Sixteen, 55 kW ABB standard drives for HVAC control 32 impulse fans, two per drive, which add momentum to the tunnel air and thrust it towards the exit points. Impulse ventilation differs from conventional ventilation in that ducting is not used. Instead, the tunnel itself acts as a duct. The drives adjust the speed and the direction of the fans air flow depending on the conditions, traffic intensity and prevailing wind. The sensors inside the tunnels measure CO, CO2 and temperature. Additionally, visibility sensors measure the amount of particles and moisture in the air. The drives help ensure safe driving conditions in the tunnel by running the fans to demand, using information from sensors connected to an automation management system.
When data from the sensors indicates that ventilation is needed, the fans at the tunnel openings start and increase speed gradually. If more ventilation is needed, the fans inside the tunnel also start, increasing the air movement through the tunnel. The fans at the tunnel openings have variable speed, while the fans inside the tunnel use traditional on/off control. This enables the fans at the tunnel openings to run at reduced speed if only a small amount of air movement is needed, providing accurate control and helping to save energy on these fans, which have the longest running hours.
In the event of fire, the system is programmed to run all fans at full speed to evacuate the smoke from the tunnel by the shortest possible route. If the impellers are already rotating on start-up, due to the natural draught in the tunnel, they are caught ‘on-the-fly’ by the drive and brought up to the required speed. This routine is known as flying-start but is not normally used in installations with more than one fan per drive. However, in this particular installation, due to the position of the fans and the way the air moves in the tunnel, flying-start can be used.
As the tunnels are fitted with sensitive measuring equipment, it is important that the drives cause as little disturbance as possible to the mains supply, to avoid interfering with the instrumentation. The ABB standard drives for HVAC feature a patented swinging choke that reduces the harmonic signature at low motor speed, fulfilling the international standard IEC/EN 61000-3-12. The swinging choke adjusts itself according to the load circumstances and cuts harmonics, especially at partial load, for a total reduction of up to 25 percent, compared to traditional choke designs.
Separate output chokes limit the electromagnetic interference from the exceptionally long motor cables in this installation. The drives are installed in the electrical equipment room, away from the tunnel itself, with the longest motor cable running over a distance of more than 300 meters.