Glass for Europe, the trade association for Europe’s manufacturers of flat glass, reports that nearly half of the windows in Europe's buildings are still single glazed. “Less than 15% of Europe's windows contain energy-saving glass, whereas these solutions have been available on the market for over 20 years,” it says “Early uncoated double glazing is still used in a vast number of buildings. Although their energy performance is limited compared to solutions available nowadays, they are too often regarded as efficient by poorly informed property owners.”
However, Glass for Europe explains that using advanced glazing solutions can significantly reduce the need for heating and cooling in buildings, thereby reducing energy consumption and associated carbon emissions. “Independent studies show that savings of more than 100 million tonnes of carbon could be achieved annually if all Europe's buildings were fitted with advanced energy saving glass.”
On the basis of these findings, the EU could achieve around one third of the energy saving targets for buildings identified in the 2006 Action Plan for Energy Efficiency simply by promoting the use of energy saving glazing. “The potential for improving the glazed facades and windows of Europe's building is enormous,” says Glass for Europe.
Among the glazing options available are low-emissivity glass and solar control glass.
Low-emissivity (Low-E) glass is specially treated with a microscopically thin, transparent coating. The coating reflects heat back into the building, thereby reducing the heat loss through the window. It also reduces the heat transfer from the warm (inner) pane of glass to the cooler (outer) pane, thus further lowering the amount of heat that escapes from the window. These properties thus reduce the demand for energy in order to heat the building.
In addition, the coating allows large amounts of free solar energy to enter the building, thereby heating it passively. Low-E insulating glazing can therefore be a net contributor of energy in buildings.
Other innovations such as triple glazing products can offer additional improvements in the window's insulating properties while the use of low-iron glass can increase light transmittance and free solar-heat gain. These technologies offer additional benefits in terms of energy efficiency.
Controlling solar input
Solar control glass is a high performance coated product that reflects and radiates away a large degree of the sun's heat while allowing daylight to pass through a window or façade. The indoor space stays bright and much cooler than would be the case if normal glass were used.
Solar control glass incorporates invisible layers of special materials on the glass which have the dual effect of allowing sunlight in, while repelling solar heat.
“This technology is particularly beneficial in warmer southern climates where it can help to reduce the load on a building's air conditioning system, thus reducing energy demand, while maintaining a comfortable working environment,” explains Glass for Europe, which stresses that energy-efficient glazing is beneficial even in the sunny climes of southern Europe.
“Preventing over-heating in summer is the main challenge for most types of building. Thanks to solar-control coatings, glazing can play a role in preventing over-heating in buildings and therefore reduce the use of air-conditioning5, which is a major consumer of energy in Southern Europe,” it says.
In addition, solar-control glazing most often comes in double glazed units, which provides insulation in winter. Solar-control and Low-Emissivity properties can be combined into a glazing unit thus further contributing to insulation from both cold and heat depending on the season. This most often provides the best energy saving balance since free solar heat gains are only limited during a few winter months and are compensated by reduced loads on air conditioning units for the most part of the year. Upgrading to energy-efficient glazing in Southern Europe is thus an efficient way of increasing indoor comfort while making substantial energy savings.
Positive life cycle impact
Glass for Europe recognises that the process of manufacturing flat glass for building applications inevitably has a cost in terms of carbon dioxide emitted; however it estimates that this is “more than compensated for by the carbon dioxide saved by replacing single glazing with energy efficient glazing”.
According to a detailed study undertaken in 2005 the manufacture of 1 square metre of low-E double glazing leads to the emission of 25 kg of carbon dioxide, and this has subsequently been further reduced by the introduction of new manufacturing technologies in recent years.
On the other hand, 91 kg of carbon dioxide per year are saved by replacing one square metre of single glazing with low-E double glazing. The carbon dioxide emitted during production is thus offset after only 3.5 months' use.
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