Development of testing procedures for assessing the thermal and optical performance of thermochromic coatings for buildings

In climates where cooling and heating demands are balanced, thermochromic (TC) building coatings represent a promising solution to reduce the overall energy consumption for space conditioning. The main TC type proposed for building application, based on leuco dye, is however affected by photodegradation and there is an increasing research interest towards more durable TC solutions. This study suggests outdoor and laboratory measurement procedures to characterize the performance of TC building coatings. In an outdoor experimental campaign, roof and façade components with leuco dye-based TC coating were tested for 13 consecutive days. Moreover, spectrophotometric measurements were carried out to: i) characterize the solar, light and near-infrared reflectance and color properties of TC panels in pristine conditions and at different aging stages in the colored/colorless phases; and ii) assess the switching process under transient thermal conditions with the newly developed procedure. In the outdoor monitoring campaign, a maximum surface temperature difference between TC panels (colorless phase) and reference ones of ~35°C was found. Moreover, a 0.1 reduction in solar reflectance of TC panel in the colorless phase was reported after 3 days of outdoor exposition due to photodegradation, and the hysteresis of the TC panels undergoing the switching process was measured.