Numerical Analyses of Radiative Cooling Behavior: a Game-Changer in the Study of Materials' Potential for Urban Overheating Mitigation

The rapid growth of the population, coupled with the escalating demand for thermal comfort in buildings, the surging global temperatures, and the emergence of the Urban Heat Island (UHI) phenomenon, highlight an urgent requirement for efficient cooling solutions. Moreover, the prevailing energy and environmental landscape underscores the importance of passive cooling techniques that do not depend on energy consumption or release pollutants. By incorporating radiative cooling (RC) materials as a city's “skin”, we can play a pivotal role in alleviating the UHI phenomenon and achieving significant energy savings. In this context, the present work delves into the study of aluminum- (“A”) and Vikuiti- (“V”) based materials for adaptive broadband and selective radiative cooling. In comparison to a pure aluminum sample, they possess unique thermo-optical properties that span from the visible up to the mid-infrared spectrum: not only they reflect most of the incident solar radiation, but they also efficiently release the absorbed radiation through the main atmospheric window (8-13 µm), enabling direct heat exchange with the outer space. The aim of the study is to explore the potential of these RC materials in achieving enhanced cooling capabilities while maintaining adaptability to varying boundary conditions. After conducting an experimental characterization of the samples in a controlled laboratory setting, a numerical model using COMSOL Multiphysics is developed and verified. A typical summer and winter scenarios are reproduced and simulated. Results demonstrate how the emissive layer improves the thermal behavior of the aluminum. “A”-based samples exhibit enhanced warmth during winter and improved cooling during summer compared to the reference sample. On the other hand, the “V” prototype performs exceptionally well in summer but displays suboptimal behavior in winter. The availability of a simulation model for RC materials allows for accurate prediction of the radiative cooling performance of samples across diverse climatic conditions. This eliminates the need for conducting multiple outdoor tests in varying climates, streamlining the research process and saving valuable resources.