CFD analysis of environmental impacts on a thermochromic smart window

Abstract

Thermochromic (TC) glazing is an advanced smart window technology that can help to achieve nearly zero-energy buildings. The glazing temperature that affects TC thermo-optical properties directly impacts its energy-saving performance. However, the impacts of solar radiation and natural convection occurring on this temperature-sensitive material are not yet fully understood. Compared to previous focuses on material properties and energy evaluation, this study aimed to provide a different view from thermo-fluid dynamics on the heat transfer characteristics of a TC window, with impacts of environmental factors addressed. A validated Computational Fluid Dynamics (CFD) model identifies the environmental impacts on the TC glazing temperatures under the coupled radiative and convective heat transfer. Furthermore, a theoretical model was developed with an empirical factor obtained from CFD results. It enables a simple calculation to obtain the TC glazing’s temperature by using solar factors, outdoor temperatures and optical properties. The model suggests that the temperature difference between the TC glazing and the ambient is a function of absorbed solar irradiation (∝q̇total0.75). The predictive model is then tested using typical climate conditions in three cities in China with different solar angles, which demonstrates good agreement with an average absolute error of 5% compared to simulated glazing temperature. This estimation method can further assist in material design, product selection and Building Energy Simulations to achieve a TC window design that is ‘smart’ on seasonal change requirements for different regions.