The thermal insulation coefficient of insulating glass (usually expressed by K value or U value) is not a fixed value and varies greatly depending on the configuration of the glass. In simple terms: The lower the K value, the better the heat insulation performance.
1. Ordinary white glass insulating glass
This is the most basic configuration of insulating glass, consisting of two ordinary float glass sheets and an insulating layer in between.
Structure: 5mm glass + 12mm insulating layer + 5mm glass (often written as 5+12A+5)
Thermal insulation coefficient (K value) : approximately 2.8 to 3.0 W/(m²·K)
Evaluation: This is currently the most common type on the market. Its heat insulation performance is average and it can meet the most basic heat preservation requirements.
2. Single-silver Low-E insulating glass (single-layer low-emissivity coated glass)
This is currently the mainstream configuration of energy-efficient buildings. Coating a low-emissivity film on the inner side of a piece of glass can reflect far-infrared heat energy and greatly enhance its heat insulation performance.
Structure: 5mm Low-E glass + 12mm argon gas + 5mm white glass
Thermal insulation coefficient (K value) : It can be reduced to 1.4 to 1.8 W/(m²·K).
Evaluation: The heat insulation performance is nearly twice that of ordinary insulating glass, with high cost performance. It is the first choice for energy-saving doors and Windows.
3. Double-silver/triple-silver Low-E insulating glass
Based on the single silver Low-E, it has more coating layers and more optimized performance. While ensuring high light transmittance, it also has higher heat insulation and sun protection performance.
Structure: More complex coated glass + insulating layer
Thermal insulation coefficient (K value) : It can reach 1.0 to 1.4 W/(m²·K)
Evaluation: It belongs to high-performance energy-saving glass and is often used in buildings with high energy-saving requirements.
4. Increase the number of hollow layers or fill them with gas
The insulation effect can be further enhanced by adding a hollow layer (made into a three-glass two-cavity structure) or by filling the hollow layer with a gas more inert than air (such as argon or krypton).
Three-glass two-cavity (white glass) : The K value can reach approximately 2.0 W/(m²·K)
Three-glass two-chamber (double Low-E + filled with inert gas) : The K value can be as Low as 0.7 to 1.0 W/(m²·K) or even lower.
Evaluation: This is a standard configuration for passive houses and ultra-low energy consumption buildings, with excellent heat insulation performance.
Important influencing factors
The type of glass: Whether Low-E coating is used is the most crucial factor affecting the K value.
Hollow layer gas: Filling with inert gas (such as argon) can reduce the K value by approximately 0.2-0.3 compared to pure air.
The width of the hollow layer: Generally, 12mm to 16mm is the most cost-effective width. If it is too wide or too narrow, it will affect convection and reduce the effect.
Warm-edge spacer bars: Using warm-edge spacer bars with lower thermal conductivity (such as TPS, stainless steel spacer bars) instead of traditional aluminum spacer bars can improve the condensation problem at the glass edges and slightly increase the overall K value.
