A study of embodied energy assessment of China's construction sector and construction projects

Abstract

Building-related energy problems are a worldwide concern. Due to its rapid pace of urbanization and industrialization, China is one of the largest primary energy users in the world which accounts for approximately one-fifth of the global total primary energy supply (TPES) and one-fourth of carbon dioxide (CO{208}) emissions, facing big challenges in environmental pollution. Therefore, this study chooses China as the jurisdiction within which to investigate the environmental implications of the construction sector because of its extremely high resource consumption and environmental burden. The primary aim of this research was to systematically quantify the direct and indirect energy transmissions embodied in China's construction sector at the regional and sectoral level, and develop a multi-regional hybrid framework for assessing embodied energy consumption at the project level. The specific objectives of this research were as follows: (1) To explore the driving forces behind the increase in energy use of the construction sector and investigate energy consumption trajectory in the past two decades. (2) To quantify embodied energy use of the construction sector at the regional and sectoral level. (3) To decompose energy transmissions and identify critical energy paths in the entire supply chain from the sectoral and regional perspectives. (4) To develop a multi-regional hybrid framework for assessing embodied energy consumption at the project level by integrating regional average data and case-specific process data. (5) To verify and validate the reliability of the developed framework in real building cases through data from project level. The study firstly explored the driving forces behind the increase in energy use of China's construction industry from 1990 to 2010 by conducting a structural decomposition analysis (SDA). A multi-regional input-output (MRIO) model was then employed to investigate the hidden linkage and economic network among regional construction sectors by considering region-specific characteristic and technological differences. An optimized algorithm was designed for structural path analysis (SPA) to quantify indirect energy transmissions through the upstream supply chain of the construction sector. Ultimately, a multi-regional hybrid framework for embodied energy assessment of construction projects was proposed by integrating three modules: the region-based sectoral energy intensity module (RBSEIM), the process-based energy intensity module (PBEIM), and the computational structure module (CSM). The hybrid framework was then validated in real cases by conducting comparative and empirical analyses. The key findings obtained in this study include the following aspects. First, the results of SDA indicate that the energy consumption trajectory of China's construction sector is the result of competition between the effect of increasing final demand and improvement in energy efficiency. Although consistent efforts in structural optimization by the central government had significant positive effects between 2007 and 2010, the potential to reduce much more energy remains dependent on optimization of energy structure, production structure, and final demand structure. Second, the results of MRIO analysis show that the construction sector consumed 793.74 million tons of coal equivalent in 2007, which is equal to 29.6% of China's total national energy consumption. Interregional imports of the construction sector represented a resource-dependent geographical distribution, implying that the energy flows are from resource-abundant areas in the central part of the country to resource-deficient areas on the eastern coast. By contrast, energy exports represent a regional discrete distribution, which exports energy in the form of labor mobility and service supply. Third, the findings from SPA revealed that the first two stages in the upstream production process consumed the highest amount of energy in the supply chain, accounting for approximately 50% of total energy consumption. The regional analysis revealed the self-sufficiency characteristic for energy consumption in the regional construction sectors. The sectoral analysis demonstrated that imports from sectors of "manufacturing of non-metallic mineral products", "smelting and pressing of metals", and "transportation, storage, post, and telecommunications" are the most important energy flows in the first stage. The sectors of "chemical industry", "production and distribution of electric power and heat power", and mining industries pose significant indirect impact on the energy use of the construction sector. Ultimately, the comparative analyses and empirical studies of the developed hybrid framework indicate that it not only enables us to explore interregional energy transfers but also exhibits 'hidden' embodied energy consumption. The framework can also reflect the effects of changes in geographical location, building type, and building structure on the total embodied energy consumption. This study contributes the sustainable construction at three levels of investigation: national level, regional level, and project level. At the national level, the research explored the driving forces and trajectory of the embodied energy consumption of the construction sector, which revealed the potential areas for improvements in sustainable construction. At the regional level, the inter-regional energy transfers and the indirect energy input through the higher order of upstream supply chain were systematically analyzed and decomposed for the construction sector, which not only enhances our understanding of overall energy flows of the construction sector at the regional level but also reinforces the importance of specific energy-intensive paths. At the project level, the embodied energy assessment system provided valuable information in terms of embodied energy use at the early stage of a construction project, which enables stakeholders to take appropriate actions and formulate effective strategies to reduce energy use embodied in the project. From an academic point of view, the sectoral and regional analysis of driving forces, energy flows, and the supply chain provided contributions to knowledge regarding SDA, MRIO, and SPA of the construction sector. In addition, recognizing the hidden linkage in the interregional trade of China's construction sector can help with a holistic understanding of the current energy consumption status of regions and also help policy makers to achieve a fair and equitable energy reduction policy. From the viewpoint of practice, the multi-regional embodied energy assessment framework is an effective tool for pre-estimating embodied energy use at the initial stage of a project, which could provide practitioners with an incentive to develop construction sustainability.