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Giving windows circulatory systems could save billions in electricity

Walk through a heavily wooded area on a hot day, and you’ll be cooled by more than just the shade. Water maintains its temperature and transfers heat much more effectively than air, and the high water content in trees keeps the air cooler and lets your relax even in the midst of a summer heat-wave. That’s just as true in humans as it is in trees; we run blood close to the surface of the skin to radiate heat away when we’re hot, and constrict veins to keep heated blood hidden deep inside when we’re cold. That principle is now being put to use by Harvard’s Wyss Institute for Biologically Inspired Engineering, and for precisely the same purpose.

In trying to control the temperature flow to and from a building, windows are a serious weak point. Dense materials such as brick act as good insulators, but the pleasant outdoor effect of large bay windows can offset their good work. Even double-paned windows can be a veritable heat-hole, letting heat out in winter and heat in during the summer. Running water through capillaries on the surface of the windows, like blood through veins near the surface of the skin, might just change that. It’s an initiative aimed at reducing the amount of electricity we waste just trying to keep our living spaces at a reasonable temperature.

Microfluidic window

Cool water flows over the surface of the window and absorbs heat from both the room and the exterior, then flows away to be cooled again. This lets the air conditioner cool only the air in the room itself without losing most of its hard work to the great outdoors. Of course, this system requires a heat sink to keep the circulating water cool enough to do the job, but the ground itself can be used for this purpose — after all, that’s how trees do it. The energy used to cool and pump the water is far less than the amount of heat energy that water carries away, making it a net energy win.

In experiment, their vascular window was able to cool down from almost 40 degrees Celsius, and just a few ounces of liquid was able to chill a full-sized window pane by a full eight degrees. That’s an impressive accomplishment, and one that could make architecture much more energy efficient. That’s important for both the enormous number of private homes, and for the fewer but comparatively window-heavy downtown office buildings.

Reducing drain on the electrical grid is more important than ever, especially in certain areas. California happens to be not only one of the most energy-starved areas, but also the hottest. In hot months, climate control for large buildings can be an enormous expense. That hurts more than just the corporate pocketbook.

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