Thursday 2 February 2023

Liquid windows: Energy-saving inspiration from squid skin

FEBRUARY 1, 2023, by Tyler Irving, University of Toronto


Prototypes of a multilayered fluidic system designed by U of T Engineering researchers contain several layers of channels that contain fluids with various optical properties. 
Credit: Raphael Kay, Adrian So

Inspired by the dynamic color-changing skin of organisms such as squid, University of Toronto researchers have developed a multilayered fluidic system that can reduce the energy costs of heating, cooling and lighting buildings.

The platform, which optimizes the wavelength, intensity and dispersion of light transmitted through windows, offers much greater control than existing technologies while keeping costs low due to its use of simple, off-the-shelf components.

"Buildings use a ton of energy to heat, cool and illuminate the spaces inside them," says Raphael Kay, who recently graduated with a master's degree in mechanical engineering from the Faculty of Applied Science & Engineering and is lead author on a new paper published in the journal PNAS.

"If we can strategically control the amount, type and direction of solar energy that enters our buildings, we can massively reduce the amount of work that we ask heaters, coolers and lights to do."

Currently, certain "smart" building technologies such as automatic blinds or electrochromic windows—which change their opacity in response to an electric current—can be used to control the amount of sunlight that enters the room. But Kay says that these systems are limited: they cannot discriminate between different wavelengths of light, nor can they control how that light gets distributed spatially.

"Sunlight contains visible light, which impacts the illumination in the building—but it also contains other invisible wavelengths, such as infrared light, which we can think of essentially as heat," he says.

"In the middle of the day in winter, you'd probably want to let in both—but in the middle of the day in summer, you'd want to let in just the visible light and not the heat. Current systems typically can't do this—they either block both or neither. They also have no ability to direct or scatter the light in beneficial ways."

Developed by Kay and a team led by Associate Professor Ben Hatton, the system leverages the power of microfluidics to offer an alternative. The team also included Ph.D. candidate Charlie Katrycz, both in the department of materials science and engineering, and Alstan Jakubiec, an assistant professor in the John H. Daniels Faculty of Architecture, Landscape, and Design.

The prototypes consist of flat sheets of plastic that are permeated with an array of millimeter-thick channels through which fluids can be pumped. Customized pigments, particles or other molecules can be mixed into the fluids to control what kind of light gets through—such as visible versus near-infrared wavelengths—and in which direction this light is then distributed.

These sheets can be combined in a multi-layer stack, with each layer responsible for a different type of optical function: controlling intensity, filtering wavelength or tuning the scattering of transmitted light indoors. By using small, digitally controlled pumps to add or remove fluids from each layer, the system can optimize light transmission.

"It's simple and low-cost, but it also enables incredible combinatorial control. We can design liquid-state dynamic building facades that do basically anything you'd like to do in terms of their optical properties," Kay says.


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