Energy-saving potential of thermochromic coatings in transparent building envelope components

Advances in the energy management of buildings are essential for reducing the carbon footprint in the building sector. Applying special window coatings of varying optical properties offers new chances for improved energy efficiency. Thermochromic vanadium oxide (VO2) is an important material for this development and is, therefore, one of the most investigated thermochromic materials. It changes its transmittance in the infrared spectral range in response to a changing temperature. In this study, VO2 coating was deposited on ultra-thin flexible glass in a continuous roll-to-roll sputtering process. The thermochromic layer had a thickness of 70 nm, and it was embedded between two zirconium oxide layers of 170 nm each. The luminous transmittance of the stack was 50%. A solar modulation of 9.6% was reached between the low and high-temperature states. The transition temperature between the cold infrared transparent and the warm infrared opaque state was determined to be 22°C. Different application scenarios for this material were evaluated. The modulation of the solar transmittance was calculated for the combination of VO2 with state-of-the-art low-e coatings. Our findings show that such a combination does not offer a benefit for reducing the energy demand of a building. However, a stand-alone implementation of thermochromic coatings has a high potential if the energy consumption of the building is dominated by cooling demands.