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Exergy Analysis of a Water Heat Storage Tank

F. Dammel[1], J. Winterling[1], K. J. Langeheinecke[2], P. Stephan[3]
[1]Institute of Technical Thermodynamics, Technische Universität Darmstadt, Germany
[2]IAV, Gifhorn, Germany
[3]Institute of Technical Thermodynamics/Center of Smart Interfaces, Technische Universität, Darmstadt, Germany

A combined heat and power (CHP) plant generates both electricity and useful heat. A heat storage tank enables a decoupling of electricity and heat delivery. In this study a cylindrical hot water storage tank is considered. Charging, holding time and discharging are numerically simulated applying COMSOL Multiphysics 4.2. The performance of the heat storage is evaluated by an exergy analysis. Exergy is the work potential of a given amount of energy and thus the “valuable fraction” of energy. Performing simulations with three different models, the contribution of heat conduction in the tank wall and heat losses to the environment on the overall exergy loss were determined. Both effects are almost negligible during charging, but dominate during holding time.