Optimal phase change temperature for energy storage based on fluctuating loads in building cooling heating and power system

Natural gas driven Building Cooling Heating and Power (BCHP) system is encouraged to develop as small-scale energy supply system in recent year. Integrating Energy Storage System (TES) with trigeneration system can improve the energy efficiency and reduce the installed capacity for energy supply equipment. However, it has never been an easy task to reasonably design the TES-BCHP system, in terms of that it is hard to determine the suitable installed capacity of energy supply devices considering the fluctuating loads and the influence of TES. In this paper, a thermodynamic model of BCHP system with phase change material (PCM) energy storage is established. According to practical user loads and considering the correspondingly hourly changing flow rate in charge and discharge processes, a simplified method is proposed to determine the optimal phase change temperature for BCHP-TES, aiming to minimize the primary energy consumption of BCHP-TES system. An illustrative example shows that the optimal phase change temperature can be obtained for given loads. It also indicates that compared to infinite NTU for PCM-TES, the optimal phase change temperature will increase as well as the corresponding minimal primary energy consumption for finite NTU. This work is of great importance for PCM optimization of BCHP-TES system design.