Résumé

Providing energy services can be achieved by various technologies or combinations of technologies and it is important to be able to characterize the quality of these different options. In practice, different indicators of the quality of energy processes can be defined: the effectiveness based only on the First Law of thermodynamics or the exergy efficiency based on the exergy balance, thus accounting for both the First and the Second Laws of thermodynamics. While the exergy efficiency definition is general and applies to all systems with values always ≤1, it is not the case of the effectiveness. Today, there is no general definition and formulation of effectiveness that can be applied to all technologies and/or energy conversion systems. The most general formulation of effectiveness given in the literature is indeed mainly valid for processes that take place above the atmospheric temperature. It must however be adapted for refrigeration systems and also for any conversion systems providing simultaneously energy services for both heating and cooling. In this article, we propose a new approach for a general expression of the effectiveness suitable for any energy conversion systems including heat pumps and cogeneration systems with combined heating and cooling. The main advantage of such a method is therefore to provide simple and generic expressions of global exergy losses and efficiencies of any systems in relation to the conventional performance indicator (the effectiveness) most commonly used by engineers to estimate energy losses of a system.

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