Super Cool Pavements through Passive Radiative Cooling Technology: Modelling and Evaluation

The Urban Heat Island (UHI) effect causes urban areas to be warmer than rural ones, exacerbated by heat-absorbing pavements covering 30% of urban spaces. To mitigate this, heat-reflective coatings are often used to increase solar reflectivity and cool surfaces. However, existing research often overlooks thermal emissivity—materials' ability to release absorbed heat, known as radiative cooling. Recent advancements in radiative cooling technology, which reflect over 90% of solar radiation and achieve high emissivity in atmospheric window bands, promise significant surface temperature reductions without external energy. This study evaluates the cooling effect of Passive Daytime Radiative Cooling (PDRC) coatings compared to uncoated and traditional cool pavements using a validated 2D finite element heat transfer model and the microclimate model ENVI-met. Findings show that white PDRC coatings can lower pavement temperatures by up to 2°C below ambient levels during the day and reduce surface temperatures by up to 32°C compared to uncoated (conventional asphalt) surfaces. Although less effective in cooling, coloured PDRC coatings can still reduce pavement surface temperatures by up to 24°C at peak daytime compared to uncoated asphalt. In addition to their cooling benefits, coloured PDRC coatings enhance pavement aesthetics and safety by reducing glare. Furthermore, microclimate model results also demonstrate that white PDRC coatings could reduce pedestrian-level air temperatures by up to 4°C during peak daytime in some areas. This evidence suggests that PDRC coatings represent a substantial advancement over conventional heat-reflective pavements, contributing significantly to urban cooling efforts.