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Fläkt Woods fans with a Saccardo jetting concept are being used in the United Kingdom on an M25 road tunnel contract it has won from Costain Limited. The M25 is an orbital motorway that almost completely encircles London. With a circumference of 188 km it is the second-longest ringroad in Europe.
The project is to supply replacement ventilation fans for the on-going refurbishment of the Holmesdale Tunnel on the M25 and fitted with special nozzles to accelerate the air through slots in the tunnel roof.
The work carried out by Costain Limited on behalf of the Highways Agency, will last for approximately 18 months and is necessary because the mechanical and electrical equipment installed at the time of construction are in need of replacement.
This is the first time Saccardo jets have been used on a UK road system, and their use was necessary because the existing system/its upgrade would not fit in the tunnel with the extra lane that is under construction.
The Saccardo nozzle 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, 5 in parallel for each tunnel, and fitted with special nozzles to accelerate the air.
The fans will be sited above ground, in a specially constructed plant room, located on top of the existing tunnel. The scope of the overall contract includes widening the eastbound carriageway by one lane through the junction. The eastbound carriageway will be widened on the east side of the junction and through the tunnel.
Costain’s contract will include the replacement of lighting, ventilation equipment, internal cladding and tunnel control systems.
Fläkt Woods was asked to carry out preliminary design due to their extensive tunnel ventilation experience, these designs were later revised and improved by others who modelled the system using Computational Fluid Dynamics.
The use of Saccardo nozzle enables clients to customise the longitudinal ventilation 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 significant cost savings in terms of fan horsepower requirements and ventilation space. The fans for the Saccardo system 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.
Alan Butcher, Fläkt Woods Group Sales Director responsible for all tunnel and metro projects world-wide comments, "There are generally only a few tunnel projects available to bid for in the UK, but Fläkt Woods reputation in this specialist field makes us the natural and preferred choice in most instances. Many customers value our expertise, as we fully understand how the ventilation system works, and can reference projects worldwide where similar design approaches are taken".
"Coupled with our in-house capability to use state of the art tools such as the CFD we can assist customers to visualise the solution, increasing their confidence in our proposal."
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