Glass - Pilkington K Glass
How does Pilkington K Glass™ work?
 You're probably wondering how a microscopic coating on a pane of glass can make such a big difference to its performance This is how it works.
The glass in your windows absorbs heat then radiates it again on the colder, outside, surface. Pilkington K Glass™ has what is called a low emissivity coating on the surface that faces into the air gap of the double glazing unit.
Low emissivity means the coating is a poor radiator. The heat absorbed by the coated glass is inhibited from radiating across the air gap and then from the outer pane to the cold outside world. Instead the heat is reflected back into the room by the coating.
It works in a similar way to a sheet of reflecting foil placed behind a central heating radiator which, as you know, bounces the heat back into the room.
 Heat losses through different materials can be compared by the their "U values". The higher the U value, the greater the heat loss through the material.
The U value of a single pane window is 5.6. Double glazing with ordinary glass has a U value of 2.8. Double glazing with Pilkington K Glass TM has a U value of only 1.9, considerably better than conventional double glazing, and as good as triple glazing.
Pilkington K Glass™ should not be used as single glazing.
Effective U value
In the case of windows and glazing, because they admit the sun's energy, the U value concept can be taken a step further Even in the winter the sun can shine and help to warm a room.
Over a typical heating period the amount of useful heat from the sun entering through windows can be subtracted from the normal U value (a measure of the heat leaving through the windows) to give an overall "effective U value" This is dependent upon the direction the window faces. In the case of south facing windows with Pilkington K Glass™ double glazing units, the normal U value of 1.9 W /m˛K is reduced to an Effective U value of virtually zero. In other words, the amount of heat
lost is balanced by the heat gained from the sun.
Effective U value can simply be regarded as "heat out minus useful heat in".
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Appearance
 Pilkington K Glass™ has high light transmission and appears virtually the same as clear float glass. However, in rare instances of strong oblique lighting, the coating may be seen as a transparent film. This is simply a transient visual effect which can be considered positive evidence of the coated surface being present.
Further evidence of the coating's presence is through the very minor effect it has on white light transmission. This effect is so small as to be generally unnoticeable. However, when a light coloured object or material is in close proximity to the glazing, dependent on local circumstances and conditions, a slight darkening can be noted.
Because Pilkington K Glass™ is so neutral in appearance, it is recommended that its presence in a double glazing unit is confirmed on installation.
This can be achieved by the use of a coating detector which unit manufacturers or installers should have available.
In certain extreme environmental conditions, low emissivity glasses might increase external condensation.
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