Nature can teach us all kinds of things about dealing with the elements, but little is applied in the design of modern facades. Take a butterfly, a cactus or a bird as an example to improve building physics, says facade researcher Susanne Gosztonyi in her PhD research.

A butterfly wing is not only super light and thin, it is also robust and resistant to the heat of sun rays. This is partly due to its geometry: the blood vessels that run through it are arranged in such a way that heat is quickly dissipated. In addition, a refined nanostructure gives the wings their colors. This “photonic” structure ensures reflection or absorption of light and also regulates heat. ‘The arrangement of light and dark colors next to each other creates thermal flows,’ says Gosztonyi. ‘This supports the wings to act as a heat exchange system. Applying such an ingenious system to a building could effectively help regulate energy efficiency.’
Unfortunately, it is technically and financially difficult to replicate a butterfly wing. But some of the principles behind it can be applied in architecture. Gosztonyi discovered that the precise position of the wings also plays a role in energy management. Together with color shades, the wing position increases heat flow. ‘And that's something that we as architects can mimic with existing resources,’ she says. ‘Blinds can be positioned in a certain position relative to a cooler surface using the sky view factor and can dissipate excess heat that way more effectively.’ Adding color with certain emissivity could further enhance this effect.

Physics

The “butterfly cooling system” is just one of nature's clever strategies that she explored in her PhD study “Physiomimetic Facade Design. Systematics for a function-oriented transfer of biological principles to thermally-adaptive facade design concepts”. In her research, Gosztonyi looks at the physics behind natural forms and at the ways plants and animals deal with heat and cold. What thermodynamic tricks do they use to avoid overheating or undercooling and how do they save energy?

Process "butterfly cooling system"

These are interesting questions for a facade researcher, because most modern facades respond much less flexibly to the challenges of the climate than animals and plants. To keep out the cold, building facades often have a thick layer of thermal insulation, but this makes it difficult to get rid of excess heat in the warm months. Canopies and awnings help a little, but active control of thermal insulation would be much more effective.
Nature provides excellent examples of how such materials can be improved, both on the nano and macro scale. In her research, Gosztonyi identified about seventy examples for cooling effects from her collection of more than two hundred, some of which she examined more closely. She discovered, for example, that the alpine plant Edelweiss has a special hairy layer to deflect harmful UV radiation high in the mountains, while cacti shade themselves with their ribbed geometric shapes supported by needles and hairs. Birds have the habit to plum up their feathers when it is cold. This way they create an extra still layer of air in the down layer under their vaned feathers, and thus adapt the thermal insulation.
Can these kinds of biological techniques be used in a facade design without sophisticated materials? Not always, many strategies from nature are technically too complex to imitate. Geometric form effects on macroscale are easiest to copy. Nevertheless, Gosztonyi checked whether the adaptive thermal insulation principle of the feathers can be applied instantly in architecture by using flexible geometries made of cellulose with adaptive cavities in a facade. These could swell or shrink when the air gets warmer or colder. Rough calculations showed that standard polyurethane insulation cannot simply be replaced by such a structure: the required thickness of this insulating cellulose geometry would double. ‘But a different material or geometry might work out better,’ says Gosztonyi. ‘Certainly, a better understanding of the physics behind the natural phenomena will give us new glasses to look at building physics.’

More information

Susanne Gosztonyi will defend her PhD thesis 'Physiomimetic Facade Design' on 30 May.

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