Low-e Glass
From Swikipedia
Introduction
Low-emission glass (Low-E) is a clear glass; it has a microscopically-thin coating of metal oxide. This allows the sun's heat and light to pass through the glass into the building. At the same time it blocks heat from leaving the room, reducing heat loss considerably.
Brief Description
Low-E glass works by reflecting heat back to its source. All objects and people give off varying forms of energy, affecting the temperature of a space. Long wave radiation energy is heat, and short wave radiation energy is visible light from the sun. The coating used to make low-E glass works to transmit short wave energy, allowing light in, while reflecting long wave energy to keep heat in the desired location.
Low-E glass comes in high, moderate and low gain panels. In especially cold climates, heat is preserved and reflected back into a house to keep it warm. This is accomplished with high solar gain panels. In especially hot climates, low solar gain panels work to reject excess heat by reflecting it back outside the space. Moderate solar gain panels are also available for areas with temperature fluctuations.
Low-E glass is glazed with an ultra-thin metallic coating. The manufacturing process applies this with either a hard coat or soft coat process. Soft coated low-E glass is more delicate and easily damaged so it is used in insulated windows where it can be in between two other pieces of glass. Hard coated low-E glass is more durable and can be used in single paned windows. It can also be used in retrofit projects.
Generally low-E windows cost between 10% and 15% more than standard. The reduction in energy loss can be 30% to 50%. Low-E windows are a larger investment initially but will pay for themselves by reducing heating and cooling costs.
Visibility was a problem with some of the first low-E glass available. Original panes were said to have a brownish tint. Technology and manufacturing has continued to improve its\ quality resulting in a spectrally selective low-E glass that allows the best possible visibility while still filtering heat.
Types of low-e glass:
On-line coated (pyrolitic process): This is a clear glass which has been coated with a metal oxide through pyrolysis when the glass leaves the tin bath (at 650°C). The coating is therefore very resistant to mechanical damage, and this Low-E glass can be cut, tempered or laminated just as normal uncoated glass.
Off-line coated (magnetron process): This is a clear glass which has received, on one of its faces, a silver coating applied by magnetically-enhanced cathodic sputtering. This type of Low-E must be used exclusively in insulating glass, with the coating on an internal face. It can be tempered and laminated.
References:
