A numerical study on using underlying parabolic trough reflectors to enhance the performance of bifacialized radiative cooling structures

Recent advancements have made passive radiative coolers (RCs) a promising, low-cost, and scalable technology for reducing cooling loads. However, their widespread adoption remains limited due to challenges: effective cooling requires unobstructed, sky-facing surfaces, and RCs are subject to heating from both atmospheric and solar radiation. These limitations can be mitigated by integrating parabolic trough reflectors beneath the RC, enabling a bifacial configuration that doubles the radiative surface area and blocks solar and atmospheric radiation incident from large zenith angles. This study employs both forward and reverse Monte Carlo ray tracing methods to investigate the influence of the RC structure and trough geometry on the RC performance. Specifically, the effects of the tubular RC's diameter and length, along with the trough's height, length, and focal length, are studied. The integration of parabolic trough reflectors enhances the net cooling power by more than a factor of two. Additionally, the effects of convective heat transfer and absorbed solar radiation are examined. This work also assesses the solar influence by considering solar directionality and concentrated solar irradiance. A solar-angle-dependent trough effectiveness diagram is proposed to guide location-specific RC system design. Using the optical properties of a hierarchically porous PVDF-HFP emitter, the bifacial RC configuration achieves a sub-ambient cooling temperature of 285.2 K under 300 K ambient condition, accounting for convection and diffuse solar radiation. These results highlight the potential of bifacial RCs for integration into building envelopes, HVAC systems, and off-grid cooling solutions.