1. Simulated thermal performance of triple vacuum glazing
Fang Y., Hyde T.J., Hewitt N
School of the Built Environment
University of Ulster
Northern Ireland, UK

2. What is triple vacuum glazing
Edge seal
Wood insulation not shown
(a)
Radiative heat flow
Wood frame
Cold side, To
Warm side, Ti
Not to scale
Heat conduction through
edge seal
Heat conduction through pillars
Glass
panes
(b)
Surface A
Surface B
Surface C
What is triple vacuum glazing
Three parallel glass sheets
Low emittance coatings, emittance = 0.03
Evacuated space vacuum <0.1Pa
Indium edge seal
Support pillar, diameter: 0.3 mm, compressive stress<1.3 GPa
U-value<0.2 Wm-2K-1

3. Simulation boundary conditions (EN ISO 10077-1)
Air temperatures
Inside air temperature 20 ºC
Outside air temperature 0 ºC
Convective heat transfer coefficients
Inside glass surface: 7.7 Wm-2K-1
Outside glass surface: 25 Wm-2K-1

4. Thermal network of a unit cell
Glass pane I
Glass pane II
Glass pane III I t II
III 2 / a
Vacuum gap 1
Vacuum gap 2
Pillar 1
Pillar 2 p i h T , o
(a)
(b) R g 1 r ,I

5. Analytic models Thermal resistance of each glass pane
Thermal resistance due to radiation between two glass panes
Thermal resistance due to heat conduction of pillar

6. Analytic models (continued)
Total thermal resistance
Total thermal transmittance

7. 3-D finite volume model Governing equation
where T: temperature of each finite volume, t: time
: thermal diffusivity, k : thermal conductivity, ρ : density, c : specific heat capacity

8. 3-D finite volume model (continued)
Radiative heat flow between two surfaces
Pillars integrated and modelled directly
Cylindrical pillars replaced by square pillars with the same area

9. 3-D isotherms of triple vacuum glazing

10. Heat transmission of 0.5 m by 0.5 m triple vacuum glazing
with the indium and solder glass edge seals
Edge seal width
(mm)
Indium sealant, total glazing U-value
(W.m-2.K-1)
Solder glass sealant, total glazing U-value
U-value deviation due to Indium and solder glass edge seal (%)
Frame rebate depth (mm) 10 3
0.77
0.60
0.76
0.59
1.30
1.67 6
0.86
0.65
0.85
0.64
1.16
1.54
0.96
0.72
0.95
0.71
1.04
1.39

11. Influence of frame rebate depth

12. Influence of glazing size

13. Conclusions For a 0.5 m by 0.5 m triple vacuum glazing
The deviation of U-value predicted by the analytic and finite volume models is 1.8%
The largest difference in U-value for indium and solder glass edge seals (3 mm) was 1.67%
Increasing the edge seal widths from 3 mm to 10 mm, with no frame, the U-value increased by 24.7%;
with a 10 mm frame rebate depth, the U-value increases by 20%;

14. Conclusions (continued)
Increasing the frame rebate depth from 0 to 15 mm decreased the U-value by 32.9%
Increasing the glazing size from 0.5m by 0.5m to 1 m by 1 m decreased the U-value by 32.2%

15. Thanks for your attention Questions?