Environmental and economic requirements put increasing pressure on the building industry concerning energy efficiency and sustainable technical solutions. Climate adaptive building shells (CABS) may well provide significant energy saving and improve the indoor environmental quality of buildings. Nowadays, the responsiveness of CABS commonly relies on extrinsic control and motorized systems based on thermal or optical stimuli. In our project we aim at developing a novel CABS system, which is based on smart wooden actuators. Wood undergoes reversible anisotropic dimensional changes due to the uptake and loss of water when exposed to changes in relative humidity. By using bilayer elements with perpendicular fiber orientation, the dimensional changes result into reversible bending movements.
In nature, deformations of several biological structures such as pine cones, orchid seed pods and wheat awns are based on this mechanism. Due to the hygroscopy of the tissues, they react to the change of the relative humidity by bending or twisting (depending on the tissue fiber disposition).
In a CABS, such wooden actuators would respond to and take the energy for the movement from the daily change in relative humidity, which is driven by the sun. The challenge is to upscale the size of such bilayers and to optimize the geometric configuration and assembly-pattern of these elements to maximize the amplitude of bending.
Minimization of the response time, is achieved by enlarging the surface to volume ratio by milling stripes into the active beech layer. This leads to a higher rate of sorption and desorption and, thus, to higher curvature in shorter time compared to bilayers without milled stripes. The final goal is the implementation of such wooden bilayers in autonomous humidity-driven CABS systems such as shading systems for building facades