Managing Heat and Light Through Exterior Shading Systems
Case Studies: Solar Control Systems
Designers facilitated solar control and glare control using venetian blinds—an exterior shading system—on the following three projects in different climates:
Photo © Richard Wilson
Custom venetian blinds were specified to accommodate irregular shapes on a London project.
An office building in Metawa, Illinois, uses interior venetian blinds to provide effective light control. Motorized blinds in the upper clerestory glazing incorporate 4-inch slats and are automatically operated. The slats are reversed from the standard configuration with the concave side facing upwards. This, combined with a high-gloss white finish on the upper surface of the slats, allows light to be effectively reflected to the ceiling. The control system automatically adjusts the slat angle between a number of pre-set positions to reflect light as deeply as possible into the office while preventing any direct sun penetration. The lower blinds incorporate half-perforated 2-inch slats and are manually operated, allowing individual users to control the light in their work areas.
Architects on a project in Bishopsgate, London, specified venetian blinds on all the glazing and to maintain a consistent appearance, even with the non-rectangular glazing modules. Custom venetian blinds were designed to address the various conditions as seen in the accompanying image. The slats of these blinds can be tilted between the open and closed positions. Because of the irregular shapes, however, they cannot all be retracted. Some of the blinds are always in front of the glazing; some can be partly retracted.
The Donnelly Centre at the University of Toronto was designed by the German architects, Behnisch, and incorporates 4-inch perforated venetian blinds in a double façade on the south elevation. The blinds, in conjunction with the ventilated façade, provide effective solar control both in the winter and summer months. They provide good light control, while still allowing outward vision as a result of the perforation, and they also assist in controlling solar gain. During the winter months, the blinds assist in heating up the façade cavity, reducing heat loss from the interior. In the summer months, the ventilation units that are incorporated in the glazing modules allow warm air in the cavity to be extracted to the exterior, reducing heat gain inside the building. Wall switches allow people to adjust the blinds to meet their needs. The blinds periodically revert to automatic operation, however, to ensure that effective solar control is achieved and to reduce HVAC requirements.
Photos © Richard Wilson
The Donnelly Centre at the University of Toronto incorporates perforated venetian blinds in a double façade on the south elevation. The blinds, in conjunction with the ventilated façade, provide effective solar control in both winter and summer months.
Heat Gain in Interior Systems
Let's now take this concept and apply it to an interior shading system. Effectively, it is the same situation as with the example of the car. Any solar energy that gets into the building will be absorbed and will turn into heat. An interior shading system will, to a certain extent, act like the silvered screen in the windshield of a car; it will reflect solar energy back through the glazing to the outside. Unlike a car screen, however, the shading system is not completely opaque; it is designed to allow some light into the building and to afford views to the exterior. It will therefore reflect some of the solar energy but some will be absorbed by the system and some will pass through it.
If the shading system has a light color, the amount of energy reflected will be increased and the amount of energy absorbed will be reduced. Dark surfaces will absorb more of the solar energy. A reflective surface facing the glazing is therefore important to improve the solar performance of the shading system. To try and address this, some shade fabrics, for example, have an aluminized finish applied to the side that faces the glazing to improve the amount of reflectivity. The solar energy that has not been reflected back through the glazing will either be absorbed by the shading system or will be transmitted through it. The absorbed energy will then be radiated into the building while any that is transmitted through the shading system will be absorbed by surfaces inside the building and will also be radiated as heat.
As with the example of the car, this energy is trapped inside the building and not much of it escapes to the exterior, particularly if a low E finish is applied to the glazing. The inside of the building and the occupants will heat up.
Photos courtesy of Draper, Inc.
An effective solar control system is one that maximizes the use of natural daylight while addressing the problems of glare and excessive heat gain.
Image courtesy of Draper, Inc.
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