Ventilation control of unidirectional urban tunnels with on- and off- ramps

A new control system is presented for ventilation systems in road tunnels with on-ramps and off-ramps. It is assumed that each limb of the tunnel has unidirectional traffic and that the ventilation system is longitudinal, based on point extract though a ventilation shaft and groups of jet fans in the main tunnel limbs. The overall objective is to find the fan settings that require the minimum power necessary to maintain acceptable air quality in the tunnel and to minimize the escape of pollutants through tunnel portals. Two control methods are described, both of which utilize a simulator to predict future conditions based on input information that can be readily available in tunnels. The simpler one, based on quasi-steady approximations, is already in practical use. The more powerful one extends the simpler method to include (i) a feed-back module that responds to differences between predicted and actual airflow velocities and pollution concentrations and (ii) a feed forward module based on a traffic simulator. The performance of both control methods is assessed using a virtual tunnel and the new method is shown to have worthwhile advantages over the quasi-steady method.