The most common gas used in Double Glazed Units (DGU), also known as Insulated Glass Units (IGUs), is argon. This inert gas is favored for its excellent thermal insulation properties and cost-effectiveness.
Double Glazed Units are designed with two panes of glass separated by a spacer, creating a sealed cavity. Filling this cavity with an inert gas significantly enhances the window's insulating performance compared to simply leaving it filled with air.
Why Gases are Used in DGU Glass
The primary purpose of using specific gases in DGU glass is to improve thermal insulation. Gases transfer heat less efficiently than air, meaning they slow down the movement of heat into or out of a building. This leads to more stable indoor temperatures and reduced energy consumption.
The science behind this involves:
- Conduction Reduction: Inert gases are denser than air, which reduces the rate at which heat can conduct through the gas itself.
- Convection Suppression: The increased density and lower thermal conductivity of these gases also suppress convective heat transfer within the sealed cavity, preventing warm air from circulating and transferring heat.
Common Gases Used in DGU Glass
While argon is the most prevalent, other inert gases are also employed, each offering distinct advantages. These gases are non-toxic, non-flammable, and do not react with the window components.
Argon
Argon is a colourless and odourless chemical that stands out as the most commonly used gas in windows. Its popularity stems from a combination of factors:
- Affordability: It is relatively cheap to produce and readily available.
- Density: Argon is denser than air, which significantly improves the insulating value by reducing heat transfer via convection and conduction.
- Performance: It offers a substantial improvement in thermal performance compared to air-filled units.
Xenon
Xenon is another inert gas used in specialized DGU applications. It is known for being the densest of all the inert gases, making it highly insulating.
- Superior Insulation: Xenon provides even better thermal performance than argon, particularly beneficial for very thin glazing units or in extremely cold climates.
- Cost: Due to its rarity and more complex extraction process, xenon is considerably more expensive than argon.
Krypton
Krypton falls between argon and xenon in terms of density and insulating properties. It's often used in thinner glazing units where the cavity width is smaller than ideal for argon.
- Efficiency in Small Cavities: Krypton's properties make it effective in narrower gaps, allowing for slimmer window profiles without sacrificing significant insulation.
- Cost: It is more expensive than argon but less costly than xenon.
Air
While not an added "gas" in the same sense, air is the default fill for any DGU that is not specifically gas-filled. It offers some insulation due to the trapped air layer, but its thermal performance is significantly lower than that of inert gas fills. Modern energy-efficient windows almost always use a gas fill.
Comparison of DGU Filling Gases
To illustrate the differences, here's a comparison of the most common gases used in DGU applications:
| Gas | Thermal Conductivity (W/m·K at 0°C) | Density (kg/m³ at 0°C) | Relative Cost | Primary Use/Benefit |
|---|---|---|---|---|
| Air | 0.024 | 1.29 | Low | Basic insulation, standard, no special fill |
| Argon | 0.016 | 1.78 | Medium | Most common, cost-effective, good thermal performance |
| Krypton | 0.009 | 3.75 | High | Superior insulation, ideal for thin units |
| Xenon | 0.006 | 5.89 | Very High | Exceptional insulation, premium applications |
Note: Thermal conductivity values are approximate and can vary slightly with temperature and pressure.
Benefits of Gas-Filled DGU
Implementing inert gas fills in double-glazed units offers a range of advantages for both residential and commercial buildings:
- Improved Thermal Performance: The most significant benefit is the reduction in heat transfer, leading to lower U-values (a measure of heat loss) for windows. This means homes stay warmer in winter and cooler in summer.
- Enhanced Energy Efficiency: By minimizing heat loss and gain, gas-filled DGUs reduce the demand on heating and cooling systems, translating into lower energy bills and a smaller carbon footprint.
- Reduced Condensation: The warmer internal pane surface, due to better insulation, helps to prevent condensation build-up on the inside of the window, leading to clearer views and reducing potential moisture-related issues.
- Increased Sound Insulation: The denser gases can also help to dampen sound waves, providing a noticeable improvement in acoustic insulation against external noise.
- UV Protection (Minor): While not their primary function, some gas fills can offer a marginal improvement in UV protection compared to air.
How Gas-Filled DGU Works
The principle behind gas-filled DGU is to create a barrier that is more resistant to heat flow than still air. When heat tries to pass through a window, it does so by conduction, convection, and radiation.
- The inert gas in the cavity slows down conduction because these gases have lower thermal conductivity than air.
- It also significantly reduces convection within the cavity because the gases are denser and less prone to circulating.
- While gas fills primarily tackle conduction and convection, radiation is typically managed by low-emissivity (low-e) coatings applied to the glass panes.
Together, these elements create a highly effective thermal barrier, making windows a crucial component of an energy-efficient building envelope. For more details on how these windows contribute to energy savings, you can explore resources on energy-efficient windows.
Considerations for Choosing Gas Type
The choice of gas fill for DGU glass often comes down to a balance between desired performance and budget:
- Budget: Argon provides an excellent cost-to-performance ratio for most standard applications.
- Performance Requirements: For projects requiring the highest thermal efficiency, such as passive house designs or buildings in extreme climates, krypton or xenon might be considered despite their higher cost.
- Cavity Width: Krypton is particularly well-suited for narrow cavities, offering optimal performance where space is limited.
By carefully selecting the right gas, alongside other window features like low-e coatings and frame materials, homeowners and builders can significantly enhance a building's comfort and energy performance.
