Dynamic characteristics and performance improvement of a high-efficiency double-effect thermal battery for cooling and heating

Recently increasing interests have been attached to the thermal batteries based on absorption thermal energy storage for renewable and waste energy utilization to address the mismatch between the energy supply and demand. The existing studies mainly focused on the improvement of energy storage density, while there are rare researches on lifting energy storage efficiency which is also a challenge. The motivation of this paper is to improve energy storage efficiency to promote practical applications of the thermal batteries. A novel double-effect absorption thermal energy storage system is proposed. With the assumption of well-conditioned external fluids, a mathematical model is established and verified by experimental data. The dynamic characteristics are presented and the results show that the charging time of the double-effect system is significantly shortened from 1.91 h to 0.68 h in the high-temperature (160 °C–200 °C) range, being shorter than that of the single-effect system when the charging temperature is 200 °C. Besides, the energy storage efficiency varies from 1.27 to 1.17 and from 1.44 to 1.33 for cooling and heating, respectively, being enhanced significantly compared to the single-effect systems, by 57.1%–61.6% for cooling and 58.2%–61.8% for heating. The slight reductions in energy storage density are 3.2%–6.9% and 2.7%–6.0% for cooling and heating, respectively. The solution mass distribution of the double-effect system has also been explored, indicating that the equal-distribution is comprehensively the best scheme. This study can provide theoretical references and suggestions for the applications of absorption thermal energy storage with high-temperature heat sources.