Spectral tuning of window glasses for improving energy efficiency of buildings

Abstract

There are significant efforts for improving energy efficiency of residential and of fice building for reducing total energy consumption and emission of greenhouse gases. Smart windows are one potential technology that can be used for achieving this pur pose. In this study, thermo-chromic glazings with VO2 pigments, promising passive alternatives among smart windows, are studied for obtaining high energy efficiency while considering visual comfort for office buildings. Such systems alter optical proper ties such as visible and solar transmittance according to their transition temperatures based on environmental conditions. This study considers two different technologies that are VO2 nano-particle embedded thermo-chromic window and attached thin VO2 pig mented thermo-chromic film on an ordinary window glass separately. Optical properties of pigmented glazings and coatings depend on design variables such as pigment size, concentration and thickness. The refractive indices are calculated by effective medium theory according to various design variables. Then, radiative transfer equation is solved by four flux method to find optical properties of nano-particle doped thermo-chromic window after scattering and absorption coefficients are determined by Lorenz-Mie the ory in the first technology. However, optical properties of whole attached system are determined by transfer matrix method in the second technology. After that, lighting, cooling and heating energy consumption constitute the total energy consumption are determined according to optical properties. Then, optimal thermo-chromic systems are determined by grid search optimization (single or multi variable search) for high energy savings performance for both technologies in various climatic conditions and transition temperatures. Consequently, significant improvement is achieved with both technologies especially in hot climates.