Sunday, December 22, 2013

The Theatre of the Sun

Moving through the sky, the sun is one of architecture’s few constants. Precisely predictable throughout the year, its presence and ferocity has shaped the nature of architecture throughout human history. Regional typologies around the world have developed to either welcome its warmth or shade from its heat. In India, the numerous geographical differences in the country have created a vast variety of mechanisms to control the sun and none is more remarkable than the humble courtyard. To the untrained eye, an empty void nestled in the midst of a dense built environment would seem like a waste of space. However, it is an architectural device of astounding value and simplicity. The light diffuses into the surrounding spaces and the courtyard itself can be used for a myraid of activities throughout the day and night.

As an architectural typology it has endured for millenia, yet it is completely absent from modern cities. The pressure on the land, soaring densities and archaic building bye-laws have all, but eradicated the courtyard from the urban townhouse – It simply isnt feasible to provide so much open space within each individual home. The agglomeration patterns do not permit all spaces to be naturally lit from exterior windows. So how is one to sufficiently illuminate all interior spaces? One of the more successful solutions is one that imbibes the best qualities of the courtyard and marries them to the best fenestration technologies prevalent today – Operable Skylights.

Skylights have been around long enough, but have always had a plethora of problems. They are essentially holes in the roof, so water penetration is always an issue.  The glasshouse effect, where the effect of the heat gets compounded because it cannot escape – is a boon for colder countries, but very uncomfortable for an already hot climate. It is also important to diffuse the light coming from a skylight for the same reason, the glare in the summer rendering the area useless for anything other than sunbathing.Also, a critical function of the courtyard was to draw out hot air from the centre of the house, forcing in fresh air from the periphery, thereby generating some much needed air movement.

Operable skylights address all of these concerns and more. Modern sealing systems use a multitude of neoprene gaskets and draining systems that allow for minimal water penetration. The little bit of water that does enter is drained through perforations in the profiles. Powder coated aluminum ensures a robust finish to the framework that holds the glass panels in place. The operable panels themselves can be electronically controlled, based on internal temperature and humidity levels. A high-performance glazing system will generally admit more light and less heat than a typical window, allowing for daylighting without negatively impacting the building cooling load in the summer. This is typically achieved through spectrally-selective films. These glazings are typically configured as adouble pane insulated glazing unit, with two 0.25 in. (6 mm) thick panes of glass that are separated by a 0.50 in. (12 mm) air gap. This construction gives the insulated glazing unit a relatively high insulation rating, or R-value, as compared to single pane glass. A low-emissivity coating is also often part of these high-performance glazing units, which further improves the R-value of the unit.

Many daylighting designs will employ skylights for toplighting, or admitting daylight from above. While skylights can be either passive or active, the majority of skylights are passive because they have a clear or diffusing medium that simply allows daylight to penetrate an opening in the roof. They are often comprised of a double layer of material, for increased insulation. Active skylights, by contrast, have a mirror system within the skylight that tracks the sun and are designed to increase the performance of the skylight by channeling the sunlight down into the skylight well. Some of these systems also attempt to reduce the daylight ingress in the summer months, balancing daylighting with cooling loads.

Daylight redirection devices take incoming direct beam sunlight and redirect it, generally onto the ceiling of a space. These devices serve two functions: glare control, where direct sun is redirected away from the eyes of occupants, and daylight penetration, where sunlight is distributed deeper into a space that would not be allowed otherwise. Daylight redirection devices generally take one of two forms: a large horizontal element, or louvered systems. Horizontal daylight redirection devices are often called lightshelves.Tubular daylight devices are another type of toplighting device. These devices employ a highly reflective film on the interior of a tube to channel light from a lens at the roof, to a lens at the ceiling plane. Tubular daylight devices tend to be much smaller than a typical skylight, yet still deliver sufficient daylight for the purpose of dimming the electric lighting.

As mentioned previously, the windows must be carefully designed to control the solar gains and potential glare stemming from a daylighting design. To this end, solar shading devices are often employed to minimize the amount of direct sun that enters the space. These can take the form of louvred slats, which soften the lighting by bouncing it off the dark wooden surfaces.

This article originally appeared in Fensterbau, a monthly tabloid of the Indo-German Chamber of Commerce

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