Modelling and experimental validation for the thermal performance of a hybrid vacuum glazing

The thermal performance of a hybrid vacuum glazing (HVG) with dimensions of 0.4 m by 0.4 m was modelled using a finite volume model (FVM). The HVG is the combination of a conventional double vacuum glazing (DVG) and a third glass sheet separated a gas filled cavity. The DVG integrated within the HVG comprises two 4 mm thick glass sheets both coated with a low-emittance (low-e) coating with emittance of 0.16, separated by an array of stainless steel support pillars with a diameter of 0.4 mm and a height of 0.2 mm, spaced at 25 mm within the vacuum gap, sealed around their periphery by a 6 mm wide indium based sealant. The thermal performance of both DVG and HVG were characterised using a guarded hot box calorimeter (GHBC). The simulation results showed that for the 0.4 m by 0.4 m HVG with the configuration parameters listed above, the thermal transmission U-value of the centre-of-glazing area was 0.64 W.m-2.K-1. Before integration with the third glass sheet, the U-value of the centre-of-glazing area of the DVG with dimensions of 0.4 m by 0.4 m was 0.85 W.m-2.K-1. No low-e coating was employed on the third glass sheet. The U-value of the HVG calculated using the analytic model was in good agreement with that predicted using the FVM with a deviation of less than 1%. Using the GHBC, the experimentally determined U-value of the centre-of-glazing area of the HVG was 0.66 W.m-2.K-1 which was in very good agreement with the prediction by the FVM with a deviation of 3.1%.