Impact of Materials Spectral Radiative Properties Use on Radiative Cooling and Building Energy Demand Assessment

Buildings are responsible for approximately 30% of the world energy consumption and 26% of greenhouse gas emissions, making energy-efficient building design a crucial factor in climate change. Building materials properties play a major role in building energy behavior. In particular, materials radiative properties govern the heat transfer between a building and its environment through the radiative channel. They influence solar heat gain under solar radiation, radiative cooling during clear sky conditions and occupants’ thermal comfort for example. Building energy models usually account for materials radiative properties using two parameters: short wavelength albedo for solar radiation and long wavelength emissivity / absorptivity for the building interaction with its environment and the sky. Those quantities are averaged over their respective spectral ranges, UV-VIS-NIR-SWIR (up to 3 µm) for the former and MIR (above 3 µm) for the latter. On the other hand, the atmosphere exhibits a transparency window in the MIR range between 8 and 13 µm which enables a radiative cooling effect by radiative transfer between a building and the outer space at 3 K. Average radiative properties in the MIR range do not enable an accurate description of this phenomenon. In this work, we investigate the radiative cooling potential of several common building materials based on their spectral radiative properties that we measured from 200 nm up to 25 µm.  Our results reveal significant discrepancies, up to 165%, when using average radiative properties and spectral radiative values in radiative cooling calculations. We also discuss the impact of these discrepancies on the energy demand of buildings by integrating our experimentally measured spectral data into building energy models. Our study highlights the importance of accurate radiative property knowledge in optimizing material selection for building energy efficiency improvement, the implementation of passive cooling solutions and urban heat islands mitigation.