The embodied energy and environmental emissions of construction projects in China: An economic input–output LCA model
Introduction
The environmental and energy challenges associated with turning society in a more sustainable direction are tremendous and urgent. Building and infrastructure construction, in step with developments in industry and transportation, has become an important energy consumer in China. This has resulted in an increase in environmental stress. In 2007, energy use in buildings accounted for 47% of the total energy consumption in China (Wang, 2005). Given the acceleration of urbanization as well as infrastructure construction, this percentage is projected to continue to increase in the future decades.
In terms of the life cycle energy use in buildings, operational energy is generally approximately 80% of the total energy consumption (BEERC, 2009). This has become the focus of recent studies. An investigation on the operational energy of commercial and residential buildings in China has found that the commercial building energy consumption statistics in the current National Bureau of Statistics of China underestimate energy consumption by 44% and the fuel mix is misleading. Energy efficiency improvements will not be sufficient to offset increases in energy intensity (particularly electricity) in commercial buildings (Bressand et al., 2007, Chen et al., 2008). In other studies, the resource consumption of urban residential buildings in China is calculated and compared with counterparts in the U.S., Canada, and Japan. It is shown that direct coal consumption will decline while electricity and natural gas consumptions will increase. Building design and operational energy technologies such as district heating should be compatible with urban planning so as to achieve better performance and energy savings (Fernandez, 2007, Zhang, 2004). To avoid the increased energy demand caused by urban housing development, design standards and codes should be revised to correspond with international norms and energy-efficient buildings should be adopted as a baseline (Guan et al., 2001, Lang, 2004, Rousseau and Chen, 2001). The widespread implementation of green building approaches as well as the effective reduction of building energy use cannot be achieved without various economic incentives such as tax rate reductions and low-interest loans. These may motivate both the supply and demand for energy-efficient buildings (Yao et al., 2005).
Researchers have been aware of the significant role embodied energy and its environmental impacts play in the creation of the energy-efficient society advocated by the Chinese government. The high energy consumption in both industrial and building sectors has been analyzed and compared with the U.S. and Japan (Rao and Qian, 2006). Focusing on construction materials in China, the embodied energy of cement, steel, and glass and their direct and indirect environmental impacts have been calculated (Gong and Zhang, 2004). Direct and indirect household emissions of CO2 in China were quantified with the help of input–output life-cycle assessment (I–O LCA) (Zheng et al, 2007). However, this study did not include other pollutants.
Generally, studies of building embodied energy as well other environmental impacts are rare in China, primarily because of barriers in obtaining quantitative data for analysis. Although I–O LCA models are very effective in quantifying embodied energy, the models are highly data-dependent, and the collection of economy-wide statistics in China is not mature nor complete enough, with the result that some critical data are not available. For example, energy consumption statistics are not available for all the 122 sectors in the I–O model, which introduces difficulties in establishing an energy intensity matrix for the I–O LCA model; environmental pollutants only cover SO2 and PM, so a broad understanding of environmental impacts is lacking.
Embodied energy deserves systematic and complete analysis. Embodied energy in products is primarily the result of activity in industrial and transportation sectors. These sectors in China have room for improvement, with relatively minimal effect on citizens’ daily life.
In this work, the embodied energy and environmental impacts of construction projects in China has been estimated. First, we briefly review the structure and development of I–O LCA models. Then, we discuss the 23 economic sectors related to the construction sector in the national economic system used in the model. Next, the derivation of the energy and environmental intensity matrices are reviewed. Finally, the implementation of the model in MATLAB® (Mathworks, 2009) and the detailed results and analysis are presented.
Section snippets
Conceptual basis of LCA
Life-cycle assessment (LCA) is a methodology for evaluating the environmental load and energy consumption of processes or products (goods and services) during their life cycle from cradle to grave (ISO, 2006). For the building and infrastructure life cycle, it can be defined as a practical management approach with the goal of achieving an optimum cost and benefit solution through the process of design, building material extraction, material processing, construction, building operation, and
Correlated sectors
The criterion for sector selection was determined by their technical coefficients with the construction sector as shown in the latest Chinese input–output statistics from year 2002 (National Bureau of Statistics of China, 2006). The sectors’ definitions, classifications, and system boundaries are those used in the national accounts and input–output table, in which the construction sector is defined to include building construction, infrastructure construction, equipment installation, and
Results and analysis
The embodied energy of construction projects in China is 436 million mtce in 2007, which accounts for 16% of the total energy consumption of the country. According to the statistics of the Ministry of Housing and Urban–Rural Development (MHURD), PR China, building operation energy is 25% of the total national energy consumption. Building construction and operational energy consumption in China, therefore, represents 40% of the total annual energy use in China. However, this figure includes only
Conclusions
This study shows that the embodied energy as well as the environmental emissions of the construction sector represent a significant percentage of the total energy consumption and environmental load in China. Since buildings and infrastructure generally have a long life, operational energy is dominant in a buildings’ life cycle energy use and therefore research on the embodied energy of construction in China is rare. This is also due to the lack of key data from the current national statistics
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