Saving energy in residential buildings: The use of fully reversible windows

New double-glazed window systems based on the possibility of reversing the window through its sash could be in a short time a reality. Actually, the windows on the market are normally reversible to a partly open position for cleaning purposes, lowering the maintenance costs. But they could also have a fundamental role in the energy performance of buildings, if realised with two different panes, an absorbing one and clear one, and if they could operate as closed windows in both normal and reversed positions. The position of the absorbing pane influences their thermal behaviour, saving a quantity of energy if the tinted pane faces indoor in the heating season and outdoor in the cooling season. The solar filtering behaviour in fact is required in summer, to reduce the penetration of solar radiation to the indoor environment, while the solar heat gain behaviour is required in winter to minimize the heating consumption, making use of the solar energy. The problem linked to the ‘‘new’’ system is the winter overheating due to the solar gain behaviour: indoor temperatures could become uncomfortable if not controlled. But the overheating control could reduce the expected energy savings in a manner that depends on the used systems and strategies. This paper analyses the energy savings connected to the potential use of the reversible windows in several Italian locations, representatives of Mediterranean climate, for buildings with no-prevalent cooling or heating requirements. Different strategies to control indoor winter overheating are analysed with their implications in energy consumption and room thermal comfort for reversible windows.