Comprehensive impact of two advanced thermotropic façades designs on building daylight and energy performance

Abstract

Thermotropic (TT) materials have emerged as a promising solution for achieving building energy savings and enhancing indoor environmental quality. However, current research has primarily focused on a single type of TT smart window design. To fully optimize the application of TT hydrogels for both energy efficiency and daylight performance, a comprehensive comparative analysis of various TT smart window configurations is imperative. Additionally, more extensive experimental evaluations across a range of climatic conditions are necessary to validate numerical models of adaptive TT smart windows in energy simulations. This study focuses on the design and development of different TT smart window systems to comprehensively evaluate their impact on building energy consumption and daylight performance. Poly(N-isopropylacrylamide) (PNIPAm), a TT material, was selected for its favourable properties, and its optical characteristics were systematically characterized through a combination of experimental methods and numerical simulations. Two TT smart window systems were designed and developed: one with a TT film integrated into double glazing (DG) and another with TT blinds. The optical properties, as well as the energy and daylight performance of buildings equipped with these TT smart window designs, were analysed using Ray-tracing, EnergyPlus, and RADIANCE simulation tools. The study was conducted for two distinct geographical locations: London (UK) and Ankara (Türkiye), allowing for a comprehensive analysis of the systems’ performance under varying climatic conditions. The reliability of the EnergyPlus model was validated through dynamic outdoor experiments conducted in Türkiye. Results indicated that both TT smart window systems effectively regulate solar energy by transitioning from a clear state at low temperatures to a translucent state at higher temperatures. Compared to conventional DG systems, TT smart windows improve daylight comfort, particularly in areas close to the window. Among the two TT smart window designs, the DG integrated with TT blinds demonstrated superior daylight comfort for indoor occupants and higher heating and lighting energy savings than the DG with a TT film. The TT blinds system exhibited the highest energy efficiency, achieving approximately 10.8 % energy savings in London and 18.9 % in Ankara at a transition temperature of 22 °C. In contrast, the TT film system showed maximum energy savings of 3.5 % in London and 11.2 % in Ankara at a transition temperature of 32 °C. These findings underscore the significant potential of TT smart window systems to enhance energy efficiency and daylight comfort across diverse climatic conditions. Optimal design and implementation of TT smart window systems can further improve both energy savings and indoor environmental quality, contributing substantially to sustainable building practices.