The Cooling Station: Combining hydronic radiant cooling and daytime radiative cooling for urban shelters

Global warming has tried the world with challenges like increased cooling energy demand, heatwaves, and unbearable summers, with accentuated nuances in dense urban areas. Here heat island effects are most pronounced and heat-safe pockets are a necessity rather than a comfort. Bus stops can act as shelters for commuters with the advantage of usually being well distributed across the cities in the form of semi-enclosed spaces. Daytime radiative cooling is a novel technology that enables free cooling of a substance under direct solar radiation. In this study, radiative cooling is combined with the hydronic radiant cooling technology in the integrated design of the Cooling Station, a bus shelter capable of providing energy-free urban thermal comfort throughout the summer. The study aims at evaluating the effect of geometry, orientation, surrounding elements, and climate on the performance of the Cooling Station. It is found that humidity and surrounding buildings diminish the performance of the radiative cooling panels, but the penalty can be significantly mitigated by applying non-reciprocal asymmetric transmission windows on top of the panels. The results indicate that the optimized design of the Cooling Station is capable of decreasing the Universal Thermal Climate Index (UTCI) by up to 10 °C in the considered scenario of a mid-rise area in Tehran, the capital of Iran. Further, the performance evaluation across all Köppen-Geiger climate classes demonstrates that in hot and semi-arid climates, the Cooling Station develops its full potential.