Cooling, Ultra-white Paint

This innovation from researchers at Purdue University –  now in development –  is worth watching.

White paint has been used for decades to reduce the sun’s heat that rooftops absorb, thereby keeping the building cooler than it would be if painted in a dark color.  However, a new ultra-white paint shows evidence of cooling buildings.  In fact, the roof’s surface temperature is lower than the air temperature immediately surrounding the roof.

The cooling is made possible because the new ultra-white paint reflects 98% of the sun’s rays plus sends infrared heat away from the surface. As proof, according to their research, tests conducted during sunny, midday hours on the roof of a campus building in West Lafayette, Indiana, the paint kept outdoor surfaces 8 degrees cooler than the surrounding ambient temperatures. At night, the paint kept surfaces 19 degrees cooler than their surroundings.

Currently, there are white paints on the market made with titanium dioxide, which reflects specific wavelengths of sunlight. But, they absorb the sun’s ultraviolet rays, causing the painted surface to heat up.

The new paint is made with barium sulfate, a known UV-reflecting compound used in cosmetics, reflective photo paper, oil paints, x-ray examinations, etc.  The barium sulfate particles in the paint vary in size, making the sun’s rays “scatter,” explains Xiulin Ruan, a Purdue mechanical engineering professor.

The researchers estimate that painting a 1,000 sq ft roof (93 sq meters) would give a cooling power of 10 kilowatts comparable to air conditioners used by most homes.

Especially if used on buildings in urban areas, this could reduce the effect of heat islands, areas where dense concentrations of pavement and structures absorb and retain heat, thereby increasing the air temperature in the city.

The research team is now working with a paint company to develop the paint into a commercially viable product. Product cost and durability are of particular concern since the innovative paint has a relatively high pigment concentration of 60%, which is excellent for durability but is expensive.

Additional research is required to ensure there is a net gain for the environment when comparing the impact of mining barium sulfate and the energy savings related to building cooling.

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