Dr. Mohammad Arif Kamal
Architecture Section, Aligarh Muslim University, INDIA
The building facade is the interface between the external and internal environments of a building. Facade systems comprises of structural elements that provide lateral and vertical resistance to wind and other actions, and the building envelope elements that provide the weather resistance and thermal, acoustic and fire resisting properties. It also has a large impact on occupant’s interface with the surrounding environment; energy efficiency and the indoor environmental quality performance of a building, such as lighting and HVAC electricity loads; and peak load to maintain good lighting level and thermal comfort for the occupants. High performance building facade systems involve selecting and deploying the right materials, advanced technologies, good detailing and installation, all of which must be contextually and functionally appropriate. It refers to designing buildings and spaces (interior and exterior) using local climatic conditions to improve thermal and visual comfort. These designs provide protection from summer sun, reduce winter heat loss, and make use of the environment (e.g. sun, air, wind, vegetation, water, soil, and sky) for building heating, cooling, and lighting. Due to the multiple important roles – i.e., aesthetics, thermal comfort, day lighting quality, visual connection to the outdoor environment, acoustic performance, and energy-related performances – building facades, especially glazing systems, have received much attention in research and development. This results in a wide range of products and technologies available to achieve high performance facade systems.
High Performance Building Facade System
Building facades perform two functions: first, they are the barriers that separate a building’s interior from the external environment; and second, more than any other component, they create the image of the building. With the global energy crisis becoming increasingly serious, ensuring and improving indoor thermal comfort whilst reducing energy consumption during a building’s operation stage are important goals . At present, energy conservation in most buildings is focused on reducing energy consumption, whereas indoor thermal comfort is less frequently considered .Building facades affect indoor thermal comfort. The dual effects of reducing building energy consumption and improving indoor thermal comfort can be achieved by adopting a passive design in a reasonable manner .Building facades are directly exposed to the external environment. Different building facades are related to varying indoor comfort and energy consumption levels. A reasonable facade design helps reduce energy consumption and improve indoor thermal comfort . Therefore, the passive design of building facades is an important aspect in managing building energy consumption . High-performance sustainable facades can be defined as exterior enclosures that use the least possible amount of energy to maintain a comfortable interior environment, which promotes the health and productivity of the building’s occupants. This means that sustainable facades are not simply barriers between interior and exterior; rather, they are building systems that create comfortable spaces by actively responding to the building’s external environment, and significantly reduce buildings’ energy consumption. The recent emerging building facade systems with reference to climatic control and energy efficiency have been discussed through the followings case studies.
Case Study 1: Al Bahar Tower, Abu Dhabi
The Al Bahar Towers in Abu Dhabi has been designed by Aedas Architects. It is a responsive facade which takes cultural cues from the ‘Mashrabiya’, a traditional Islamic lattice shading device. The Mashrabiya type double facade are on south, east and west portions. The North facade left open due to minimized solar issues and to allow for a primary view to the city beyond. The responsive system opens and closes according to solar path. The ‘mashrabiya’ at Al Bahar Towers is comprised of a series of semi-transparent PTFE (polytetrafluoroethylene) umbrella-like components that open and close in response to the sun’s path. Each of the two towers includes over 1,000 individual shading devices that are controlled via the building management system to create an intelligent second facade. This view shows the screen in its fully closed mode.The shading system operates as a curtain wall, located two meters outside the building’s exterior on an independent frame. Each unit responds to the movement of the sun. However, in the evening, all the screens will open.
Each unit is comprised of a series of stretched PTFE panels and is driven by a linear actuator that will progressively open and close once per day in response to a pre-programmed sequence that has been calculated to prevent direct sunlight from striking the facade and to limit direct solar gain to a maximum of 400 watts per linear meter. The entire installation is protected by a variety of sensors that will open the units in the event of overcast conditions or high winds. The benefits of this system include: reduced glare, improved daylight penetration, less reliance on artificial lighting, and over 50% reduction in solar gain, which results in a projected reduction of CO2 emissions by 1,750 tonnes per year.The effects of this system are tremendous: improving the penetration of daylight, reduce glare and less artificial lighting. By running the self-customized program, the Aedas team did a comprehensive solar analysis. The result shows that over 50% solar gain has been reduced, which results in a reduction of CO2 emissions of 1,750 tons per year. In addition, the shading ability to filter light has allowed architects to be more alternative in the choice of glass .
