Buildings Cooled with Sweat Mats

Photo courtesy: © Rotzetter ACC et al. / Advanced Materials

Heating and cooling systems are by far the most power hungry things in a building. Ways to make your home more energy efficient typically revolve around ways to make heating and cooling more efficient -- better insulation, weather proofing, smart thermostats, etc. But what if there was a way that buildings could cool themselves just like the human body does -- by sweating?

Researchers at ETH Zurich are developing a synthetic mat that could be applied to roofs and essentially allow buildings to sweat in order to cool off. The mat would soak up water when it rains and then, in high temperatures, shrink and "sweat" out that moisture, cooling down the building through perspiration.

In the human body, water is secreted from our skins and then the heat on the surface of our skin turns the water into vapor, which removes the heat and cools us down. The researchers says that same concept would work with these mats.

ETH Zurich explains, "For the sweating mats, the researchers used a special polymer, abbreviated to PNIPAM, which is protected by a water-permeable membrane. The mat can thus fill with water when it rains. PNIPAM's storage capacity is temperature-dependent. If the material becomes warmer than thirty-two degrees in direct sunlight, it shrinks up and adopts hydrophobic properties. This forces the water through the membrane to the surface of the mat, where is evaporates like sweat on our skin."

The researchers have tested this material on small model homes. One was covered with a 5 millimeter-thick PNIPAM mat while the other was covered with a conventional polymer. A lamp was shone on the houses to heat the surfaces. When the inside temperatures were compared, the PNIPAM-covered house warmed much more slowly. You can see the difference in the image above. The PNIPAM-covered house is on the right.

By the team's calculations, a full-size home with just a few-millimeters thick mat on the roof could shave off up to 60 percent of the energy needed to cool the house with air conditioning on a sunny July day. The researchers now want to make sure the material is frost-resistant before an full-scale trials are done.