Holmesdale Tunnel, M25

Holmesdale Tunnel, M25

Client: Highways Agency, United Kingdom
Type of works: supply of Fläkt Woods JM Aerofoil Axial Fans and SaccardoJetting Concept

Fläkt Woods fans are being used with aSaccardojetting concept on an M25 road tunnel contract.

The project is to supply replacement ventilation fans for the refurbishment of the HolmesdaleTunnel on the M25 and fitted with special nozzles to accelerate the air through slots in the tunnel roof.The work carried out byCostainLimited on behalf of the Highways Agency is necessary because the mechanical and electrical equipment installed at the time of construction are in need of replace-ment. This is the first timeSaccardojets have been used on a UK road system, and their use was necessary because the existing system and its upgrade would not fit in the tunnel with the extra lane that is under construction.

The Saccardonozzle system operates on the principle that a high-velocity air jet is injected longitudinally into the tunnel to induce a high volume airflow in the tunnel. For this to be successful, the fans have to be carefully matched to optimise performance. The system uses blocks of JM Aerofoil axial fans, five in parallel for each tunnel, and fitted with special nozzles to accelerate the air.

Fläkt Woods was asked to carry outpreliminary design thanks to their extensive tunnel ventilation experience.The use ofSaccardonozzle enables clients to customise the longi-tudinalventilation system so that it can incorporate the most beneficial aspects of booster fan systems and central ventilation systems. The implementation of the customised ventilation system permits signifi-cant cost savings in terms of fan horsepower requirements and ventilation space.The fans for theSaccardosystem are not located within the tunnel but in a dedicated plant room; this means that tunnel closures are not necessary in order to carry out maintenance.

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