Windows are critical for improving building energy efficiency. Over a quarter of a building’s energy is lost through today’s glass-pane windows. Now, drawing inspiration from the color-changing skins of squids and krill, researchers have designed liquid-filled panels that dynamically change how they let light through. Retrofitting windows with these panels could cut the energy costs of heating, cooling, and lighting buildings by well over 40 percent, they say.
Krill and squid mechanically move pigments in their skin to actively change their skin’s appearance. The device emulates that by moving various liquids—dye solutions, glycerol, and carbon powder suspensions—through channels carved into thin plastic sheets, says Benjamin Hatton, a professor of materials science and engineering at the University of Toronto. “It’s an advantage that this approach can use simple, relatively inexpensive, non-toxic, aqueous fluids.”
Buildings consume about a third of the world’s energy, and that footprint is expected to double by 2050. Making existing and new buildings more energy efficient is going to be imperative if countries are to meet their emissions-reduction goals.
Researchers have been working on passive technologies that can reduce energy loss without using power. Window coatings that block the sun’s infrared rays or keep heat from escaping, for example, can reduce the cooling burden on air-conditioners.
Smart windows that change their optical properties in response to a trigger offer more precise control over indoors conditions. Examples include windows that darken or become cloudy when triggered by electricity or by the sun’s heat.
The University of Toronto team wanted to make such a dynamic system using simple, low-cost components. They sandwiched together three thin Plexiglass sheets, each containing roughly 2–3mm high channels patterned into it. Through each layer, the researchers pump various fluids: water-based dye solutions or glycerol that absorb light of certain colors; carbon pigment suspensions that control light transmission; and titania nanoparticle suspensions that direct the light passing through. “The net effect on light transmission is through the additive effects of the combined layers,” Hatton says.
The researchers conducted experiments and ran whole-building computer simulations to see how the squid-inspired windows improve building energy performance. They calculated estimated annual savings of 75 percent on heating energy, 20 percent on electricity for lighting, and 43 percent on total energy use compared with the best available darkening windows on the market today. The energy saving would be even higher when compared to plain glass windows, he says. The work appears in the journal Proceedings of the National Academy of Sciences.
Hatton says that the movement of fluids through the windows could be digitally controlled using solar electricity. The panels are only 30 x 30 cm right now, but he says they are working on larger scale designs. “There’s a real need for smarter, dynamic buildings, so we hope this work might stimulate some new design thinking.”
Source: Raphael Kay et al. Multilayered optofluidics for sustainable buildings. PNAS, 2023.
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