From Thermodynamics to Economics and Ecology - Thanatia: The Destiny of the Earth's Mineral Resources - page 73

sensitive to quality, the problem is that its units (energy/temperature) are not very
practical. As with energy, it only provides one dimension. In fact both properties:
energy and entropy are required for analysing a process in its entirety.
Although exergy is also a one-dimensional property, it incorporates both sets
of information. It has energy dimensions and is sensitive to both the quantity and
quality of the energy exchanged. Hence, exergy is a good candidate for the measure-
ment of cost. As a concept, it participates in all cost characteristics: it is additive
and can be calculated in all flows interacting within any manufacturing process. It is
not a function of how much one appreciates things but a function of the quality and
quantity of useful energy that could be expended throughout the system. Its most
important contribution is its ability to objectify all the physical manifestations in
energy units, independent of their economic value. Thus any product, any resource
or any waste or polluting emission can be objectively evaluated from an exergy per-
spective. Exergy measures the minimum quantity of useful energy required to form
a system from its constituent elements found in the Reference Environment (R.E.).
Once the R.E. has been defined, the minimum thermodynamic cost or exergy of any
material or energy flow can be calculated. Accordingly, exergy takes into account
all physical manifestations that differentiate the system from its environment - the
height, velocity, pressure, temperature, chemical composition, concentration, etc.
As discussed previously, conventional Thermodynamics states that the exergy
balance accounts for the degradation of the exergy whereby the incoming exergy
will be always greater than the outgoing one:
Exergy Input - Exergy Output = Irreversibilities > 0
Yet this expression only points out the existence of irreversibilities within a
process. So it is for Thermoeconomics to take it a step further by including in
the equation the concept of purpose by means of an e ciency definition. There is
after all, an implicit classification of those flows crossing the system boundary: the
production objectives, P, the resources required to carry out the production, F,
and those that are residuals or wastes, R.
One should not however just associate the resources with input flows, nor the
products solely with output flows. One must instead have a clear idea of what is to
be produced before e ciency is defined. Such information is not itself implicit in
the Second Law and is in fact the most important conceptual leap separating and at
the same time connecting Physics to Economics. Therefore results stemming from
Thermoeconomics will always depend on what the designer wants to produce. Even
the physical cost, unlike exergy, becomes an anthropic concept.
From this moment on, the authors move beyond the field of objective Physics
and put into the heart of Thermodynamics the very concept of purpose. In an
Aristotelian sense, F is the “causa materialis”, or that from which something else
arises, and P is the “causa finalis”, or the end, the reality towards which something
tends. The principle of change, or “causa eficiens” is embedded in the inexorable
degradation of natural resources, quantified in term I. At the very end the “causa