Windows provide views, daylight and passive solar heating for buildings. However, too much sun or sun at the wrong time of day or year leads to overheating, decreased comfort and unnecessary cooling costs. Solar shading for windows controls the sun entering windows to prevent overheating and excessive cooling costs.
A simple and effective way to shade south-facing windows is with overhangs. Even fixed overhangs, when properly designed, can provide shade when needed and allow direct sunlight in when it is desired. During the summer, when shading is most desired, the sun is high in the sky. Overhangs can provide full or nearly full shade to a south-facing window. In winter, when more sun is desired, the sun is lower in the sky, allowing direct sunlight to pass under the overhang and through the window.
Awnings function similarly to overhangs but are more versatile and can provide shading for east and west windows as well as south-facing windows. East and west sun is low in the sky and shines directly into windows, unimpeded by overhangs. By extending down in front of the window, and to the sides, awnings can protect east- and west-facing windows from intense, low-angle sun. Adjustable awnings can provide needed shade in the summer and be retracted in the winter to allow warming sun to passively heat the interior.
Insulated shades can be installed on the interior or exterior of windows; they will not only block sunlight, but also provide insulation to reduce heat transfer through the window. During the summer, they should be drawn in the daytime to provide shade, but opening them on cool summer nights will allow heat to escape and reduce cooling energy required. In the winter, insulated shades should be drawn during the night to hold heat in, but left open during sunny days to allow passive solar heating. They are usually installed on south windows for shading, but their insulating properties are effective on any window orientation.
Reflective window shades are colored white on one side to reflect heat away and black on the other to absorb heat. In summer, the reflective side should face out to bounce heat away. In winter, they can be reversed to absorb solar energy and bounce interior heat back inside. Unfortunately, to be effective, these shades must be drawn at all times, limiting daylight and views. These window shades are most effective on south and west windows.
Solar mesh screens block direct sunlight but allow diffuse light into a room. They are installed on the exterior and are removable seasonally, much like storm windows, for use in the summer season only. They work well on south windows and also provide effective shading for east and west windows which are otherwise difficult to shade. Benefits of solar screens are that they allow diffuse daylight to enter the space but reduce glare and overheating associated with direct sunlight.
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