Buildings use a lot of energy to heat, cool and light the indoor environment when outside conditions change. Designing building facades that can instantly achieve versatile climate control could significantly reduce this energy footprint.

Currently, certain ‘smart’ building technologies are already available, such as automatic blinds or electrochromic windows – which change their opacity in response to an electric current. But these systems are limited — they can’t distinguish between different wavelengths of light, nor can they determine how that light is distributed spatially.

Now a team of researchers from the University of Toronto – led by Prof. Ben Hatton – has developed a multi-layered fluid system that can reduce the energy costs of heating, cooling and lighting buildings by optimizing the wavelength, intensity and dispersion of light passing through windows are allowed through.

The platform is inspired by the dynamic color-changing skin of organisms such as squid, squid and krill. It offers much more control than existing technologies, while keeping costs low through the use of simple, ready-to-use components.

The prototype “liquid window” contains several stacked sheets of transparent plastic permeated by a series of millimeter-thick channels through which liquids can be pumped. Custom pigments, particles or other molecules can be mixed into the fluids to determine what kind of light passes through them – such as visible versus near-infrared wavelengths – and in which direction this light is then scattered.

These sheets can be combined into 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. The fluid window system can optimize light transmission by using small, digitally controlled pumps to add or remove fluids from each layer.

Using computer modeling based on the physical properties of each prototype, the scientists were able to analyze the potential energy impact of covering a hypothetical building with this type of dynamic facade. The team also simulated different control algorithms for activating or deactivating the layers in response to changing environmental conditions.

“If we had just one layer that focuses on modulating the transmission of near-infrared light – so not even touching the visible part of the spectrum – we could save about 25% annually in heating, cooling and lighting energy over a static baseline,” says recent college graduate Raphael Kay, lead author of a new paper. “If we have two layers, infrared and visible, it is more than 50%. These are very significant savings.”

“Buildings use a lot of energy to heat, cool and light the spaces in them,” says Kay. “If we can strategically control the amount, type and direction of solar energy entering our buildings, we can vastly reduce the amount of work we put on heaters, coolers and lighting.”

Magazine reference:

  1. Raphael Kay, J. Alstan Jakubiec, Charlie Katrycz, and Benjamin D. Hatton. Multi-layer optofluids for sustainable buildings. PNAS, 2023; DOI: 10.1073/pnas.2210351120