Key characteristics of NOVENCO tunnel jet fans
- Compact and reliable design
- Uni-directional or fully reversible versions
- Tested and certified for smoke control systems up to 400 °C for at least 2 hours
- High thrust efficiency and low sound levels
- Special deflectors for high installation efficiency
- High thrust at minimum installation height
Meet the height-saver
Drawing on decades of tunnel ventilation experience, NOVENCO has developed a compact range of rectangular tunnel jet fans. These innovative jet fans reduce installation height by almost 200 mm compared with traditional round fans. Combined with aerodynamic airflow deflectors, these fans significantly increase overall system efficiency. The reduced ceiling height translates directly to substantial construction savings across the entire length of the tunnel project.
NOVENCO added value for tunnel systems
Background information on tunnel ventilation
Tunnel ventilation is essential for safe and healthy tunnel operation. It reduces pollutant levels during normal traffic and manages smoke and heat during fires or other calamities inside the tunnel.
- Maintain air quality both inside the tunnel and in the surrounding areas.
- Ensuring escape routes and providing access for fire and rescue services during a fire.
- Regulate the tunnel temperature in specific situations.
During normal operation, traffic releases exhaust gases and dust particles. These accumulate in the tunnel and can impact health, visibility and safety. Short, uni-directional tunnels may rely on natural ventilation and traffic drag. Longer tunnels typically require mechanical ventilation.
Mechanical ventilation with jet fans keeps concentrations within safe limits and considers background pollution levels.
Factors determining ventilation demand
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Tunnel altitude and length
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Cross-sectional area, driving lanes and geometry
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Gradients (uphill traffic can emit up to ten times more)
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Emission standards of the vehicle fleet
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Engine type and traffic driving speed
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Ageing factors and catalytic converter efficiency
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Traffic composition and truck weights
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CO, NOx and visibility limits
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Roadwork conditions
A tunnel fire exposes users and emergency teams to hot gases, heat radiation and most importantly toxic smoke with low to no visibility. Visibility loss is often the main cause of injury. Ventilation must support safe evacuation, allow access for emergency services and protect the structure from excessive temperatures.
Key safety priorities
- Prevent tunnel users from becoming trapped in smoke
- Keep escape routes smoke free
- Ensure safe access for emergency services
- Support rescue operations
- Control fire spread and smoke migration
Longitudinal ventilation with jet fans
In longitudinal systems, fresh air enters at the tunnel portal on one end and exits at the opposite end. Tunnel jet fans generate thrust that moves air through the tunnel. Along the tunnel length, pollution is added to the ventilation airflow. Gas detection systems and visibility sensors control the ventilation system.
Typical maximum tunnel length for longitudinal systems is up to 6 km, depending on tunnel configuration, gradients, traffic and pollution limits.
Smoke control in case of a tunnel fire
Tunnel jet fans can control smoke movement even during large fires. By controlling the smoke, the upstream section of the tunnel remains smoke free, enabling safe evacuation and access for emergency teams. Downstream sections fill with smoke, which is acceptable in uni-directional tunnels as traffic continues to exit.
Tunnel jet fans located downstream must be able to withstand high temperatures. NOVENCO jet fans are tested and certified up to 400°C for 2 hours by independent, accredited institutes. Injection jet fans (open injectors) at the tunnel entrance add further safety by drawing in cold outside air and improving installation efficiency through angled positioning.
Static and dynamic thrust factors
The static thrust is measured on a test bench. However, the dynamic thrust required in the tunnel is influenced by:
- Required air velocity for ventilation and smoke control
- Inlet and outlet tunnel losses
- Friction losses
- Traffic composition and speed
- Frontal areas of vehicles
- Tunnel altitude and air density
- Temperature and humidity
- Jet fan installation factors
- Jet fan distribution along the tunnel length
- Wind on portals
Additional factors during fire in a tunnel
- Fire power and position
- Pressure drop over the fire
- Chimney effect / tunnel gradients
- Temperature differences
- Upstream and downstream thrust differences
- Risk of fan failure at high temperatures
Jet fans installed close to walls or corners deliver less effective thrust. NOVENCO’s aerodynamic wing-shaped deflectors significantly improve installation efficiency and lower sound generation.
Calculation of longitudinal systems
NOVENCO can assist tunnel ventilation system design with deterministic and probabilistic calculation models. Performance can be validated using CFD calculations and 3D simulations. On large-scale projects our tunnel specialists also use IDA Tunnel software for detailed fire and airflow analysis.
Deterministic calculation models use fixed design conditions, while probabilistic models simulate many input combinations using probability distributions. These design conditions include fire size, fire position, wind load and traffic distribution. With probabilistic calculation models, the design of the tunnel ventilation system can be validated. Recommendations and maximum failure allowance follow the Dutch Rijkswaterstaat “Recommendations Ventilation for Road Tunnels” (Available in Dutch only).
Products for tunnel ventilation systems
Since the early 1970s, NOVENCO has supplied tunnel jet fans for road, rail and metro tunnels. Many Dutch immersed-tunnel projects with rectangular tunnel profiles use our space-saving rectangular tunnel jet fans, which cut installation height by up to 20% while maintaining thrust and efficiency. More silencing material can be applied due to the shape, further reducing sound levels.
Alongside tunnel jet fans, NOVENCO also offers exhaust and supply axial fans up to 2 m diameter and 110 m³/s airflow. Smoke exhaust versions are certified up to 400°C for 2 hours.
Since 2020, NOVENCO fans are available as certified variable speed smoke fan packages according to EN 12101-3. These operate at variable speed during fires without bypassing the frequency converter. This ensures reliability and optimised smoke control with reduced running costs for both axial smoke fans and jet fans.
A comparison at the same airflow and pressure between a standard NovAx™ ACN 1250 F300 and ZerAx® AZN 1250 axial smoke fan shows a 14% power reduction, resulting in lower operating costs and smaller power supply requirements. In most cases, ZerAx® also delivers a significantly lower sound level.
For more information about products and support for road, rail and metro tunnel projects, please contact us.
Tunnel ventilation brochure
Life safety flyer
