Multi-objective optimization of a concrete thermal energy storage system based on response surface methodology

This paper focusses on the numerical investigation of a concrete thermal energy storage (CTES) system using air as heat transfer fluid (HTF). To reduce the number of simulations and treat complex interactions between parameters, the response surface models for multiple responses are established based on 27 specific design points which are determined by central composite rotation design (CCRD). With the response surface models, the effects of the CTES system's design parameters on its performance are analyzed. The results indicate that the HTF velocity is the most important factor affecting the charging time and charging energy efficiency. The HTF inlet temperature substantially influences the energy storage. The interactions also have a crucial influence on the performance indices. The optimization is carried out to minimize the charging time, and maximize the energy storage and the charging energy efficiency simultaneously. The optimal parameter combination is optimized by the desirability function. The discharging process is further considered, so that the overall performance of the cycle process is optimal. The geometrical parameter of 22 tubes and 4 fins is considered appropriate under the selected operating conditions. The proposed method provides an efficient means to efficient design of CTES unit.