Performance Optimization of Tunnel Surrounding Rock Heat Storage System Using Taguchi Design and Its Engineering Application

Abstract:

The large-scale storage of unstable renewable energy has great potential. Therefore， a heat storage heat pump system for tunnel surrounding rock is proposed， and a 3D heat exchanger coupled model in tunnel surrounding rock is developed. Additionally， an optimization method for heat storage performance of tunnel surrounding rock heat pump system is proposed using Taguchi design， and applied to the Stuttgart-Fasanenhof energy tunnel project. The rationality of the model is well verified by on-site thermal response test data， and the simulation results of the heat storage performance of the thermal tunnel show that， the heat storage efficiency of the tunnel surrounding rock heat storage heat exchanger system is at least comparable to that of the traditional vertical borehole heat exchanger heat storage system， Moreover this system reduces the high borehole construction costs and minimizes the required underground area. Four operating parameters for the heat storage tunnel at three levels are assumed， and L₁₀（3⁴） orthogonal array is employed. The optimal control parameter combination and the contribution rate of each parameter are obtained by conducting signal-to-noise ratio and ANOVA analysis using Minitab statistical analysis software. The maximum percentage contribution is observed in factor D （heat storage and extraction temperature difference）， followed by the operating ratio， the initial temperature of the surrounding rock and the thermal conductivity of the surrounding rock， respectively. The optimal parameter combination is obtained， i.e.， the initial temperature of the surrounding rock is 18 °C， the thermal conductivity of the surrounding rock is 1.5 W·m^－1·K^－1， the operating ratio is 1：2， and the temperature difference between heat storage and extraction is 45 °C. The research results can provide theoretical methods and technical support for the optimization of heat storage performance of tunnel surrounding rock.

Key words:tunnel surrounding rock heat storage heat pump system;Taguchi method;operation optimization;thermal storage performance