Factors influencing the performance parameters of vacuum glazed smart windows to net zero energy buildings

The progression of smart technologies such as vacuum glazed windows are considered a realistic achievement of the net energy zero buildings (NZEBs). From designers to researchers to builders, there has been an increasing concern about understanding the inter-dependencies between the parameters and influencing factors that determine the performance of vacuum glazed smart windows. This research reviews the performance parameters such as thermal transmittance (U value), thermal resistance (R value), solar transmittance (g value), visible light transmittance (v value) and thermal resistance of residual gas space (Rgas value). These are inter-dependent on factors such as edge seal, support pillar array, low emittance coatings, getters, and effective evacuation process. This research implicates that effective hermetic edge seal provides longevity such as fusion and solder glass edge sealed vacuum glazing could be cost-effective and energy efficient solution. Stainless steel support pillar array is an unavoidable compromise on U value. This review shows that an increase of the size of glass sheet increases support pillar array improving the overall U value. Also, an addition of low emittance coatings enhances U value whilst maintaining v value. To improve the overall life span of the vacuum glazed smart window, an incorporation of combo-getter that absorb any gases released from the internal glass surfaces in to into the vacuum cavity from the glass surface which prevents degradation of vacuum pressure and provide long term vacuum pressure stability in the vacuum glazed smart window. A recent improvement in the understanding of evacuation process shows that hot-plate surface heat induction of 60˚C improved the vacuum pressure and mitigates the pump-out hole sealing process whilst lessening the temperature induced stresses.