Derivative Life cycle Concepts: Sustainability Metrics and Rating Systems
Physical measures of sustainability employ the concepts of thermodynamics in their calculations. There are two approaches for measuring sustainability; Exergy and Emergy. These concepts are derivatives from the second law of thermodynamics. The law states that a closed system with constant mass and no energy inputs tends towards higher entropy.
Exergy is a combination property of a system and its environment because it depends on the state of both the system and environment. It refers to the maximum work that can be obtained from a system as it approaches thermodynamic equilibrium. It is used in the study of the efficiency of chemical and thermal processes.” Exergy accounting provides insights into a system’s metabolism and its effect on the environment using a common denominator. It can address energy utilization, design and analyze energy systems, and quantify waste and energy losses reflecting resource use. Exergy can account for an economic component, labor input, and impact of emissions on human health.”
Exergy analysis can be applied in varied energy systems such as utility, industrial, residential-commercial, and transportation for performance comparison, assessment, and improvement. In the utility sector, which includes processes for electricity generation that uses both renewable and nonrenewable sources, conducting exergy analysis could be meaningful in making assessments and improving all the conventional sources with low efficiencies.
The energetic analysis provides a meaningful assessment of plant component efficiency and determines magnitudes, location, and causes of irreversibilities in the plant. This analysis also can be used to optimize the quality of energy. Total Cumulative Exergy Loss (TCL) is a method used to compute energetic sustainability. This indicator is the sum of all the internal exergy losses in the plant and includes losses in the construction phase, operation, and the losses due to its abatement of emissions and waste flow in the system. High TCExL means that the energetic sustainability of the system is low.