Well, this is an invention that I’ve been waiting to have happen … and, sadly, it comes
just too late for my recent window replacement. The KSD Window from Eco-Logical Innovations (the US sister company of ÖKO-LOGIC GmbH in Germany) is “the every season window with the right spin”. The 
KSD window has three panes with high insulative value.
The innovation … the been waiting for idea … is in that center pane. It has heat reflective capabilities, in one direction. Thus, in summer, flipping the window with the green side facing out and there is minimal heat gain, reducing the cooling burden. In winter, flip it the other way, and it reduces heat loss (while allowing solar heat gain during the day), reducing the heating load.