Spectrally resolved finite‑element modelling of radiative cooling under real atmospheric conditions: validation and benchmarking framework

Passive daytime radiative cooling (PDRC) promises zero-energy thermal management, but reported performances vary across studies due to local atmospheric conditions and non-standard experimental configurations. A spectrally resolved finite-element model has been developed and validated for predicting 24 h thermal response under realistic outdoor conditions. The model couples wavelength-dependent material optical properties and sky emissivities derived from libRadtran using real atmospheric data. Validation against different outdoor measurements of nanoporous anodic aluminium oxide and cellulose-based radiative coolers under Madrid summer conditions yields a normalised mean bias error within ± 10 % and coefficient of variation of the root mean square error < 11 %, fulfilling ASHRAE Guideline 14–2014 (gold standard for the validation of thermal models). Parametric studies reveal that geometric and design parameters dominate over atmospheric variations, with temperature differences relative to aluminium up to 25 °C vs. ∼ 0.2 °C for realistic humidity and temperature variations, reaching peak daytime net cooling powers ∼ 120 W·m −2 . Cloudy conditions are included (a cloud optical depth of 1 reduces the daily cooling power by 26 %) and global portability to other regions and climates is demonstrated (e.g., a 56 % decrease in cooling power predicted from Madrid to Singapore). This framework facilitates PDRC climate-specific optimisation and supports benchmarking for real-world applications. Furthermore, an initial benchmarking framework is introduced to mitigate historical discrepancies in outdoor PDRC characterization. Ultimately, this framework lays the foundation for developing digital twins of PDRC systems, bridging the gap between nanoscale material properties and macroscale building energy simulations.