| Energy is already an important and indispensable factor in both of economic and social development.The exploitation and usage of fossil fuels increase the risk of environmental degradation.In recent years,the construction area and the energy consumption of buildings have been increasing in China.Besides the consumption of various mineral resources in the process of urbanization in China,a large number of emissions have been generated,which has restricted the environment and economic development.The traditional energy supply system has lower efficiency of energy utilization.As a new type of energy system,district energy system has the advantages in optimally allocating resources and increasing energy utilization efficiency.Thus,district energy system will be one of the main directions of energy system development in the future.In this thesis,a hybrid model based on environmental input-output analysis and life cycle assessment was developed for the disctrict energy system in China.Life cycle assessment method can calculate the environmental impacts of each production process in the whole life cycle of a product.This method is based on the bottom-up method,but it has truncation error.Environmental input-output analysis is more suitable for macro calculation.Considering all supply chain paths of the national economy,it expands the system boundary of life cycle assessment.However,the data used in the environmental input-output analysis is the average data of industries,which cannot accurately describe the life cycle impact of specific products or services.A hybrid model combined by these two methods can solve the "truncation error" problem and accurately depicts the product or service.The district energy system is divided into four stages,including the production of raw materials and equipment,system operation,transportation,and waste disposal.In comparison with the traditional energy supply system,the life cycle inventories are compiled by collecting data and consulting relevant literatures.A hybrid life cycle assessment model was constructed using the 2012 China input-output table of 139 sectors and China environmental extended input-output database.Six types of environmental impacts,including resource consumption,acidification,eutrophication,greenhouse effect,human toxicity,and photochemical oxidation,were compared between district energy system and traditional energy system.Further,contribution analysis and sensitivity analysis were conducted.The results show that with the same cooling and heating loads,the consumptions of ferrous and non-ferrous ores of district energy system and traditional energy system are similar,but the environmental impacts of traditional energy systems are greater than that of district energy systems.The primary energy consumption,acidification,eutrophication and greenhouse gases of the two energy systems are quite different.The above four environmental impacts of the traditional energy system are about 2.5~4.2 times of that of the district energy system.The contribution analysis shows that the various environmental impacts in the two energy systems are dominated by raw materials and equipment production and system operation processes.For the district energy system,raw materials and equipment production processes are the main contributors to the consumption of ferrous,nonferrous and nonmetallic minerals,accounting for 58%,83% and 49%,respectively.The system operation processes are the major contributors to the remaining categories of environmental impacts,accounting for more than 70% of the total.Sensitivity analysis shows that the two systems have the same trend of sensitivity to input changes,and the range of sensitivity to heating coal consumption is the largest.The primary energy consumption and acidification,which are most sensitive to the change of coal consumption.When the coal consumption is reduced by 10%,the sensitivity parameters of regional energy system and traditional energy system to these two terms are 13.8%,6.5%,11% and 8.7%. |
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