Metamaterial Cools Buildings without Using Energy

Engineers at the University of Colorado Boulder have built a metamaterial that can be used to cool structures without drawing on any energy. The material can also cool objects placed in direct sunlight without using water.

A metamaterial is an artificial substance with remarkable properties not possessed by natural substances.

According to Xiabo Yin, an assistant professor at Colorado Boulder and a director of the research, the new metamaterial could be a game changer in the field of radiative cooling technology. Since the technology does not make use of water and electricity, it presents a huge opportunity in the fields of power generation, agriculture, space research, and several other areas.

The metamaterial, which could make for an environmentally friendly and cost-effective technique for cooling homes and industrial applications, has been discussed in the journal Science. Thermoelectric power installations, which need a large amount of water for maintaining the low temperatures of the cold junction could instead make use of this material for cooling purposes. The hybrid material can be fabricated in the form of glass-polymer sheets in thickness of 50 micrometers. It is only marginally thicker than the kitchen aluminum foil and can be manufactured on rolls, making it economically viable for large-scale production.

When placed over an object, the film cools the surface beneath it by reflecting the incident solar energy radiations back. At the same time, the film helps the object lose the heat contained by emitting low frequency infrared radiations. Field demonstrations were conducted at Cave Creek in Arizona and Boulder in Colorado. The tests showed that at both places, the metamaterial had an average radiative cooling power of 110 W/square meters for 72 hours at a stretch. During direct sunlight at noon, the radiative power recorded was 90 W/square meters.

Gang Tan, an associate professor in the Department of Architectural and Civil Engineering of Wyoming University, explains the test results imply that about 20 square meters of the material installed on the roof of a single family home could achieve reasonably good cooling in summer.

Apart from cooling buildings and power plants, the new polymer-glass hybrid material can serve to enhance the efficiency and life of solar panels put up for electricity generation. Intense sunlight tends to damage solar panels. Yin explains that a layer of the material applied to a panel can boost the efficiency by almost 2%.

The cooling power of the material is approximately equal to the electricity produced by a solar panel of the same area. However, while solar cells can operate only during the hours of sunshine, the new material provides radiative cooling at all hours.

The researchers are now waiting for a patent for the new material and the technology. They are also working with the Technology Transfer Office at CU Boulder to look at prospective commercial applications. A potential project in the offing involves the creation of a model cooling-farm in Boulder sometime this year.

The team has been awarded a grant of $3 million for the invention of the metamaterial and the related research projects by the Advanced Research Projects Energy Agency connected with the DOE.