Transitioning from neutral to active positions and back
Images courtesy TBM Designs Transitioning from neutral to active positions and back

Attempts to mitigate solar heat gain and glare through glass curtain walls often involve electrified systems such as automatic blinds, active fritting, or tinting controlled by sensors and software. However, Doris Sung, Assoc. AIA, co-founder of New York– and Los Angeles–based TBM Designs, associate professor at the University of Southern California, and principal of Do|Su Studio Architecture has an elegant, new solution that relies on nothing but the mechanical properties innate to its materials. InVert Self-Shading Windows is Sung's latest exploration into thermobimetals, the subject of her two previous ARCHITECT R+D Award–winning projects: an active façade and a self-assembling structure.

This product is like a sunflower, mimicking nature. I loved that it uses thermobimetals and phase-change materials to make the action happen, which is super simple and super organic.

—Juror Steve McDowell, FAIA

Thermobimetals consist of two different alloys laminated together. Because the two metals expand at different rates, the laminated sheet curls in different directions when heated or cooled, predictably and repeatedly, and with no degradation. Designed to be sealed within the cavity of an insulated glass unit, the InVert system consists of an array of bimetal pieces mounted on a stainless-steel network grid. When sunlight hits the window, the individual bimetal pieces warm and begin to curl, flipping into a new orientation that blocks the direct light.

After experimenting with 50-plus shapes and sizes for the pieces, Sung and her team settled upon a 0.0027-inch-thick notched ellipse that resembles a pair of butterfly wings. “The shape and size of the pieces are based on the performance of the material to curl and behave the way we want it to, and the performance of the system to block the right amount of sun,” Sung says. The angle of the V-shaped opening in which each piece sits controls the degree to which the piece can invert, allowing custom tuning for different climates and exposures.

The thermobimetal pieces invert due to thermal expansion and contraction of the alloy composite.
courtesy TBM Designs The thermobimetal pieces invert due to thermal expansion and contraction of the alloy composite.
Hardware and installation process of the InVert Self-Shading System inside an insulated glass unit.
courtesy TBM Designs Hardware and installation process of the InVert Self-Shading System inside an insulated glass unit.
A stainless-steel network grid determines the density and inverting range of the bimetal pieces.
courtesy TBM Designs A stainless-steel network grid determines the density and inverting range of the bimetal pieces.

TBM’s InVert system also preserves the color spectrum of incoming daylight, which researchers have linked to occupant wellness. It offers a visible light transmission level between 60% and 70%, and a solar heat gain coefficient of 0.37 when used with low-iron glass; use with coated glazing would bring the SHGC under 0.25.

Following a successful field test of two prototypes, Sung intends to manufacture the windows for the commercial market. The bimetal sheets, which were laser-cut for the prototype, will be die-stamped and shipped to a local IGU fabricator for new or retrofit curtain wall and storefront installations.

Rendering of full-scale installation
courtesy TBM Designs Rendering of full-scale installation
Early studies to balance between solar heat gain reduction and visibility
courtesy TBM Designs Early studies to balance between solar heat gain reduction and visibility
Geometry optimization of the individual thermobimetal pieces
courtesy TBM Designs Geometry optimization of the individual thermobimetal pieces

Project Credits
Project: InVert Self-Shading Windows
Company Name: TBM Designs, Los Angeles and Katonah, N.Y.
Architect/Designer/Inventor: Doris Sung, Assoc. AIA (DOSU Studio Architecture founder, University of Southern California associate professor, and TBM Designs co-founder)
Product Development Team: Justin Kang, Adelfrid Ramirez, Esther Ho, Stephanie Truong, Assoc. AIA, Lisa Phillips, Hung-Ming Chen, Rene Zarate, Thomas Gin, Belinda Pak, Assoc. AIA
Insulated Glass Unit Manufacturer: Triview Glass Industries (closed); Pulp Studio
Sales and Manufacturer: TBM Designs