Architectural Record BE - Building Enclosure

Managing Daylight with Automated Solar Control

Motorized shades lead to sustainable solutions
[ Page 4 of 6 ]         
Sponsored by Draper, Inc.

Importance of Fabric Selection

It is important to note that while designers often select the fabric for a shading system based on its color, that color has important ramifications for solar control and daylight management. Failure to appreciate the potential of color in this respect can lead to not only wasting its potential benefits, but actually having adverse effects, such as creating glare at workstations and making interior spaces unnecessarily hot or cold.

The amount of solar energy and heat gain that enters a space through a window will be dependent on the type and color of the fabric chosen. Every fabric has three properties: solar absorption, solar reflection, and solar transmittance.

Solar absorption is the amount of solar radiation absorbed by the fabric. Solar reflection is the amount of solar radiation reflected back out of the space by the fabric. Solar transmittance is the amount of solar radiation that passes through the fabric into the interior of the space. These are the three ways that a shade can manage solar energy. When added together these always equal 100 percent.

Each type of fabric will have differences and hence advantages and disadvantages in managing solar energy. There are four properties of shade fabrics and openness factors. Dark color fabrics generally have the greatest solar absorption and least reflection, which normally enables them to provide better glare control. Darker color fabrics also provide a better view to the outside, and make it easier to view inside at night. Light colors, on the other hand, have a higher solar reflection, and a lower solar absorption compared to darker colored fabrics. They do not afford as clear a view to the outside as darker color fabrics, and they are harder to view through at night.

Importance of Fabric Selection

Image courtesy of Draper, Inc.

 

There is a type of hybrid fabric, however, called a duplex fabric that provides the best of both of both worlds: a high solar reflection factor along with good visibility. The inside of the fabric is a dark color, and the outside of the fabric facing the glass is either white, a light color, or metalized. The combination of these two features allows greater visibility and greater solar protection, along with glare control and heat control.

Another factor to consider in fabric selection is openness. Openness refers to the amount of the material’s open and/or closed space, that is, the density of its weave. A shade with low openness reflects more infrared rays, offers the best glare reduction and the greatest privacy during daytime hours. Designers looking for a fabric that affords a better view without reflecting as much infrared heat, while admitting more natural light into the building, should opt for a fabric with a high degree of openness; that is, a less dense fabric.

Image courtesy of Draper, Inc.

 

To put it succinctly, openness selection should be based on building position, geographical location or exposure area, office activity, elevation, and view, either clear or obstructed. In the accompanying map, there are recommendations for the window shade openness factor to control glare and work station reflections, for UV protection and for better view-through capabilities based on location.

Image courtesy oc Draper, Inc.

 

Fenestration Data

Designers should look to manufacturers for the following information about their products, which proves to be quite useful in specifying shading systems that control light and heat, view and privacy, and glare level.
 

  • Solar transmittance (TS), reflectance (RS), and absorptance (AS) add up to 100%, indicating that all the sun's energy striking the shade is reflected, absorbed, or passed through.
  • Visible transmittance (TV) indicates the amount of glare likely to be perceived.
  • Openness factor (OF) concerns the density of the weave.
  • Shading coefficients (SC) indicate shading efficiency.

Further, manufacturers often have computerized tools to enable proper fabric selection based on the above-mentioned factors.

 

[ Page 4 of 6 ]         

Notice

Academies