Skyscraper architecture is booming, and architects are redirecting their focus on the skins of structures to deliver green credentials.
The skin of a building acts as a protective membrane, and double glass facades have been recognised for their ability to maximise energy efficiency by contributing to the ventilation and thermal properties of a building.
Along with an ethical focus from designers and developers, this new technique responds to governments around the world identifying the built environment as the largest contributor to carbon emissions and stressing the need to meet and exceed guidelines such as Australia’s Green Star, the UK’s BREEAM and the US’ LEED assessments.
The application of glass, internal cavities, shading and ventilation techniques are bringing skyscraper facades to life by using solar radiation and the local climate to allow the outdoor environment to influence the indoor environment.
Building inhabitants also reap huge benefits such as increased productivity due to the presence of natural sunlight, ventilation, thermal and climate-controlled environment achievable at such heights.
Double façades feature two layers of material, typically hard external glass and a thermal insulated or double/triple pane glass on the inside. The amount of solar gain absorbed by the glass is determined by the angle and placement of the façade and the orientation of the building.
The 30 St. Mary Axe in London, a building also known as The Gherkin, is a good example of this. The circular skyscraper is enveloped by mullions and triangular shaped window pieces to maximise daylight penetration. This skin technique provides sky-high ventilation, the primary benefit of applying the double façade to skyscrapers.
Fan supported natural ventilation or mechanical ventilation can be implemented but using only mechanical ventilation is not recommended as the building must be sealed and monitored, defeating the purpose of energy reduction and the opportunity to mimic the natural environment.
Natural ventilation works using outside air movement and wind pressure conditions, and occupants can often control their environment by opening the internal window for example to allow a fresh breeze in on high floors.
The $240 million Tower at PNC Plaza in Pittsburgh, currently under construction, is expected to exceed LEED Platinum standards upon completion, with the building’s double glass façade and largest green walls in the US set to make it make it the world’s greenest skyscraper.
The 33-storey building will feature two panes of glass separated by a three-foot enclosed cavity to bring in external air and the façade will boast operable doors and windows that can facilitate the amount of natural light and fresh air allowed into the building based on the weather.
The architects wanted the building occupants to feel like they were working on a park bench, on a laptop with a fresh breeze circulating. With this sustainable strategy, the tower is set to use up to 50 per cent less energy than a typical new office building while being able to sufficiently cool the building 42 per cent of the total yearly working hours in Pittsburgh.
The cavity in a skyscraper effectively gathers energy (solar radiation) and insulates the interior. It can range from a couple of centimetres to a few metres wide to be able to integrate shading technology, or it can be even larger and double up as an atrium space.
While internal shading devices within the cavity such as blinds or curtain walls can help reduce solar gain, external louvers and devices are sometimes applied to the external façade as demonstrated in the Al Bahar Towers automated shading system.
The building has an aesthetically stunning façade which is also dynamic with more than 1,000 geometric patterned elements that open and close depending on the sun’s position.
This system has successfully reduced glare, encouraged sunlight and the need for artificial lighting in the building while achieving over 50 per cent reduction in solar gain resulting to a reduction of 1,750 tonnes of carbon dioxide emissions each year.
In Sydney, the tower at 1 Bligh Street is renowned for its curved double glass façade which, according to the buildings website, “facilitates a 42-percent CO2 reduction when compared with similar sized conventional office towers.”
Ultimately, the performance of a double glass façade lies in its cavity’s components and its ability to contribute to the thermal regulation of the building.
Glass skyscraper façades are no longer purely ornamental but enveloped in active “smart skins” designed to respond to the environment. They are fast becoming the first point of a sustainable building strategy to assist with energy reduction.