Effect of charging operating conditions on open zeolite/water vapor sorption thermal energy storage system

Sorption thermal energy storage (STES) is one of the most promising solutions to realize inter-seasonal thermal energy storage for building heating. However, the analysis of charging operation parameters on the thermal energy storage performance of STES system is insufficient. In this paper, a STES experimental bench using zeolite 4A/water vapor as the sorption working pairs was built, and the charging/discharging experiments were conducted. The thermal energy chain during the full charging-discharging process was analyzed. The experimental results indicated that approximately 60% of the thermal energy provided by the heater was directly lost through the reactor outlet in the charging process, which seriously hindered the improvement of the thermal energy storage performance of the STES system, such as the coefficient of performance (COP). In addition, the influence of charging conditions on the thermal energy storage performance of the system was also investigated. Both the improvement of charging temperature and the reduction of charging air humidity are beneficial to enhancing the thermal energy storage performance of the STES system. When the charging temperature was 150 °C, the energy storage density of zeolite reached a maximum of 251 kWh/m3. The COP of system reduced by 28% when the relative humidity of charging air rose from 20% to 70%. The effect of the volume flow rate of charging air on the thermal energy storage performance of the system is insignificant. The COP of system maintained around 0.212 at different charging air volume flow rates.