What Makes an Energy Efficient Window
The aim of an energy efficient window is to reduce the need to consume energy in a home through heating or cooling a room.
Energy efficient windows are constructed so they reduce as much heat loss as possible. They can also be constructed to reduce as much heat gain as possible, where overheating is an issue e.g. large south west facing windows.
There are three parts to a window that contribute to energy efficiency:
Apart from the glass, the material used in the frame makes a difference in heat loss from the window. The thermal conductivity of the frame contributes to how much heat is transferred from a room to the outside. Wood has a low conductivity and metals have the highest thermal conductivity. Modern aluminium profiles have been developed with an internal thermal break that makes them much more efficient. uPVC windows are still among the most energy efficient available and have insulating five-chamber profiles that reduce thermal conductivity.
The distance between the panes of glass makes a difference in thermal conduction and heat loss through the glazed area. A sealed unit filled with an inert gas such as Argon has a lower transmission and is more efficient. A unit with wider spaced panes of glass is also more efficient.
The spacer bar used to separate the panes of glass also acts as a thermal bridge to conduct heat. Older double glazed units with aluminium spacer bars have a high conduction rate and are not efficient enough to meet today's standards. Modern spacer bars known as 'warm edge' are made from a steel-reinforced polymer and reduce thermal conductivity to an acceptable level.
The glazing is the most significant part of a window and makes a big difference in efficiency and performance. All glass is not the same and there are several types of glazing that all have specific uses.
Low-E glass has a metal oxide micro-coating. This allows the shortwave radiation solar gain from sunlight into a room but reflects the longwave radiation back into the room.
Solar Control glass provides excellent thermal insulation and can reduce the amount of solar energy that passes through the window to prevent overheating.
By combining solar control glass and Low-E glass in the same unit, you can create a balance of climate control during summer and winter.
Everest Ultimate Glazing uses solar control glass to reduce solar heat gain and provide high thermal insulation, combined with Low E glass to reflect heat back into the room. This makes it a great choice for those looking to reduce their energy bills and lower their carbon footprint.
Read more: Everest Glass...
How Windows Gain Heat
Standard glazing reduces heat loss and acts as a barrier against the cold but it doesn't stop the warmth from the sun, known as solar gain.
Sunlight produces shortwave infrared radiation that is absorbed by the glass from the outside and becomes re-radiated from the inside of the glass as longwave infrared.
Shortwaves can pass through glass but the longwaves can't, so the thermal energy of the infrared radiation becomes trapped and the room begins to overheat. This process is known as the greenhouse effect.
To help reduce overheating low energy transmittance glazing, known as Solar Control Glass is used. This type of glass is made by adding a high-performance coating to the surface of the glass using a process called magnetron sputtering. The microscopic coating reflects the sun's rays and reduces heat transfer, which creates a more comfortable interior by reducing overheating, whilst at the same time noticeably reducing heat loss.