It used to be said that windows are little more than holes in the insulation. It is true to some extent that poorly insulated and drafty windows in certain climates defeat the purpose of wall insulation. However, modern high performance windows are almost as good as opaque insulated wall sections, at least in terms of total energy savings over long periods of time. In some cases, they can be shown to actually out-perform insulated walls. Of course, they have the priceless additional benefits of providing views to the outdoors and natural daylight illumination indoors important issues of quality and comfort.
The main purpose of a building and its windows is to provide comfort to the occupants as the sun moves through the sky, as the outdoor air temperature and humidity vary, and as the wind and rain come and go. If comfort can be achieved while reducing the building's energy use and lowering monthly utility bills, so much the better.
This Energy Guide focuses on choosing window options for residential buildings in hot climates. Many of the principles offered here apply as well to non-residential buildings. However, there are major differences in the types of windows available for these two building classes, and there are normally major differences in their building occupancy schedules. This is important because unoccupied buildings don't need illumination. Nonresidential buildings are most generally occupied during daylight hours. This provides a greater opportunity for the use of daylighting in these buildings to displace electric lighting, saving energy in the process.
Residential buildings are usually less occupied during daylight hours, so there is less chance to save energy by using daylight to displace daytime electric lighting. With its relatively higher fraction of retirees, however, Florida offers numerous exceptions to this general rule. Proper use of windows for daytime lighting of residential building interiors can displace the electric lighting that might otherwise be needed.
Florida Solar Energy Center and McCluney, Ross, "Industry Guide To Selecting The Best Residential Window Options For The Florida Climate (Revised)" (2001). FSEC Energy Research Center®. 582.