An insulating glass unit consists usually of two panes of glass that are separated by a spacer material and sealed together at the edge. This creates nearly twice the insulation, as single glazed units, and the overall energy efficiency of windows increase. For further level of insulation, three panes can be used with windows. The reason why triple pane windows are becoming more popular, is because they are believed to be significantly more energy efficient compared to double glazed units. When you are comparing factors such as SHGC and U-value there is 20%-30% improvement with triple glazing’s values.
U-value
U-value measures how effective a glass is as an insulator. Low U-value translates to the higher resistance of heat flow through windows. The single pane windows have average U-factor of 5.0 and older double-glazed windows score average 3.0. Over the years double glazed units has undergone significant improvements, and now they can score average 1.4. However, modern triple glazed unit can have U-factor as low as 0.8. This is notable improvement compared to even modern double-glazed units.
“In the winter insulation declines and U-value increases especially with double glazed windows because of cold and windy weather. Triple glazed windows are not affected that much by weather conditions.” says Executive Director Jenni Heikkilä from The Finnish Associations for Flat Glass. This is one of the reasons why triple glazing is pretty much standard nowadays e.g., in Scandinavia.
Gas Filling
To improve insulating performance, noble gas such as Argon, Krypton or Xenon can be filled between airspaces of panes. Gas improves significantly thermal efficiency of glass. Argon is the most used gas because it is cheapest in the market and in the most cases it is the most suitable option. The only difference between double and triple glazing is that triple pane glass has gas injected in two spacers instead of one. This increases energy efficiency of triple glazed windows and deceases heat loss through windows.
Low-e coating
Low-emissivity coating can be applied to one of the glass surfaces to make double IGUs more energy efficient. These coatings are one of the main enhancements to minimize the U-value. Low-E and Solar Control coatings can also block selective wavelengths of sunlight from entering the building, which reduces the Solar Heat Gain Coefficient (SHGC). For better efficiency, triple pane glazed offer an option to add an extra layer Low-E or Solar Coating due to the additional pane of glass.
The main benefit of double-glazed windows is a lower price compared to triple glazed windows. Overall higher weight of triple glazed unit can also cause some problems for the project. However, triple glazed unit offer multiple benefits by improving insulating performance and energy efficiency of windows such as lower energy costs, managing coldness and heat, and protecting items in the building from sun’s ultraviolet rays. When addressing the question if triple glazed IGU indeed are necessary to obtain energy efficient windows, the answer is yes and no. This is because more important matter to address is the quality of the IGU. If IG units are produced with adequate gas fill and high quality low-e coating, the rest is matter of individual preferences and geographic location.
