Thermodynamic performance of organic rankine cycle based pumped thermal energy storage system with different working fluids

In the context of global efforts toward energy transition and carbon neutrality, thermal integrated pumped thermal energy storage (TIPTES) systems, especially those utilizing low-grade heat sources, have garnered significant attention due to their large capacity, flexibility, and environmental advantages. This paper explores a TIPTES system that harnesses industrial waste heat as a heat source. The system's heat pump (HP) subcycle and Organic Rankine Cycle (ORC) subcycle are equipped with regenerators to optimize system configuration and enhance efficiency. Five working fluids-R245fa, isobutane, isopentane, MM, and R1336mzz(Z)-are selected for analysis based on parametric evaporation temperature (<i>T</i> ₁) and thermal storage temperature (<i>T</i> ₈).Parameter analysis results reveal that both round-trip efficiency (<i>η</i> _ptp) and exergy efficiency (<i>η</i> _ex) increase with rising <i>T</i> ₁, with the system using MM demonstrating optimal performance: at T1 of 70 °C, <i>η</i> _ptp reaches 71.34 %, and <i>η</i> _ex is 37.42 %. The <i>η</i> _ptp for each system decreases as T8 increases, with the isobutane-based system showing the slowest decline; <i>η</i> _ptp remains relatively unaffected by <i>T</i> ₈, while <i>η</i> _ex for the isobutane- and R245fa-based systems initially decreases and then increases with rising <i>T</i> ₈.Key system parameters-<i>T</i> ₁, <i>T</i> ₈, and cold thermal storage temperature (<i>T</i> ₇)-are further analyzed in a single-objective optimization focused on round-trip efficiency. Results indicate that the isopentane-based system performs optimally at <i>T</i> ₈ of 388.65 K, <i>T</i> ₇ of 359.15 K, and <i>T</i> ₁ of 338.15 K, achieving a maximum round-trip efficiency of 71.60 %. This study offers theoretical insights to support the future development and application of TIPTES systems.