What is solar heat gain coefficient?
The SHGC is the fraction of the solar radiation external to a window system that is transmitted as well as admitted through inward flowing surface radiation and convection. This coefficient is angular dependent and varies according to the incident angle of the source, whether it is direct light, diffuse, or a reflected component of solar radiation.
- What is a good solar heat gain coefficient in Denver? The solar heat gain coefficient (SHGC) measures how much solar radiation passes through your window and enters as heat into your residence. The SHGC has a rating value of 0 to 1, and just like the U-factor rating, lower values are better for solar climates like the one in Denver, Colorado.
The solar heat gain from a window glazing system consists of two components:
1. Solar radiation passed through the window and absorbed indoors and
The solar optical calculation determines the first of these two quantities. In residential windows, it is usually the more substantial component because these windows are designed to provide excellent visible daylight, which customarily results in relatively high solar transmittance as well.
2. Solar radiation absorbed within the glazing system and redirected to the indoor space by heat transfer.
The second component of solar gain must be found using both the solar optical analysis and the heat transfer analysis. The optical calculation determines the amount of solar radiation absorbed at an individual glazing. A portion of this energy ends up going to the indoor space. The size of this "inward-flowing fraction" depends on how the thermal
resistance of the glazing system is distributed from the indoor side to the outdoor side. Therefore, the heat transfer analysis must be complete, yielding the required values of thermal resistance at each step through the glazing system, before a Solar Heat Gain Coefficient (SHGC) can be quantified.
What does the solar heat gain coefficient (SHGC) have to do with windows?
Windows can substantially alter the amount of purchased energy required to maintain comfort. Well-designed, they can provide a net energy gain; poorly designed, they can be an enormous energy burden. Improving the solar heat gain coefficient in replacement windows provides a strategy to make windows energy conserving. Each element of new windows is directed at improving one or more of the overall energy functions of windows, which are: providing winter solar heat, providing year-round daylighting, rejecting summer solar heat, providing insulation and air tightness during periods of heating or air conditioning, and providing natural ventilation during temperate weather.
When we talk to homeowners about replacing windows, we know that glazing and performance matter with the glass packages. In the past, single pane glass didn't insulate well, and it didn't have Low-E (silver oxide) coating to help with Solar Heat Gain or energy efficiency. Low-E coatings help reduce harmful UV and Infrared rays from the sun. This is why it gets so hot in your home with direct sunlight on poor performing glass. When the temperature soars, ordinary window glass can’t handle the heat. And tinted glass spoils the view. Low-E glass, however, has been specially formulated to reject the sun’s heat without affecting the view. It lets more light in and keeps more heat out. So, your home stays cool and comfortable. What’s more, Low-E provides exceptional fading protection as well. It can block 95% of the sun’s damaging ultraviolet rays (a leading cause of fading), so it will help your furniture, carpets, art and wall coverings stay beautiful.
In the end, you want a lower solar heat gain when choosing new windows in your home. Look at U Factor and SHGC ratings to make an informed choice on your window purchase.
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