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Q: Does vacuum glass lose thermal performance when installed horizontally as a skylight?
A: No. Vacuum glass maintains stable thermal performance when installed horizontally because its vacuum cavity contains virtually no gas, eliminating convection heat transfer within the cavity.When conventional insulating glass is installed horizontally, the gas inside the insulating cavity can become heated and generate convection currents. Heat is then rapidly transferred upward through the cavity, causing the overall heat transfer coefficient (U-value) to increase significantly. This is one of the key reasons why many skylights experience excessive heat gain in summer and heat loss in winter.
Measured data: A conventional 6 mm + 12A + 6 mm argon-filled coated insulating glass unit has a U-value of 1.45 W/(m²·K) when installed vertically in a wall. When the same glass is installed horizontally as a skylight, its U-value increases to 2.14 W/(m²·K), representing an approximately 48% increase in U-value when installed horizontally.
Five Advantages of Vacuum Glass for Skylights
1. High energy efficiency with stable thermal performance
Vacuum glass can achieve a U-value as low as 0.3 W/(m²·K), providing approximately 2–4 times the thermal insulation performance of conventional insulating glass and potentially reducing overall building energy consumption by around 20%.
More importantly, the vacuum cavity contains no gas, eliminating convection heat transfer within the cavity. As a result, vacuum glass is not significantly affected by installation orientation, maintaining stable thermal performance when installed horizontally as a skylight.
2. Reduced condensation risk
The vacuum cavity contains no moisture, while the inner glass surface can maintain a temperature closer to the indoor environment. This significantly reduces the risk of condensation, making vacuum glass particularly suitable for applications such as hospitals, schools, museums, and other buildings with strict requirements for indoor environmental conditions.
3. High strength and wind-load resistance
Vacuum glass can be combined with a laminated glass structure, in which the PVB interlayer helps hold the glass fragments together in the event of breakage, reducing the risk of falling fragments.
With a fully tempered glass substrate, the structure can achieve wind-load resistance of up to 7,200 Pa, depending on the specific glass configuration and application requirements.
4. Thin, lightweight, and highly efficient
A single 8.3 mm vacuum glass configuration can provide thermal insulation performance comparable to that of a much thicker traditional wall structure, while being significantly thinner than triple-glazed units.
Compared with a triple-glazed configuration, it can reduce the glazing weight by more than 10 kg/m², helping reduce structural loads while maintaining high thermal insulation performance.
5. Suitable for different climates and applications
Vacuum glass can be used across a wide range of climates, from hot and humid regions to cold northern climates and high-altitude areas.
Depending on project requirements, configurations can be customized with options such as Low-E coatings, insulating cavities, and different laminated structures, allowing vacuum glass to meet diverse architectural and climatic requirements.
