Of the building materials used in India, aluminium and burnt clay bricks are among the most energy intensive, finds a recent study. The study has developed a framework for assessing the energy consumed during production of building materials, in an attempt to quantifying energy expenditures from buildings.
India uses more than 2 billion tonnes for construction materials per year, with energy expenditure for manufacturing building materials amounting to 20-25% of India’s total energy demand. There is thus an increasing demand for energy efficient building materials.
A team of researchers from Indian Institute of Science has designed an assessment framework for quantifying the total energy expenditure, called “Embodied Energy” (EE) in their paper. The production of building materials also results in emission of greenhouse gases (GHG). As K I Praseeda, a co-author on the paper says, “Focus of the construction industry should be on using low energy alternative building materials”. A first step would be to know which building materials are energy intensive and which are low energy.
Though earlier studies have contributed in calculating the energy expenditure, they lack agreement on the method of assessment. Praseeda said, “Current researches in energy conservation in buildings focus more on limiting “operational energy” (lighting and air conditioning energy) in buildings, without much regard on embodied energy of buildings. This is mainly due to lack of data on energy consumption in manufacture of building materials in the country.”
Prof. Venkatarama Reddy and his team have developed an assessment framework for quantifying the total energy consumed during building material production and tried to bridge this gap in knowledge. The study is based on actual industrial data, which considered certain basic building materials like cement, steel, glass, coarse aggregate, aluminum and some building products like burnt clay bricks, concrete blocks, laterite blocks, ceramic tiles, clay roofing tiles and polished granite and marble slabs.
The team narrowed down on process analysis as the method of assessment instead of input/output analysis (I/O method), as the first method focuses exclusively on the actual process ignoring remote upstream and downstream processes, which are less significant for product specific EE assessment. I/O methods use input-output transaction tables (IOTT). After identifying the assessment framework for calculating the EE, the team then embarked on the task to measure appropriate EE values of building materials used in the Indian construction sector.
EE values are dependent on the type of energy i.e. primary or end use. Primary energy considers total natural energy spent for generation of secondary energy source like electricity, its transportation, distribution losses, etc., while end use energy only considers electrical energy measured at the final use level. The study observed that considering primary energy would give a more accurate idea about EE than just end use energy.
The final analysis showed that among the basic materials, aluminum is found to have higher EE (141.55 MJ/kg- 549.16 MJ/m2) than steel (32.24 MJ/kg), glass (7.88 MJ/kg) and cement (2.38-3.72 MJ/kg). On the other hand, among the masonry units, burnt clay bricks have higher EE than concrete and laterite blocks. Ceramic floor tiles are also found to have higher EE.
Praseeda also mentioned that, “Energy expenditure for a building construction is highly variable as it depends on the location of the building, its function or use, the selection of building materials and many other factors”. Thus, it is quite difficult to arrive at an accurate value of EE for a building; at best, a range of values can be obtained.
The study has to be looked from the broader point of green buildings code and energy ratings. “The building codes and building energy rating guidelines should mandate assessment of embodied energy of buildings and evaluation of relative significance of embodied and operational energy” says Praseeda. This would help in comprehensive building energy assessments.
About the authors
Monto Mani is an Associate Professor with the Center for Sustainable Technologies, Indian Institute of Science, Bangalore. K.I. Praseeda is a Research Scholar and B. V. Venkatarama Reddy is a Professor with the Department of Civil Engineering, Indian Institute of Science.
The paper has been accepted in the journal Energy and Buildings and appeared online in November 2014.