Performance analysis and optimal charging time investigation of solar air heater with packed bed sensible heat storage device

The amount of stored thermal energy and the stratification in the packed bed thermal energy storage systems decrease in the afternoon because of the reduction in the solar power and solar-air heater panel's collector outlet temperature, so the charging process must be ceased at a particular instant. The optimal charging period is determined by considering the degree of stratification, energy/exergy stored, and the energy discharged during the 6 h of space heating. The proposed packed bed is divided into three sections lengthwise. Different bed materials have been placed separately in these regions regarding their volumetric heat capacity to promote stratification and sensible heat storage during charging. The bed's stratification level is determined via an exergy analysis to evaluate the discharge efficiency of the bed. The particle diameter and discharge air velocity on the system's thermal and hydrodynamic performance are inspected. The fan energy consumption during the discharge process is evaluated in the analyses. Distinctively, the air velocity is varied to obtain a minimum heat load of 18 kW for 6 h discharge process. A transient, one-dimensional finite-difference model is developed and validated with an experimental study conducted in the literature. Thermal energy storage and the stratification level are improved thanks to segmented bed by 85% and 135%, respectively.