As a better option to urban sprawl, the skyscraper has proven to be a meaningful solution for today’s environmental challenges. As modern cities face an exponential growth in population and a continuous rise in the cost of real state, the skyscraper encourages land conservation and the reduction of material expenditure. Despite the large quantity of material and energy involved in its production, the skyscraper’s smaller footprint and large vertical surfaces offer an opportunity to balance our urban environment through renewable energy use, resource conservation, and waste management. Green architects are now focusing on the development of skyscrapers that exploit the use of concepts such as passive, mixed and productive building operational systems. As Ken Yeang explains “Green or ecological design means building with minimal environmental impact, and where possible, building with positive, reparative and productive consequences for the natural environment, while at the same time integrating the built structure with all aspect of the ecological systems of the biosphere over its entire life cycle” (Yeang, 1999). Ecological Skyscrapers should reflect the latest advances in sustainable technology by using and optimizing a building's operational systems with technical means that mimic the way that nature works as oppose to the use of full mode mechanical means.
At the onset of creating Ecological Skyscrapers, the architect must give consideration to the technical means available for the operational systems of the building that could either be: passive mode, mixed mode or productive mode. The type of operational system to adopt is dependent on the climate of the locality of the building and its ecology. According to Yeang, the provision of operational systems at the passive mode level is ecologically ideal. Ecological design, in imitation of natural systems, tries to optimize the use of all passive systems of operation and of the climate and solar condition of the locality. Passive mode design is mainly achieved by using simple cooling, heating and lighting through the building’s morphological organization and orientation. Passive-mode design does not preclude using mixed-mode or productive mode devices, although, they should be the last option for creating optimal comfort levels inside the building. The mixed mode level design uses partial mechanically assisted systems that optimize the usability of the building. In temperate zones, the basic mixed-mode approach encourages natural ventilation in summer and mid-season when outside temperatures are conducive and employs a mechanically assisted ventilation system during the winter. On the other hand, productive mode level design is the use of systems that generate on-site energy such as photovoltaic cells (PV), which provides a clean, quiet, and pollution-free energy source (Yeang 1999).
Buildings are usually powered by fossil fuel and nuclear reactors using 45 percent of non-renewable energy. In cities such as London, tall buildings can consume up to 72 percent of non-renewable energy (Maunsell, 2002). Nevertheless, Skyscrapers use the same amount of energy as that of the embodied energy of its material every year of its operation and about 60 percent of this operational energy is used in the heating and cooling of spaces (Yeang, 1999). The concept of building tall in itself is an energy conservation strategy not only for savings in the transportation and the use of materials, but also for the encouragement of transit oriented developments.
Building orientation has a mayor impact in a building’s energy efficiency and can be used for passive cooling and heating techniques. Bioclimatic façade design allows different degrees of permeability of light, heat and air to the building. In addition, material and body mass considerations can improve the relation to the specific climatological characteristics of the locality, using body mass to harness heat gain during the day and releasing it during the night. Climate responsive buildings designed with these passive means can be a better strategy for energy savings than those with mixed or productive mechanical systems; producing larger investment cost returns.
A good example of the use of simple passive techniques of renewable energy use and conservation is the Commerzbank Building by Foster and Partners, the tallest building in Europe and the world’s first eco-tower. Its four stories sky-courts, spiraling up every 10 floors, ensure light and ventilation to every working space assisted by a wind convection chimney through the central core that ventilates the building; thus drastically reducing air-conditioning use and producing minimal environmental impacts. In addition, the building’s double skin façade permits the interior windows to be opened at any floor level despite external air pressure and wind conditions.
Norman Foster’s recent work, the Swiss Re Headquarters, a 41 Stories cylindrical tower in London, demonstrates a sophisticated integration of ecological systemic elements. The building features spiraling gardens atriums as part of a triple skin façade that creates pressure differentials to naturally ventilate the interior spaces using natural convection through slots in the cladding. Similarly, air is drawn out or recycled to provide warmer air for use in thermal heating creating a mixed acclimatization system. Once the building is fully operational, the system is expected to be so effective that air-conditioning won’t be needed for most of the year (Gissen, 2003).
The Malaysian architect Ken Yeang has written extensively about the systemic technology of the Ecological Skyscraper. Yeang’s work shows a new ecological aesthetic through vertical landscaping and focuses on the importance of systemic building aspects by designing through biomimesis, making buildings function as urban ecosystems. His work is exemplary in the use of passive and mixed bio-climatic strategies as well as in the use of clean means of reducing buildings inputs and outputs. His Sky Garden designs increase the biotic mass of the earth’s surface and contribute to the energy conservation of the building by mitigating solar radiation, absorbing heat during the day and releasing it slowing during the night thus balancing the internal an external temperatures and helping to alleviate the urban heat-island phenomena. “Cooling needs can be cut as much as 30 percent if enough trees are planted” (Yeang, 1999).
