilation system in a confined space like a tunnel is important for safety.
In fact,
- we must ensure the comfort of passengers’ ears—what is known as tympanic comfort; when a train enters a tunnel, it generates a pressure wave that can be very unpleasant for passengers. The ventilation system includes outlets to relieve this pressure so that it remains at an acceptable and comfortable level.
- We must also maintain good air quality for passengers. To this end, we monitor a number of pollutants and can remove them using the ventilation system.
- Finally, safety must be ensured in the event of a fire. The ventilation system plays a major role in the event of a fire. It is essential for maintaining safe, smoke-free evacuation routes so that passengers and train crew can be evacuated safely.
In a tunnel, the air is constantly monitored, directed, and regulated. In the event of a fire, ventilation systems help contain hazardous smoke within a section of the tunnel to ensure the safe evacuation of passengers and allow firefighters to respond effectively.
How do these large ventilation systems work?
A ventilation system in a tunnel necessarily requires high-powered fans of 350 kW, whereas a residential system is around 9 or 10 kW.
A fan is generally installed approximately every 800 m in a tunnel to manage smoke and provide ventilation on a section-by-section basis.
We sometimes supplement them with boosters, which are large fans; they force air through the tunnel and move it as needed.
What major projects are you working on?
Among the major projects in Europe is the Grand Paris Express, which involves the construction of four new metro lines to expand the transportation network in the Paris region; 90% of these lines will run through tunnels.
This represents 200 km of tunnels to be equipped with ventilation systems. For Equans, this involves deploying more than 200 fans with a power rating of 350 kW.
How does Equans reduce the energy footprint of facilities of this scale?
Our customers have high expectations regarding the carbon footprint of our installations and their electricity consumption.
If we were to install our systems throughout the Greater Paris area, we’d be looking at 60 megawatts of ventilation power in the tunnels.
To give you an idea, let’s take the example of the Fécamp wind farm, which was recently installed offshore and brought online. It has a capacity of 500 MW. A little over 10% of that wind farm’s capacity is the power we’re installing for ventilation. As you can see, ventilation has a very significant impact on the project’s energy balance. Our role is to optimize energy consumption and system operation by defining the appropriate operational level. We won’t run the fans if there’s no need to.
We take a reasoned approach and optimize the facility’s energy balance as much as possible, given that ventilation has a relatively significant impact on the overall balance.
One of our areas of expertise is also conducting an assessment of an existing system, even if we did not perform the original installation. We are able to conduct an assessment and recommend renovation to the client rather than a complete replacement. In this way, we improve the carbon footprint by avoiding the need to source new equipment elsewhere.
What about the carbon footprint of the equipment purchased for our facilities?
Let’s return to the example of the Grand Paris project. For this project, we primarily purchased European fans, which emit fewer emissions than models from Southeast Asia. This technical and fundamental expertise has been part of my daily work for about fifteen years.
I previously worked at Bouygues Travaux Publics, which was responsible for constructing tunnels and drilling through them. Sometimes we had to deliver a turnkey tunnel, complete with systems such as ventilation. In fact, I occasionally collaborated with Equans on the ventilation aspect. The Group’s mobility policy allowed me to join Equans.
In conclusion, I would say that what makes me proud in this profession is seeing how users embrace a tunnel and use it on a daily basis once the project is delivered. I feel the same way when I revisit a project completed 10 or 15 years ago that I helped build. A project like a tunnel is a true human adventure.
