NSAI Agrément has introduced an independent
Window Energy Performance (WEP) Certification scheme for the Irish consumer market.
The WEP rating is provided for a standard window to represent typical window sizes. This enables a comparison between different products. Each WEP rating label is specific to a unique window frame and glazing assembly from a single manufacturer. This WEP label is non-transferable.
The WEP Certificate value combines the following characteristics to allow consumers to determine how well each window assembly will perform.
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THE THERMAL TRANSMITTANCE (U window) is a measure of the insulation properties of the window assembly and allows the consumer to compare how effective each window assembly is at containing and conserving heat within a building in the winter. The lower the U-value, the greater the thermal performance of the window.
THE SOLAR FACTOR (g window) or Solar Heat Gain Coefficient (SHGC) measures how well a product blocks heat caused by sunlight. Heat gain can be beneficial in winter months but can also present consumers with additional cooling loads in summer months. The Solar Factor is expressed as a number between 0 and 1. A lower Solar Factor means less heat gain.
THE AIR LEAKAGE (L factor) is a measure of the air tightness of a specific window assembly.
Good quality windows tested to the appropriate standards should have no air leakage and therefore, makes little difference to energy performance however, for leaky windows, the impact is significant. The lower the air leakage value, the greater the air tightness of the assembly.
Finally the CONDENSATION RESISTANCE FACTOR (CR), while not directly used in calculating the WEP Rating, is a measure of the ability of a window assembly to resist the formation of condensation on the interior surface of that product. The higher the CR rating, the better that product is at resisting condensation formation. While this rating cannot predict condensation, it can provide a credible method of comparing the potential of various products for condensation formation.
The Rating Index for each window assembly is derived by combining Uwindow, g window and the L factor. The WEP Rating Band is based on the Rating Index.
For example:-
- a C WEP Rating band has a rating index in the range of -20 to -30 kWh/m²/year.
- an A rated window has a rating index of >0 kWh/m²/year.
A positive (+) WEP rating represents a better energy performing window. For example a passive standard window could achieve a WEP rating index of +30 kWh/m²/year.
For detailed information download: NSAI Window Energy Peformance (WEP) Scheme Booklet.
Click on window type links below to view energy rating label of each certified window.