Tunnel Jet Fan Selection Basics: Thrust, Reversibility and Fire Duty

Select by thrust and installed performance

Jet fans transfer momentum to the surrounding air. Required quantity and spacing depend on tunnel length, cross-section, traffic, gradient, portals, obstructions and aerodynamic installation losses.

Catalogue thrust is only one input. Mounting clearance, silencers and nearby surfaces can affect installed performance.

Define every operating mode

Normal pollution control, congestion, incident response and fire scenarios may require different fan groups and directions. Confirm whether the unit is unidirectional or fully reversible and state the required reverse-thrust ratio.

• Required thrust and air velocity
• Unidirectional or reversible operation
• Temperature-time fire rating
• Noise and silencer requirements
• Motor, cabling and control philosophy
• Mounting and maintenance access

Coordinate with system analysis

Complex tunnels and car parks may require network modelling or CFD analysis. Fan selection should follow the approved ventilation and smoke-control concept rather than replace it.