Analysis of the Effect of Thermal Energy Storage Temperature on the Thermodynamic Performance of Thermally Integrated Pumped Thermal Energy Storage

In order to study the relationship between thermal energy storage temperature and the thermodynamic performance of Thermally integrated pumped thermal energy storage (Ti-PTES), the thermodynamic model for Ti-PTES is established in this paper, and the effect of thermal energy storage temperature on the round-trip efficiency of Ti-PTES is discussed. The results show that with the increase of the thermal energy storage temperature by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1{ }^{\circ} \mathrm{C}$</tex>, the charging power of Ti-PTES increases by 13.17 kW, and the discharge power only increases by 4.95 kW. With the thermal energy storage temperature from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$90^{\circ} \mathrm{C}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$130{ }^{\circ} \mathrm{C}$</tex>, the round-trip efficiency of Ti-PTES decreases by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$42.58 \%$</tex>. The thermodynamic efficiency of organic Rankine cycle (ORC) increases with the increase of the thermal energy storage temperature, while the coefficient of performance (COP) of the heat pump decreases; Since the increase of thermodynamic efficiency of ORC is less than the decrease of COP, the roundtrip efficiency of Ti-PTES is decreased. Therefore, higher heat pump performance is the primary condition to ensure higher round-trip efficiency, and the thermal energy storage temperature should not be set too high.