The exergy of stratified thermal energy storages

The performance of energy and exergy analyses of TES systems incorporating thermal stratification are described, along with the resulting insights and benefits. Six temperature-distribution models for stratified TESs are considered (linear, stepped, continuous-linear, general-linear, basic three-zone and general three-zone) which facilitate the evaluation of energy and exergy contents. The selection of a particular distribution is' seen to involve a trade-off between result accuracy and calculational effort. It is shown using the temperature-distribution models how improving stratification can increase TES efficiency, and how the use of stratification can increase the exergy storage capacity of a thermal storage. Consequently, exergy analysis is shown to provide illuminating and meaningful assessments and comparisons of such TES systems that can assist in improving and optimizing designs. It is hoped that the results will facilitate the development of standardized exergy-based methodologies for the evaluation and comparison of stratified TES systems. (C) 2001 Elsevier Science Ltd. All rights reserved.