Abstract
The current method used for calculating societal aggregated exergy efficiencies is reviewed. Cooling is introduced as an end-use category; conversion efficiencies for heating processes are obtained for each energy carrier; and electricity shares per end-use are retrieved for each sector, improving the accuracy of the estimated values of aggregated exergy efficiencies. We show that: (1) cooling uses are a relevant end-use in Portugal and that their introduction decreased overall efficiency by 3.4% in 2009; and (2) disaggregating the heating second law efficiencies for each energy carrier has a significant effect on the aggregated efficiencies of the country, decreasing aggregated efficiency by 1.3% in 2009. We studied two other factors that showed no significant impact on aggregated exergy efficiency: a technological lag of 10 years in the efficiency of stationary mechanical drive devices and the use of a year-specific ambient temperature to compute exergy efficiencies of heating processes.
Highlights
Energy consumption worldwide has been increasing at a very high rate, and despite current investments in renewable sources of energy, fossil fuel consumption still plays an important role in the economies of both developed and developing countries
The method used to estimate useful exergy values and second law efficiencies is described in the previous section
A disaggregation of the heating efficiencies by energy carrier is undertaken, to assess if this level of detail is relevant in a useful exergy analysis
Summary
Energy consumption worldwide has been increasing at a very high rate, and despite current investments in renewable sources of energy, fossil fuel consumption still plays an important role in the economies of both developed and developing countries. Exergy analyses tell us the distance from the ideal process, which relates to (1) a mismatch between the energy carrier (its potential to do work) and the end-use (the work needed to achieve it) and (2) irreversibilities in the process itself. Societal exergy studies are undertaken at the various stages along the energy flow, namely primary, final and useful energy. The final to useful conversion is related to the way energy is used to provide an end-use, such as heat, movement or light. Cooling is an important end-use category in Portugal. The effect of the introduction of cooling on the aggregated efficiency of Portugal, shown, was 3.4 percent in 2009 and has been increasing. A disaggregation of the heating efficiencies by energy carrier is undertaken, to assess if this level of detail is relevant in a useful exergy analysis.
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