Overcoming the Challenges of Facade Solar Control

Sun is undoubtedly amongst the most important natural resources that can be harvested by a building. However, this can be done effectively only by applying certain sun control strategies and specific shading devices.  As an example, the solar gains must be minimised in warm and sunny climates because it may otherwise lead to extreme cooling loads. On the other hand, in colder regions, incident solar rays can contribute significantly to passive as well as active solar heating.  Additionally, elimination of glare by controlling direct and diffuse sunlight is a major requirement. Mentioned below are some of the basic principles of solar shading that can help address the challenges of facade solar control.

Basics of Solar Geometry:

Efficient shading device designing depends heavily on the building envelope’s solar orientation. To ensure proper designing of shading devices, understanding the sun’s position throughout the year is important. This is expressed most commonly in terms altitude and azimuth angles. The sun’s angle above the horizon is referred to as the altitude angle and this angle is the maximum during the solar noon on any given day. Also known as the bearing angle, azimuth angle is the angle of the projection of the sun on the ground. In case of northern hemisphere, this angle is measured relative to the south and just the opposite is done for southern hemisphere.

Efficient Shading System Design:

Fixed and movable shading devices can have a serious impact on the aesthetics of the building. Though this impact can be positive, it may also destroy the architectural design intent of the building in some instances. This is particularly true when the shading devices are applied to pre-existing structures. Therefore, the shading devices are more likely to be well-integrated into the building envelope when they are considered early in the design process. One of the most important considerations during this process is the degree of window shading.

Exterior Shading Device Strategies:

Exterior shading devices re more effective compared to interior devices in terms of blocking solar heat gains. Here are some ideas for ensuring that your building envelope has the best possible shading devices.

  • In case the owner or the architect doesn’t allow attachments, try to design the building in a way so that its geometry provides shade to the building.
  • Please note that horizontal shading devices like recessed windows, overhangs, and awnings are applied mostly in the south orientation. They also have some impact on west or east facades. However, for the north oriented surfaces, there is no impact of these devices.
  • If you are planning to apply overhangs in the windows, try to achieve less projection by putting it on a small slope or dropping the edge. While providing shade to a high curtain wall, less projection can be achieved by breaking up the overhang into smaller parts and positioning them all over the surface.
  • In case you are looking to allow more direct daylight, you may substitute dropped edge by small scale louvers. To increase the amount of diffused light without reducing the shade, small scale louvers can be used instead of solid surface.
  • In case of west and east facades, vertical shading devices are extremely convenient. In north orientation, they can also help block late afternoon and early morning low sun. If there is a tight budget, you should focus more on west and south shading because the morning sun makes no significant contribution towards heat gains.
  • Glare reduction is another serious concern that must be addressed. This involves blocking the bright sky from the vision of the occupant, and can be achieved only by exterior shading.
  • Please note that if you are looking for diffuse daylight, use of shading devices with light colors is recommended. However, if you are looking for maximum reduction in heat gain and light, darker shading devices should be used.
  • Though the installation and maintenance costs are much higher compared to that of fixed exterior shading systems, the movable systems are exceptionally efficient in lowering energy demands. They can also be controlled by a central BMS and combined with sun sensors for enhanced efficiency.

Window Plane System Shading Strategies:

  • Though not very effective, roller shades can be an inexpensive and movable alternative.
  • Glazing treatments such as films, tints, and reflective coatings are capable of reducing the heat transfer significantly. However, they allow direct penetration of the sun rays.
  • Fritted glass is a great option for sunlight control, but it may lead to an increase in glare.

Interior Shading Device Strategies:

The ability of interior shading alone to control solar gains is rather limited because the sun rays already enter the building by the time they can start functioning.  However, the following strategies can be used for better results.

  • In case interior shading is your only available option, you may use light coloured louvers or blinds to reflect back the solar heat. Semi-translucent shading devices can also be used, but glare control may be a concern.
  • Interior shading devices are most effective when used in tandem with primary exterior shading, providing back-up shading as well as glare control as per your exact requirement.
  • Always avoid interior shading devices that block light completely.

At CGS Façade Group, we have a long history of providing state-of-the-art building façade solutions all over the world. Please get in touch with us today to discuss whatever doubts you may have about facade solar control.