Scientists at the Ben-Gurion University of the Negev have created a novel window design that is an effective and even eco-friendly way to cool hot property in summer and warm-up chilly rooms in winter. And like most of the very best designs, the "Seasons Window" is terribly simple.
It's made of three panes of glass mounted to a single swiveling frame. There's a single clear air-tight double-glazed sheet, and a tinted inner pane that doesn't cover the whole frame area--there's a gap at the top and bottom.
In "winter mode" you face the airtight pane outwards--it lets sunlight through to both illuminate the room and heat the inner pane of tinted glass. This then re-radiates heat into the room, and heats the room's air that circulates by convection around the smaller pane, and then gains 20ºC of heat from the circulation. The outer double-glazed pane, which could even be given a special low-emittance coating, effectively traps heat inside the room.
In summer the window gets rotated in its frame to face the dark panel outwards. This absorbs some of the incoming solar radiation and prevents it falling into the room and heating it up further. More heat-scattering is caused by the double-glazed clear-panel that now protects the room from unwanted heat. Obviously it won't prevent all solar-heating effects, but it should lower the load on cooling equipment.
According to Prof. Evyatar Erell, a researcher at the university, the window is the "only glazing system that permits effective passive heating in winter without glare or high radiant temperature near a window and reduces unwanted solar gains in summer without obstructing the view outdoors." There's just one issue, though it's a minor one--during the winter, the inwards-facing darkened pane is going to reduce incoming visible light too, and that is no way to cheer up a dreary winter's day or help a sufferer of S.A.D. Still, it's uniqueness is its simplicity and potential low cost--it's due to be marketed in Israel first, where the weather conditions are about right for the window to achieve maximum effect.