RE: [Fis] Exergy analysis and ascendancy

From: by way of Luis Serra <ebotero@logos.upb.edu.co>
Date: Fri 05 Dec 2003 - 14:48:53 CET

Dear Luis
Dear All,

Luis, I have seen your interesting posting and I would like to add some comments.

Actually, the Exergy Replacement Cost is our proposal (Valero and me) in order to evaluate the physical cost of natural resources based on Second Law of Thermodynamics. However, in agreement with Valero, the evaluation of physical cost of natural resources is a very complex task: for instance, what is the thermodynamic value of a forest? Of course the wood can be used for producing energy, but what about the ecological functions and services provided by a forest: oxygen production, soil protection, climate regulation…?

Up to now, the way we have found for evaluating those functions is comparing the resources that humans would consume, with the present state of the art of technology, in case they would substitute for nature. This approach also presents the problem of technological efficiency, which is far away from the theoretical (thermodynamic) maximum.

I think that the comparison with respect to the equilibrium state is a good reference for establishing the ecological limits and the carrying capacity of the Planet. In agreement with Valero and Naredo, this procedure should be internationally accepted in order to measure the distance of ecosystems with respect to the equilibrium.

In my opinion, one of the most important key aspects is the production of mixtures. Industrial pollution basically is provoked by mixtures of low concentration, most of them non-reactive i.e. stable since a chemical viewpoint, and as a consequence very difficult to be separated. In some cases the damage could be measured through the entropy generation, or the exergy destruction, which is very similar. In my opinion, if a good (comprehensive) evaluation method could be developed, this could be a good measure of the pollution damage provoked to the Planet.

Moreover, applying Life Cycle Assessment methodology, the damage provoked by the consumption of natural resources with high exergy content and the effect on the sinks (atmosphere, rivers, oceans, soil…) could also be evaluated through the entropy generated by the resulting mixtures. Again, I think, that it would be a good measure of the environmental impact on the Planet.

There is a lot of work to do yet regarding the distance of ecosystems to the thermodynamic equilibrium, and the function that ecosystems perform in the address of reducing the entropy generated by humans. This could be roughly the measure of the carrying capacity. However, it remains full of unanswered questions. For instance, what happens with non-renewable resources? What is the appropriate velocity of their consumption?

Greetings to all

Edgar Botero

(English version from the Spanish original by Luis Serra)