Evapo-transmission, besides being a more ecological way of water exhaust from the building, can be an effective cooling device. “Façade planting can lower temperatures in the street as much as 5C and lower wall temperatures as much as 17 percent reducing air-conditioning costs by 25 to 80 percent (Yeang, 2002). During the winter façade planting can also reduce heat loss while letting the sun filter in. Examples of these strategies can be seen in Yeang’s Menara Mesiniaga building built in Malaysia and, in a larger scale, in the Bishopsgate tower design for the city of London. “The vegetation in both of these buildings is design in an ascending spiraling pattern allowing the plants to receive maximum sunlight and rainwater” (Gissen, 2003).
The use of high performing cladding systems as a component of mixed mode system and automated or user controlled mechanized façades could help balance the usual contradiction between thermal comfort and light transmission providing an efficient way of providing light and ventilation throughout the year. New responsive glazing systems are also being developed which could have positive consequences in terms of climatic response. When used as a double or triple layer configuration, these systems can increase the body mass, thus increasing thermal efficiency by acting as buffer between external and internal temperatures. Furthermore, the incorporation of shading devices integrated into the glazed façade is the best method to achieve solar heat and light control levels. Control of interior space ventilation can be achieved when the spaces between glasses are ventilated by opening the interior façade, in turn, cooling or heating the spaces through the stack effect. Double skin systems can operate differently in response to seasonal changes. During winter the skin system acts as a buffer between inside and out. The inside heated air can also be used as thermal heat reducing heating costs. During the summer, the skin can be opened to allow for natural ventilation and can be sealed so that the blinds inside the cavity produce shade while the air is extracted out letting more ambient air to come in.
Such concepts are evident in the cylindrical tower for the RWE headquarters by Ingenhoven Overdiek und Partner in Essen, Germany. The RWE is unique for its sophisticated façade system that allows natural light and ventilation to provide a comfortable environment while consuming less energy than other buildings of similar size. The double façade has like-valve horizontal mullions between floors, around the perimeter of the building, that allows airflow and temperature control. The building’s climate control computerized systems monitor exterior climate data and make climatic adjustments as necessary through the air inlets and the shades integrated into the cavity. In addition, the building includes an operable window control system that allows for user localized adjustment by single control panels in every room to control lighting and temperature throughout the operable façade. The building also features photovoltaic panels on the roof that move and operate the abovementioned mechanic systems, besides an integrated chilled water pipe work for cooling. The Hearst Tower by Foster and Partners, to be built over the Art Deco landmark by Joseph Urban, also proposes an ecologically responsive building with a very sophisticated and bioclimatic interactive curtain wall system.
The use of productive systems can supplement passive and mixed operational system by an on-site energy production, in turn reducing the dependence on non-renewable materials. Passive tools, such as the orientation and aerodynamics of the built form, can optimize the efficiency of power generation in productive mode systems. Since wind power increases in direct relation to height, the orientation and the built form of Skyscrapers offer a great opportunity for harnessing this resource by using wind turbines and thus reducing the consumption of fossil fuel. The Wind Tower by Richard Rogers, a design for a small triangular plot in a hill of central Tokyo, is an example for this type of development funneling the high wind velocities of high altitudes for efficient wind energy generation design. The building’s shape encourages wind to pass through a gap between the main building and a freestanding service tower. The curve of the building compresses and accelerates the wind by 200 percent providing a greater amount of clean power. Computer models for this design indicate that, if built, the Tower will not require additional power and perhaps export saved energy to the city grid. The service tower also acts as chimney ventilation under the action of the sun and wind.
Daniel Libeskind’s and Davis Childs’s Freedom Tower will generate 20 percent of the building’s energy (LMDC) through 30 wind mills located at the building’s third upper section. The torque shape of the building optimizes wind harvesting at the top and minimizes wind impact at the pedestrian level. The building design also includes sustainable resources such as, low energy HVAC, which allow for a 3 percent saving in the building’s electricity costs by combining waste heat technology (CHP). “CHP can produce power, heat and chilled water for air-conditioning simultaneously. In this case an electricity generator produces energy and the heat it generates is then recycled. The heat also can use used to produce chilled water for air-conditioned systems and to generate electricity” (Maunsell, 2002). The design also contemplates at solutions of high-performance coated glass façades with computerized controls for lighting, heating and wind conditions.
