# Effect of Cavity Vacuum Pressure Diminution on Thermal Performance of Triple Vacuum Glazing
## 3 Results and Discussion  
### Thermal Performance Analysis of 10-mm Wide Edge-Sealed TVG  
The \(U_{c}\) and \(U_{t}\) values of 0.28 Wm\({}^{-2}\) K\({}^{-1}\) and 0.94 Wm\({}^{-2}\) K\({}^{-1}\) were simulated for the triple vacuum glazing at the cavity vacuum pressure of 0.001 Pa, and the solar heat gain coefficient (G value) was predicted to be 0.7. A decrease of 15.15% in the \(U_{c}\) value and 10.47% in the \(U_{t}\) value compared with the results of [PERSON] et al. [16] were found. Such decrement in the \(U_{c}\) and \(U_{t}\) values can be attributed to the fact that the secondary edge seal was not used in the current model and due to the integration of cavity thermal conductivity assigned to achieve 0.001 Pa (high vacuum pressure). The \(U_{c}\) value of 0.2 Wm\({}^{-2}\) K\({}^{-1}\) was predicted by [PERSON] et al. [14] for a TVG made with 6 mm, 4 mm, and 6 mm thick glass panes and four coated surfaces, each with the emissivity value of 0.03, whilst in the present case, all glass panes are 4 mm thick and have three SnO\({}_{2}\)-coated surfaces, each with emissivity of 0.15. By accounting for all parameters, the present model is in good agreement with [PERSON] et al. [14], with an error of approximately 4.7%. In comparison to the results of [PERSON] et al. [33], a \(U_{c}\) value of 0.26 Wm\({}^{-2}\) K\({}^{-1}\) and \(U_{t}\) value of 0.65 Wm\({}^{-2}\) K\({}^{-1}\), an increase of 7.14% in \(U_{c}\), and 30.85% increase in \(U_{t}\) values obtained from the modelled TVG was found. [PERSON] et al. [33] used a 500 mm \(\times\) 500 mm size TVG with a 6 mm-wide edge seal and four coated surfaces each having emissivity of 0.03. One of the potential reasons for such an increase in the \(U_{t}\) value obtained from the current model is linked to edge effects. A 10-mm wide edge seal is used in this study, as compared to 6 mm wide, to simulate the design fabricated by the author given elsewhere [16]. Glazing size, due to edge effects, also influences the total thermal transmittance; for a TVG with size of 500 mm \(\times\) 500 mm, \(U_{t}\) was calculated to be 38% greater than that of a 1 m \(\times\) 1 m glazed area ([PERSON] et al. [34]). The emissivity of the surface coatings used in this study is 0.15, as compared to that of 0.03 in the literature. A model with same sample size, surface emissivity, and seal materials' properties developed to validate the method and results were in good agreement to those presented by [PERSON] et al. [34], with an error of 6.3%. The isothermal temperature distribution of the simulated TVG for the cold-side, middle, and warm-side surfaces, as shown in Figures 3-5, illustrate significant heat-transfer characteristics necessary in assessing the performance of TVG at high vacuum pressure, in which the heat flux from the warm side of the space in a building applied to the indoor glass surface, the thermal radiation between two inner glass surfaces, heat conduction via the edge seal and support pillars, and the heat flux from the outdoor (cold) surface of the glass to the outdoor ambient as per ASTM standard temperatures [35] are required. The average warm-side (indoor) and cold-side (outdoor) surface temperatures are simulated to be 19.22 \({}^{\circ}\)C and \(-\)9.44 \({}^{\circ}\)C for the total surface area, respectively, whilst being 20.14 \({}^{\circ}\)C and \(-\)14.13 \({}^{\circ}\)C for the centre-of-pane surface area, respectively. Figure 3 shows the simulated warm-side isothermal temperature distribution of the surface of the TVG, showing the temperature dissimilarity from the edge area headed to the central area and around the support pillars in the central glazing area.