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How much does each factor of the window affect the energy demand?

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This study, which is published by the Spanish Association of Aluminium and Surface Treatments and carried out by TECNALIA R&I, determines the importance of the influencing factors of a window in the energy demand of a building.

The study simulates a real building according to CTE and it gets the total energy consumption for all the possible combinations of the factors which affect the thermal performance of the window for two climatic zones: cold and warm. We remember that we saw how much it is saved when replacing the windows, with another study of the same laboratory.

For a cold climatic zone, we note that the most important factor would be the thermal transmittance of the glazing, because if we decrease its value from 2 to 1 we would get a saving of nearly 12% in energy consumed.

The results in a warm climatic zone reflect the importance of the solar factor which is placed in the first position with an average saving of over 10% when we go from a solar factor of 0.5 to a 0.69. Comparing this figure with the cold climatic zone (zone E) we see the need to choose the type of glazing according to the place where is going to be placed. In second place we have glass transmittance, with an average saving of almost 4%.

After analysing all the results of the study we notice that we have to focus on the glass performance, which is logical because the glass takes up a large part of the surface of the opening (up to 80%).

So we get the conclusion that we have to choose a frame for its supporting function, which ensures the reduced permeability for its whole lifetime, allowing a great entry of light through a reduced section of the framework, which will offer the finish we want and give us security in case of burglary and fire.

In addition to providing high thermal performance, the Aluminium with Thermal Break stands out clearly in all these aspects compared with the other materials.

Note: Information extracted from the report Ref. 058061 written by Tecnalia Research & Innovation entitled “Determination of the importance of the influential factors of a window in the energetic demand in a building”.

The full text can be obtained in the AEA web:

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