Thermo-optical performance of building glass under salt sedimentation

Abstract

The phenomenon of salt sedimentation on the building glass surface occurs in coastal salt-fog climates, leading to the changes in surface heat transfer characteristics and optical properties, which affects the indoor environment and gradually reduces building energy performance. Regrettably, there remains a paucity of research concerning the impact of salt sedimentation on the thermal and optical performances of building glass. This study investigated the salt sedimentation features of building glass using an indoor accelerated test, and explored the relationships between surface heat transfer coefficients, optical properties and salt sedimentation. As the spray duration grew, the sedimented salt stains appeared more dispersed and less dense, but their dimensions increased, exhibiting an exponential growth tendency. The salt sedimentation per unit area grew logarithmically with the spray duration, with the magnitudes being 14.4 to 40.0 mg/m² and 15.6 to 44.3 mg/m² under 5% and 10% brine concentration conditions, respectively. The convection heat transfer coefficient (CHTC) and radiative heat transfer coefficient (RHTC) showed a linear monotonic increase with the salt sedimentation, in contrast to the control condition, with the maximum growth rates reaching 178.7% and 97.2%, respectively. The extended CHTC model could be used to calculate the CHTC regarding the impact of salt sedimentation and wind speed. The entire solar spectral transmittance and reflectance was affected by salt sedimentation, and the visible light transmittance, reflectance, hemispherical emissivity, and shading coefficient of low-E and clear glasses all decreased linearly with the increase of salt sedimentation.