The impact of thermal insulation on cooling energy consumption and optimal insulation thickness for underground tunnel

The provision of mechanical cooling in deep mines comes with a significant energy cost as a significant amount of heat transfers from surrounding rock to the airflow. Thermal insulation can be applied to reduce such heat transfer, thereby cutting down the cooling load. In this study, the impact of thermal insulation on reducing the heat flux through the rock was analytically investigated. The optimal insulation thickness, life cycle saving and the payback period were also evaluated by using the life cycle cost method as the economic benefit is heavily dependent on the insulation thickness. Results show that heat flux between tunnel and airflow can be significantly reduced by the use of thermal insulation, but the reduction varies with the tunnel and insulation conditions. The total cost associated with using the thermal insulation firstly decreases and then increases when the insulation thickness increases, implying an optimal insulation thickness. Nonetheless, both the optimal insulation thickness and maximum life cycle saving can be increased by a rising rock temperature, eventually leading to a reduced payback period.