Combined ventilation mode in extra-long road tunnels: Energy efficient channel utilization with the inclined shafts

Abstract

The ventilation mode plays a dominate role in addressing the feasibility of an extra-long tunnel. In this paper, a combined ventilation mode, i.e. energy efficient channel utilization with the inclined shafts, is proposed to ensure the air quality and fire safety in the extra-long road tunnel. Combined with the equations of ideal air, mass and energy conservation, and boundary conditions, the velocity of internal airflow and the energy consumption of tunnel can be analytically solved. As regards the case study in the Tongzi Tunnel in China, the scheme of combined ventilation mode of single channel and inclined shafts was proposed. The effects of natural wind pressure, traffic wind pressure and mechanical ventilation pressure on tunnel ventilation energy consumption were considered. In addition, the energy efficient channel is a strong substitution for shafts to enhance the efficiency of the ventilation. Based on the results, the position of the vertical shaft and single channel in combined ventilation was optimized. Compared with original ventilation scheme, the new method can save up to 40% ventilation energy consumption in daily operation, and saving 1.02 million CNY in electricity costs per year and improving long-term economic efficiency. In the fire emergency, the combined ventilation mode can more effectively control smoke for larger scale tunnel fires. In particular, when the power of the fire source exceeds 30 MW, the required critical wind speed increase rate is reduced to 0.01 m/s per MW. The analysis of ventilation mode undertaken here, has extended our knowledge of reducing energy consumption and maintenance costs in the extra-long tunnel operation.