There are many different types of window available, which can be confusing for the consumer. Fortunately, the British Fenestration Ratings Council (BFRC) has calculated an energy performance rating for windows using a label to classify windows from A to G.
Eko Window Systems do not use anything less than A rated windows.
These ratings are not final since they do not take into account the size and orientation of a window, but they are a very good indication of overall performance. The values used in calculation are:
- Solar Heat Gain Co-efficient (SHGC) – also known as solar factor, or g-value, measures how much a window will absorb heat from sunlight. It is a number between 0 and 1, where a low SHGC means less heat gain.
- Air Leakage (L50) – measures how much air leaks in and out of a window when it is closed.
The BFRC rates the energy performance of a whole window, by considering both the frame material and glass characteristics.
Energy efficient windows have two or more panes of glass separated by an air gap to slow heat transfer and provide noise insulation. These are known as double paned or insulated windows. Traditionally air or dry nitrogen was used between the panes, but recent models use low conductance gas fills of argon or krypton that gives even better thermal performance and significantly lowers the U-value.
Another new development in window technology is low-emittance coating also known as low-e. These are microscopically thin layers of metal or metallic oxide that are coated onto the window glazing. Different types of coating have different properties, but all are designed to lower heat flow through the window – some reflect heat back into the building and others reflect heat back outside.
Spacers are used in between the layers of glass in a window, to hold them together at the required distance. Conventional spacers were made from aluminium, but because of their high conductivity they provided poor thermal insulation and created condensation problems around the window edges. New spacer products, known as warm spacer technology, or warm edge spacers, have been developed from materials that have a low conductivity rate and high thermal efficiency, and include fibreglass, vinyl, silicone foam and reinforced thermoplastic. Some warm edge spacers incorporate a thermal break in their structural design.