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Frequently Asked Questions

1. What is low emissivity low-E glass? How many types of low-E glass are there on the market? Is all low-E glass the same?

2. Currently the industry offers low-E on both surface #2 and surface #3. On which surface would you recommend to position the coating to achieve the best solar performance?

3. What is the difference between heat strengthened glass and toughened glass? How do I determine which to use for my project?

4. What are the important values to consider when specifying glass for my project?

5. What is the u-value?

6. What is the shading coefficient?

7. Should I use air or argon in my insulating glass units?

Low-e glass

1. What is low emissivity low-E glass? How many types of low-E glass are there on the market? Is all low-E glass the same?

Low-E glass refers to glass with a low-emissivity coating applied on one surface. It is designed to reflect long-wave infrared (heat) back into a building to improve the u-value and energy efficiency of the glazing. Low-E glass is relatively neutral in appearance, so is widely used in both commercial and residential buildings.
ClimaGuard Low-E coating is applied by a process known as magnetron sputtering, which applies several thin coatings of various metal compounds to one surface. Guardian sputter coated low-E glass is available in toughenable versions. There are other types of coated low-E glass and they can be visually different in appearance.

Glass coating

2. Currently the industry offers low-E on both surface #2 and surface #3. On which surface would you recommend to position the coating to achieve the best solar performance?

Many buildings in Europe are glazed with the low-E coating on surface #3 in order to reflect the heat back into the building as efficiently as possible. Reducing solar heat gain is most important in commercial buildings where air conditioning costs can be high. Low-E on surface #2 reduces the solar heat gain buy the glazing may appear visually different in reflection when viewed from outside. Low-E coating is often on surface #3 when body tinted or solar control coatings are used on surface #2.

3. What is the difference between heat strengthened glass and toughened glass? How do I determine which to use for my project?

Heat strengthened and toughened glasses are manufactured during a similar process on the same type of machinery. The only difference during manufacture is the application of different levels of stress induced into the product. As a consequence of this, toughened glass breaks into small relatively harmless pieces when broken and as such is considered to be a safety glazing material. Heat strengthened breaks in larger pieces similar to annealed glass and is not considered a safety glazing material unless it is made into a laminated product.
Heat strengthened glass may be installed in any situation that does not require a safety glass. Both glass types are resistant to thermal breakage as they are stronger than annealed glass. However, unlike annealed glass, neither can be cut or drilled after being manufactured and any alterations such as edge grinding, sand blasting or acid etching will weaken the glass and can cause premature failure.

4. What are the important values to consider when specifying glass for my project?

The specification of glass can be a complex and lengthy process. It begins with the external aesthetics, light transmission and energy performance in combination with local Building Regulations, which are developed as the design team and architect define the requirements from the glazing.
Guardian has developed a Product Performance Comparison Tool to assist in comparing existing projects supplied with SunGuard Advanced Architectural Glass products. Please contact your local representatives for further advice and information.

5. What is the u-value?

The u-value is a measure of the heat flow through the glazing measure in Wm-2K-1. The lower the u-value the lower the heat loss to the outside of the building and the greater the energy costs are reduced. The performance data provided by Guardian are for the glass performance only, often referred to as the centre pane u-value, which does not take account of any heat loss through the perimeter of an insulating glass unit or frame.

6. What is the shading coefficient?

The solar factor (total transmittance) of a glass configuration is relative to that of 3mm clear float glass (0.87) and is used as a performance comparison. The lower the shading coefficient number, the lower the amount of solar heat transmitted. The short wave shading coefficient is the direct transmittance (T) of the glass as a factor of the solar factor or total transmittance (g or TT) of 3mm clear float glass (T ¸ 0.87). The long wave-shading coefficient is the internally re-radiated energy that the glass has absorbed as glass. It is determined by subtracting the direct transmittance from the solar factor (total transmittance) of the subject glass and then dividing by the solar factor ( total transmittance) of 3mm clear float glass (g-T ¸ 0.87).

7. Should I use air or argon in my insulating glass units?

The use of air or argon is usually defined by the u-value requirement for the insulated glass units for each specific project. In Southern Europe it may be sufficient to use air filled units whereas in Northern and Central Europe, in order to minimise heat loss during the cold winter period it is often essential to incorporate argon within the cavity. Local Regulations often dictate the level of insulation required.