Ventilation is one of the most important aspects to consider in a road tunnel project. Each project requires applied engineering solutions to adequate the tunnel’s length, average weather conditions, traffic expectations and so on. In this article, we’ll talk about different types of tunnel ventilation systems and why they’re so important.
Important Tunnel Ventilation Terms and Definitions
Road tunnels are defined by a minimum length, which can vary from one place to another. Also, it needs to go underground or through a headland to be considered a tunnel. Structures built under bridges or roads aren’t considered as tunnels.
For instance, the minimum length for road tunnels in Europe ranges between 105m and 150m. However, not all tunnels require ventilation. Some of them are so short that the natural airflow from one portal to the other is enough to keep good air quality inside them.
In countries like the United States, the general rule for applying mechanical ventilation in a tunnel has to do with its length. Any tunnel longer than 1,000m should have it. In some places, the minimum requirement is 500m.
Why Is Road Tunnel Ventilation Essential?
In long tunnels, where natural ventilation and infiltration systems can’t cope with the amount of pollution, mechanical ventilation becomes mandatory. Otherwise, it’s impossible to ensure road workers' safety performance during construction.
In long tunnels, it may be impossible to breathe in some parts due to the accumulation of carbon monoxide, nitrogen dioxide, and other harmful gases. The accumulation of smoke can also create a fog inside the tunnel, impairing visibility. So, it’s important to have proper tunnel ventilation to ventilate all of these harmful gases and circulate the air.
Additionally, it helps remove smoke and vitiated air in the case of a fire or other accident involving volatile components. Carbon monoxide levels and visibility are the most important aspects managed by a tunnel ventilation system.
Although other harmful gases are involved in car emissions, they shouldn’t pose a threat if carbon monoxide levels are kept low and visibility is kept clear. Ventilation systems are also necessary for mitigating a tunnel’s environmental impact on its surroundings. Filters, dampers, and other equipment are used to mitigate the impact on the air quality outside of the tunnel.
Main Types of Road Tunnel Ventilation
A wide array of ventilation equipment is available for all kinds of road tunnel projects. Not all of them involve process automation and engineering solutions. Yet, all of them require high-quality engineering planning. Here are the main types of road tunnel ventilation:
Natural Ventilation
Natural ventilation is typically used in short tunnels. The natural airflow and the “piston effect” caused by traffic are enough to remove the vitiated air from the tunnel. This kind of ventilation works perfectly under normal weather conditions. However, foggy conditions or changes in the wind direction can impair visibility inside the tunnel. That’s why this solution is only viable for short stretches of road.
Transverse Ventilation
A transverse ventilation system uses two ducts running parallel to the tunnel. One duct is for blowing fresh air in, and the other is an exhaust to extract vitiated air. Transverse ventilation requires the use of motorised dampers controlled remotely. Commonly, these fans are installed in tunnel entrances or shafts. The number and size of the fans depend on various factors, including the tunnel’s length and expected extraction rates.
Longitudinal Ventilation
A longitudinal ventilation system uses air jet appliances, called “jet fans”, mounted on the tunnel tube. Several jet fans are positioned along the tunnel, accelerating the airflow and preventing vitiated air from building up inside the tunnel. The effectiveness of this system depends on where the jet fans are installed. They may lose efficiency if installed in a niche, near the soffit, or the tunnel walls. In such cases, additional equipment might be required.
There’s another aspect to consider before installing jet fans in a longitudinal ventilation system: noise. Many fans or poorly placed, so they increase noise levels to the point that those in the tunnel can no longer hear each other. It creates several risks for those working or driving in the tunnel.
Equipment Used for Road Tunnel Ventilation
The equipment involved in a road tunnel project should be ready to withstand the expected conditions, i.e. resistance to heat and humidity. Tubes, pipes, fans, dampers and other equipment should display information regarding their performance in both longitudinal and transverse systems. Typically, these parts also require regular industrial service and maintenance.
Here are some of the equipment you’re likely to find in the ventilation system of a road tunnel, provided by the best management services engineering industries.
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Fume extraction hoods
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Deviation dampers
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Accelerators
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Speed sensors
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Air quality sensors
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Smoke sensors
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UPS
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Batteries
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Fire doors and walls
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Silencers.
Ventilation Systems
There are three types of ventilation systems, each involving a different array of equipment. There are systems for blowing fresh air, pulling vitiated air out, and combining both features. Combined systems are mostly used in long tunnels, where simply blowing or exhausting isn’t enough. In such cases, the blowing system would create a fog inside the tunnel without the support of exhausting equipment.
Road Tunnel Ventilation From Premel
Premel is a leader among global companies providing power engineering and smart engineering solutions for a wide array of projects, including a vast number of projects for road tunnel ventilation systems. Since 1947, the company has built a solid name thanks to its best quality policy and ISO 9001 standards. Premel also offers industrial automation, program management and system maintenance solutions.
Premel isn’t only one of the leading industrial equipment suppliers for tunnel ventilation and road tunnel maintenance. Such projects involve a varied pool of professionals, from environmental engineers to general electromechanical equipment suppliers. You can find complete engineering solutions to ensure the technological successes of your project right here at Premel.
Premel also provides trained engineers and technicians to assist your team onsite, offering a world-class after-sales service. So, speak to the experts at Premel today and learn more about Tunnel Ventilations from Premel.
