Development of exergy-based control strategies for building energy systems
Aachen / E.ON Energy Research Center, RWTH Aachen University (2018) [Book, Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (xxix, 148 Seiten) : Illustrationen, Diagrammen
The development of recently-designed energy efficient components and complex energy concepts has heightened the need to develop advanced control strategies. In contrast to most of the advanced control strategies, which have been developed to be energy efficient, this research proposes to apply exergy, which is the maximum available work that can be extracted from a system, to control energy systems. The main objective of this study is to develop an exergy-based control strategy for building energy systems. The control strategy is expected to regulate a building energy system in a way that the most exergy efficient operation of the system is achieved. The validity of the proposed thesis is assessed in this study. It is also explored what kinds of energy systems can be controlled from an exergy point of view and what specifications an energy system should possess to be a potential candidate for the implementation of the exergy-based control strategy. The challenges of applying the theoretical concept of exergy into the practical control of energy systems are realized, and methodologies and solutions to them are proposed. A reference environment for exergy that suits control applications is selected. It is defined how the exergy destruction and efficiency of the system are obtained. Moreover, control techniques suitable for the implementation of the developed exergy-based algorithm in a building energy system are suggested and their advantages and disadvantages are discussed. In order to assess the performance of the exergy-based control strategy, the approach of software-in-the-loop simulation is suggested in this research. For evaluation purposes, a case study is defined, regulated by both a reference control and the exergy-based control under the same circumstances. Furthermore, a medium model capable of calculating the thermodynamic properties required for the dynamic exergy analysis is developed. In order to systematically perform the dynamic exergy analysis, a generic exergy analysis tool is introduced. To distinguish the role of exergy in the reduction of the energy consumption from that of the control technique, an energy-based control strategy is defined and implemented in the case study using the same control technique applied in the exergy-based control strategy. In addition to the conventional evolution of electricity, the exergy content of the grid electricity is evaluated globally to reduce the primary energy consumption. The results show that the exergy-based control strategy is able to reduce the exergy destruction and the energy consumption while maintaining the room air temperature at the same level of the reference case, however, the magnitude of the improvement depends on the applied control technique. Finally, the functionality of the exergy-based control strategy is demonstrated through its implementation in the E.ON Energy Research Center's main building in Aachen, Germany.