As cities face continual rise in temperatures and urban heat islands, researchers are exploring innovative passive cooling strategies to mitigate excessive heat loads on buildings.
Since the 1980s, scientists, researchers, and industry have been investigating coatings technology for heat mitigation. The ultimate goal of these coatings is to lower cooling energy demands while improving thermal comfort, but their methodologies and performance vary significantly.
Urban overheating, where cities experience higher temperatures than surrounding rural areas, is a growing global challenge. Temperature differences can exceed six degrees Celsius, sometimes reaching 10 degrees, affecting cooling loads, energy demand, air quality, and sustainability.
A key contributor to urban overheating is heat reradiation from hard surfaces, which warm surrounding structures through broadband infrared energy transfer, primarily absorbed and transferred as conductive heat.
Researchers from Princeton and UCLA have identified another possible distinction in how heat moves between buildings and their surroundings: radiant heat dissipates to the sky in a narrow portion of the infrared spectrum (the ‘atmospheric transmission window’), whereas heat moves across the entire infrared spectrum at ground level.
While this is a new research theory, it needs to be compared with decades-old coatings that have proven insulation properties. Aaswath Raman, Associate Professor of Materials Science and Engineering at UCLA, explained: “By coating walls and windows with materials that selectively radiate or absorb heat in the atmospheric window, we can reduce heat gain in summer and heat loss in winter while maintaining the cooling benefits of the sky.”
However, effective thermal coatings must address all forms of heat transfer to be successful. The study highlights the potential for widely available materials, such as polypropylene from household plastics, to act as thermal coatings.
Compared to traditional cool roof paints, which rely primarily on reflective white surfaces but cannot block infrared heat, these new coatings attempt to optimise heat absorption based on seasonal needs, which is challenging.
Other materials, such as proven ceramic coatings, have been ASTM tested at higher ambient temperatures, including thermal diffusivity testing at 25, 50, 75, and 100°C. Different properties and materials have varying thermal attributes based on their thickness and inherent characteristics.
Specialised multi-ceramic coatings are applied at just 0.25 mm thick and block 96 per cent of total solar heat, including 99 per cent of infrared heat, tested for 35 years.
While the UCLA study introduces an innovative concept, further research, large-scale testing, and real world application studies are needed before polypropylene coatings can be considered a viable alternative to existing cool roof and insulation coating solutions.
A study from the University of New South Wales, led by Scientia Professor Mattheos Santamouris, evaluated the impact of adopting cool roof technologies, with results showing that some of Australia’s regions stand to gain significantly from large-scale adoption.
“The need for cool roofs and other heat mitigation strategies should be a top priority. Without action, the cost of climate change in the next 10 to 15 years will be enormous,” Professor Santamouris noted.
The study found that cool roofs could reduce cooling energy consumption by up to 40 per cent, lower indoor residential temperatures by up to four degrees Celsius, and significantly improve the health and wellbeing of vulnerable populations.
While cool roofs and thermal insulation coatings present significant advantages, a comprehensive approach to urban cooling should incorporate multiple strategies.
Combining insulation coatings, advanced materials, ventilated roofing systems, and passive design principles ensures optimal performance for different climate zones and building types.
When researching insulation coatings and heatreflective paints, examining their testing, performance, and longevity is essential to meet specific needs. By leveraging advanced material science and smart
design, urban environments can become more resilient to climate change while reducing overall energy consumption by protecting the building envelope for the future heat challenges.
