An active hydronic radiative sky cooling system for mitigating envelope thermal-resistance penalties and enabling climate-adaptive cooling-energy savings in Chinese residential buildings

Radiative sky cooling can reject building heat through the atmospheric infrared window, but its surface-level cooling potential may differ substantially from building-side electricity savings because of envelope resistance, source-load mismatch, dew-point constraints, and auxiliary electricity use. This study develops a mechanism-resolved system-level accounting framework for an active hydronic radiative sky cooling system (AHRC) serving a single-zone residential archetype. The framework couples liquid-cooled radiative panels, a hydronic loop, chilled-water storage, dry terminal coils, dew-point protection, auxiliary HVAC backup, and parasitic electricity accounting within hourly June–September simulations. Through a staged comparative design, roof-resistance attenuation, hydronic bypass capture, storage shifting, terminal sensible-cooling delivery, and net electricity savings are separately quantified. Eight Chinese cities spanning dry inland, semi-arid, temperate monsoon, and hot-humid monsoon conditions are used to examine climate-dependent AHRC applicability. The results indicate that, as the roof thermal resistance increased from 0.8 to 10.3 m 2 ·K·W −1 , the passively available cooling energy decreased by approximately 92%, whereas the active liquid loop reduced the system's dependence on heat conduction through the roof. Cold storage increased the seasonal cooling delivery across different cities, with the incremental delivery amounting to 1.33%–9.28% of the baseline cooling load, indicating that its benefits are influenced by cooling availability, load timing, and control strategies. For the 48 m 2 panel system, the net electricity-saving rate ranged from 10.5% to 61.0%, while the sensible cooling-load replacement ratio ranged from 20.2% to 72.1%. Solar heat absorption, ambient convective heat transfer, dew-point constraints, and latent heat loads jointly limited the system's electricity-saving benefits. These findings clarify where the source-side cooling potential is offset within the panel surface energy balance, how the remaining cooling is distributed along the hydronic path, and the climate-dependent operating boundaries of AHRC-assisted residential cooling.