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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 DVGintegrated within theHVGcomprises two 4mm(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 25mm(0.98 in.) within the vacuum gap.TheDVGwas 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 0.4m(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·°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·°F). The U-valueof theHVGcalculated usingthe analyticmodelwas0.63 W·m-2·K-1 (0.11 Btu·h-1·ft-2·°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·°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.

Citation: ASHRAE Transactions -- Volume 119, Part 2, Denver, CO.