WINDOW ‘U’ VALUES
Doors & Windows
Monday 28 February 2010
The Glass and Glazing Federation (GGF), is the recognised leading authority for employers and companies within the flat glass, glazing, window, door, home-improvement, plastics and film industries. GGF Members can be found throughout the UK.
Membership of the Federation is not automatic. Companies must have been trading for three years, and there is a strict vetting procedure that includes looking at company accounts and site visits. The Federation represents more than 60% of the industry’s turnover.
The GGF has been active in the areas of energy and the environment for many years. It has worked with the Government to promote the issue of energy efficiency to the consumer and is supportive of Tony Blair’s objective, announced at the United Nations Earth Summit II in New York - to cut Britain’s greenhouse gas emissions by a fifth by 2010.
Currently the GGF is involved with the Government and the Energy Saving Trust in the Energy Efficiency Initiative specifically in the area of double glazing and explaining the benefits of double glazing and Low-E glass to consumers
It has also produced with the Department of the Environment, Transport and Regions’ Energy Efficiency Best Practice programme a good practice guide - “Selecting Energy Efficient Windows’ for specifiers.
Double-glazing can halve heat loss through windows. The optimum space between two panes of glass is 20mm. A smaller one leads to greater heat loss. A larger one makes little difference to the level of thermal insulation.
Low emissivity glass - for extra energy efficiency
If low emissivity glass, or Low-E as it is often called, is used even more energy can be saved. A microscopically thin-coating on one surface of high quality glass makes this possible.
The glass forms the inner pane of a double glazing unit. Its coating faces the cavity. The coating reflects longer wavelength heat from radiators and room surfaces back into the building. Meanwhile it allows in warming short wavelength solar energy.
Conveniently, these incoming short wavelengths of solar energy are re-radiated by internal building surfaces as longer wavelengths which are then reflected, by the coating, back into the room.
Double glazing using Low-E glass has energy conservation properties as good as normal triple glazing, without the 50% increase in weight
Advantages
o Improves insulation
o Reduces heating bills
o Reduces carbon dioxide emissions into the atmosphere
o Reduces condensation
o Reduces cold spots and down draughts
o Makes good use of the sun’s heat
o Durable
o Available on laminated, toughened and ordinary glass
Energy saving is further improved if an inert gas such as argon is enclosed in the units instead of air.
This also means you can sit closer to the windows and feel less cold because double glazing with Low-E has a higher internal surface temperature than conventional double or single glazing. Also, the reduction in condensation means frames and surrounding surfaces will need less maintenance. Low-E looks identical to ordinary clear glass. The coating is almost invisible, except in rare instances where strong oblique lighting may cause it to resemble a transparent film for a short time. Its effect on light transmission and reflection is barely perceptible.
*U values W/m2K
The U value of single clear glass
With ordinary double glazing this is improved to
With Low-E glass the U value is reduced by over 1/3 to
If argon gas is used to fill the air gap, the U value reduces further.
Applications
Low-E can be used in double glazing everywhere from the largest office block application to domestic conservatories, windows and doors.
Where extra safety or security is required, Low-E toughened or laminated glass can be specified.
Low-E is designed for use in double glazing, it is not suitable for single glazing, it can, however, be used as the inner pane in secondary glazing. The coating should, again, face the cavity.
low-E-Glass
Thursday 03 March 2010
Low E glass is a form of glass which when added to double glazing allows you to save even more energy.
Typically double glazing using Low-E glass has energy conservation properties as good as normal triple glazing but without the 50% increase in weight.
The advantages of using Low-E glass are:
Better heat insulation
You save money with reduced heating bills
Reduced carbon dioxide emissions into the atmosphere
Reduces condensation on your window frames internally
Installing argon gas within the sealed units instead of air can have even greater energy savings. Argon is an inert gas, which has better thermal properties than dry air. In the UK we express the rate of heat loss in ‘U values’. The lower the U value, the greater the thermal insulation and savings on your fuel bill.
Typical U values:
The U value of single clear glass is 5.4
With ordinary double glazing this is improved to 2.6
With Low-E glass the U value is reduced to 1.8
If argon gas is used to fill the air gap, the U value will reduce to 1.6
Red Deal units are 1.2 and overall including the frame are 1.4