For hundreds of years, people have used venetian blinds to keep buildings cooler in summer and warmer in winter. Simply adjust the angle of the blinds and you control how much solar energy enters the room. Modeling that effect isn't quite so easy, however.

Existing computer programs can accurately model heat gain and loss through unshaded windows. Where they fall short is when you add attachments like blinds or drapes to the window. That's a problem for green building design since the…