A self-regulating device passively activated by an SMA for solar responsive shading

The heating and cooling of buildings consume a significant amount of primary energy contributing to global CO2 emissions. A changing climate and energy security concerns are challenging the construction sector to explore novel passive low-energy design solutions for which facades with adaptive properties in response to the prevailing dynamic environment could contribute to reducing the energy demand for cooling in buildings.

A rotational two-state device is presented for operating a facade system to either provide shading under direct sunlight or daylight under overcast conditions. The device is enclosed in a glazed tube supported on a pivot around which the shading system rotates. A Ni-Ti SMA actuator displaces the device's centre-of-mass either side of its pivot point in response to solar energy availability, which is amplified by the greenhouse effect.

Two concurrent models were developed to simulate the device’s thermal-to-mechanical energy conversion: a solid geometry mechanical CAD model of the joints between components together with a thermal network model.

The device and the building facade share exposure to the available solar energy, when the device's self-regulated response operates the facade shading it mitigates the risk of the building overheating and allows beneficial daylight access under overcast conditions while deactivated.

Results from observational studies of a proof-of-concept prototype under realistic conditions verified the two-state function of the device's mechanism predicted by the thermal and mechanical models. The result of the design, methodology and prototype contributes toward establishing the potential for SMAs as sensor-actuators in facades to promote a more sustainable architecture.