Micro and Nano-structured Materials with Controlled Radiative Properties for Radiative Cooling Applications

In response to global environmental crises, such as climate change, urban heat islands, and escalating energy demands, this thesis investigates innovative solutions to these challenges through the development of radiative cooling (RC) materials and systems. The research first examines the potential of RC technologies to mitigate climate change by assessing their impact on global warming potential (GWP) and radiative forcing (RF) through life cycle assessment (LCA) methods. The study analyzes RC materials in comparison with conventional construction and roofing structures, highlighting their significant potential to mitigate global warming impacts. A RC material exhibiting an average solar reflectance (R ̅_solar) of 98.2% and an average long-wavelength infrared emittance of (ε ̅_LWIR) 98.5%, achieved a net cooling power of 160.8 W·m⁻², leading to a GWP of -252 kgCO₂-eq·m⁻² over 20 years and -333 kgCO₂-eq·m⁻² over 100 years, with an RF value of -1.01 W·m⁻² when covering 1% of the Earth's surface, indicating a substantial reduction in radiative forcing compared to conventional materials.

The thesis then explores the incorporation of underside reflective surfaces to boost RC performance by redirecting thermal emissions toward the sky and reducing heat loss. Numerical simulations using Monte Carlo ray-tracing (MCRT) techniques were employed to evaluate the cooling effectiveness of various configurations, including flat and parabolic reflectors. Results show that considering an ideal selective emittance spectrum, in the absence of solar absorption and convective heat transfer, at an ambient temperature of 300 K, the steady-state temperatures using parabolic reflectors with the mentioned geometrical features can be cooled down to approximately 230 K.

An important objective was to design and analyze novel configurations of micro- and nano-structured materials with controlled radiative properties for passive daytime radiative cooling (PDRC) applications. Key advancements included the development of enhanced PVDF-HFP-based porous materials with high solar reflectivity and long-wave infrared emissivity, such as the aforementioned (1-8-1.25) sample, fabricated via the phase inversion method. These materials were designed to maximize cooling by minimizing solar heat absorption and enhancing thermal radiation through the atmospheric window.

Finally, experimental validation was conducted via outdoor testing and controlled dew condensation experiments in a dedicated setup, demonstrating the practical applicability of the developed PDRC systems. The findings underscore the significant potential of RC technologies to reduce cooling energy demands and mitigate global warming, making them a promising approach to enhance sustainability in urban and building environments.