Fundamental Research On Prefabricated Residential Building Envelope Based On Thermodynamic Method

With the improvement of people's living standards,residents' demands for comfortable dwelling environments have constantly increased,which makes building energy efficiency an even more significant problem.In March,2016,the 13th Five-year Plan was released in which the popularization of prefabricated buildings and enhancement of building technologies were highlighted in Chapter eight,the progress of new-type urbanization,giving a straightforward direction for building industry.In this paper,the thermodynamic property of prefabricated residential building envelope is explored,also the energy consumption and environmental impacts are analyzed based on life cycle theory.Based on the previous research and statistics,the life cycle calculation model of energy consumption,exergy consumption and CO2 emissions for prefabricated residential building is established.According to the investigated data from prefabricated components factory,a prefabricated residential building is taken as an example,and the life cycle energy consumption,exergy consumption and CO2 emissions of the case building are calculated.The analysis mainly focuses on the envelope formation period which includes material transportation,manufacture of prefabricated component,transportation of refabricated component and construction.The results show that the additional energy consumption,exergy consumption and CO2 emissions due to the prefabrication are 664.4MJ/m2,538.9MJ/m2,41.8kg/m2,respectively,accounting for 62.7%,63.2%,48.8%in the envelope formation period,whose effect cannot be ignored.What is more,the life cycle differences between traditional residential building and prefabricated buildings are compared,and the comparison focuses on the formation period of building envelope which shows great discrepancy.The results indicate that although the construction period of prefabricated building reduces certain amount of consumption,the total energy consumption during the formation period is much higher than traditional building,the increment of which is 603.7MJ/m2.During the demolition,the prefabricated building has more potential to recycle building materials like concrete and steel.Results show that energy consumption,exergy consumption and CO2 emissions reduce 671.1MJ/m2,533.9MJ/m2,159.4kg/m2,separately.Besides,comparing the life cycle energy exergy ratio of two residential buildings,the ratio of prefabricated building is slightly higher than that of traditional buildings.Considering the energy consumption during material production and building operation period,the equations for energy consumption per unit area of building envelope are obtained in order to search for the minimum value.In the end,to have a comprehensive look and judgment on prefabricated components,three indicators are put forward which are equivalent concrete energy consumption,exergy consumption and CO2 emissions of prefabricated components,calculated based on the volume of consumed concrete.They serve as an evidence to compare and judge the thermodynamic property of prefabricated components under poor market PC standardization.The three PC indicators of the case building are calculated.Under the condition of different service lives,a life cycle analysis is conducted on prefabricated external wall which consumes more energy and resources compared with other types of PC.The calculated value of the three indicators can be a reference and foundation for further research.