It all depends on the purpose and area of the windows used in the building system. The walls and windows in a building is a energy system just as much as the HVAC system is.
For instance in So. Cal., if you have a room with a large south facing window, which would be better in winter: 1) a clear triple-pane window or 2) a low-e double-pane window. #2 would usually be better. The sunlight will have a bigger energy impact than thermal properties of the two windows.
Think of the # of panes as as you would wall insulation (R-11, R-13, R-19, R-30). More panes have more insulation for thermal loads. The more glass you have, the more R-Value you need to meet the minimum average R-Value for Walls for Title 24 requirements. Clear single-pane is about R-1. Clear double-pane Glass is about R-2. Low-E double-pane glass is about R-2.6 to R-3.5. Low-E triple-pane glass is about R-3.5 to R-5.6. In order to put a lot of glass in homes you must increase the R-value of the walls. This means going to 2×6 wall construction with R-30.
Windows also allow solar heat gains. To minimize this effect, films (measured in shading coefficients) are applied to the inside surfaces of the glass in warmer climates. In colder climates, this costs heating energy in the winter.
I use to do energy studies and Title 24’s for commercial buildings. Based on the amount of glazing designed into the building, we would tell the architect what type glazing was need: Single, Double, or Triple pane and shading coefficient. Sometimes they would come back after reducing the window height, adding overhangs and/or wing walls to provide more shading effects.
For most of So. Cal., where temps are usually less than +/- 20 deg delta from inside temps, energy savings or thermal comfort would not be a driving reason for using triple-pane glass. Noise may be an issue to use triple-pane if you live next to a busy road, highway or airport.
Btw, I work near Torrance Med. Love seeing those Robinson copters fly over our building.