Case Study 2: The Doha Tower, Doha, Qatar
The Doha Tower designed by Ateliers Jean Nouvel, located in Doha, Qatar also uses a hybrid double facade arrangement (Fig. 3). In this instance the Mashrabiya screen creates a very complete second skin and encloses the entire building. Except the entrance, no large expanses of vision glass are maintained. Instead the density of the screen is varied according to the solar orientation of the building.
The exterior skin of the Doha Tower is fixed or non-responsive. It is instead composed of four “butterfly” aluminum elements of different scales to evoke the geometric complexity of the Islamic ‘Mashrabiya’ while serving as protection from the sun (Fig. 4). The pattern varies according to the orientation and respective needs for solar protection: 25% towards the north, 40% towards the south, 60% on the east and west. The variation in opacity of the aluminum screen addresses the variation in solar avoidance required on the façade orientations. Due to the round shape of the tower, some shading is required on the “north” facade as it will receive sunlight in the early morning and late afternoon hours.
While the screen may appear quite dense from the exterior, the interior view shows the amount of sunlight that still enters the space. Additional blinds are provided on the interior to cut out glare and penetration when needed. The system relies on contemporary precision cutting methods in combination with the selection of solid aluminum plate to achieve a durable element that is easier to maintain than other finishes. The fixed Mashrabiya screen is situated more than a meter from the high performance curtain wall. This is to allow for cleaning access to the space. The metal grating at each floor provides additional shading for the glass. This view inside the air corridor and looking out gives a good appreciation for the density and texture of the exterior skin. The diamond grating of the walkway allows for air circulation up the facade which is essential to prevent the entrapment of hot air at each level (Fig. 5).
Case Study 3: The Pearl River Tower, Guangzhou, China
Pearl River Tower, located in Guangzhou, China is a green skyscraper designed by Skidmore, Owings & Merrill. The building is 309 meters tall having 71 stories (Fig. 6). It is a high performance building that claims to be the most energy efficient super – tall tower building in the world .The building has double wall insulation. The double envelope accommodates venting and solar shading devices within the cavity (Fig. 7). These design approaches facilitate thermal comfort and air quality, as well as day-lighting and energy savings.
The building has embedded photovoltaic transistor system for solar energy. The Building Integrated Photovoltaics (BIPVs) in the Pearl River Tower act both as the building skin (spandrel panels) as well as power generator (Fig 8). The wall surfaces are angled for maximum sun exposure. The building is designed in such a way that it funnels and pushes the air through wind tunnels at a great speed which is 1.5 to 2.5 times greater than the ambient wind speed. It has a curved glass facade that directs air flow through narrow openings in the facade that will drive large, stainless steel wind turbines to generate electrical energy. It generates 15 times more energy than the ‘freestanding’ wind turbines. Wind has a great impact on the design of tall buildings. When the air is allowed to pass through the building, the difference in pressure between the windward side and the leeward side is reduced. As a result, the forces on the building are also reduced. This approach allows for a reduction in the quantity of steel and concrete to maintain the building’s stability. Therefore, it is a sustainable approach towards design as far as structural standpoint is considered. Moreover, vertical axis wind turbines are implemented in the building, which are capable of harnessing winds from both prevailing directions and greatly reduce efficiency loss. This building also employs geothermal heat sinks, ventilated facades, waterless urinals, integrated photovoltaic and daylight responsive controls. According to reports, the Pearl River Tower would help emit less carbon dioxide by approximately 3,000 tons and achieve an overall energy saving of 30.4 percent a year .
Case Study 4: Q1 ThyssenKrupp, Essen, Germany
ThyssenKrupp AG worked with TKQ architect consortium JSWD Architekten and Chaix & Morel to design a new seven building corporate campus in Essen, Germany (Fig. 9). The German Sustainable Building Council (DGNB) has awarded the project a Pre-certificate in Gold based on the new German Certification for Sustainable Buildings. Unlike the fabric of Aedas’s design, Essen’s smart sun shading system is made of stainless steel slats in a featherlike pattern. It is one of many sustainable features of an 11-storey office building in the corporate campus of ThyssenKrupp. The shading system helps reduce solar gain while often leaving gaps that allow external views and let natural light enter, reducing the need for artificial light. “This is very important, because the greatest energy use in a building is electric energy, especially for lighting,” says Jürgen Steffens, a partner at JSWD Architects. Because of the shading system and other green features, the building uses less than 120kWh/m² of energy a year, a low amount for a glass high-rise.
Energy requirements are expected to be 20 to 30% below statutory requirements. All of the buildings are simple glazed structures but their appearance is unique because of their second facade. The buildings are wrapped in automated sunshade systems with Type 316 stainless steel horizontal and vertical slats or custom perforated sunscreens (Fig. 10). These active motorized sunshade systems have moveable triangular, square and trapezoidal fins are automatically adjusted with changing conditions to save energy. Used in combination with natural ventilation, the system eliminated the need for air conditioning.
