Biomimicry#03: Self-Shading Window that Blossoms like a Flower
- Gregers Reimann
- 2 days ago
- 3 min read
Imagine a timelapse of a flower that unfolds it petals when it by sunlight. Imagine a building window doing the same. Yes, it is an actual building product, the InVert window, which comes with a pattern of "flower petals" consisting of small slim bimetallic metal strips placed in the air-gap of the double glazed window. When the hot sun starts to hit the window, almost like magic, the "flower petals" move to face the sun hereby shading the window.
How is that possible? What makes the "flower petals" move? The movement comes from laminating two metals together, each of which has a different thermal expansion coefficient. When the temperature changes, one metal expands faster than the other, and the bimetallic metal strip starts to curve. Most of us already know the principle, namely from bimetallic coil thermometers:
Measurements
We undertook a number of temperature and light level measurements to monitor and document the performance of InVert self-shading window sample (30x30 cm) that the inventor, Doris Sung (TBM Designs), kindly shared with us.
We also set up a GoPro camera to record timelapse videos. In order for the camera not to run out of battery, it was connected to a USB power socket. A couple of the best timelapse videos are included for this article.
The above video shows how the Invert shading elements remain open during overcast weather conditions, and quickly close once exposed to direct sunlight. A biomimicry design emulating the movement of flowers and plant leaves.
The graph below shows the light and temperature measurements for two successive dates with very different weather, namely an overcast day (4 Aug) and a sunny day (5 Aug). We tried determining the temperature at which the bimetallic shading strips move from closed to open position. As we were unable to measure the temperature inside the sealed air gap of the InVert double-glazed window, we instead measured - as a proxy - the surface temperature of the external and internal surface of the InVert window sample.
The above measurements show that the InVert window temperature increases on sunny days with the external and internal window surface temperatures reaching about 50°C and 40°C, respectively. For comparison, on an overcast day both temperatures only reach about 30°C, which is insufficient to activate the bimetallic shading strips.
Interestingly, the overcast day has a short 6 minutes period of direct sunlight around 10 am, but it is insufficient to heat up the window panes. While the thermal capacity of the bimetallic blinds is low, hence, giving it a relatively fast reaction time, the timelapse video shows that blinds did not move.
This highlights a potential weakness of the InVert self-shading blinds, namely the delayed reaction time of the blinds. While such 5-10 minute delay in reaction time is acceptable for building spaces like lobbies, corridors, exhibition halls, it becomes more critical for spaces with fixed location occupancy like offices, where sitting in direct sun for more a minute likely will not be deemed acceptable, at least not in the tropics.
We look forward to making use of the innovative and beautiful InVert Self-Shading window in one of our tropical building projects, insofar we can find the right client. So, stay tuned for future updates on this biomimicry inspired window shading system!
References and acknowledgements:
DO|SU STUDIO ARCHITECTURE by Doris Sung and team DOSU is developing smart materials, such as thermobimetals, to self-ventilate, sun-shade, self-structure and self-assembly in response to changes in temperatures--all with zero-energy and no controls. Website: https://www.dosu-arch.com/
Download the measured temperature and light measurements by IEN Consultants (TXT and XLSX file formats available below)
Many thanks for Doris Sung, founder of DOSU and inventor of the InVert Self-Shading window, to send us the product sample that was studied in this article
Also thank you to Charles Loo (IEN Consultants) for assisting with the temperature and light measurements and datalogging of the InVert window.
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