Ventilation System Design for a Roadway Tunnel in Acapulco, México

There are several industrial methods for tunnel ventilation system design. In particular, for tunnels where axial flow fans are applicable, there are specialized computer programs that calculate the various pressure drops that consider wall friction and local losses due to signs and appurtenances, and considering vehicle emission factors based on up-hill or down-hill conditions, determine the number of axial fans that satisfy the tunnel ventilation requirements. Based on drag coefficient factors, they can also estimate the effect of favourable or adverse traffic lane direction. Given the magnitude of the capital investment in the electromechanical installation for a new 3 km tunnel that would reduce access time to the port city of Acapulco, Mexico, from 1 h to 10 minutes, a PHOENICS simulation was performed that would optimize the number and distribution of axial flow fans. The model was set up for the prototype dimensions of the Acapulco Tunnel and simulations were performed based on maximum CO concentration criterion, considering three lane traffic with two adverse and one favourable with the axial fan flow. Based on the analysis of results, the number of fans implemented in the operating tunnel was significantly reduced from a design derived from the aforementioned computer programs.