Energy Ratings Explained
During recent years, increased levels of environmental awareness have led to energy efficiency equirements of buildings to be improved. Choosing the correct window specification minimises energy loss which can save on heating costs, in addition to reducing the impact on the environment.
Window Energy Ratings (WER) were launched in March 2004 by the British Fenestration Rating Council (BFRC), an independent government-supported body established to develop and administer a system of Window Energy Ratings in the UK.
The idea was to develop a consumerfriendly method of illustrating which windows performed well in terms of energy efficiency, using the same type of labels already seen on white goods. Full details relating to Window Energy Ratings can be found on the BFRC website: www.brfc.org. A BFRC rating and label apply to a whole window (i.e. frame and glass). They do not apply to either the frame, or the system or the glass individually. Therefore it is at the point at which all these components come together to produce a whole window that the rating and label are obtained.
A window’s energy rating is determined by a formula which takes into account available solar heat gains (window g Value) and subtracts the thermal losses (window u-value and air leakage).
WER = Solar Gains – (Thermal Losses + Air Leakage)
The resulting value (energy index) is then placed into a band on an A-G scale consistent with other energy performance labels already familiar to the consumer. The A-G rating system provides a means of promoting energy-efficient windows to the consumer and should also help the government to incentivise their uptake.
- Windows with a C Rating or higher are endorsed by the Energy Saving Trust’s Energy Efficiency Recommended (EER) scheme and may also carry their logo.
- C Rated windows are also included on DEFRA’s (Department of Environment, Food and Rural Affairs) illustrative list of possible energy efficiency measures’ as part of the Energy Efficiency Commitment (EEC), paving the way for possible future subsidies.
The Energy Saving Trust (EST) has also produced a series of Best Practice Guides for windows in new dwellings which use BFRC ratings as the measure of window performance. Good practice is achieved by the use of D Rated windows and best practice via the use of C Rated windows. Whilst not mandatory, these guides will be used in any governmentfunded construction (e.g. social housing)
A BFRC RATING IS AWARDED HAVING FOLLOWED THREE STAGES
- A BFRC Certified Simulator produces an assessment report of the window. The Certified Simulator’s report gives an assessment of the BFRC Rating, which takes into account U Value, g Value and L Value (air leakage). The U Value would normally be produced by the Simulator using approved software. The g Value comes from the glass manufacture; and the L Value from testing to BS 6375. The U Value simulation is performed for a window to the standard GGF configuration, and the result can be applied to all products of other configurations using the same system/profile.
- A BFRC Independent Agency ensures the window company has a satisfactory quality management system, approves the Certified Simulator’s report and informs BFRC.
- BFRC authorises, and informs the window company of the product’s rating and gives permission for them to use the labels. BFRC places the product on the database on its website. The Energy Saving Trust, on receipt of the appropriate rating, allows the use of the Energy Efficiency Recommended logo on the window.
SGG PLANITHERM TOTAL® is a low-E glass supplied as standard on all our double glazed units. This advanced low-emissivity product provides superior performance in thermal insulation. With centre pane U Values as low as 1.2 W/m2k this ensures minimal thermal losses for frames incorporating this glazing. SGG PLANITHERM TOTAL® has several advantages over traditional low-E glazing: Better thermal insulation – Reduces heat loss, saving money on heating bills and hence reducing use of energy and the impact on the environment. More comfortable homes – Better insulation means less drafts and cold spots near windows and doors. Less condensation – A warmer interior surface of the glazed unit reduces the probability of condensation. Less of a tint to the glass – Allows more natural light into the building whilst also giving clearer vision through the windows. Energy efficiency – Improved thermal insulation combined with greater solar gains make SGG PLANITHERM TOTAL® one of the most energy-efficient products on the market.
HOW DO WINDOW ENERGY RATINGS IMPROVE?: The overall performance of a window is dependent upon the combined effect of the frame and the glazing components and the air tightness of the finished window. Each frame style is then a fixed element and ratings within each frame style are then varied by calculating the decreasing thermal losses and/or increasing solar gain that vary with the glazing specification.
U VALUES: The U Value is a measure of the rate of heat flow through a window. A lower U Value indicates less energy loss through the window. U-values should always be representative of the entire window. U Values for individual components of the window such as the glazing should not be used in any calculations. Heat is lost through the window by conduction, convection and radiation. Various measures can be taken to reduce heat loss through the window. Using a low-E coating to the glazing helps to reflect the heat back into the room. Filling the double glazed unit with an inert gas such as argon reduces the amount of heat lost through the glazing unit through convection. Warm edge spacer bars can also be used instead of conventional metal spacer bars to reduce the conduction through them.
SGG SWISSPACER®V - THERMALLY EFFICIENT SPACER BAR
SGG SWISSPACER® V is a thermally improved, or warm edge, spacer bar for insulating glazing. Manufactured from a highly insulating composite plastic, this spacer bar helps to reduce thermal losses giving a greater level of energy efficiency and reducing the cost to both heating bills and the environment. The spacer works by reducing heat exchange from the inner pane to the outer pane, virtually eliminating any internal condensation at the edges of the window. (see below)
SGG ECOCLEAR® - HIGH PERFORMANCE GLAZING SYSTEM: Howarth offers the option to specify SGG EcoClear ®, the most technically superior glazing solution available today.
Incorporating the new SGG Planitherm® Total coated glass technology, windows can now achieve the highest possible Window Energy Ratings (WERs) and will qualify for Energy Saving Recommended status with most frame systems.
Windows glazed with SGG EcoClear ® allow optimal amounts of the sun’s energy to pass through the glass into the room, benefiting from free solar heat gain. At the same time, using advanced glass coating technology, SGG EcoClear ® reflects the heat inside back into the room rather than allowing it to escape. Both features reduce or eliminate the need for additional heating. SGG EcoClear ® offers up to three times more thermal insulation than standard double glazing and 20% better insulation than old fashioned thermally insulating glass. All this without compromising the amount of natural light passing through the glass.
Reduce energy bills: Windows glazed with SGG EcoClear® can drastically cut the cost of heating bills over their lifetime.
Reducing carbon footprints: In the UK, homes create over a quarter of all CO2 emissions. SGG EcoClear® windows will help reduce energy loss and significantly lower CO2 emissions.
