Glass and Glazing – Safety Glass, U Values,
Low E glass and Double Glazed Windows Information – in association with
WindowsToday.co.uk
Low E Glass and Document L of
Building Regulations
Most people are aware that effective 1st
April 2002 - all replacement window installations in England & Wales
are subject to BUILDING REGULATIONS. This new regulation in particular
affects the minimum levels of insulation that replacement windows must
have when fitted in your home. Levels of insulation are measured as U
values. The lower the U value, the better the insulation level. To get the
required level of insulation some sort of LOW E glass (typically
Pilkington K in the UK - although there are other brands) will have to be
used. It may also be necessary for the sealed double glazed units to be
Gas Filled (probably Argon).
There are two ways
that you can ensure compliance with relevant regulations, firstly you may
employ a contractor or installer who is registered under the FENSA
self-certification scheme. This contractor will be approved to carry out
the work in accordance with relevant regulations without inspection by the
council and will inform FENSA when installation has been completed. Random
inspections of completed work are carried out.
If you are
not using a FENSA registered contractor or if you're doing the work
yourself (DIY) then you will need to arrange building regulation approval
yourself. Contact the building control department at you local council
reference this.
Low E, the glass for the future
Introduction
Low-e glass stands for low
emissivity glass. This glass varies from normal clear glass in that one
side of the glass has a special metal coating, technically known as a low
emissitivity, or Low E. coating. Low-E glass is a type of insulating
glass, which increases the energy efficiency of windows by reducing the
transfer of heat or cold through glass. That means in the winter your
house stays warmer, and in the summer it stays cooler.
There are
two types of Low-E (low emissivity) glass available - Pyrolytic (hard
coat) is considered to be a medium performer, and sputtered (vacuum
deposition or soft coat) is considered to be the highest
performer.
As energy saving will become more and more important in
our daily lives, implementing low-e glass in our houses will soon be a
standard we all have to comply to.
Low-e glass, how does
it work?
The radiation coming from your heating system
and your furniture and furnishings is long wave radiation. This type of
radiation should be contained in your room as best as possible, while the
radiation from the sun should be shielded and reflected back
outside.
Winter Time
The sun's energy is "SHORT WAVE
RADIATION" which passes through the window and is absorbed by carpet,
furniture, etc. The energy is then transformed into long wave radiation.
The long wave radiation wants to flow from warm to cool. Naturally, it
will try to escape from the glass. At night the heat produced from
radiators, wood stoves, etc., will also want to escape out through the
glazing. The Low-E coating prevents this when the radiant room-side heat
is reflected back into the building. This results in a lower winter
U-value. For winter comfort, the higher the indoor glass temperature, the
better the product is for comfort.
Summer Time
The
Low-E coating manages the sun's heat in the summer by reducing the amount
of heat transferred through the window in the summer. The Low-E coating
filters the sun's short-wave radiation, which cuts down on the amount of
solar heat gain into your building. For summer comfort, the lower the
indoor glass temperature, the better the product is for
comfort.
More on the two types of
Low-e glass
Hard Coat Low E
Hard coat Low
E, or pyrolytic coating, is a coating applied at high temperatures and is
sprayed onto the glass surface during the float glass
process.
Advantages
- The advantage is that the coating is
relatively durable, which allows for ease of handling and
tempering.
- Can be tempered after coating
application.
- Can be used in single glazing
applications.
- Utilizes passive solar heat gain.
Disadvantages
- Higher U-values compared to soft coat
Low-E products
- Slightly higher haze levels
- Higher solar heat gain coefficient
compared to soft coat Low-E products.
- Hard coat glass also has the possibility
of a slight haze, which can be visible under certain angles.
Suppliers include www.pilkington.com
NOTE: Pilkington do supply a type of soft coat
low E glass also (Pilkington Optitherm™ SN) - but in the UK most of their
Low E supply is in the form of Pilkington K Glass - a hard coat version of
Low E.
Soft Coat Low E
Soft coat Low
E, or sputter coating, is applied in multiple layers of optically
transparent silver sandwiched between layers of metal oxide in a vacuum
chamber. This process provides the highest level of performance and a
nearly invisible coating.
Advantages
- High visible light transmission
- Ultra-low emissivities giving optimum
winter U-values
- Up to 70% less UV transmission compared
with standard clear glazing
- Optical clarity - minimal color
haze
Disadvantages
- Soft coat Low E must be used in a double
glazed unit; the soft coating is sensitive to handling.
- Most soft coat Low-E products require
tempering the glass prior to the coating application.
- Edge deletion of the coating is required
to insure a proper seal in an insulated unit
- There can be slight color variations of
coating.
- Generally speaking, a more expensive
alternative than Hard Coat Low e glass.
Suppliers of SOFT COAT include
Saint-Gobain Glass
http://www.saint-gobain-glass.com/uk/b01.asp?product_id=636
SGG
PLANITHERM
Saint-Gobain Glass Comfort Product
Family
Low-emissivity glass - first generation soft
coating
SGG PLANITHERM is a clear float glass, which has
been coated with metallic oxides by magnetically enhanced cathodic
sputtering under vacuum conditions.
This sputtered coating is
highly reflective to long-wave heat radiation, otherwise known as a "low
emissivity" or low-e coating. This greatly reduces heat loss and ensures
that double-glazed units incorporating SGG PLANITHERM provide excellent
thermal insulation.
SGG PLANITHERM is neutral in appearance and has
a high light transmittance
factor. |
