A Novel Building Component Hybrid Vacuum Glazing-A Modelling And Experimental Validation

The thermal performance of a hybrid vacuum glazing (HVG) was simulated using a finite volume model (FVM) and theoretically analysed using an analytic model. HVG is the combination of a conventional double vacuum glazing (DVG) and a third glass sheet separated by a gas-filled cavity. The DVG integrated within the HVG comprises two 4 mm (0.16 in.) thick glass sheets both coated with a low-emittance (low-e) coating with emittance of 0.16, sealed around their periphery by a 6 mm (0.24 in.) wide indium based sealant and separated by an array of stainless steel support pillars with a diameter of 0.4 mm (0.02 in.), a height of 0.2 mm (0.01 in.), and spaced at 25 mm(0.98 in.) within the vacuum gap. The DVG was fabricated using the pump-out method and subsequently integrated within the HVG. No low-e coating was employed on the third glass sheet. To validate the simulation results, the thermal performance of both the DVG and HVG were analyzed using a guarded hot box calorimeter (GHBC) constructed in accordance with the requirements of ISO 8990 (ISO 1996). The simulation results showed that for the 0.4 by 0.4 m (1.31 by 1.31 ft) HVG with the configuration parameters listed above, the thermal transmission U-value at the centre-of-glazing area was 0.64 W.m(-2).K-1 (0.11 Btu.h(-1).ft(-2).degrees F). Before integration with the third glass sheet, the U-value of the centre-of-glazing area of the DVG was 0.85 W.m(-2).K-1 (0.15 Btu.h(-1).ft(-2).degrees F). The U-value of the HVG calculated using the analytic model was 0.63 W.m(-2).K-1 (0.11 Btu.h(-1).ft(-2).degrees F,) which was in good agreement with that predicted using the FVM with a deviation of less than 1.5%. Using the GHBC, the experimentally determined U-value at the centre-of-glazing area of the HVG was 0.66 W.m(-2).K-1 (0.12 Btu.h(-1).ft(-2).degrees F) which was in very good agreement with the prediction by the FVM with a deviation of 3.1%. The thermal performance of the HVG compares favorably with conventional three-pane insulating glazing systems and offers significant potential as an energy saving building component.