Thermomechanical Analysis And Exergy Based Assessment Method For The Energy Use In Building Energy Systems

Improving the energy efficiencies and controlling energy consumption are the major tasks of building energy conservation. However, the existing energy analysis methods are fundamentally flawed. There is no unified datum point when analyzing the use of different kinds of energy source. Based on the first law of thermodynamics, the energy analysis concentrates on the effective use of energy only, but ignores the difference on quality between energy sources. In addition, most existing energy analyses regarding energy use consider only the important components or the key processes, it lacks an overall analysis for the whole energy chain, so it is hard to assess the performance on energy use of building energy systems.In order to set up a unified datum point for different kinds of energy source, this study analyzes the source and assistant energy consumption in the upstream phase of energy products. Furthermore, the input-output relationship between energy products is quantified by using exergy as the quantitative standard. Exergy cost analysis method is proposed to unify the datum point of different kinds of energy products.As for the energy use equipments, the study modularize the building equipment system by analyzing the functionality features of different building equipments, and constructs exergy imformation libraries for the basic modules. A building equipment system can be formed by calling the equipments in the exergy imformation libraries. Combining the exergy transfer characteristic and the assistant exergy consumption of building equipment system, the study defines the overall exergy efficiency of the equipment system, which can be used to assess the thermal performance of the equipment system and serve as basis for improving the equipment system.For energy use in buildings, the study analyzes the basic energy consumption amount and the energy quality level of each energy uses in buildings, and establishs the relation formula between the basic exergy consumption amount of each energy uses and its influence factors. The effect of exergy use in buildings is analyzed according to the matching relation between exergy output of equipment system and the basic exergy consumption amount of building. In addition, the study analyzes the exergy uses in the Chinese residential and public building sectors using statistical data. The results show that the exergy efficiencies of energy use in the Chinese residential and public building sectors are all much lower than the corresponding energy efficiencies, there exist huge potential of exergy savings. However, the energy saving measures used in the past dacade have little effect on the imptovment of exergy efficiencies. Furthermore, the study obtains the distributions and causes of exergy losses in the Chinese residential and public building sectors.For the whole energy chain including energy supply, equipment system and buildings, the study unifies the datum point of different kinds of energy source using exergy cost analysis method and constucts a unified exergy analysis model for the thermal performance of building equipment systems, in addition, the effect of exergy use in buildings is analyzed. The exergy analysis method for the building energy system is obtained by combining the exergy analysis of energy supply, equipment system and buildings. An exergy based indicator system in assessment of building energy conservation is proposed as well. Besides, the study analyzes the exergy use of common heating and air conditioning system and finds out low-exergy optimization methods.In conclusion, the exergy analysis provides an overall assessment method for the performance of energy use in building energy systems. Besides, the distributions and causes of exergy losses are identified as well. The exergy analysis results of building energy systems can points out the methods of low-exergy optimization and serve as basis of regional energy planning.