Low-temperature compression-assisted absorption thermal energy storage using ionic liquids

Abstract

Abstract Thermal energy storage technologies play a significant role in building energy efficiency by balancing the mismatch between renewable energy supply and building energy demand. The absorption thermal energy storage (ATES) stands out due to its high energy storage density (ESD), high coefficient of performance (COP), low charging temperature and wider application flexibility. A hybrid compression-assisted ATES (CATES) using ionic liquid (IL)-based working fluids is investigated to address the problems of the existing ATES cycle. Models for mixture property and cycle performance are established with verified accuracies. Four ILs ([DMIM][DMP], [EMIM][Ac], [EMIM][DEP], and [EMIM][EtSO4]) are compared with H2O/LiBr. Results show that the CATES effectively avoid the crystallization, decreases the circulation ratio, lowers the charging temperature, and improves the COP/ESD. H2O/[DMIM][DMP] has the highest COP and performs better than H2O/LiBr with generation temperatures above 86 °C, while H2O/[EMIM][EtSO4] shows the highest COP with generation temperatures below 75 °C. Among the H2O/IL mixtures, H2O/[EMIM][Ac] shows the highest ESD with generation temperatures above 86 °C, otherwise H2O/[EMIM][EtSO4] shows the highest. The optimal compression ratio is 1.6–2.8 for H2O/[DMIM][DMP] under the generation temperatures of 90–70 °C with the maximum COP of 0.758–0.727. The ESD increases significantly with the compression ratio.