My dad recently changed his windows and advised we consider various low-E coatings to shield from the sun on the west facing part of the house. At our previous house, we had brand new Andersen windows which probably had no low-E coating. At the end of the afternoon, the sun would beat into the west part of the house and heat it up to 80-90 degrees. We had no AC living in the San Francisco bay area so the only low cost solution was to install mylar coated blinds that would refelect some of the heat. We also had significant fading on our dining room chair fabric and oak hard wood floors wherever the sun would hit.
Windows that have a low-E coating are what you want to look for. The low-E coating was developed for the space shuttle and if you put it thick enough on a window, the window becomes like a mirror. So think of it as a mirror coating that, depending on the thickness, blocks the sun's rays. The higher the solar heat gain, the higher the insulation value too.
My dad's choice (for his house in northern Canada) was to go with windows classified as Low-E RLE2 which have a "solar heat gain coefficient" of 0.26. This means that only 26% of the sun's UV rays will get through. He put RLE2 windows on the west and north faces. He chose low-E LOF3 (which has a solar heat gain coefficient of 0.48) for the east and south faces.
The LOF3 with higher sun penetration was important for getting greater sun penetration in winter. The lower penetration RLE2 on the west side allowed less air conditioning use later in the day when the sun is strongest and the RLE2 on the north face was better for insulation in winter.
We are considering Pella brand Pro-line windows that have a solar heat gain coefficient of 0.37. They have product lines across the board for solar heat gain so be informed when you are buying!
For more info on this, see www.efficientwindows.org/energystar.cfm for your zone and solar gain recommendations.
