Study of thermochromic glass performance in the Danish climate and visual comfort perspectives

Windows are key elements in the building envelope in terms of energy performance and comfort. The recent development of a new generation of so-called smart thermochromic glazings with the purpose of improving thermal comfort inside buildings raises the question of the visual comfort level offered by such glazings. This paper looks into the response of several commercial products to the specific Danish climate by running numerical simulations of a single-room building with the Energy Plus (DesignBuilder) software. The study case has a central window on each wall. The study highlights that the thermochromic effect is not activated for a major part of the year. In addition, we point out the decisive influence of the sky condition, as well as the non-negligible wind influence on the thermochromic response. Regarding indoor illuminance comfort, we observe a very variable annual performance depending on the tested thermochromic glazings. Moreover, we notice that thermochromism causes an increase in under-lighted annual time, which raises comfort issues, especially in a Nordic context.