In rail and metro projects, the ventilation system forms a major component of the infrastructure and can guide the overall arrangement of stations. Elements can include a trackway exhaust system (TES) to remove heat during normal operations and smoke during emergencies from the station trackway areas. A tunnel ventilation system (TVS) to provide ventilation to the running tunnels adjacent to stations is also typically provided.rnGiven the different fan duties that are likely between the TES and TVS, where these systems are both installed they are usually independent of each other (i.e. different fans). Careful fan selection, duct design and fan control with variable speed drives provides the possibility to combine these fan systems. If the systems are combined there is scope to reduce capital costs.rnWhen a new project is in the planning stages, various cost saving options will be considered. This could include whether or not fan systems are to be combined. This paper will outline various aspects of this design decision showing what the main considerations that will need to be made are, and whether the specific characteristics of a project lend themselves to a combined fan arrangement.rnThis paper uses a generic station arrangement and some limiting assumptions to make comparisons of a series of design outcomes between separate fan systems and combined fan systems. It highlights how the various operating modes required for a metro system can be achieved. The potential limitations of a combined system, such as dealing with multiple train congestion and the complex duct and damper arrangements that may be required, are also discussed. Differences in spatial arrangement and provisions that are required for fan rooms and ventilation paths are made. Indicative savings that can be achieved with a combined system in terms of plant costs and excavation volume are estimated. Complexities in operating and balancing multiple duty points necessary with a combined system is also considered along with various service building arrangements.
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