Dual-responsive energy-saving chromic smart windows with active/passive controlled radiative cooling

Conventional building windows suffer from numerous limitations in light modulation, thermal insulation, and energy utilization, struggling to meet the dual demands of modern buildings for high energy efficiency and consistent thermal comfort. In response to the various stages of energy loss through windows, a design concept for a hydrogel-based smart material that dually regulates solar transmittance and infrared emissivity has been proposed. Stimulated by temperature or humidity, this hydrogel can achieve significant changes in visible light transmittance (86.8 %) and infrared emissivity (50.1 %) autonomously and independently, exhibiting excellent solar modulation capability (78.7 %) and controllable radiative cooling performance (switching between a heat dissipation layer and an insulation layer). The hydrogel exhibits passive response to dual stimuli either independently or synergistically, with the capability to restore its initial properties through active interventions such as water mist spraying. In various application conditions, indoor temperatures and window surface temperatures can be reduced by up to 23.1°C and 13.2°C, respectively. Moreover, simulation results indicate that this design can be applied across various climatic zones globally (achieving annual energy savings of 2.6 % - 55.9 %), providing new design ideas and technical directions for building energy saving.