Active-passive dual-control smart window with thermochromic synergistic fluidic glass for building energy efficiency

Windows are the least energy-saving part of the building envelope. To realize building energy-saving, smart windows have been developed. However, traditional fully passive thermochromic smart windows cannot adjust their transparency according to the complex outdoor climate “intelligently”, and only adjusts the solar radiation, ignoring the indoor temperature increase caused by heat entering the room in the form of convection. Here, we embed poly (N-isopropylacrylamide) (PNIPAm) microgel into a highly transparent polyacrylamide (PAM) matrix, the PNIPAm-PAM hydrogel exhibits an ultrahigh luminous transmittance of 90.6% and solar modulation of 65.5%. By introducing nanoparticles into thermochromic hydrogels and combining the advantages of fluid glass in heat convection control, we develop a new type of active and passive dual-control smart window (APDC smart window) for the first time. In the indoor demonstration, it is proved that the smart window injected with 1-cm PNIPAm liquid has the best energy-saving ability, and the greenhouse installed with a 1-cm PNIPAm liquid smart window reduces the indoor air temperature by 15 °C compared with normal glass. In the outdoor demonstration, the indoor air temperatures of the APDC smart windows are reduced by ∼14 °C, ∼16 °C, ∼8.5 °C, and ∼9.5 °C respectively in different orientations of east, west, south, and north than normal glass window, and it is reduced by ∼4–8 °C compare with the 1-cm PNIPAm liquid smart window. This opens a new avenue for energy-efficient buildings and greenhouses.