1. What is low-E glass?
Low-E glass, namely low emissivity glass, is a kind of glass that is covered with low emissivity coating on one surface. It can reflect infrared light back into the building to improve the U-value and energy efficiency of the glazing. Due to its relatively neutral appearance, it is commonly seen in commercial and residential buildings.
2. Low-E glass is available for both surface #2 and surface #3 on the market now. In order to get the best solar performance, on which surface should the coating be placed?
Many buildings are glazed with low-E coating on surface #3 to reflect the heat back into the building as efficiently as possible. For commercial buildings, the cost for air conditioning is usually very high. So, it is of great importance to prevent solar energy from penetrating through the window and into the room. Low-E coating on surface #2 cuts down the amount of solar energy that is gained by the glazing, and it may look visually different in reflection when viewing from outside. Low-E coating is often on surface #3 when body tinted or solar control coatings are on surface #2.
3. What is the difference between heat strengthened glass and toughened glass, and how could I know which is better for my project?
The heat strengthened glass and toughened glass are fabricated via a similar process on the same type of machinery. The only difference during production is the application of different levels of stress induced into the glass. As a result of this, the toughened glass will break into relatively smaller and harmless pieces when it is broken, and this is considered to be a property of safety materials. On the other hand, the heat strengthened glass will break into larger pieces similar to annealed glass, and it is not a safety material unless it is made into a laminated product.
The heat strengthened glass can be installed in any situation where safety is not taken as a major concern. Both of these two types of glass are resistant to thermal breakage because they are stronger than annealed glass. However, unlike the annealed glass, neither of them can be cut or drilled after being produced, and any alteration such as edge grinding, sand blasting or acid etching will weaken the glass which may lead to premature failure.
4. What factors should be taken into account 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 performances in combination with local building regulations, which are developed as the design team and architects.
5. What does the U-value stand for?
The U-value reveals the property of heat flow through the glazing, and it is shown in the unit of Wm-2K-1. It is a very important parameter, because the lower the U-value is, the lower the heat loss to the outside of the building will be, thereby cutting down the energy cost. Moreover, the performance data are for the glass only which means that the heat loss through the perimeter of an insulating glass unit or frame is not taken into consideration, and this is often referred to as the centre pane U-value.
6. What is the shading coefficient?
The solar factor (total transmittance) of a glass configuration is relative to that of a 3mm clear float glass (0.87), and is used as a performance comparison. The lower the shading coefficient is, the lower the amount of solar heat is 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. It is determined by subtracting the direct transmittance from the solar factor of the subject glass and then dividing by the solar factor of 3mm clear float glass (g-T ¸ 0.87).