With the global temperature rise by global warming, population growth, and urbanization, space cooling and air-conditioning are developing into a major challenge in building comfort and liveable habitation. The traditional air-conditioning system requires greenhouse gases such as Hydrofluorocarbon (HFC) and consumes a vast amount of fossil fuel. Solar and thermal radiation modulation by smart windows and adaptive radiative cooling devices are drawing great interest as alternative cooling systems. Thermochromic hydrogel-based smart windows are promising indoor temperature regulator which undergoes reversible solar transmittance change at around the phase change temperature. Adaptive radiative cooling devices can passively or actively change their thermal radiation emissivity, thereby man...[ Read more ]

With the global temperature rise by global warming, population growth, and urbanization, space cooling and air-conditioning are developing into a major challenge in building comfort and liveable habitation. The traditional air-conditioning system requires greenhouse gases such as Hydrofluorocarbon (HFC) and consumes a vast amount of fossil fuel. Solar and thermal radiation modulation by smart windows and adaptive radiative cooling devices are drawing great interest as alternative cooling systems. Thermochromic hydrogel-based smart windows are promising indoor temperature regulator which undergoes reversible solar transmittance change at around the phase change temperature. Adaptive radiative cooling devices can passively or actively change their thermal radiation emissivity, thereby manages indoor temperature. At present, these technologies can only change from neutral to cooling mode, and thus, their energy-saving potential is revealed only in hot and sunny weather. In this work, all-weather energy-saving windows were realized. This thesis introduces two novel solutions to achieve all-weather energy saving by smart windows. The first work presents the solar and thermal regulating (STR) window made of poly(N-isopropylacrylamide) (pNIPAm) hydrogel and silver nanowire (AgNWs) composite which reversibly switches between transparent heat preservation mode and opaque heat dissipation mode via solar and thermal modulation. The solar ( Δ?_??? = 53.8% ) and thermal radiation ( Δ?_?ℎ? = 57.1% ) modulation successfully regulated indoor temperature. The performance of the STR window was tested under simulated summer and winter conditions. The STR window maintained the indoor temperature ~15℃ and ~6℃ cooler than Low-e glass and bare hydrogel smart window, respectively, in summer. In winter, ~1℃ higher indoor temperature was determined in the STR window equipped house. The second work introduces ethyl cellulose (EC) based radiative cooling and transparent photothermal heating dual-mode window. The porous EC film with high hemispherical solar reflectance (?_??? = 97%) induced ~1.7 ℃ daytime cooling during at noon, from 12:30 to 13:30. When the window was turned to the heating mode, the transparent photothermal coating raised the temperature by ~16.8 ℃ at most. The accelerated durability test ensures sustainable material stability of the STR and dual-mode windows under repeated operation cycles and UV light exposure. It guarantees the feasibility of the two presented works in practical uses. At last, the potential improvement was discussed with the possible cutting-edge technologies applicable to the windows.