A research team at an Indiana university, Purdue University, has developed a white paint that, according to its creators, reflects up to 98.1 percent of sunlight and can help reduce heating of the surfaces it covers. . Researchers have proposed it as a means of reducing the energy consumption of buildings, and helping to combat climate change, in part due to the production of energy needed to heat and cool homes, offices and shops. According to the researchers, using this 'ultra-white' to cover the roofs and walls of houses and other buildings could reduce the need for air conditioning.
It is too early to say whether this new paint will be really useful, but all over the world research has long been carried out on materials that can reduce energy consumption by allowing greater thermal insulation of buildings: in some countries initiatives have already been carried out to make the whiter roofs, since white is the color that reflects the light the most.
Purdue University's ultra-white has been advertised as “whiter” than other white paints, but what really sets it apart is not so much its color, but its greater ability to reflect sunlight, which other white paints reflect from. '80 to 90 percent. Ultra-white also reflects infrared radiation, the one with a wavelength slightly longer than visible light, and therefore absorbs less heat than other paints.
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Ultra-white is made of barium sulfate, a material used in the production of photographic film and some cosmetics. Other white paints also contain the same substance, but the ultra-white has the particularity of having been obtained using barium sulphate particles of many different sizes. For those who do not remember or have never known the laws of optics: materials and electromagnetic waves interact in a different way based on the microscopic characteristics of the former and the frequency of the latter. For this reason, ultra-white reflects light radiations of different frequencies, and therefore wavelengths.
Xiulin Ruan, head of the research team that made the ultra-white barium sulfate, says that using the paint to paint a portion of the roof across nearly 100 square meters could achieve the same cooling effect as a 10-inch air-conditioning system. kilowatts – the split air conditioners we have in the house consume about half a kilowatt each.
In some countries of the world, such as Greece, it is traditional to paint the roofs white to increase the thermal insulation of buildings. In recent times the same thing has been done in some large American cities: both in New York and Chicago there are projects to paint the roofs of buildings white in some disadvantaged neighborhoods, those where the discomfort associated with high summer temperatures are greatest. In New York in particular, more than 900,000 square meters of roofs were painted white between 2009 and 2019. In Los Angeles, however, it is mandatory to provide a cool roof, literally “fresh roof”, for every new building since 2014.
The expression cool roof is also used in Italy by those who market the most energy-efficient coatings, even if not white: painting the surfaces white is the simplest approach and the one that lends itself best to flat roofs, on that is, the sunlight arrives direct throughout the day.
Whether Purdue University's ultra-white will make a significant contribution to more energy-efficient roofing and global warming solutions cannot yet be said. Some experts in this field have expressed doubts about the solution proposed by Xiulin Ruan and colleagues.
For example, Andrew Parnell, a physicist at the University of Sheffield, told the Guardian that, to assess the contribution of ultra-white to the reduction of greenhouse gas emissions from air conditioning systems, it would be necessary to calculate those that are produced in the sulphate mines of barium, and make a comparison. According to Parnell, green roofs, those on which plants are grown and in turn allow good thermal insulation, can be more effective than white ones in reducing emissions.
Ronnen Levinson, head of a research group on urban heat islands at Lawrence Berkeley National Laboratory, a laboratory in the US Department of Energy, told the Washington Post that ultra-white is not particular compared to paints already available on the market. advantages, and that indeed could have a contraindication. Since it also reflects ultraviolet radiation, those with wavelengths slightly shorter than visible light, in cities it could facilitate the formation of smog, which is created by an interaction between nitrogen oxides and particulate matter produced by pollution.
