Nanotech Cooling Curtain Offers Alternative to Air Conditioners

Electricity savings at summer heat: Mario Stucki developed a new type of membrane that cools rooms.

Photograph: Peter Rüegg / ETH Zurich

When Stucki realized how well the water transport works across the various layers, he came up with the idea of the cooling curtain. “Water evaporation requires a lot of energy,” he says. “Heat is extracted from the air, it cools and at the same time humidifies the surrounding area.” Conventional humidifiers work in the same way – but they need a lot of power, whereas Stucki’s system is passive. “The sunlight that falls through a window on to the curtain provides enough energy for this type of air conditioning.”

Such curtains could be a real blessing in hot and arid regions. In 2015, people in the Arabian Peninsula endured a heatwave with temperatures of more than 50°C. Climate scientists forecast even higher temperatures and severe aridity for desert regions, which could lead to certain climate zones becoming uninhabitable. Cooling buildings and rooms is thus becoming increasingly essential, but it devours vast amounts of electricity. In the US, for example, about 15 percent of energy consumption can be attributed to air-conditioning equipment, and a huge amount of this energy comes from fossil fuels. The passive cooling curtain would be an environmentally and climate-friendly alternative.

Stucki attracted attention back in 2013 with his Master’s thesis at ETH Zurich, when he developed a new material for outdoor use in no time. In contrast to conventional functional textiles, it does not contain fluorine compounds, which are harmful to the environment and human health.

His current research makes use of that invention: he functionalized his textile using placeholders, for which he mixed tiny lime stone particles into the liquid polymer, which is later processed into the textile. The lime stone particles are then removed from the solid material with hydrochloric or acetic acid, so that tiny holes are formed at the sites of the nano particles. These are necessary for the material to function and to “breathe”. The outer walls of the cooling curtain are made of this porous material in order that the middle hydrophilic layer can deliver water to the surrounding area.

Stucki used a method developed in 2012 by ETH professor Wendelin Stark and his group to combine the different layers into one material. These layers are not glued together, as is customary in industrial processes; instead, they are placed on top of each other in a suitable solvent, whereby the outer layers dissolve slightly and connect to the middle layer. This is the only way that the researchers can ensure that the outer material of the membrane remains porous.