The use of productive mode systems such as PV panels has become more affordable and comparable to the high performing cladding needed for skyscrapers. The new improvements in PV panel design allow different admittance of light and heat, and in combination with a double façade can become a more efficient energy consumption feature of skyscrapers. PV panels provide a clean, noise free energy source. New amorphous PV cells can be applied to others materials such as glass and walls as a thin film. The La Courts Building, designed by Perkins & Will architects, with over 6,000 m2 of PV Panels, promises to be auto-sufficient in energy consumption and are considered by some to be at the cutting edge of technology and sustainable design. Hot air collected from the Trombe-wall-like space between the PV façade and the building is drawn to the roof and is used to heat water while letting cool air in to cool the building. The building has also a water collection system and a natural air dehumidifying system through the use of desiccants such as silicon as well as venting and shading strategies in the façade.
The use and development of Hydrogen Fuel technology is also promising as a productive mode method. It act as a pollution-free energy source that uses hydrogen and oxygen to yield electrical output with only heat and water vapor as by-products.
The Conde Nast Building by Fox and Fowle architects is the first green skyscraper in New York City and the largest building in the United States with integrated energy production systems, recycling systems, and the use of sustainable materials. The building has two 200-kw fuel cells located at the 4th floor that provide 100 percent of the nighttime electricity demand without combustion. The hot water by-product of the fuel cells is used to help heat the building during winter and also for hot water production, integrating other productive systems that make it as much as 40 percent energy auto-sufficient. The systems use PV Fuel Cells as well as gas-fired absorption chillers/heaters located on the roof that do not use ozone-depleting chlorofluorocarbons. State-of-the-art curtain walls provide shading -light controls and insulation with integrated PV cladding and E-coating to filter out ultraviolet light- while letting light in. It has sophisticated mechanical systems that ensure high air quality by introducing fresh air into the offices. In addition, the tenant guidelines, developed by the architects, establish power usage, furniture and materials use standards, to ensure sustainability and indoor air quality throughout the useful life of the building. Recycled materials make 20 percent of the buildings fabric. The Conde Nast had a quick return on investment, recuperating its initial investment in approximately five years (Fowle, 2001).
In the design of skyscrapers we should design for reuse, recycling and durability in an attempt for efficiency, flexibility, upgradability, and recoverability of the material used (Yeang, 1999). The building construction and management process consumes 40 percent of resources, and according to a report by the World Recourse Institute is projected to increase by 300 percent as economic activity accelerates over the next 50 years. Such activities have a substantial impact in the environment by depleting natural resources, and polluting water and air. About 25 percent of land waste comes from building construction, in addition to 25 percent of solid waste and 50 percent of carbon emissions related to the operational waste of buildings. Construction related activities such as mining, also impact our environment by the destruction of natural habitats.
As waste continues to pile up in landfills, polluting the soil, air, and, water, atmospheric carbon dioxide levels also rise, creating climatic changes which will continue to deteriorate if we don’t take remedial steps. A designer can either eliminate or reduce waste, or manage the already produced emissions. Of the two choices, waste source reduction in the built environment is preferable (Yeang, 1999). Waste reduction, reuse and recycling is key for sustainability. The selection of material can make a significant impact in the sustainability of any building proposal by minimizing the potential environmental impact at the site of materials production from the amount of waste and carbon dioxide emissions produced during their fabrication. It is by these circumstances and because of the skyscraper’s density, that a cradle-to-cradle concept and the scale of skyscrapers acquire importance and offer great opportunities for recycling.
Many architects are trying to address the negative effects of buildings through passive methods that use materials in a more efficient manner or employ high-tech materials, such as light weight, fiber reinforced composite materials. Because of their inherent structural strength, these materials can minimize the embodied energy produced during their use, encouraging eco-efficiency. A good example of this “dematerialization” of the Skyscraper is the Carbon Skyscraper By Peter Testa Architects that uses resin-impregnated carbon fiber that is lighter and stronger than steel (Gissen, 2003). The Lloyd’s of London Headquarters by Richard Rogers has an intensive use of modularized pre-fabricated components that reduce construction waste, time and pollution. This building also uses energy conservation systems through natural illumination and ventilation by the use of operable windows.
Solid waste and wastewater discharge control is also very important in the development of sustainable skyscrapers. There are several strategies we can use to conserve water, such as rainwater and gray water recycling. The water collected from the rain can be used to flush toilets and urinals throughout the building and for vegetation irrigation. Biological Waste water systems that links wetlands and marches to buildings discharge or their replication in in-site solar green houses facilities that can recycle clean water for its reuse and can be very economical. In-site recycling of waste and organic solid waste technologies are becoming more common among environmental architects.
