Abstract
The energy performance of a window can be described by the thermal transmittance, the total solar energy transmittance, and the air leakage. In fact, the total heat flow is given by the transmission heat losses or gains, which depend only on the temperature difference between the two sides, by the gains due to incident solar radiation, and by the losses due to leakage through apertures in the frame and between frame and wall. As the air leakage actually accounts only for a small percentage of the conduction losses, its contribution can be omitted. Moreover for new installations it could be considered as a constant value, independent from the selected window and glazing system.
As regards the two other terms, their contributions to the building thermal balance are not independent each other. As evidenced by the utilisation factors in the quasi-static methods of the international standards (EN ISO 13790:2008), the evaluation of solar gains effective contribution (or the evaluation of the effective losses through the envelope) has to consider their impact on the ambient overheating.
The most effective thermal insulating glazing systems, as the triple glazing windows, are also characterized by low solar transmittance which strongly reduces solar gains. The thermal energy balance of the building is then affected both in summer and winter season, with potentially increased heating energy need. The present work is aimed to evaluate the impact of different kind of glazing systems (two double and two triple glazing), window size (considering a range from 16% to 41% of window to floor area ratio), orientation of the principal windowed wall and internal gains on the winter and summer energy need and peak loads of a well insulated residential building. The climatic data of four localities of central and southern Europe have been considered: Paris (Trappes), Milan, Nice and Rome. A statistical analysis has been performed on the obtained results in order to identify the most influencing parameters.