The effect of thickness and dimensions of glass panes on the thermal performance of triple vacuum glazing

Thermal performance of 0.4 m by 0.4 m and 1 m by 1 m triple vacuum glazing (TVG) with 2 mm and 4 mm thicknesses were simulated using a finite volume model. The simulated TVG consists of three glass panes separated by two narrow internal vacuum gaps. Separation of the vacuum gaps is maintained by an array of 0.4 mm diameter and 0.12 mm height support pillars arranged on a regular square grid with an inter-pillar separation of 25 mm. The four internal glass surfaces within the two vacuum gaps are coated with 0.03 emittance low-e coatings. It has been found that 1) by using a smaller middle glass pane compared to both warm and cold side glass panes, disconnecting the middle glass pane from the vacuum edge seal reduces the thermal transmission U-value by 52.3% for 0.4 m by 0.4 m TVG and by 51.0% for 1 m by 1 m TVG compared to the TVG with three same size glass panes, since the lateral heat conduction from the middle glass pane to the edge seal is eliminated, given the marginal improvement in U-value at the centre of glazing area compared to the TVG with three same size glass panes; 2) Since the lateral heat conduction of 0.4 m by 0.4 m TVG is larger than 1 m by 1 m TVG in terms of the ratio of lateral heat conduction over the total heat transfer though the total glazing, the reduction in U-value of the total glazing area of the 0.4 m by 0.4 m TVG due to the disconnection of the middle glass pane from the edge seal is larger than that of the 1 m by 1 m TVG; 3) the thinner the two exterior glass panes of TVG, the lower the U-value of the total glazing area.