Fundamental design principles related to orientation, massing, and openings can have a greater overall effect than the application of advanced technology. The best architecture can function in an “unplugged” state in good weather and then take advantage of climate control only when needed. This approach, using shading devices, provides “energy security,” allowing buildings to remain occupied without outside energy.
By overlaying a shading mask in the proper orientation on the sun-path diagram, you can read off the times when the sun rays will be intercepted. Masks can be drawn for full shade (100 percent mask) when the observation point is at the lowest point of the surface needing shading, or for 50 percent shading when the observation point is placed at the halfway mark on the surface. It is customary to design a shading device in such a way that, as soon as shading is needed on a surface, the masking angle should exceed 50 percent.
WHAT IS A SHADING MASK?
According to the U.S. Green Building Council, a shading mask is “a representation of the sky as viewed from a reference point, indicating the portion of sky that is visible and obstructed.” This tool is part of the passive solar design process that helps determine solar access, along with a sun-path diagram. Software is available that can be used to create a shading mask.
SHADING DEVICES AND SHADING COEFFICIENT
Each individual fenestration system, consisting of glazing and shading devices, has a unique capability to admit solar heat. This property is evaluated in terms of its shading coefficient (SC), which is the ratio of the amount of solar heat admitted by the system under consideration to the solar heat gain factor for the same conditions. In equation form, this becomes:
Solar heat gain(Btu/sq.ft.*hr)=SC×SHGF
Values of the shading coefficient also are given in the ASHRAE Handbook of Fundamentals (1981), Chapter 27, for the most widely used glazing materials alone and in combination with internal and external shading devices. Selected values for single and double glazing are given below:
SHADING COEFFICIENT FOR SELECTED GLAZING SYSTEMS
|TYPE OF GLASS||SOLAR TRANSMISSION||SHADING COEFFICIENT|
|Insulating glass: clear both lights|
|1/8″ + 1/8″||0.71||0.88|
|1/4″ + 1/4″||0.61||0.81|
|Clear in, 1/4″||0.36||0.55|
For combinations of glazing and shading devices, also refer to the ASHRAE Handbook of Fundamentals, Chapter 27.
TYPES OF SHADING DEVICES
Vertical Rolling Shutters
Rolling shutters provide sun control not only by shading windows from direct sun rays but also by way of two dead airspaces—one between the shutter and window, the other within the shutter extrusions to serve as insulation. The dead airspaces work as well in winter to prevent the escape of heat from the interior. In addition, shutters are useful as privacy and security measures. They can be installed in new or existing construction and are manufactured in standard window sizes. They are also effective for storm protection. They are composed of vertical rolling shutters with head box, metal angle brace, shutter slats PVC or extruded aluminum, guide rail, and rod or cord control.
External Venetian Blinds
External blinds protect the building interior from solar gain and glare and can be raised partially or fully to the head when not needed. Manual or electric control is from inside the building. They are composed of aluminum slats, side guide or wires, and rod control for tilting or lifting.
Horizontal Rolling Shutters
These miniature external louvers shade windows from direct sunlight and glare, while allowing a high degree of visibility, light ventilation, insect protection, and daytime privacy. The solar screen is installed in aluminum frames and can be adapted to suit most applications. They are composed of a head and sill with fixed and side-hinged horizontal sliding and aluminum frames positioned in different angles—45ᴼ, 30ᴼ, 15ᴼ, and 0ᴼ.
Architects are graphically oriented professionals and need quick access to potential shading device options with components that will adapt to a variety of overall floor plans. For more than 85 years, Architectural Graphic Standards (AGS) has sought to provide architects with graphic illustrations of the most current design practices and standards. Now, AGS Online provides these graphic illustrations for “Shading Masks and Shading Devices” in a downloadable format.