Composition of a typical triple glazed window

One of the most important factors to consider while planning a home upgrade, is to make it more energy efficient. But not many people know that the windows of your home are one of the greatest contributors to energy efficiency while also having a very big impact on the look and style of your home.

For an effective thermal envelope around a building, the walls are required to have a U value of less than 0.3. If the windows of the house are not effective in creating a thermal barrier, they can act as weak points that allow draughts to enter the house and causing cold spots to form around windows. A well-designed home with sufficiently insulated windows, doesn’t only have an increased market value. When sufficient planning has gone into a home’s thermal barrier, the operational costs of the property will also be much lower and the level of comfort inside the home will be significantly higher.

Heating systems within a house are more effective when energy efficient windows are installed. They not only assist in heating up the house much faster, but also help to maintain a constant temperature within the house by reducing the amount of the heat that is allowed to escape to the outside. In effect, the energy needed to maintain that constant temperature is much less. Triple glazing has been found to retain heat 30-50% more than double glazing, while reducing energy consumption at the same time.

THE WINDOW

A triple glazed window is made up of 3 layers of glass with 2 gas-filled cavities, inside a sealed frame. Let’s look at these elements individually.

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Glass


Glass is a material that has been used for architectural purposes from the 1st century when addition of manganese dioxide to molten sand was found to produce clear glass. Over the years, glass has become an integral part of every home because of its properties of allowing light to pass through, while retaining heat and reducing the amount of sound entering from outside. As technology has advanced, so has window making. With the introduction of triple glazing, windows have been taken to a new level by adding efficiency to architectural aesthetic.

Before we look at the types of glass used in triple glazing, let’s briefly mention U-factor. In short, the U-factor of a window is the amount the heat that is transferred through the window from the inside of the home to outside, or the rate of heat loss. The lower the U-value, the lower the amount of heat lost through the glass. The higher the U-value, the higher the amount of heat lost.

For reference, a single pane of glass typically has a U-value of 5, double glazing has a value of around 2.8, and triple glazing has a U-value of 0.8.

There are different types of glass used to make windows, but the commonly used ones are:

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1)     Tinted glass


This glass utilizes a type of glaze that reacts to heat by absorbing it and changing the colour of the glass. A tint does not lower the U-factor of a window because there is loss of heat by re-radiation and conduction. To counter this, additional layers of clear glass or some special coatings have to be applied to reduce heat transfer.

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2)     Low emissivity glass (Low-E)


This glass employs a transparent microscopic metallic oxide coating on its surface that allows visible light to pass through while reflecting infra-red light, or heat. This lowers the U-factor of the window, making it more thermally efficient. The unique feature of this glass is that while it keeps the sun’s heat away in summer, it retains the warmth of the house in winter by reflecting the heat back into the house, and so preventing it from escaping.

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3)     Reflective glass


Usually used in warm and sunny regions, this glass consists of layers of thin metallic coating in different colours like bronze and silver. This glass reduces solar radiation by blocking light and thus reducing glare.

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4)     Low Iron glass


This glass is made from low iron silica containing very low amounts (about 0.01%) of ferric oxide, which removes the green-blue tint typically seen in standard glass panes. This glass has very high clarity.

The glass most suited to triple glazed windows is the low-iron glass allows most of the short-wave solar or light to pass through, and the low-E glass that is installed as the inner pane and reflects long-wave infrared energy, or heat, back into the house. The central glass pane is also toughened to prevent thermal stress cracking due to hot and cold temperature variation between the outside and the inside of the home.

The three 4mm glass panes have two 16mm gaps between them, filled with Krypton gas, bringing the total width of the unit to 44mm. These carefully insulated window units easily integrate safety, durability, and thermal and acoustic insulation.

Triple glazing permits optimal penetration of natural light while preventing loss of heat. A properly installed triple glazed window will prevent excess heat absorption from the outside in summer, while preventing loss of heat in winter from inside the house. External noise is also greatly reduced because of the layers of glass and gas creating efficient acoustic insulation.

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Gas


The triple-glazing unit is not merely made up of 3 panes of glass. Between these panes of glass, are two cavities filled with Krypton gas [Kr], which has 34% lower conductivity than air. By incorporating two of these gas cavities, the thermal and acoustic insulation of the sealed unit is greatly improved. Krypton gas can improve the efficiency of the window by up to 30%, compared with window cavities filled with air alone. (source)

Krypton gas is odourless, non-toxic, non-corrosive, and although expensive, it performs better that the Argon gas typically used in double glazing when looking at energy saving and sound proofing. It prevents condensation from forming on the inside on the window, because it can maintain a surface temperature far above dew point. Frosting may however occur on the exterior face of the window because of the thermal variation between the sealed unit and the external temperature.

Frames

Triple glazing windows are sealed systems that ensure maximum thermal insulation. The frame is an important part of this unit because it is custom-made for each property according to its size and style, but also because the glass panes are perfectly fitted into the frame to prevent the gas from leaking and to ensure that there are no gaps where hot air can escape, or cold air can enter.

Frames are typically made from 4 different of materials. Based on the style of the house, you can choose from wood, uPVC, aluminium and aluminium-clad wood.

WOOD

Wood is generally the most desired option but is also expensive and requires maintenance. Using cheaper wood may limit the life of the window and also compromise the sealing capacity of the unit.

UPVC

uPVC is a versatile, moulded material that can be manufactured with different finishes, colours and textures, and is very easy to maintain.

Aluminium

Aluminium frames are non-corrosive, tough and light-weight and can be anodized to many desired colours.

Aluminium-clad

Aluminium-clad frames consist of wooden frames clad with aluminium. This double layer increases the life-span of the window by helping it to better withstand natural elements, while maintaining the wooden look inside the home.

If you are planning to change the windows to your home, it would be advisable to get a good opinion on the style and materials that will best suit your needs, budget and climatic conditions. While triple glazing requires a big investment, the superior performance and energy-savings make it a great choice for any home owner. The overall reduction in energy consumption and improved Energy Performance Certificate (EPC) for your home, will cause a considerable rise in the market value of the property. It therefore makes complete environmental and financial sense to upgrade to triple glazing.

Published on : 21th February 2017

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