Interior
and exterior shading systems both have roles to play in handling glare and
solar heat gain issues. While interior solutions, such as roller shades, are
best known in North America, often an exterior solution is can be a better
option.

So how do
you know when to use an exterior shading system? Here are four questions for
understanding the benefits of exterior solutions:

1. Why is an exterior system more effective than an interior one?
Energy from the sun is short wave and carries little heat. Heat is only produced when the solar energy is absorbed by a surface (carpeting, furniture, clothing) and is then radiated as long wave infrared (IR) energy.

An
interior shading system can transmit, absorb, or reflect solar energy back
through the glazing, depending on factors such as openness and color.

Reflected
solar energy is not an issue—it remains short wave and does not cause any heat
gain. Transmitted energy is absorbed by surfaces in the building and is
radiated as heat. Energy absorbed by the shades is radiated as heat, most of which
is trapped inside the building.

An
exterior system can also transmit, absorb, or reflect solar energy, but anything
absorbed by the shading system is radiated as heat on the building’s exterior.
Glass is not transparent to long wave energy and, as a result, little of this
radiated heat gets inside the building. By eliminating one of the two sources
of heat gain, solar gain inside the building is greatly reduced.

An exterior system (right) keeps much more solar energy from getting into the occupied space than an interior system (left).

2. What are the main benefits of an exterior system?
Shading systems reduce the amount of solar gain in the building, which allows the size of the HVAC system to be reduced. The resulting savings in capital cost can wholly or partly offset the shading system’s cost.

Some
buildings need to be cooled in the summer and heated during the winter months.
If a retractable exterior shading system is used, it can be turned off in the
winter months, allowing the solar gain into the building to supplement
mechanical heating.

Exterior
shade systems can also reduce the need for artificial lighting by optimizing
diffused daylight to illuminate interiors. More than 30 percent of the energy
costs of an office building relate to artificial lighting, so if lighting needs
can be reduced, significant savings can result.

A good
shading system manages both heat and glare while providing access to outside
views. More comfortable working conditions can lead to increased productivity.

3. What are the most common attachment methods?
Installation of an exterior shading system may involve attaching directly to the curtain wall mullions, to brick or concrete masonry units (CMUs), or through cladding to steel structure. Different brackets will probably be required for each situation and will be developed to meet specific project requirements.

Exterior
roller shades and venetian blinds are installed just above or at the top of the
glazing. They are relatively lightweight and, because they are retracted during
high winds, they do not apply significant loads to the facade, so lighter aluminum
brackets can be used.

Exterior
louver and brise-soleil systems remain fixed in place, so they apply more
significant loads to the facade. Brackets, bolts, and other fasteners will be
in accordance with the loads defined in local building codes. If the systems
are being connected to the curtain wall, it is possible the mullions will need
to be reinforced with steel. Structural calculations will always be undertaken
to determine the applied loads and the impact on the facade design and building
connections.

Other
issues that need to be considered include separation of dissimilar metals, cold
bridging, and water penetration, as well as relative expansion and contraction
between the shading system and the facade.

4. How do exterior systems cope with adverse weather conditions?
Fixed louver systems are designed to take account of maximum applied loads. With brise-soleil systems, the loads at the attachment points might be significant, particularly if they project very far out from the building. If this is the case, diagonal brace rods might be incorporated into the design to allow the load to be shared between two attachment points. With fixed systems, ice buildup and the risk of falling ice must also be considered. Therefore, brise-soleil systems might be inappropriate for tall buildings in urban areas.

Retractable
roller shades and venetian blinds are more lightweight than fixed systems and
are designed to retract when the wind speeds are high. Standard roller shades
need to be retracted at relatively low wind speeds and will not be appropriate
for windy locations or on tall buildings. However, “zipper” shading system allow
the fabric to be locked into side tracks. This type can operate in higher wind
speeds and is suitable for tall buildings.

Ice is a
potential issue, but should not be a problem if systems are protected in the
raised position. Automated controls will ensure the systems are only deployed
when there is sun. Temperature and humidity sensors can also be used to stop
the blinds or shades from being operated when there is a risk of icing.

For a more in-depth exploration of exterior shading solutions, click here for a free white paper on the subject.

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