A large percentage of a building’s energy usage is consumed by heating and cooling, but a new dynamic shading system designed by researchers at the University of Toronto could help. Inspired by the skin of krill, the system uses cells of blooming pigment that can block light on demand.
Krill are tiny marine organisms that are usually transparent, but have the ability to move pigments around in the cells beneath their skin, allowing them to turn darker to protect themselves from UV damage in bright sunlight. This, the UToronto team reasoned, would be a useful ability for windows and building facades to have.
The team's krill-inspired prototype is made up of optofluidic cells that can switch between transparent and opaque on demand, using relatively little energy. Inside the cell is a 1-mm layer of mineral oil between two sheets of plastic. To make it turn darker, a small amount of water containing a pigment or dye can be injected into the cell through a connected tube, creating a “bloom” of the darker color.
The more pigment that’s pumped in, the bigger the bloom, and the flow rate can dictate the shape it creates. Low flow rates make for a circular pattern, while higher rates produce branching tree-like structures. The pigment can later be pumped back out to return the cell to its transparent state.
“We’re interested in how ‘confined fluids,’ of green, sustainable chemistries, can be used to change material properties,” said Ben Hatton, lead author of the study. “It’s very versatile: not only can we control the size and shape of the water in each cell, we can also tune the chemical or optical properties of the dye in the water. It can be any color or opacity that we want.”
The team envisions a network of these optofluidic cells being used in windows or building facades as a low-energy temperature regulation system. In the heat of a summer’s day, the cells could be switched to opaque to block sunlight, before switching back to transparent when the Sun goes down.
The researchers modeled how well such a system might work at building scale, and compared the potential energy savings to two other systems – motorized blinds, or electrochromic windows, which use voltage changes to change the transparency of a glass coating.
“What we found is that our system could reduce the energy required for heating, cooling and lighting by up to 30% compared with the other two options,” said Raphael Kay, corresponding author of the study. “The main reason for this is that we have much finer control over the extent and timing of solar shading. Our system is analogous to opening and closing hundreds of tiny blinds at different locations and times across a facade. We can achieve all this with simple, scalable and inexpensive fluid flow.”
The team also says that optofluidic displays could be used to create large-scale works of art.
The research was published in the journal Nature Communications. The cells can be seen in action in the video below.
Source: University of Toronto
