Chinese paint cuts wall temperature by 25 degrees Celsius in summer test: report

"If this paint can make any surface cooler than ambient, why isn't it used everywhere?" Condensation is a serious problem, and then also the fact that seven months out of the year in temperate climates you don't want your building's exterior envelope to cool off even faster!

China has begun mass production of a super-coating that can cut wall temperatures by 25 degrees Celsius in summer, according to the state-run Science and Technology Daily.

The material, which has undergone six months of real-world testing at a petrochemical plant in the southern island province of Hainan, uses the principles of radiative cooling. It requires neither electricity nor cooling agents and its overall performance is reportedly the highest among known global competitors, according to the report published on September 7. The coating may also have potential for broader use in public infrastructure and homes.

The need to reduce the effects of heat on buildings was apparent in Europe this summer when record heatwaves left many residents sweltering in homes without air conditioning.

The coating has already transitioned from a laboratory innovation into mass production.

Following dozens of trial batches, the research team has established manufacturing standards – spanning raw material grinding and formulation, right through to final product testing. The annual production capacity was 600,000 tonnes, the report noted.

At a petrochemical refinery in Hainan, the scorching sun routinely bakes a row of 3,000 cubic metres (106,000 cubic feet) spherical liquefied gas tanks. Without immediate cooling, internal pressures would surge, posing severe safety risks.

Previously, the facility relied on highly water-intensive sprinkler systems to cool the tanks. Now, clad in this super-coating, the tanks achieve a remarkable self-cooling effect with zero energy consumption.

Composed of tailored inorganic fillers and polymer resins, the coating boasts the dual properties of high solar reflectance and strong thermal emittance.

It reflects most solar radiation while emitting the tank’s accumulated heat outwards as infrared energy – without the need for power or refrigerants. The pioneering material was jointly developed by the state-owned China Construction Eco-Development Company, headquartered in Suzhou, and the Harbin Institute of Technology (HIT) in Heilongjiang province.

According to an R&D director from the Suzhou-based venture, on a clear 30-degree (86 Fahrenheit) day, a treated tank’s surface temperature can drop by roughly 25 degrees, reducing internal temperatures by about 7 degrees.

Achieving an equivalent cooling effect via traditional sprinklers would consume an estimated 35 tonnes of water daily per tank, by some estimates.

“Even during extreme heatwaves, the cooling coating can maintain the tank’s interior at a safe temperature,” the report quoted Li Xiang, head of the R&D centre at China Construction Eco-Development, as saying.

This is made possible by a specific infrared emission window. Scientists have long known that within the atmospheric infrared band of 8 to 13 micrometres, heat can penetrate the Earth’s atmosphere and dissipate directly into the freezing vacuum of space.

However, thick applications are required for traditional radiative cooling materials to be both highly reflective and highly emissive. This bulkiness leads to a host of drawbacks, including higher costs and impaired heat dissipation efficiency.