The EDITT tower project by T.R. Hamzah and Yeang demonstrates a passive mix approach to skyscraper design. With an unprecedented amount of greenery (1:05 ratio) that provides cooling and insulation, the building contains a gravity fed-soil bed water recycling and purification system. The recycling system results in the use of half the amount of water as most buildings its size will use. The building also includes a sewage recycling system that can recover sewage waste water and treats it to use elsewhere as a fertilizer or bio-gas fuel and a build waste management system that sorts waste material to make it available for pick-up and recycling at the ground level.
After the publication of “ The Green Skyscraper”, Ken Yeang published another book in 2002 called “Reinventing the Skyscraper” which presents the reinvention of the skyscraper as a three-dimensional “City in the Sky”. The book also presents an even more humane and socially responsive solution to the building of skyscrapers. According to Yeang, the skyscraper should not be a simple box in the sky, but a more humane and usable community presenting itself as a viable solution for our urban problems. The concept of “Sky Cities” becomes more important as cities today devote more than 60 percent of available land for roads and automobiles services. The multi-use character of this type of development locates living and working spaces closer together making walking and other low-consumption, cleaner, vertical and horizontal means of transportation within the city more feasible; creating a condition where less structure is needed to satisfy the necessity of a given population.
Yeang’s Elephant and Castle, focal point of the Elephant & Castle redevelopment initiative in London (in construction), demonstrates the concept of “Sky Cities”. The design takes the model of a general geographical area of a city with its systems, zoning and infrastructure and inverts it into a skyscraper form, containing in itself the inherent elements of the city block, i.e. parks, shops, etc (Yeang, 2002). Exuberant sky gardens create wind buffers and make the open spaces more comfortable for the user; with naturally ventilated and illuminated spaces on all 35 stories. The tower is split in two volumes surrounding a naturally ventilated central core that communicates with what could be a small vertical city, through a widely mixed program and creation of urban spaces. The double-glazed façade allows the occupants to regulate the amount of circulating fresh air according to the “mode” (passive or mixed depending on the temperature) that the building is working under and mechanical system can calibrate the temperature appropriately throughout the year.
Another example of this concept is the Eco-Tech City Master Plan for Rostock, Germany showing the kind of urban forms that can result from the use high-rise tower with a intensive landscaped surroundings. “The Eco-City will use pedestrian routes, light rail transit systems and automated people movers” (Gissen, 2003).
Yeang’s theoretical work encourages a building design that “tries to achieve a symbiotic relationship between our manmade system and the ecosystem and assuming a positive solution for a more balance system between the biotic an abiotic elements of our environment. Yeang has been able to introduce air cleansing and recycling, water conservation, recycling and reuse, onsite waste management, passive solar design and on-site energy generation systems in his designs through the use of passive, mixed passive and productive building operational systems. Yeang's theoretical approach radically changes the current design approach to tall buildings to make them into more humane environments and be more satisfying to its inhabitants, recreating the ideal conditions at the ground, now up in the sky.
The creation of skyscrapers is the best economical and physical solution for the densification of our cities. Current trends indicate that the skyscraper as a building type will continue to be built in most World cities. The question remains then how can the architect today design these massive building types to be ecologically-responsive to avoid otherwise multitudes of high-energy consuming, polluting-waste-producing intensive buildings. The creation of an ecological skyscraper is a very complex task that cannot be conceived in isolation. In a quest for a more sustainable approach for skyscraper design, architects also need to consider the needs of investors and developers for creating more marketable skyscrapers. Ecological skyscrapers offer the opportunity of having a beneficial impact in the environment by integrating the built-environment with ecological systems of the locality and to positively contribute to the ecology and biodiversity of the place. All the above mentioned theoretical propositions and design concepts if applied with an right aesthetic, social, and political approach and in conjunction with other disciplines could radically change the current design approach to tall buildings and make them integral part of our ecological future.
Works Cited
Gissen, David, ed. Big & Green, New York: Princeton Architectural Press, 2003.
Höweler, Eric. Skyscrapers: Vertical Now, New York: Universe Publishing, 2003.
Khermouch, Gery. “Alternative Energy Sources” Architectural Record, March 2004
Yeang, Ken. The Green Skyscraper, London, Munich, New York: Prestel Verlag, 1999.
Reinventing the Skyscraper, Great Britain: Wiley-Academy, 2002.
The Ecological Design of Large Buildings and Large Sites, Issues and the Future of Ecocity Development. Abstract. 2003 <http://www.ias.unu.edu/proceedings/icbs/ecocity03/papers/kenyeang/