Talk:Exergy: Schneider/Sagan

From Patterns

Insights, Round 1

--Norbert 18:33, 2 February 2008 (EST)

Schneider/Saga spin a fascinating tale, suggesting that "nature abhors a gradient" is a driving force behind the development of complexity, evolution and ecosystems. Unfortunately, he sometimes does not 'connect the dots' and is not as exact with terminology as I would like. The gist of the argument is that resource gradients build up when energy flows through a system, due to limitations in the rate at which the energy can be dissipated. Complex structures emerge in many physical and chemical systems to degrade the gradient more thoroughly. For example, conduction is limited in how it can degrade energy because it is driven by random motion of atoms or molecules. Convection (organized motion) is much more efficient. Similar examples are seen in biology and ecology, based on the correlation between energy dissipation and organization/complexity. Energy quality (exergy) is key: the challenge is to degrade high quality energy into low quality energy (typically heat). This heat is often exported into the encompassing system, increasing entropy and balancing the reduced entropy due to greater organization within the system.

I found Schneider/Saga confusing about the rate at which gradients are degraded. He states that the 2nd law does not require that the gradient be degraded quickly. However, gradients and energy flows are all about rates - if you do not dissipate the energy fast enough, the gradient grows. I think there is confusion between energy dissipation and usage of other resources. The 2nd law talks about gradients imposed on a system. Schneider/Saga sometimes implies that biomass represents a resource gradient that can be dissipated through burning or decomposition, but my suspicion is that this outside the 2nd law (there may be a gradient that can be used, but the gradient is not the same as that imposed by incident solar radiation.

"Into the Cool" explores how mature ecosystems use cycling and storage to slow down the rate at which energy and other resources are consumed. I am not sure if this is due to NET or other factors (Schneider/Saga points out that survival is another imperative, sometimes at conflict with the 2nd law). The implication is that you are burn fast and flare out, or husband resources and last. Again, I suspect some confusion between different types of gradients. All resources on earth are constrained. However, energy resources are constrained not only due to quantity but also because processes using energy are often irreversible due to loss of energy quality (you can convert work to heat, but you cannot convert the heat to an equivalent amount of work). Material resources can technically be cycled indefinitely if you are smart enough (although material quality may play a part). On the other hand, linear processes or processes that cycle extremely slowly can make material resources unavailable. Maybe these questions will be resolved in the last part of the book.

I have a few ideas on what the 2nd law and NET might mean for designers - at the moment they are pretty vague and philosophical:

• there is a continuum between systems driven by the 2nd law imperative: physical, biological, natural and human
• most biological systems use non-heat pathways to manipulate resources and degrade energy
• ecosystems seem 'tuned' for endurance rather than sprints - Schneider/Saga hints at reasons but does not directly link back to the 2nd law or NET
• system resource 'cascades' are the norm, linear processes the exception
• we should look for 'enabling' (rather than 'point' solutions) - Ducks Unlimited focuses on wetlands, not directly on ducks

Insights, Round 2

--Norbert 23:44, 5 February 2008 (EST) I think I incorrectly distinguished between energy and non-energy gradients in 'Round 1'. Both can allow complex systems to emerge.

Insight	Implications	Questions/Complications
Many systems maintain themselves at some distance from equilibrium.	Most research is on equilibrium systems, which are a poor model of reality (in the case of living systems, equilibrium implies death).
Non-equilibrium systems are driven by energy gradients.	A gradient requires: an energy source, an energy sink, and some restriction that prevents free flow from source to sink.
Energy quality (exergy) is a measure of the energy gradient and is a key factor in how much work can be done.	It should be possible to calculate a maximum exergy value and determine the exergy efficiency of a process	Real systems often tap multiple gradients. For example, a ground source heat pump dissipates an electrical gradient to dissipate the gradient between the ground and ambient air temperature, and in the process heats or cools the building interior (creating a gradient). The heat pump is more efficient that resistive heating because it better taps the quality of electrical energy.
The 2nd law of thermodynamics can be restated as "nature abhors gradients".	Degradation of gradients does not need to be uniform throughout a system - entropy can be reduced locally as long as overall entropy increases.	Where do you draw the boundaries?
Complex systems appear to emerge that 'feed' off and thereby degrade these gradients more thoroughly that simple systems.	These systems locally reduce entropy, but increase entropy in the surrounding system	The mechanism by which these complex systems form is unclear. Schneider/Sagan claim "we naturally gravitate toward not coming to equilibrium - because by doing so we continue our gradient-reducing function." Are these two different forms of non-equilibrium?
Complex systems can embed many linked dissipative processes. Rainforests are cooler than deserts (reduce gradient between earth's surface and outer space) partly by creating clouds through transpiration (reflect more solar radiation into space), partly by capturing solar energy in biomass.	These interconnected cycles may explain how interdependence emerges without any overall plan.
Complex systems can create local gradients, which can spawn new complexity.	Other organisms can feed off the rainforest biomass, which is itself a gradient.	Although the observations are compelling, the principles underlying them are not clear. Where are the boundaries?
Real energy transformation processes are irreversible: work can be converted to heat, but heat cannot be completely converted back into work. On the other hand, materials can be recycled indefinitely (although it may require energy to decompose and reconstruct).	Energy may be inexhaustible (until the sun dies out), yet be a limiting factor.	Where does 'material quality' (Julian Vincent) fit in? Does preserving material quality reduce energy requirements?
These systems are active, rather than passive.	Streamlining is a passive; Fil found a reference that the bumps on humpback fins make the whale hydrodynamically unstable and therefore more maneuverable. Introducing a bit of turbulence on an airfoil can increase lift, at least up to the point of stalling. Each of these may be active examples of more effective gradient dissipation.
There are many different kinds of gradients. Heat seems to drive complex physical systems. Chemistry seems to drive biological systems.	Humans rely heavily on heat energy, or convert chemical energy into heat and then work.	What would the impact be if we switched to non-heat pathways? For example, use fossil fuels to drive fuel cells not internal combustion engines? Another approach is Julian Vincent's idea that we 'beat information out of materials and then use even more energy to put the information back in'.
Efficiency is only important if resources are constrained and there is competition for these resources.	It may be more important to look at what resources are available, rather than focusing on efficiency. McDonough argues that going slower in the wrong direction can help delay the inevitable, but only changing direction will get you where you need to go (effectiveness vs. efficiency).	How does one define and measure effectiveness? In Self-Organizing, Open, Hierarchical Systems, future states can be difficult to predict.
All gradient-dissipating systems export entropy into the surrounding system, ultimately as low-grade heat at (or near?) equilibrium.	All dissipative systems create 'waste' of some sort.	It would be great to see some examples, to help understand where the boundaries are.
Sustainable systems husband resources and last (at least until bad luck strikes). Unsustainable systems 'burn fast and flare out'.		It is not clear why most ecosystems appear to follow the former course. Kay states that survival can be counter to the 2nd law - maybe organisms/systems that 'do not play the game' simply disappear without a trace. Perhaps the restrictions inherent in renewable energy combined with co-evolution level the playing field, enforcing a degree of balance that we have managed to escape (for the moment).