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".
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.
