In order to improve window performance in your home, you must take into consideration selection in terms of design and installation. ENERGY STAR® has developed an energy performance ratings of windows to highlight minimum performance that will help you select the proper window specifications for your particular climate. This will help you to determine which types of windows will work best to promote the energy efficiency that is needed for your home.
Passive solar home design has been incorporated into the design strategies of builders for many years, which utilizes solar energy at the site to provide heating, cooling and lighting for the home. Windows are the most important element in this design concept, but of course the strategies vary due to location and regional climate. However, basic guidelines for window selection, orientation and size remain the same in order to maximize heat gain in the winter timeframe and solar reduction in the summer months.
In heat dominated climates, large windows, or major glazing areas, should generally face south in order to collect more solar energy in the winter. To prevent excessive heat gain in the summer, overhangs or other shading elements should be used. Energy performance ratings are available, but the general equation for effectiveness is:
A solar heat gain coefficient (SHGC) of 0.6 or higher is desired for south facing windows to maximize solar heat gain during the winter. To reduce conduct heat transfer, you need a U-factor of 0.35 or less with a high visible transmittance (VT) for maximum light transfer.
To allow adequate daylight, windows on the east, west and north facing walls should be minimized. This may be difficult to control due to the sun’s placement, so these windows should have a low SHGC and/or have shades for extra protection. On the north side, these windows should primarily be used for lighting only, since there is very little solar heat contributed. In this case, low-emissivity (low-e) window glazing can help to control solar heat gain and loss.
Different strategies work in colder climates. Use of north facing windows with low SHGCs on the north facing windows prove effective at reducing the cold.