Life cycle assessment of a real residential building in Tehran

Among many aspects considered to evaluate the low energy buildings, the Life Cycle Energy Consumption (LCEC) is the most comprehensive factor that can properly direct engineers and architectures to the buildings’ optimum design. The LCEC is introduced as the total energy usage associated with all stages of a building’s life cycle mainly consists of production of its materials, transportation of the materials and components, on-site construction, operation, maintenance, demolition and waste treatment. This study aims to evaluate the LCEC factor of a real building located in Tehran, Iran. Due to the lack of the investigations in this field in Iran, the methodology of estimating the building’s energy consumption is comprehensively introduced in this paper. For this purpose, a real multi-family residential building with common architectural plan and residences is selected and the process of evaluating the building’s energy consumption during various periods of its life cycle is discussed in detail. These periods include the material production, transportation, on-site construction, operation, and maintenance stage. Demolition and disposal stage is excluded from the scope of this study because of the lack of the clear information about the waste treatment process in the country. Beside, the energy usage of this stage is reported to be less than 1% of the buildings’ total LCEC according to the literature. The results of this analysis show that the embodied energy of the considered case is about 15% of its LCEC. This embodied energy that is indeed in the range of the internationally reported values can be divided into three separate parts including: 1) 12% energy usage for the building material production, 2) 1% energy usage for the material transportation and on-site construction, and 3) 2% energy consumption for the building maintenance stage. In this regard, it seems that the energy usage during on-site construction period of the building has the minimum effect on the building’s LCEC (about 0.2%) and consequently may be ignored in the LCEC process. It is also concluded that 85% of the considered building’s LCEC belongs to the operation stage in which the effect of climate change in terms of global warming is considered via a simple method based on the change of the thermal comfort setpoints. Although this operational energy is in the range of the values reported in the common international investigations, it is too high for Iran where the lifespan of the residential buildings is respectively short. If the lifespan of the considered building in this study increase from 35 years to 60 years, the portion of the operational energy can increase up to 91% of the building’s LCEC. Therefore, proper estimation of the building’s lifespan is demanded for most of the energy assessment studies. Accurate estimation of the energy content of the building materials in Iran is also highly necessitated. If the material production industry in Iran consumes averagely 30% more energy respect to the average values of the world’s industry, the building’s operational energy will reduce about 3% and respectively its total embodied energy will increase about the same amount.