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

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

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

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

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

Analytic models (continued) Total thermal resistance Total thermal transmittance

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

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

3-D isotherms of triple vacuum glazing

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

Influence of frame rebate depth

Influence of glazing size

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%;

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%

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