Outdoor adaptive temperature control based on a thermochromic hydrogel by regulating solar heating

In outdoor environments, solar heating in summer leads to the overheating of equipment or buildings while in winter these objects would overcool and would necessitate heating to maintain their suitable operating temperature. Temperature regulation based on cooling and heating accounts for global energy consumption and global greenhouse gas emissions. In this work, a strategy based on a high emittance polymer, thermochromic hydrogel, and black solar absorber was proposed to passively control temperature by regulating solar heating under sunlight. The system can seamlessly transition between "cooling" and "heating" modes based on the critical temperature Tc of the thermochromic hydrogel. Tc can be adjusted within a range of 25 °C to 45 °C to accommodate diverse temperature control requirements. When the temperature of the coating material stack increased from 20 °C to 60 °C, the heating/cooling power ranged from 675.0 W·m−2 to − 86.2 W·m−2, switching from the "heating" to "cooling" modes, respectively. The designed coating demonstrated a potential energy-saving capability, with approximately 20.3 % reduction in energy consumption compared to conventional coatings. Outdoor experiments revealed that the temperature of the coating remained more stable and was approximately 10 °C or 7 °C lower than that of reference coatings. These results indicated combining solar heating and radiative cooling with thermochromic hydrogels can provide a potential approach to achieving outdoor adaptive temperature control for energy saving.