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Sustainable Design

DRAFT Currently, this is a summary page of other documents pertaining to sustainable design.

Points of interest

  • 90% of resources taken from the earth become waste within three months [Cha05].

Bio-inspired design

One emerging area of interest in design theory and methodology is that of design inspired by nature. Of course, nature doesn't “design,” but it does achieve the same ends - the development of increasingly complex biological structures that tend to interact with one another to the mutual benefit of all participants. We know that there's something beneficial going on because life has continued to spread (the only alternative is extinction) and become more complex at the same time, and life has been around on Earth for over three billion years - so it's got quite an established track record.

There is an entire field of research here, that cannot be distilled into one section of one web page. However, there are some particularly interesting points of interest worth mentioning.

Energy and information

Consider the following two images, taken from [VBB06]:

Copyright © 2006 The Royal Society - A diagram relative resource consumption/allocation by nature at different scales.

Copyright © 2006 The Royal Society - A diagram relative resource consumption/allocation by engineered artifacts at different scales.

Notice the difference between how organisms and how artifacts use energy and information. Artifacts are designed to require (much) more energy than information, whereas the opposite is true in organisms1).

This tells us that if we want to mimic nature because nature is so successful, then we need to look at how we use energy and information.

Leaves and solar panels

Consider how a flower or a leaf turns to face the sun (called phototropism), which maximizes the amount of energy the organism can receive by keeping the broadest possible surface (roughly) orthogonal to the incoming solar light. The sun's light itself causes chemical changes that result in changes in the shape of the plants cells on the unlit side of the plant. Note that, all else being equal2), it is unavoidable that the plant acts that way because that is the only physical way it can behave. In this case, the key resource is information - that is, then information “coded” in the molecules of the plant that amount to instructions on how to change the plant's shape to achieve a goal of facing the sun. The amount of energy needed to do this is relatively minor3).

Now consider how we might typically turn a solar panel to track the sun. Notice that we would want the panel to track the sun for exactly the same reasons that a leaf turns to follow the sun. We would have a separate sensor on the panel that identifies the sun's position in the sky; we would then have an entirely separate, energy-consuming system of computing what should be done (a controller); we would then install a series of energy-consuming motors and actuators that force the panel to change its orientation. Even though the panel would naturally be hinged to permit the movement, we are still forcing it to move, because without the motors, the panel would just fall limply to its “natural” (!!) resting position.

While some have suggested that solar panels are “natural” like leaves, there really isn't anything natural about it. We have designed solar panels to require a whole other system to constantly force it to do what we want, yet something as “stupid” as a leaf can do it all by itself.

Exercise for the reader Can you come up with a more “bio-inspired” design for orienting the solar panel?
(Please think about it before clicking the “Here's an idea” area below to read about one answer to this question.)

<hidden Here's an idea.> A shape-memory allow is a metal the shape of which changes by itself when exposed to changes in temperature4). The sun produces heat as well as light. We might use shape-memory alloys in the actual structure of the solar panels, so that the panel's supporting structure will literally change shape and cause it to follow the sun.

This has actually worked on spacecraft. Can you imagine why we're not doing it yet for conventional earth-based solar panels? </hidden>

Human veins

There are “valves” in your veins, tiny flaps that will close automatically if you suffer substantive blood loss on the side of the valve furthest from your heart. What's really neat about them is that they require no neural activity whatsoever to operate. That is, if your hand is accidentally cut off, then all the valves in the severed veins will close without being directed to do so by any part (conscious or otherwise) of your brain. This works because of the physics of the valves. The vein/valve structure has certain mechanical properties. These properties are such that when operating normally the veins open and close on each heartbeat to prevent backflow of blood. They do so because they cannot do otherwise; their natural response to the forces exerted on them by the flowing blood is such that the loads exerted on the valve causes it to open and close just so that backflow is prevented. Incidentally, when there is a massive drop in blood pressure “downstream” of the heart, the very same effect causes the valves to close tightly.

The important point here is that the valve requires no sensors, no actuators, and no controllers to operate. It is a one-trick pony - it opens and closes in response to changes in surrounding pressure, and it does so “naturally.”

An interesting case of bio-inspired design arising here is documented at Nature magazine.

Design Principle

Based on the foregoing (and other similar cases reported elsewhere), one may propose the following design principle for bio-inspired design:

Design principle Design artifacts that produce desired effects by responding naturally to their environment; use no sensors, actuators, or controllers.

See Also

References

Cha05. a J. Chapman. 2005. Emotionally durable design. Objects, experiences, and empathy. London: Earthscan.
1)
Note that at large scales, artifacts tend to use little energy and information because we just don't make huge things that are particularly “intelligent.” That's why substance and structure are most important for huge artifacts. Compare this to how organisms and natural systems use structure and substance at large scales.
2)
and thanks to climate change and pollution, all else is no longer equal
3)
It's not as if a whole tree bends towards the sun; only its leaves do that.
4)
There are also other types of materials besides metals that can dynamically change shape in response to external stimuli.
design/sustainable_design.txt · Last modified: 2020.03.12 13:30 (external edit)