Thermal performance of PEGylated silica aerogel-based smart composite for energy efficiency of building glazing

Achieving carbon neutrality in modern architecture requires energy-efficient passive design strategies that integrate green materials, smart technologies, and high-performance insulation. Windows and skylights play a critical role in Net-Zero Buildings (NZBs), demanding high transparency, superior thermal insulation, and year-round thermal comfort. This study introduces and investigates a novel smart composite material, polyethylene glycol-mediated silicon aerogel (Siag@PEG), as a transparent insulation material (TIM) with dual thermal and optical properties. A key innovation is the use of PEG as a solid-solid phase change material (PCM), which effectively resolves the potential leakage issues associated with solid-liquid PCMs when integrated into window glazing units. A comprehensive numerical model was developed to simulate phase transitions and thermal energy dynamics using a transient conjugate heat transfer approach coupled with the enthalpy-porosity method including thermal radiation. The thermal performance of a double-glazed window filled with Siag@PEG was evaluated and compared to conventional air-filled and pure PEG-filled systems under standard solar irradiance conditions (1 SUN, AM 1.5). Results demonstrate that an optimized Siag@PEG composite with a 5% mass loading of silica aerogel exhibits promising thermal benefits. Specifically, it achieved a decrease in indoor temperature and thermal gradients of 2.57 K, 3.39 K, and 6.41 K at 30, 60, and 90 min, respectively. The optimum energy consumption was determined to be 221.27 kJ/kg, yielding an impressive energy efficiency improvement rate (EEIR) of 86.45%. Furthermore, at the indoor glass surface of the double-glazed unit, the Siag/PEG@5% system showed superior inner heat transfer (−21.21 W), surface heat flux (−424.11 W/m2), and an EEIR of 22.02%, significantly outperforming conventional and pure PEG-filled window glazing systems. These findings reveal the optimal thermal and energy storage/release performance of the Siag@PEG composite, underscoring its significant potential to enhance the energy efficiency of transparent building envelopes and contribute to the realization of Net-Zero energy buildings.