Solar Radiation on a Residential Window

The sun's energy provides a source of heat radiation for residential windows.

A house's windows are typically the weakest points of contact with the outside environment. This can result in heat loss or heat gain during the hottest and coldest months of the year. Manufacturing technology has developed ways of redirecting solar radiation to help reduce energy costs, while maintaining normal window visibility.

Solar Radiation

Solar radiation, or sunlight, is a form of electromagnetic radiation contained inside the visible and infrared portions of the electromagnetic spectrum, with a small portion within the ultraviolet range. Solar radiation effects are strongest when the sun's rays are vertical, or directly overhead according to Energy Savers, a solar energy resource site. As the Earth rotates, sun rays slant accordingly depending on location, which accounts for the changes in seasons. As a result, the effects of solar radiation on residential windows can vary depending on the time of year.

Effects

As sunlight makes its way through a residential window, different amounts of visible light and solar heat may penetrate to a home's interior, according to the Florida Solar Energy Center. Research studies conducted by the National Research Council of Canada show a home with double-pane clear-glass windows can take in as much as 10 to 27 percent in solar or heat gain throughout the winter, during periods of sunlight. On the other hand, these same windows may also account for more than 27 percent of a home's total heat loss during night time hours and on cloudy days.

Solar Sheeting

To make the most of solar radiation effects, some window manufacturers incorporate a solar sheet covering within window designs. Solar sheeting works to maximize the effects of infrared radiation or heat, while maintaining a window's natural visibility. Low solar heat (LSG) gain and high solar heat gain (HSG) are different types of coverings designed for hot and cold climates. Low solar heat gain coverings work to reduce the amount of heat that passes through a window, while high solar heat gain coverings work to keep interior heat from exiting through window surfaces.

Climate Types

Reducing the amount of infrared radiation that goes through a residential window may benefit those who live in warmer climate areas. Infrared radiation makes up the longer wavelengths, or rays contained inside sunlight. The LSG covering works by reflecting these rays back outside so they don't enter the house according to the Florida Solar Energy Center. The opposite effect is had with HSG sheets when used in a cold climate, where heat is reflected back into the house rather than escaping through the window pane.

Considerations

According to the National Research Council of Canada, any form of window protection--whether LSG or HSG--is better than no protection at all as far as energy savings is concerned. And while many residential areas are located in climates that fluctuate between hot and cold temperatures, solar sheeting can provide some degree of cost savings if only during certain times of the year. Ultimately, the difference between heating and cooling costs may determine which type of sheeting will provide the most benefit from solar radiation energy.

References

• Florida Solar Energy Center: About Solar Gain
• National Research Council Canada: Selecting Residential Window Glazing for Optimal Energy Performance
• Energy Savers: Solar Radiation Basics

Resources

• EO Earth: Solar Radiation