Embodied Energy

Also called “emergy,” embodied energy is defined as the available energy that is used in the work of making a product. It has also been said to be an accounting methodology that aims to find the sum total of the energy necessary for an entire product life cycle. This life cycle encompasses raw material extraction, transport, manufacture, assembly, installation, disassembly, deconstruction, and/or decomposition.

The associated environmental implications of embodied energy such as resource depletion, the production of greenhouse gases, maintenance of biodiversity, and environmental degradation are embedded in the measurement of embodied energy. The energy is expressed in units of megajoules (MJ) or gigajoules (GJ) per unit of weight (kilogram or tonne) or area (square meter).

Embodied energy plays a large role in the choice of any product and is an important factor to consider when assessing the life cycle of a product because it relates directly to the concept of sustainability of that product. Closely related to the embodied energy of materials or products is the concept of life cycle assessment (LCA). LCA is the assessment [Page 166]of the environmental impact of products, buildings, or other services throughout their lifetimes. The assessment includes the entire life cycle of a product, process, or system, encompassing the extraction and processing of raw materials; manufacturing, transportation, and distribution; and use, reuse, maintenance, recycling, and final disposal. LCA is a much-explored concept and has been used as an environmental management tool worldwide since the late 1960s.

A derivative of LCA, life-cycle energy analysis (LCEA) ties in closely with embodied energy of materials because it considers energy as the only measure of environmental impact of any product. Emerging in the late 1970s, the purpose of LCEA is to present a more detailed analysis of energy attributable to products, systems, or buildings to enable decision-making strategies concerning energy efficiency and environmental protection. LCEA was not developed to replace LCA but, rather, to compare and evaluate the initial and recurrent embodied energy in materials, energy used during the operational phase, and during recycling and disposal. It is often used to estimate the energy use and savings over the product's or building's life, and more important, to find out the energy/carbon dioxide payback period (the time spent for the initial embodied energy cost to be paid back by energy savings during operational and disposal/recycling stages).

The concept of embodied energy has become very central in the design of buildings. When sustainability is the driving force in the creation of a building, quantity surveyors and architects need additional knowledge to assist them in making decisions about the choice of building materials and the way in which they are used. Some standards exist for making this comparison. The two most common are the U.K. Code for Sustainable Homes and the U.S. Leadership in Energy and Environmental Design standards. These standards rate the embodied energy of a product or material, along with other factors, to assess a building's environmental impact.