Researchers at Nanyang Technological University Singapore (NTU) have done a real-world study that shows the efficacy of cool paint coatings. 

Per their research which was published in Sustainable Cities and Society, this paint coatings can help pedestrians feel up to 1.5C (34.7 F) cooler. That makes the urban environment more comfortable for work and leisure. 

Paint coatings with additives can reflect the sun’s heat, thanks to its special cooling properties. In turn, this reduces surface temperatures and emissions.

Many have applauded its ability to tackle urban heat island (UHI) problems. UHI is a phenomenon where cities are hotter than their surroundings.

So far, research on coatings like these has mostly focused on small-scale models and simulations. Therefore, its understanding of real-world application is limited.

So recently, researchers from NTU have carried out a groundbreaking study in the tropics. They want to assess the effectiveness of cool paint coatings in reducing urban heat.

In Singapore, they coated roofs, walls, and roads in an industrial area. Compared to nearby uncoated surfaces, the coated area was up to 2°C cooler in the afternoon.

Additionally, pedestrian comfort improved by up to 1.5C, as measured by the Universal Thermal Climate Index. It is an international standard which considers temperature, humidity, radiation, and wind speed.

Lead author Dr E V S Kiran Kumar Donthu said, “Our study provides evidence that cool paint coatings reduce heat build-up and contribute to the cooling of the urban environment.

“This is a minimally intrusive solution for urban cooling that has an immediate effect, compared to other options that often require major urban redevelopment to deploy. Moreover, by reducing the amount of heat absorbed in urban structures, we also reduce heat load in buildings, consequently reducing indoor air-conditioning energy consumption.”

Lead investigator Associate Professor Wan Man Pun underlined the broader implications of the study. 

The researcher stated that these findings wouldn’t be applicable just to Singapore where it got hot all year round. As global temperatures rise, people will want to beat the heat too, particularly in hotter urban areas worldwide.

“Our study validates how cool paint coatings can be a strategy to reduce the urban heat island effect in future,” the associate professor said. 

This study supports NTU’s 2025 strategic plan. It aims to tackle sustainability challenges and speed up the transformation of research breakthroughs into concrete, practical environmental solutions.

Experimenting in “street canyons”

The NTU team did their real-world experiments in “street canyons.” Meaning, they selected four rectangular buildings in an industrial area, creating two parallel “street canyons”. They’re basically narrow streets flanked by buildings. 

One canyon, known as the “cool canyon,” was coated with cool paints on roofs, walls, and roads. The other remained unchanged as a control.

Using environmental sensors, the researchers monitored conditions in both canyons for two months. Specifically, they monitored air movement, surface and air temperature, humidity, and radiation. 

These were done to assess the effectiveness of cool paint coatings in reducing urban heat.

The study revealed that over a 24-hour period, the cool canyon experienced a significant decrease.

It saw a decrease of up to 30% in heat emitted from the surfaces of buildings. That resulted in temperatures being up to 2C cooler than the conventional canyon. The effect was particularly noticeable at 4 pm, the hottest part of the day. 

This led to pedestrians feeling around 1.5C cooler in the cool canyon.

The NTU researchers also found that the cooler temperatures in the cool canyon were due to reduced absorption and storage of heat in building walls, roofs, and roads, which would otherwise contribute to heating up the air or building interiors.

Compared to regular roofs, those with cool paint coatings reflected 50% more sunlight. Moreover, they absorbed up to 40% less heat, especially during peak sunny hours. In addition, the coated walls prevented most of the heat from entering the industrial buildings.

Co-author Assistant Professor Ng Bing Feng stated that the study demonstrated how applying cool paint coatings on roads lower peak temperatures significantly in urban areas. Cool paint coatings could be a promising way to make such areas cooler and more comfortable.

 

 

“We hope findings from our study will encourage more urban planners to adopt cool paint coatings on more built-up surfaces, on a large scale,” the co-author said.

Future research by the NTU team will focus on monitoring the long-term performance of cool paint coatings in the same experimental location.

We can see how cool paint coatings on roads can help us pedestrians stay cool. Wouldn’t it be better if cool coatings or something similar are applied to parts of the building like windows?

Blocking heat from windows using a breakthrough window coating

I personally love buildings with a lot of windows because I very much love natural light. But speaking from personal experience, without proper ventilation or AC, such a house can feel like a big sauna room.

A new coating for windows may address this issue by blocking heat-producing ultraviolet and infrared light. At the same time, the coating allows visible light to pass through, regardless of the sun’s position. 

One can apply this versatile coating to existing windows or car windows. So, it offers significant energy savings, particularly in hot climates. This coating, according to the researchers, can reduce air-conditioning costs by over one-third.

Lead researcher Tengfei Luo at the University of Notre Dame explained, “The angle between the sunshine and your window is always changing. Our coating maintains functionality and efficiency whatever the sun’s position in the sky.”

Previous window coatings optimized for light entering at a 90-degree angle. Compared to those, this innovative coating considers the sun’s rays at various angles. It’s especially useful during peak sunlight hours like noon.

Previously, Luo and his postdoctoral associate, Seongmin Kim, developed a transparent window coating. Back then, they used ultra-thin layers of silica, alumina, and titanium oxide on a glass base. 

For this recently developed coating, they enhanced its cooling capabilities by adding a micrometer-thick silicon polymer. Now, the coating reflects thermal radiation through the atmospheric window, dissipating heat into outer space.

Further refinement of the layer order was actually essential to ensure the coating could effectively handle sunlight from various angles. 

However, due to the vast number of potential combinations, a trial-and-error approach was impractical, Luo explained.

The team wanted to optimize the layer arrangement for maximum visible light transmission and minimal heat passage. So, they turned to quantum computing, specifically quantum annealing. Next, the researchers confirmed their findings through experimental validation.

Their approach produced a coating that maintained transparency while reducing room temperature by 5.4 to 7.2C, even with light entering at different angles. 

Luo drew similarities between the coating and polarized sunglasses. Those sunglasses reduce light intensity, but unlike them, the coating remains clear and effective regardless of its orientation.

One thing that I can say about innovations like these is: keep ‘em coming! To me, it’s always nice to have things to help cool things down which don’t require more ACs. 

I do hope that applying those coatings comes at an affordable price so more can have access to it. And, maybe in the (hopefully) near future, the window coatings also come with bird-friendly properties to help protect migratory birds.

 

Sources:

https://phys.org/news/2024-03-cool-coatings-pedestrians-15c-cooler.html
https://www.sciencedaily.com/releases/2024/04/240402192558.htm