Case Study 5: The Capital Gate, Abu Dhabi
Capital Gate, also known as the Leaning Tower of Abu Dhabi, is a skyscraper in Abu Dhabi that is over 160 meters tall, 35 stories high, with over 16,000 square meters of usable office space (Fig. 11).Capital Gate is one of the tallest buildings in the city and was designed to incline 18 degree westward lean, holding the Guinness World Record for the “world’s furthest leaning manmade tower.” The building has a completely asymmetric shape. No two rooms are the same and all 12,500 panes of glass on the facade are a different size. A diagrid structural system was utilized in which all 8,250 steel diagrid members are of different thicknesses, length and orientation and each of the 822 diagrid nodes are of a different size and angular configuration. The sustainable agenda was very high on the priority list in the design of Capital Gate in Abu Dhabi. It was recognized that the reduction in solar gain provided by the double facade system would be of great benefit to the building. For this reason the designers used two distinct types of systems that worked with the specific conditions of the project that resulted from the offset of spaces from the vertical elevator core.
A diamond shaped prefabricated curtain wall system is attached to the structural steel diagrid of the tower and forms the outside layer (Fig. 12). The interior layer uses a less expensive rectilinear glazing system. There are no shading devices used in the cavity. The cavity width is sufficient to provide access for cleaning. The lower office floors are protected by a large metal mesh canopy called “the splash” which starts at the entry level as a sun shade over the car drop-off area and climbs the facade, terminating at the projecting pool level provided at the 19th floor. The mesh is supported on an Architecturally Exposed Structural Steel Frame and is 90% open. The mesh allows for air circulation while blocking approximately 30% of the solar radiation from striking the curtain wall of the office spaces (Fig. 13).
Architecture, as a significant part of our society, is putting a great deal of effort into sustainability nowadays. In the general context, sustainable architecture pursues to lessen the negative environmental impact of buildings by raising efficiency and innovating the use of materials . The facade is one of the most significant contributors to the energy budget and the comfort parameters of any building. As energy and other natural resources continue to be depleted, it has become clear that technologies and strategies that allow us to maintain our satisfaction with the interior environment while consuming fewer of these resources are major objectives for contemporary facade designs. In recent years, architects and consultants have been coming up with an array of designs for digitally controlled sunscreens that move in response to shifting environmental conditions. The recent wave of concern about sustainability and reducing buildings’ carbon footprints has spurred interest among architects in such systems. Control of physical environmental factors (heat, light, sounds) must be considered during the design process, as must design strategies that improve occupant comfort (thermal, visual, acoustic, and air quality). Therefore, sustainable facades must block adverse external environmental effects and maintain internal comfort conditions with minimum energy consumption. The location and climate thus are crucial factors in selecting appropriate design strategies for sustainable facades.
 Lewis A, Riley D, Elmualim A (2010) Defining High Performance Buildings for Operations and Maintenance. International Journal of Facility Management 1:145-156.
 Jian X, Jin Z, Feng X, Guo-qiang Z (2012) Evaluation index for indoor thermal environment of residential buildings based on thermal comfort in hot summer and cold winter zone. Journal of Central South University 43: 3693-3697.
 Zhifeng W, Liding C (2016) Thermal Comfort Evaluation and Urban Thermal Environment Study. Journal of Ecology 35: 1364-1371.
 Ajla A (2015) Design Methods For Sustainable, High-Performance Building Facades. Advances in Building Energy Research 10: 240-262.
 Aksamija A., High-Performance Building Envelopes: Design Methods for Energy Efficient Facades, 2015.
 Aksamija A., Sustainable Facade: Design Methods for High Performance Building Envelopes, John Wiley & Sons, Inc., New Jersey, 2013.
 Doerr Architecture, Definition of Sustainability and the Impacts of Buildings [online]. Available: http://www.doerr.org/services/sustainability.html
 Frechette, R and Gilchrist, R. “Towards Zero Energy: A Case Study of the Pearl River Tower, Guangzhou, China”, Conference Proceeding, CTBUH (Council on Tall Buildings and Urban Habitat) 8th World Congress, Dubai, March 2008.
 http://solarairtech.com/news/24-chinas-pearl-river-tower-aims-for-zero-net-impact-on-energy-consumption.html (accessed on 1st August 2019)
 Cilento, Karen,“Al Bahar Towers Responsive Façade, Aedas”. ArchDaily. Accessed 2nd August 2019.