Heat transfer through glass windows remains a major obstacle to energy-efficient buildings.

5 August 2013 — People love clear glass. It allows in natural light, which has been associated with improved mood, enhanced morale, lower fatigue and reduced eyestrain. And this means productivity benefits for workers.

However, along with delivering better views and productivity outcomes, glass façades can also bring in higher airconditioning bills, thanks to increased heat loads, which can account for as much as 40 per cent of a building’s energy costs.

Researchers at Harvard University may have found a solution, using biomimicry to create a circulatory system for windows that dissipates heat while still letting in sunlight.

The researchers from the Wyss Institute for Biologically Inspired Engineering created a circulatory system for glass windows that functions like mammals’, which have an extensive network of tiny blood vessels near the skin’s surface that dilate when hot, allowing more blood to circulate and promoting heat transfer to the surrounding air.

“In contrast to man-made thermal control systems, living organisms have evolved an entirely different and highly efficient mechanism to control temperature that is based on the design of internal vascular networks,” said study lead author Benjamin Hatton,  in the July 29 online edition of Solar Energy Materials and Solar Cells..

The window cooling system contains a network of ultra thin channels through which water can be pumped. The channels are made up of long, narrow troughs moulded into a thin sheet of clear silicone rubber that, when stretched over a flat pane of glass, create sealed channels. The channels, when filled with water, are transparent to the eye.

“The water comes in at a low temperature, runs next to a hot window, and carries that thermal energy away,” said Hatton.

The study found that pumping a few hundred millilitres of water through the window’s circulatory system would cool a full-sized window pane by 8°C. The energy required to pump the water would be far less than the heat energy absorbed by the water, generating a big “net win”.

The same circulatory system could also be used to cool rooftop solar panels, allowing them to generate electricity more efficiently, the researchers found. The heated water could also be used for existing hot water services or go to a heat storage system, they said.

“The idea of using nature’s lesson to create kind of a living skin on a building is a very important and promising direction for how buildings should and will be constructed in the future,” said Wyss Institute visiting scholar Chuck Hoberman.

“Our new window technology marries advances in microfluidics with creative thinking about adaptive architecture, and it’s the sort of cross-disciplinary research that the Wyss Institute was designed to foster.

“We are optimistic that microfluidic windows will go a long way toward helping us cool our homes and commercial buildings more efficiently.”

The Wyss Institute said that building insulation and construction methods had done a good job keeping heat from leaking through walls, but heat transfer through glass windows remained a major obstacle to energy-efficient buildings.

The researchers now plan to work with architecture researchers to predict how much energy microfluidic windows would save if installed over an entire building.

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  1. But how long does silicon last in direct sunlight before it yellows? It’s much better to design buildings with less glass to start with. Even a standard insulated brick cavity wall performs better than triple-glazed low-e glazing.