"Like a Cactus in the Desert"... Building Opens Windows by Itself to Control Temperature

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[Asia Economy Reporter Kim Bong-su] Like a cactus that survives in harsh deserts by opening and closing its stomata, a moving building with windows or exterior walls that open and close automatically according to temperature has been developed by Korean researchers.

The National Research Foundation of Korea announced on the 29th that Professor Lee Hwang's research team at Ajou University developed an architectural envelope (shading) module that automatically moves in response to temperature changes through 4D printing of smart materials.

Energy used for heating and cooling buildings accounts for the largest share among non-industrial sectors. To address solar heat gain through external windows, an exterior system that automatically opens and closes the building's facade as needed is required. The research team took inspiration from the stomatal opening and closing mechanism of cacti that thrive even in harsh deserts. The developed composite module smoothly unfolds at high temperatures to block heat and sunlight, and automatically reopens at comfortable temperatures to allow air and light in, thereby regulating the indoor environment. Although there have been previous attempts using smart materials that change shape according to temperature, their shape recovery ability to return to the original form was low.

The research team used shape memory materials that restore their form according to temperature, rather than mechanical systems like electromagnetic motors that involve noise, vibration, and complex electronic circuits. These materials have a shape memory effect (where the material's structure changes due to chemical reactions, temperature, light response, etc.). One such shape memory alloy, Nitinol, has been experimentally used in medical stents and automobile air conditioning devices.

By utilizing distinctive materials and 4D printing design, the team proposed a method to reduce indoor cooling loads, and they expect it can also be applied to road noise barriers and solar panels.

The research team combined nickel-titanium alloy wire, which has low deformation (within 6%) but high recovery, with shape memory polymers that have low recovery but can deform freely (up to 800%), raising the deformation rate to about 20%. They succeeded in creating a composite that repeatedly recovers and deforms on its own without external force. By proposing changes in exterior materials using 4D printing, they significantly reduced manufacturing complexity. It is expected to contribute to producing various types of moving exterior modules at low cost.

The results of this study were published on the 8th in the international academic journal in the architecture and construction field, ‘Journal of Building Engineering’.

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