Smart Windows Use Iron Nanoparticles to Harvest Heat

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Many of the previously dumb devices in our homes are getting smarter with the advent of internet-connected lights, thermostats, and more. Surely the windows can’t be smart, can they? A team of engineers from the German Friedrich-Schiller University Jena have created just that — a smart window that can alter its opacity and harvest energy from the sun’s rays.

There have been a number of “smart” electrochromatic window designs over the years, but these are mostly aimed at changing tint or opacity only. The windows designed by Friedrich-Schiller University researchers are vastly more functional. The so-called Large-Area Fluidic Windows (LaWin) design uses a fluid suspension of iron particles. This fluid is contained within the window in a series of long vertical channels. These “functional fluids” allow the window to change opacity, but also absorb and distribute heat.

The iron-infused fluid remains diffused until you switch the window on — the nanoparticles cloud up the channels and block light. When you flip the switch, magnets drag the nanoparticles out of the liquid to make the window fully transparent. When the magnet is switched off, the nanoparticles are resuspended to darken the panel. In general, the more nanoparticles you add, the darker the window becomes. You can even completely black it out with enough iron.

According to the designers, the greatest advantage of Large-Area Fluidic Windows is that they can stand in for indoor air conditioning systems. The suspended nanoparticles can harvest heat from the sun, transporting it to a heat pump elsewhere in the system (no electrical connections are needed inside the window). Alternatively, the heat can aid power generation or warming water inside the building. The total efficiency in terms of heat gain is similar to that of a modern solar thermal system for power production. For a building that has a mostly glass exterior, the LaWin windows could bring cooling costs down dramatically.

The designers say LaWin panels integrate well with current glass manufacturing technologies. The channels are about a millimeter wide etchings in the glass, then another layer is laminated on top. It’s not that dissimilar from double and triple glazing glass technologies. Friedrich-Schiller University Jena has been working on this technology since 2015 with funding from the European Union’s Horizon 2020 Programme. The team hopes to commercialize the technology in the coming year. For now, it sounds like something more suited to office buildings than homes, but maybe one day you’ll have iron nanoparticles in your windows, too.

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