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Recognizing that the energy-saving potential of combined heat and power (CHP) systems is underused, the Council of the European Union has issued a Cogeneration Directive. In terms of specific guidelines and rating parameters based on energy efficiency, the objective was to promote "high-energy cogeneration." This paper makes a critical review of the Directive using the rational exergy management model (REMM), which is a common sustainability metric that can better bridge the compound benefits of CHP systems with the environment. REMM is a common rationality metric, which is an indicator of how the supply and demand exergies in the energy sector are balanced. In this respect, the primary energy savings equation of the Directive was modified in order to factor in rational exergy benefits on the environment, which remained hidden so far. Sample calculations made in the Euoropean Union (EU) FP6 Research Project HEGEL show that the rational exergy benefits in conserving primary energy resources are 62% more than what the Directive can indicate. Using parametric analyses, this study draws a new roadmap for better and optimized cogeneration systems. [ABSTRACT FROM AUTHOR]

Floor heating has been the most basic version of panel heating and cooling systems since ancient times. Recently newer applications are becoming widely used, especially in Europe. For all panel applications, whether the most basic or the most innovative, their attributes are mainly focused on energy efficiency and better comfort. So far, little attention has been paid to their exergy efficiency, which in fact is a more insightful means of analyzing and comparing HVAC systems to optimally resolve the quadrilemma of human comfort, environment, energy, and economy. This paper shows that panel systems, especially when coupled with a convective component in a hybrid HVAC panel, are more exergy-efficient when they are tied into low-exergy energy sources. A typical analysis for a residential home indicates that the exergy efficiency of a hybrid panel utilizing a low-enthalpy energy resource and a heat pump is almost tenfold higher than a forced-air system utilizing natural gas and grid electricity. This paper draws an energy-based roadmap for the next-generation HVAC systems. [ABSTRACT FROM AUTHOR]