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Pine cones inspire self-adjusting shades for houses

(Credit: Grempz/Flickr)

Researchers have created a new shading system that adjusts independently over the course of the day, without any sensors or motors. This largely maintenance-free system also runs without electricity, making it an alternative to motor-driven shades.

It gets hot in the city in summer, and buildings in direct sunlight get particularly warm. At night, it can then be difficult to get rid of that accumulated heat. These days, many people dream of efficient air conditioning. Chiara Vailati dreamed of creating an adjustable and autonomous sunshade for houses as a way to reduce the amount of heat that enters a building and, therefore, the need for cooling.

“I wanted the system to be made of environmentally friendly materials, use very little energy, and have low installation and maintenance costs,” says Vailati, who designed the system during her doctoral studies at ETH Zurich’s Institute for Building Materials.

Inspired by pine cones

The design uses shade-producing wooden planks and requires no sensors or motors—or even electricity. However, it does still change to suit to the weather conditions: the planks move autonomously.

“Like its natural model, the double layers of wood make use of changes in humidity throughout the day.”

Multiple pairs of planks aligned in parallel create a kind of roof that opens and closes itself. The construction can be placed, for example, horizontally over a window on a building’s facade.

“We were inspired by pinecones when it came to the autonomous movement of the planks,” says Vailati. The scales of pine cones react to changes in humidity. For example, if the humidity decreases, the scales bend and move from a straight to a curved shape—so the cone opens in dry weather. It is the cone’s structure that makes this possible because the scales consist of two connected layers that contract to different degrees as the humidity decreases.

Responsive materials

Vailati transferred this operating principle to bilayered wooden planks. The layers consist of different kinds of wood, whose fibers are also oriented perpendicular to each other.

“Like its natural model, the double layers of wood make use of changes in humidity throughout the day,” explains Vailati. In the humid morning air and at night, the planks are flat and vertical, while at midday, when the sun is high and the air is drier, they bend noticeably and thus provide shade.

This apparently simple idea required years of research. Vailati had to master two challenges in particular. First, it was necessary to increase the initially very small bilayer structures to the standard plank length of half a meter, without the material deforming uncontrollably.

Second, the system reacted too slowly compared to conventional motorized planks. “I had to find a way to accelerate the bilayer kinetics,” says Vailati. Striped patterns in the wood and a finely adjusted ratio of layer thicknesses helped to speed up the movement.

Finally, Vailati made use of her experience as a civil engineer: to increase the amount of shade, she coupled the bilayered planks. “That significantly increased the reaction time,” she says.

ETH Zurich patented her invention. The work has appeared in the journals Energy in Buildings and Materials and Structures.

Source: Michael Keller for ETH Zurich