Volume 8: Advances in Energy Innovation and Development

Structure and Control Co-Optimization for a CO2 Heat Pump with Thermal Storages Fang Liu*, Jiaxin Deng, Qiu Mo, Qunzhi Zhu

Abstract

Optimal design and control are coupled tasks for enhancement of energy system performances. Model based dynamic optimization can enhance system performances significantly. However, it is difficult to obtain the optimal structure and control solution for a complicated nonlinear physical system model simultaneously, thus we proposed a coupled dynamic optimization method for structure and control co-optimization and implement it successfully for a transcritical CO2 ejector expansion heat
pump coupled with hot and cold thermal energy storages during energy charging process. A complicated nonlinear dynamic system model with genetic algorithm were used to obtain the structure and control co-optimization solution of the coupled system during energy charging. The structures of gas cooler, evaporator, hot and cold thermal storage tanks were optimized, and dynamic optimal control strategy was obtained for energy charging process. Compared to the constant control parameter strategy, the overall coefficient of performance can be increased by 21.1%. The performances can be enhanced more significantly if the water temperature at the hot tank outlet remains at a low level, i.e. the charging time reduced. This study would be helpful for a structure and control co-optimization of other dynamic energy systems.

Keywords structure and control co-optimization, nonlinear dynamic system model, ejector expansion heat pump, thermal energy storages