Thermal performance of vacuum glazing with tempered glass panes

The thermal performance (U-value) of 0.4 × 0.4 m and 1 × 1 m double vacuum glazing (DVG) and triple vacuum glazing (TVG) using annealed and tempered glass panes with pillar separations of 25 and 50 mm respectively was simulated. It was found that (1) for both dimensions of DVG with 0.03 emittance low-emittance (low-e) coatings, the U-values at the centre of the glazing area of the DVG made of annealed and tempered glass panes were 0.57 and 0.30 Wm−2 K−1, a reduction of 47.4 %; (2) for both dimensions of TVG with 0.03 emittance low-e coating, the U-values at the centre of glazing area of the TVG with annealed and tempered glass panes were 0.28 and 0.11 Wm−2 K−1, a reduction of 60.7 %. The reduction in U-values for both DVG and TVG results from the significant reduction in pillar number, leading to the large reduction in heat conduction through the pillar arrays. The reduction in U-values from using tempered glass panes instead of annealed glass panes for TVG is larger than that for DVG; this is because the radiative heat transfer of TVG with three glass panes is much lower than that in DVG with two glass panes; therefore, the heat conduction through the pillar array in TVG plays a larger role compared with that in DVG. The reduction in pillar number in TVG results in a larger reduction in U-value compared to DVG; thus, using tempered glass panes in TVG confers a greater advantage compared to DVG, given that DVG can also achieve a large reduction in U-value when switching from using annealed glass panes to tempered glass panes