“Sustainable” and “Ecological” are becoming fashionable words for advertising products. This trend applies also to buildings, with “Sustainable Architecture” gaining momentum. In the last century, and especially in the last few decades, the architectural language has given more and more emphasis to the “lightness” and the “transparency” of buildings, pushing towards fully glazed envelopes.

The question then is: to what extent fully glazed buildings are actually sustainable? This is not a minor question, given their role of being model examples of the rising new culture of sustainable building design. This article discusses the effectiveness of widely used envelope technologies such as, all glazed curtain wall and double skin taking into account luminous, thermal and acoustic comfort and their connection to the energy use, on the basis of the most recent findings available in specialised literature.

Pearl River Tower
Pearl tower by US-based architectural firm Skidmore, Owings & Merrill's (SOM) is designed to use wind and sun power as natural resources. The Pearl tower structure is designed as a high performance building that is shaped by the sun and wind. The tower is designed to absorb its environment and use it to its advantage.

The design features solar collectors to provide solar power and heating for the building's hot water supply. Wind gets directed into openings on the mechanical floor to power turbines that operate the tower's heating, cooling and ventilation systems.

High Performance “Intelligent” Façade
The design incorporates a dynamic high-performance building envelope. The orientation of the façade is designed to optimize the use of daylight while controlling solar loads:

• The north and south orientation of the building features an internally ventilated high-performance double skin façade with automated blinds
• An energy efficient triple-glazed façade with external shades and automated blinds within the glazing cavity is used for the east and west elevations.
• An intelligent photovoltaic system is integrated into the building's external shading system and the glazed outer skin.

All these factors in the design maximize the use of natural daylight and minimize solar heat gain in turn significantly reducing energy consumption.

In addition, exhaust air is routed through the cavity of the double-layer curtain-wall, heating up, as it travels upward to the mechanical floor. The ventilation and dehumification system uses this hot, dry air from the double-wall as an energy source.

The trend towards mixed high-rise developments is giving designers greater opportunities to improve environmental performance. This is an iconic, high-performance building that is designed in harmony with its environment. Scheduled for completion in fall 2009, in Guangzhou, China, the project aims remarkably high: the first zero-energy super-tall building in the world. The tower will harvest wind, humidity, and solar power from the environment and use it to maximum efficiency through myriad interwoven systems.