Performance Comparison of Selective and Broadband Emitters in Passive Radiative Cooling

Abstract The present study consists of a comparative numerical investigation of thermal performance of broadband high-emissivity emitters and spectrally selective emitters for passive radiative cooling (PRC). Atmospheric longwave radiation profiles across a parametric range of ambient temperature and relative humidity levels were calculated employing MODTRAN® software and integrated into an EnergyPlus model through a Python-based simulation workflow. A generalized parametric framework was developed and implemented to systematically determine the performance crossover and operational boundaries of daytime and nighttime PRC. Results show that broadband emitters achieve superior net cooling power under dry atmospheric conditions when operating near or above ambient temperature, owing to their maximized broad-spectrum thermal radiation emission. Conversely, spectrally selective emitters - optimized for the 8–13 µm atmospheric window within longwave radiation - are favored in sub-ambient regimes, whereas broadband emitters become advantageous as the surface approaches or exceeds ambient temperature. Moreover, atmospheric humidity shifts the crossover boundary through its effect on downwelling longwave radiation. Clear crossover regimes between broadband and selective behaviour are identified as a function of relative humidity, ambient temperature and diurnal operational modes. These…