Thermal storage and exergy analysis: The impact of stratification

The importance and usefulness of second-law analysis for evaluating and com paring thermal energy storage (TES) systems in meaningful ways is discussed . Some of the main thermodynamic factors to be considered in evaluating TES performance are identified and described, including determining important analysis quantities, obtaining appropriate measures of efficiency, pinpoint ing losses, assessing the effects of stratification, and accounting for tim e duration of storage. As an illustrative example, exergy analysis, a parti cular type of second-law analysis, is applied to stratified TES systems in order to evaluate the effects and benefits of thermal stratification. It is concluded based on the results of the example that (i) the use of stratifi cation in thermal storage designs should be considered as it increases the exergy storage capacity of a thermal storage, and (ii) exergy analysis shou ld be applied in the analysis and comparison of stratified thermal storage systems.