Appropriate Thermodynamic Performance Measures for Closed Systems for Thermal Energy Storage

[+] Author and Article Information
M. A. Rosen

Department of Mechanical Engineering, Ryerson Polytechnical Institute, Toronto, Ontario M5B 2K3, Canada

J. Sol. Energy Eng 114(2), 100-105 (May 01, 1992) (6 pages) doi:10.1115/1.2929986 History: Received August 16, 1990; Revised January 02, 1991; Online June 06, 2008


Several definitions of energy and exergy efficiency for closed systems for thermal energy storage (TES) are developed and discussed. A simple model is utilized in which heat quantities are transferred at specified temperatures to and from a TES. Efficiency definitions are considered for the overall storage process and for the three component periods which comprise a complete storage process (charging, storing, and discharging). It is found that (1) appropriate forms for both energy and exergy efficiency definitions depend on which quantities are considered to be products and inputs; (2) different efficiency definitions are appropriate in different applications; (3) comparisons of different TES systems can only yield logical results it they are based on a common definition, regardless of whether energy or exergy quantities are considered; and (4) exergy efficiencies are generally more meaningful and illuminating than energy efficiencies for evaluating and comparing TES systems. A realistic, but simplified, illustrative example is presented. The efficiency definitions should prove useful in the development of valid and generally accepted standards for the evaluation and comparison of different TES systems.

Copyright © 1992 by The American Society of Mechanical Engineers
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