An actual-world study by researchers at Nanyang Technological University, Singapore (NTU Singapore) has shown that using cool paint coatings in cities may also help pedestrians feel as much as 1.5 degrees Celsius cooler, making the urban area more comfortable for work and play.
Cool paint coatings contain additives that reflect the sun’s heat to scale back surface heat absorption and emission. They’ve been touted as one strategy to cool down the urban area and mitigate the Urban Heat Island (UHI) effect, a phenomenon through which urban areas experience warmer temperatures than their outlying surroundings.
To this point, most studies of cool paint coatings have been either simulation-based or tested in scaled-down models, and understanding of its application in real-world scenarios is proscribed.
Now, NTU researchers have conducted a primary of its kind real-world study within the tropics to comprehensively evaluate how well cool paint coatings work in reducing city heat.
The team coated the roofs, partitions, and road pavements of an industrial area in Singapore and located that by comparison with an adjoining uncoated area, the coated environment was as much as two degrees Celsius cooler within the afternoon, with pedestrian thermal comfort level improving by as much as 1.5 degrees Celsius, measured using the Universal Thermal Climate Index — a standard international standard for human outdoor temperature sensation that takes under consideration temperature, relative humidity, thermal radiation, and wind speed.
Lead creator Dr. E V S Kiran Kumar Donthu, who accomplished the work as a Research Fellow at Energy Research Institute said, “Our study provides evidence that cool paint coatings reduce heat build-up and contribute to the cooling of the urban environment. It is a minimally intrusive solution for urban cooling that has an instantaneous effect, in comparison with other options that usually require major urban redevelopment to deploy. Furthermore, by reducing the quantity of warmth 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 on the NTU School of Mechanical & Aerospace Engineering (MAE), said, “Findings from the study will not be just relevant for cities in Singapore where it’s hot all 12 months round, but for other urban areas all over the world too. With global warming, people will increasingly look for methods to remain cool. Our study validates how cool paint coatings generally is a strategy to scale back the urban heat island effect in future.”
The study, published in Sustainable Cities and Society in March, supports the NTU 2025 strategic plan, which seeks to deal with humanity’s grand challenges on sustainability and speed up the interpretation of research discoveries into innovations that mitigate human impact on the environment.
Real-world experiments in ‘street canyons’
To perform their real-world experiments, the NTU researchers chosen 4 rectangular buildings that created two parallel ‘street canyons’ — narrow streets flanked by buildings — in an industrial estate west of Singapore managed by JTC Corporation.
One canyon, or ‘cool canyon’ was coated with cool paints on the roofs, partitions, and road pavement, while the opposite (conventional) canyon remained because it was as a ‘control’ for the experiment.
Using environmental sensors, the NTU team monitored the conditions within the two canyons over two months, which included air movement, surface and air temperature, humidity, and radiation, to see how well the cool paint coatings worked in reducing city heat.
The researchers found that in a 24-hour cycle, the cool canyon saw as much as a 30 per cent reduction in heat released from the built-up surfaces, leading to the air temperature within the cool canyon being cooler than the traditional canyon by as much as two degrees Celsius throughout the hottest time of the day, at around 4pm. Because of this, pedestrians within the cool canyon can feel as much as 1.5 degrees Celsius cooler.
The NTU research team also found that air temperature within the cool canyon was lowered because less heat was absorbed by and stored within the constructing partitions, roofs, and roads, and which might subsequently have been released to either heat up the encompassing air or the constructing’s interior.
Compared to traditional roofs, the roofs with the cool paint coating reflected 50 per cent more sunlight and absorbed as much as 40 per cent less heat consequently, throughout the hottest time of a sunny day. The coated partitions also prevented a lot of the heat from entering the economic buildings.
Co-author, Assistant Professor Ng Bing Feng on the NTU School of MAE, said, “Our study showed that cool paint coating on the road significantly helped lower the most well liked temperatures within the cool canyon, confirming that cool paint coating generally is a promising strategy to make urban areas cooler and more comfortable, especially during hot weather. We hope findings from our study will encourage more urban planners to adopt cool paint coatings on more built-up surfaces, on a big scale.”
In future research, the NTU team will deal with how the cool paint coating holds up over time in the identical experiment location.
The research is supported by JTC Corporation and Singapore’s Housing & Development Board.
