New mat cools buildings by letting their roofs sweat
We're used to the thought of humans sweating to cool down, but what about buildings? Researchers at ETH Zurich have applied the biological cooling mechanism to the task of keeping a building cool, and in the process have hit upon a novel and inexpensive method of cooling houses which could prove useful for homes in both developed and emerging nations.
Led by Wendelin Stark, professor at ETH Zurich's Institute for Chemical and Bio Engineering, the researchers have developed a mat designed to be placed atop roofs. If it should rain, the mat soaks up rainwater like a sponge. When direct sunlight subsequently warms the mat to reach its internal temperature threshold, the collected rainwater “sweats” from the mat's surface and is turned into vapor, cooling the building below.
The mats are constructed from a special polymer known as Poly(N-isopropylacrylamide) – or PNIPAM – which features a water-permeable membrane that allows it to soak up and retain water. However, once the PNIPAM’s internal temperature reaches 32 degrees Celsius (89.6ºF), it begins to shrink and adopt hydrophobic properties, forcing the water back out through the same membrane whence it came.
So far, the researchers have tested the new mat on a small scale, covering the roofs of model railway buildings with 5 mm (0.19 inch) thick mats, while using a lamp to provide "sunshine." The team found that a model house fitted with the new mat remained significantly cooler than a model house sporting conventional polymer.
According to calculations by the ETH Zurich researchers, even a thin mat could potentially save up to 60 percent of the energy typically expended by air conditioning during a day of strong July sunshine. The team further posits that the sweating mat could be ideal for use in developing and emerging countries located in warm regions of the world, as it should prove very inexpensive to produce.
However, Stark's team also cautions that work still remains to be done to ensure the technology works as effectively on a larger scale – one question which still needs to be answered is whether or not the mat is frost-proof, for example.
The research is not patented, so we may well see a company take up the challenge and bring a version of the sweating mat to market.