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To analyse a system from an environmental/energy perspective, different conceptual indicators can be used as a base. This is a short presentation of the thermodynamic concept Energy, in comparison with Emergy, Exergy (Work energy) and Embodied energy and how they reflect an “energy memory” or historical energy use in a resource/matter. From a thermodynamic perspective Energy has a clear definition referring to what 1 J actually is. The emergy unit 1 sej is more difficult to capture, but can be viewed as an attempt to reflect the total energy input (based in solar radiation). The Exergy value in matter is thermodynamically defined as energy stored in the molecular structure. The idea to use this as an indicator of environmental load is logical in the sense that the energy stored in the structure needs to correspond to the energy needed to shape the structure, but of course it does not say anything about the efficiency between input energy and stored energy. Embodied energy is often defined as the energy needed in all the processes involved in a production process (or similar). It can be compared to an LCA energy value of matter. The embodied energy is thus the sum of inputs following a production process. It is in way part of the Emergy value for the same process/matter, disregarding primary energy input (solar radiation) and normally labor and other indirect consumers. From an engineering perspective there are no limitations in the use of energy in an analysis. Using the Emergy concept means we transfer measures of energy as Joule into sej, and it is more difficult to follow the actual process energy efficiency. By applying the Emergy concept we might be able to capture a “philosophical dimension” as a quantification of an energy memory in a system resource, but the drawback is we cannot use the quantification and relate to the physical reality when it comes to analysing alternative system efficinencies. The aim with an analysis is the base for the choice of suitable indicator. My conclusion is that an Emergy analysis is interesting, but often lacks direct relation to the basic engineering concepts when it comes to detailed analysis of the system efficiency as a base for improvements or comparisons of alternate use. I therefore find it difficult to find applications for how to use the results from an Emergy analysis, which probably is due to my engineering background and the fact that my references are the normal energy concepts. |
