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Embodied energy
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Embodied energy refers to the quantity of energy required to manufacture, and supply to the point of use, a product, material or service. (As an analogue of embodied water, embodied energy might also be called "virtual energy", "embedded energy" or "hidden energy").
Traditionally considered, embodied energy is an accounting methodology which aims to find the sum total of the energy necessary - from the raw material extraction, to transport, manufacturing, assembly, installation as well as the capital and other costs of a specific material - to produce a service or product and finally its disassembly, deconstruction and/or decompostion.
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Encyclopedia
Embodied energy refers to the quantity of energy required to manufacture, and supply to the point of use, a product, material or service. (As an analogue of embodied water, embodied energy might also be called "virtual energy", "embedded energy" or "hidden energy").
Traditionally considered, embodied energy is an accounting methodology which aims to find the sum total of the energy necessary - from the raw material extraction, to transport, manufacturing, assembly, installation as well as the capital and other costs of a specific material - to produce a service or product and finally its disassembly, deconstruction and/or decompostion. Different methodologies produce different understandings of the scale and scope of application and the type of energy embodied. Some methodologies are interested in accounting for the energy embodied in terms of oil that support economic processes. Other types of methodologies are concerned to account for the energy embodied in terms of sunlight that support ecological processes. And others like systems ecology are concerned about the support of the ecological-economic process as a whole. Embodied energy as a concept used in systems ecology seeks to measure the "true" energy cost of an item, and has extended this to the concept of "true" value. Methodologies such as emergy have also sought to link embodied energy with fundamental concepts, such as capacitance for example, in physical, electronic and chemical sciences.
The UK Code for Sustainable Homes and USA LEED Leadership in Energy and Environmental Design are standards in which the embodied energy of a product or material is rated, along with other factors, to assess a buildings environmental impact. Embodied energy is a new concept for which scientists have not yet agreed absolute universal values because there are many variables to take into account, but most agree that products can be compared to each other to see which has more and which has less embodied energy. Comparative lists (for an example, see the Bath University Embodied Energy & Carbon Material Inventory below) contain average absolute values, and explain the factors which have been taken into account when compiling the lists. Typical embodied energy units used are MJ/kg (megajoules of energy needed to make a kilogram of product), tCO2 (tonnes of carbon dioxide created by the energy needed to make a kilogram of product). Converting MJ to tCO2 is not straightforward because different types of energy (oil, wind, solar, nuclear and so on) emit different amounts of carbon dioxide, so the actual amount of carbone dioxide emitted when a product is made will be dependent on the type of energy used in the manufacturing process. However, the Australian Government research web site (see CSIRO link below) gives a global average of 0.098 tCO2 = 1 GJ. This is the same as 1 MJ = 0.098 kgCO2 = 98 gCO2 or 1 kgCO2 = 10.204 MJ.
Embodied energy methodologies
Different methodologies use different scales of data to calculate energy embodied in products and services of nature and human civilization. International consensus on the appropriateness of data scales and methodologies is pending. This difficulty can give a wide range in embodied energy values for any given material. In the absence of a comprehensive global embodied energy public dynamic database, embodied energy calculations may omit important data on, for example, the rural road/highway construction and maintenance needed to move a product, human marketing, advertising, catering services, non-human services and the like. Such omissions can be a source of significant methodological error in embodied energy estimations (Lenzen 2001). Without an estimation and declaration of the embodied energy error, it is difficult to calibrate the sustainability index, and so the value of any given material, process or service to environmental and human economic processes.
Classification of embodied energy methodologies
There appear to be three main differences in contemporary embodied energy methodologies. Following Tennenbaum (1988) these may be identified as ‘anthropocentric’ and ‘capitalcentric’, with a third identified as ‘ecocentric’. According to Tennenbaum, the difference in methodologies is determined by how they treat, and where they attribute energy depreciation in a network of ecological system energy flows. In all the methods, depreciation is taken away from the production process under consideration and reassigned elsewhere in the total system. What characterises a method is where they assign this energetic loss. According to David M. Scienceman (1987), the principal point of difference is whether embodied energy is partitioned at work intersections and apportioned among pathways.
Anthropocentric embodied energy analysis
Anthropocentric embodied energy analysis is interested in what energy goes to supporting a consumer, and so all energy depreciation is assigned to the final demand of consumer but not to storages of ‘assets’ or ‘capital stocks’. It is associated with Hannon’s work. There is no requirement that energy must be expressed as one energy form or quality.
Capitalcentric embodied energy analysis
Capitalcentric embodied energy analysis is interested to know what supports assets, energy depreciation is therefore assigned to storages of ‘assets’ or ‘capital stocks’, but not to final demand. This method is associated with Herendeen's and Costanza's works, where embodied energy is apportioned among pathways and partitioned at work intersections, and is therefore additive just like first law heat energy. As with the anthropocentric view, there is no requirement that energy must be expressed as one energy form or quality.
Ecocentric embodied energy analysis: Emergy
"Embodied energy is an energy function that is intended to make energy flows of different types comparable" (Wang, Odum & Costanza 1980, p. 185)
In ecocentric embodied energy analysis, depreciation is assigned to a unit of production, that is, assigned to both storages of ‘assets’ or ‘capital stocks’, and to final demand. This method is associated with Howard T. Odum's works, where embodied energy is not apportioned among pathways and is therefore not additive just like first law heat energy. Energy is only partitioned at work intersections that are diverging, and flexible. The notions of feed back, and energy amplifier effect as used in electronic circuits inform the theory behind this definition.
"Energy used in developing energy of higher quality is 'embodied energy'" (H.T.Odum 1994, p. 251).
Emergy
Dr. D.M.Scienceman coined the term 'Emergy' to make this method distinct from the above types of analysis: "The prefix em- can, fortuitously, even be taken to indicate an energy memory property, a record of source energy transformed." In the emergy methodology there is a requirement that energy must be expressed in one energy form or quality. Non-emergy approaches most often evaluate only nonrenewable resources, depending on what human technologies are able to extract from them (user-side quality). The Energy Systems Language is used to help make emergy algorithms transparent.
Historical perspective of calculation methods
The history of constructing a system of accounts which records the energy flows through our environment can be traced back to the origins of accounting itself. As a distinct method, it is often associated with the physiocrat's "substance" theory of value (Mirowski 1999, pp. 154-163), and later the agricultural energetics of Serhii Podolinsky, a Ukrainian socialist physician (Martinez-Alier 1990), and the ecological energetics of V.V.Stanchenskii (Weiner 2000, pp. 70-71, 78-82). However, the main methods of embodied energy accounting as they are used today grew out of Wassily Leontief's input-output model and are called Input-Output Embodied Energy analysis. Leontief's input-output model was in turn an adaptation of the neo-classical theory of general equilibrium with application to, "the empirical study of the quantitative interdependence between interrelated economic activities" (Leontief 1966, p. 134). According to Tennenbaum (1998), Leontief's Input-Output method was adapted to embodied energy analysis by Hannon (1973) to describe ecosystem energy flows. Hannon’s adaptation tabulated the total direct and indirect energy requirements (the ‘energy intensity’) for each output made by the system. The total amount of energies, direct and indirect, for the entire amount of production was called the ‘embodied energy’.
Embodied water
In the 2000s drought conditions in Australia have generated interest in the application of embodied energy analysis methods to water. This has led to use of the concept of embodied water.
See also
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