The impact of the model of the environment in exergy analyses

The values of absolute exergy and energetic efficiency depend on the assume d values of the "reference states," which are essentially a model of the en vironment of the processes and components considered The environmental mode l plays an important role in any optimization process that uses any form of exergy-based analysis. This paper examines the influence of eleven previou sly proposed models for the environment on the absolute values of the energ y and on the energetic efficiencies, associated with the operation of three different powerplants: a methane cogeneration plant a coal-fired plant, an d a dual-flash geothermal powerplant. It is observed that although there ar e some common characteristics in most of the values obtained from all the m odels, the absolute energies and energetic efficiencies calculated using so me of these models deviate substantially from those obtained with the other s. The reasons far these deviations are also examined here.