Review on window technologies and future prospects: A comprehensive state of the art analysis.

Fenestrations account for more than 40% of the energy consumption in the residential building sector, this by means of the heat gain-loss occurring by glazing materials. Highly efficient glazing technologies include vacuum glazing systems, which consider multipane glazing with evacuated interlayer for heat transfer optimisation, reporting heat transfer values lower than 1.0W/m²K compared to values for soda lime glazing which are 5.5W/m²K in average. The aim of this paper is to investigate the relation and efficiency of evacuated glazing in comparison to static (traditional) and dynamic (advanced) solutions in windows for the heat transfer reduction. The heat transfer interaction will be analysed contrasting parameters as thickness, coatings, multiple panes, gap fillings, and advanced active solutions for variable transmittances and energy harvesting. Considering the solar incidence, the use of coatings is the most effective way to reduce and control the solar heat gain coefficient in a passive and active way by the use of LowE, anti-reflective and self-cleaning coatings. Alternatively, the visible transmittance adjusts by including tinting materials in fenestrations, but is a reported drawback when integrated in multiple layered fenestrations such as triple and quadruple glass windows. Triple glazing windows resulted an effective method to reduce U-value in windows reducing 22.2, 33.3 and 41.4% when includes filled cavities of argon, krypton and xenon gas respectively and when compared to Air filled gaps. Although vacuum glazing reported heat transfer coefficients lower than 0.7W/m²K with merely double panes; therefore VG expects to surpass reported results if it is effectively reduced the heat transfer through internal pillars and edge conduction.