Study of Embodied Energy consumption in Residential Sector: Case Study of Shiraz

Introduction and Literature Review: Reducing energy consumption and greenhouse gas emissions to alleviate the effects of global warming have become a worldwide necessity. This matter has significant importance in Iran, because Iran has the seventh ranking position of global greenhouse gas emissions and its rate of growth is above global average. Building construction sector is experiencing a fast-paced growth in developing countries, like Iran, due to growth of economy and rapid urbanization. A large number of buildings are being built for residential, commercial and office purposes every year. Built environments are responsible for about 40 percent of energy consumption in Iran and it is generally approved that the greatest portion of built environment is dedicated to residential use. Energy consumed in producing and processing building materials and in the processes of building a house, is usually calculated using embodied energy concept. Until recently, it was generally accepted that the energy used during the occupation of a building represented a much higher proportion than its embodied energy; thus, great efforts were put into reducing energy use in this phase. New and improved technologies have reduced the operational energy through a variety of solutions, including energy-efficient equipment and appliances, improved insulation levels, low energy lighting, heat recovery systems, the provision of solar hot water systems, photovoltaic panels for generation of electricity, and other renewable technologies. However, these measures often imply an increase in materials use and energy demand for their production, which explains the growing importance of other phases in the total life cycle. According to the global literature, embodied energy of a building accounts for one third to one fifth of the total life cycle energy consumption of a specific building. However as the global trend for the new developments moves toward the zero energy/carbon buildings, the importance of the embodied energy increases. In fact embodied energy is one of the leading parameters in assessing building’s environmental performance, because in building projects, vast amounts of building materials are needed which consume great amounts of embodied energy and thus have negative effect on environment. With this preamble, improving energy efficiency of the existing dwelling stock of urban regions will increasingly be part of achieving sustainable development in future. Although this aspect of achieving sustainable development has been the subject of many global practices in recent years and global literature is almost rich in the calculations and analysis of embodied energy and life cycle energy consumption, this matter has been neglected almost completely in Iran and those few studies conducted focusing on energy in urban planning and designing fields, are mainly concentrating on transportation sector. Thus the main goal of this study is analyzing the sustainability of urban residential sector with focusing on embodied energy consumption. Methodology: In this regard, residential sector in Shiraz Metropolitan has been divided into seven different dwelling types including central-yard houses, attached terrace houses (one story houses, two story and three story houses), apartments (which are buildings of four story and above), villas and declined houses. Gathering raw data in this study was challenging, considering the fact that house building in Iran is far from industrialized and prefabricated building is really limited. Unfortunately there is no data available on the average material consumption of different dwelling types in Iran and the only study similar to this was done focusing on building structures. Using this only available data, we built our data bank in Microsoft Office excel and then focused on computing average embodied energy via multiplying embodied energy of common building materials extracted from a report conducted in the University of Bath titled “Embodied Carbon: The Inventory of Carbon and Energy (ICE)” into average material consumption based on building structures. Another point we had to take into account was the unit of the available data; while embodied energy of materials were presented in gigajoules per square meter, average material consumptions of dwellings were presented in different units from square meters, to cubic meters, kilograms and blocks. So using density of materials we established a second data base with similar units. Normalizing this raw data through dividing average embodied energy of residential dwelling by dwelling area we calculated the capitation of embodied energy for each dwelling. Afterwards we prioritized embodied energyconsumption of dwelling types from lowest embodied energy capitation to the highest as follows: brick and wood structures with about 3 GJ/m^2 embodied energy, clay brick concrete structures, clay brick steel structures, brick concrete structures, brick and iron structures, and at last brick steel structures with about5.35 GJ/m^2 embodied energy Results: To be sure of the validity of these comparisons analysis of variances (ANOVA) and Post Hoc Tests (Least significant difference- LSD) have been applied to these data in IBM SPSS statistics 19, and the result has been positive. Then collected data were shifted from structure types to dwelling types and we found out that central-yard houses with 3.6 GJ/m^2 embodied energy per capita are the most energy efficient dwelling types. After this type in sequence lay one-story terrace houses (4.21GJ/m^2 ), apartments (4.26GJ/ m^2 ), two story terrace houses (4.67GJ/m^2 ), declined houses (4.81GJ/m^2 ), villas (4.84GJ/m^2 ), and three story terrace houses (5.21GJ/m^2 ). Discussion and Conclusion: This paper highlights the need to use location-specific data in the development of building assessment schemes and the issues related to the use of embodied energy assessment for the building sector. Absence of localized data base on building material consumption on the basis of dwelling type and lack of data on cradle to grave embodied carbon and energy of common building materials were the most important obstacles in this research. On the basis of international research, paint, bitumen, platevirgin, sheet Galvanized-virgin, steel, ceramics, primary glass, iron bars, lime, cement, and common brick are the most energy intensive materials. So on account of lack of localized data, we used international embodied energy of common building materials (cradle-to-gate) to calculate embodied energy of different dwelling types. Despite of major shortcomings in data base, noteworthy conclusions have been deducted from this work which are summarized as follows: traditional form of housing in Shiraz which is known as central yard houses in this paper with brick and wood structures (in which there is a yard in the center of the block and the residential parts are located at its periphery) are the most sustainable form of housing according to this research criteria and case study. This may owe its accomplishment to the low embodied energy of common materials used in this type of housing which we may call the most environmental friendly form of housing in Shiraz. Furthermore there is a substantial lack of data on embodied energy and carbon of materials in general, and in particular on the embodied energy and carbon of buildings to be able to do an entire evaluation of buildings in their life long period. So to do a complete research in building sector (life cycle assessment), including embodied energy, gray energy, operational energy, induced energy, Demolition/Recycling Energy, and retrofit energy are unavoidable.