Predicted thermal performance of triple vacuum glazing

The simulated triple vacuum glazing (TVG) consists of three 4 mm thick glass panes with two vacuum gaps, with each internal glass
surface coated with a low-emittance coating with an emittance of 0.03. The two vacuum gaps are sealed by an indium based sealant and
separated by a stainless steel pillar array with a height of 0.12 mm and a pillar diameter of 0.3 mm spaced at 25 mm. The thermal transmission
at the centre-of-glazing area of the TVG was predicted to be 0.26 W m2 K1. The simulation results show that although the
thermal conductivity of solder glass (1 W m1 K1) and indium (83.7 W m1 K1) are very different, the difference in thermal transmission
of TVGs resulting from the use of an indium and a solder glass edge seal was 0.01 W m2 K1. This is because the edge seal is so thin
(0.12 mm), consequently there is a negligible temperature drop across it irrespective of the material that the seal is made from relative to
the total temperature difference across the glazing. The results also show that there is a relatively large increase in the overall thermal
conductance of glazings without a frame when the width of the indium edge seal is increased. Increasing the rebate depth in a solid wood
frame decreased the heat transmission of the TVG. The overall heat transmission of the simulated 0.5 m by 0.5 m TVG was 32.6% greater
than that of the 1 m by 1 m TVG, since heat conduction through the edge seal of the small glazing has a larger contribution to the total
glazing heat transfer than that of the larger glazing system.