In Southwest Florida, 30 percent of the summer cooling load is attributed to glass and windows. The use of glass as a home building material is becoming more and more popular. However, glass causes special concerns for homeowners in a summer-dominant climate because glass and windows offer an entrance for solar heat to invade your home.
All transfer of heat energy occurs as the result of convection, conduction or radiation. Convection occurs when heat energy, embodied in a substance, usually air, moves from place to place as the embodying substance moves. According to the Florida Solar Energy Center, convection caused by leaky window gaskets or door thresholds account for only three percent of the typical home’s air conditioning load.
Conduction occurs when heat energy moves from molecule to molecule through a substance. The typical summer temperature difference between outside and inside a Southwest Florida home is very small (10 to 20 degrees Fahrenheit). The amount of heat that can be conducted into your home through windows is equally small. This is why LCEC energy advisors warn that multi-pane glass does not provide a reasonable payback in Southwest Florida, unless a “spectrally selective” window is chosen.
Radiation is how most heat energy enters homes in Southwest Florida. Every object stores heat energy and some of it leaks away in the form of infrared radiation or radiant heat. Clear glass windows offer practically no resistance to radiant heat. Radiant and solar heat together account for 31 percent of the heat load on the typical air-conditioning system, with 26 percent of all heat loads coming right through the windows in the form of sunlight.
LCEC offers the following tips when it comes to windows:
- Block solar heat before it reaches the window by using heat-reflecting glass or tinting
- Awnings, storm shutters, shade trees and lanai roofing are effective in blocking solar hear. Eliminating direct light from touching the window surface is ideal.
- South-facing windows experience direct sunlight in the winter but are shaded by the roof overhang in the summer.
- Skylights are in direct sunlight for many hours of the day and should be avoided if possible.
Visit www.lcec.net for more energy saving tips.