The sun is a great source of lighting… if you can control it. The trick with sunlight is toning it down without cutting it out. Sunlight itself, on a clear day, has a brightness of over 100,000 lux, and full daylight outdoors measures about 10,000 lux. Recommended indoor illumination for normal office work is about 500-1000 lux. So, full daylight on a façade facing the sun is just too bright for comfortable daylighting.
One solution is the brise soleil, a sun baffle or sun screen that stands outboard of the windows, deflecting some or all of the incoming sunlight. Brises soleil may be individual baffles for each window, or a complete secondary façade at some distance from the actual building envelope.
The sun is strong in Madrid, where digital banking giant BBVA is building its mammoth new headquarters. To shield against the sun and still get the benefit of daylighting – a major objective in this environmentally conscious project – architect Herzog & de Meuron designed a system of brises soleil made of an FRP sandwich. The hinged panels range in height from 1 m to 4 m, and are individually operable to adjust to the weather conditions and the sun’s position.
The specification for the FRP panels was developed by the José Cristos, a composites consultant who worked closely with the panel maker, Innova Composite. The panels are a vacuum-infused sandwich of glass fiber over a PET foam core, using a fire retardant laminate system developed by Scott Bader, consisting of Crestapol 1212 high performance urethane acrylate resin with intumescent in-mould spray Crystic FIREGUARD 75PA (IMS) EXCEL fire protection gelcoat. This system achieves a B-s2 d0 ‘low flammability’ fire rating under UNE-EN 13501-1, the European standard for products used in construction.
Because the panels are designed expressly for sun exposure, they also had to be UV resistant, which the fire-resistant gel-coat is not. Resistance to the damaging solar radiation was provided by a polyurethane overpaint.