Fabrication of thermally insulative and highly transparent cellulose aerogel for climate-adaptive energy efficient window

Minimizing the energy demand of buildings by utilizing innovative materials for transparent building envelopes, such as windows, represents a promising strategy to enhance energy efficiency and contribute significantly to carbon neutrality at worldwide. Windows are less energy efficient than non-transparent building components, primarily due to their higher U-value and increased solar heat gain. Designing an ideal energy-efficient window requires a synergistic combination of high visible light transmittance, superior thermal insulation, and effective solar heat regulation capabilities. In this study, an advanced energy-efficient glazing system was developed by integrating thermally insulative features and different surface optical properties. To assemble such structure, a key component of a transparent and insulating film was synthesized from sustainable and renewable cellulose with high length-to-diameter ratio and optimized size distribution, originated from high-pressure homogenized modification and sonication. The as-synthesized film exhibits excellent transparency (∼90 %) and outstanding thermal insulation (0.027 W/m·K), accompanying with attachable capability onto glass surfaces via electrostatic forces. Hot stage and outdoor demonstration tests revealed that a single-pane glazing applied with this film presented superior insulation properties compared to conventional double-pane glazing while high visible light transmittance was still reserved. Based on this transparent cellulose aerogel, a composite window structure combining thermal insulation and spectral selective feature was fabricated for various climates. The results of building energy simulation supported that the energy saving performance of the composite window was superior to that of existing counterparts, and it could achieve up to 40 % energy savings compared to single-pane glazing. The proposed energy-efficient windows, made from cost-effective materials derived from biomass resources, hold significant potential as replacements for commercially available glazing systems in large-scale applications. • The aerogel with high light transparency and high thermal insulation was synthesized. • A composite film combined thermal insulation and spectral selection was fabricated. • The designed window can save up to 40 % of energy compared to single-pane glazing.