New insights into building-integrated radiative cooling for near-ambient temperature regulation

Passive sub-ambient daytime radiative cooling (RC) presents a promising strategy for building energy conservation by creating a radiative thermal insulation layer through enhanced solar reflection and direct heat emission into the cold universe (∼3 K). Although spectral-engineered radiative cooling (RC) materials have been widely proven to achieve daytime sub-ambient cooling, their production depends on energy- and equipment-intensive processes to attain high solar reflectance. Significant challenges remain in scaling these materials from lab prototypes to practical building applications, particularly in manufacturing scalability. This study investigates the cooling performance of building-integrated radiative cooling materials by considering the thermophysical properties of building substrate materials, such as density, specific heat capacity, and thermal conductivity, providing new insights into the RC technology with moderate solar reflectance for building energy conservation. An unsteady and integrated spectrum-selective heat transfer model (ISHTM) was developed and validated through outdoor field tests on a full-scale office building with a concrete roof, which was then used to evaluate the overall cooling performance of radiative cooling roofs. The results suggest that a moderate solar reflectance for the radiative cooling roof could effectively achieve a 24-h sub-ambient or near-ambient cooling effect. Specifically, roofs with high thermal mass, such as concrete, could achieve temperature reductions of approximately 3 °C below the ambient during nighttime due to radiative cooling, allowing them to store significant cooling energy, which can enhance the daytime cooling performance of the RC materials. Consequently, the roof incorporating a radiative cooling coating with a solar reflectivity of 83 %–85 % could effectively maintain its external surface temperature at near-ambient or sub-ambient levels throughout the day, even under direct sunlight. This achieves optimal radiative insulation by maximizing radiative performance and minimizing non-radiative conduction/convection. As a result, it provides researchers and architects with greater flexibility to balance energy savings, cost, and scalability in designing RC materials, thereby promoting the integration of radiative cooling in buildings.