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Theses

Exergy-based performance assessment and optimization potential of refrigeration plants in air-conditioning applications

Abstract : A significant amount of energy consumption in buildings is due to heating, ventilation and air-conditioning systems. Among other systems, refrigeration plants are subject of efficiency improvements. However, actual operating conditions of such plants and the performance must be known as well as any eventual optimization potential identified before enhancements can take place. Energy and exergy analyses have been widely used to assess the performance of refrigeration systems. Among others, exergy efficiency is used as an indicator to determine the system performance; however, the practical achievable values are unknown. Therefore, this work proposes a practice-oriented evaluation method for refrigeration plants, based on exergy analysis and technical standards as baseline. The identification of possible enhancements is highly relevant in practice, as measures which improve the system effectiveness most likely prevent frequent shortcomings during refrigeration plant operation. With the introduced optimization potential index (OPI), the achievable enhancements compared to the state of the art in technology and the performance are identified at a glance regardless the complexity of the system. By dividing the plant into different subsystems, each of them can be assessed individually. Laypersons can easily determine the system operating state and subsequently, if needed, initiate a detailed analysis as well as appropriate countermeasures by specialist. Moreover, modeling is seen as an appropriate method to determine additional reference values for refrigeration machines if none are available according to technical standards. Among different modeling techniques, artificial neural network models reveal the best performance for the present application. The application, functionality and purpose of the presented method is exemplified on two numerical test cases and on a real field plant as a case study. The investigation reveals an adequate operation of the studied field plant in general, where three out of seven cooling locations have performance issues. The reason should be identified in a subsequent detailed study. Overall, the auxiliary electrical exergy input shows the same magnitude as the thermal exergy input. This emphasizes the importance of minimizing the electrical energy usage, as it is the main overhead in the operating cost of refrigeration plants and also to achieve an increase in system performance. Moreover, measuring concepts of real systems are analyzed and the corresponding retrofitting costs for the application of the presented approach are identified. It is shown that a retrofit of the instrumentation can be worthwhile if the refrigeration plant already comprises a measuring concept close to the state of the art.
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https://tel.archives-ouvertes.fr/tel-03213647
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Submitted on : Friday, April 30, 2021 - 2:57:45 PM
Last modification on : Saturday, May 1, 2021 - 3:27:05 AM
Long-term archiving on: : Saturday, July 31, 2021 - 7:09:28 PM

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  • HAL Id : tel-03213647, version 1

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Lorenz Brenner. Exergy-based performance assessment and optimization potential of refrigeration plants in air-conditioning applications. Thermics [physics.class-ph]. Université de Lyon, 2021. English. ⟨NNT : 2021LYSEI014⟩. ⟨tel-03213647⟩

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