The Third AIN SHAMS UNIVERSITY INTERNATIONAL CONFERENCE ON ENVIRONMENTAL ENGINEERING April 14-16 2009
GREEN SKYSCRAPERS Criteria for Dynamic Sustainable Tall-Buildings Dr Abdel-moniem El-Shorbagy (Ph.D. Canterbury) Assistant Professor in Architecture Effat University, Jeddah, KSA Email: aelshorbagy@effatcollege.edu.sa elshora1@hotmail.com
Key words: Skyscraper, Sustainability, Eco-architecture, Technology
Abstract In the late 20th century, building skyscrapers became a controversial issue among the architectural profession. They questioned the ability of tall buildings to adapt environmental issues as well as to provide a realistic answer to modern environmental problems. In the 21st century, the phenomenon of building skyscrapers has been acknowledged by the majority of architects, planners, landscape architects as well as by societies. Today we are witnessing the emergence of new cities, towns, and villages, which consequently created new locations, cultures, economies, climates and purposes for which skyscrapers now may make logical sense. However, the architectural profession should be concerned of formulating new design criteria and principles appropriate for reinventing the skyscraper as something green, and environment-user friendly. This paper will explore ways of managing the embodied energy content of a skyscraper in order to both, enhance the social aspects of the building and control its impact on global resources. It also reviews the new generation of progressive green skyscrapers, recently completed or under construction, in order to explore how they embraced sustainability and green building strategies in their dynamic design.
1. INTRODUCTION Skyscrapers became phenomena that began to be visible in most of the world cities. They can be regarded as symbol of the technological progress as well as a landmark that signify a city worldwide. Unfortunately, cities are being overbuilt with these skyscrapers at the expense of the environment and the quality of life. The ideas and approaches about the role of design in human settlement, should be optimized to produce architecture and planning projects with social, environmental, and aesthetic integrity. Today, life is dynamic, and peoples’ needs and requirements change continuously and rapidly, so the space we are living in should be also dynamic as well as able to satisfy peoples’ needs. However, the main objective of architects is to strive to achieve these needs and desires, enrich the built environment and provide opportunities for enhancing the human experience.1 The rapid urbanization, limited land available for development, and the competition for higher buildings has created more inhuman massive buildings. However, of prime importance is the need to look at issues associated directly with these gigantic developments as a whole, such as transportation and overall life cycle resource efficiencies as well as individual buildings.2 Sustainability initiative is important factor that will add a unique perspective and brings innovation, relevance, and timelessness to architectural project. In addition, green solutions have been a top agenda, which aim to overcome and reduce the suffocating environment and build cities full of greens to create the harmony between urban life and nature. These are signs of the growing environmental consciousness and redevelopment that uses green building approaches in many parts of the world, in order to minimize long-term environmental damage and maximize long-term return on investment. In developed countries a "green building," should be certified by the LEED (Leadership in Energy and Environmental Design). LEED is the current standard measuring the five areas of environmental protection: site planning, water efficiency, energy efficiency, materials and resources and indoor environmental quality. According to the LEED, a building systems and construction technology need to be evaluated for their impact on occupant health, environmental sensitivity, and energy reduction. In addition, a building should meet, satisfy and adopt state-ofthe-art standards for energy conservation, indoor air quality, recycling systems, and the use of sustainable manufacturing processes.3
2. SKYSCRAPER Skyscrapers are not new inventions of the post-industrial world, they are as old as 500 years ago. Shibam, ‘the Manhattan of the desert’, a city in the desert of Yemen (fig.1), reveals buildings of mud brick that reach up to fourteen stories in height, parts of which date back to thousands years. Shibam’s structures are built of load-bearing walls, as opposed to modern frame-and-cladding techniques of the contemporary skyscrapers. The inhabitants of Shibam conceived the idea of building upwards, which can truly be considered innovative at the time, and created the world's first environmentally friendly skyscrapers. Shibam became a World Heritage city over 20 years ago, and this has at least helped preserve both the buildings and aspects of the regional culture that might otherwise have been lost.4
The concept of building the contemporary skyscrapers depends on realizing an artificially regulated interior environment, while being locked out to the exterior environment in order to achieve the desired human comfort. In doing so, skyscrapers work as colossal engines that consume a huge amount of fossil fuels to operate and release enormous amount of carbon dioxide into the atmosphere. Although many critics believe that skyscrapers should not be built anymore for its inappropriate use of resources both in building and maintenance, tireless efforts have been made to build skyscrapers that would adhere to the principles of environmentally sustainable design. Thus, another phenomenon of building the so called “green skyscrapers” began to dominate the thinking of many of the architectural profession.5 The Eco-Tower Menara Mesiniaga (fig.2), is a representative example of a new, climate-responsive tall building. There are many aspects of this structure that are environmentally and site-conscious. The tower has a sun-shaded roof, recessed and shaded windows on the east and west sides, spiraling vertical landscaping, naturally sun-lit spaces and low energy mechanical systems.6
Figure (1) Shibam, ‘the Manhattan of the desert’, Yemen (Source: unesco.org)
Figure (2) Eco-Tower Menara Mesiniaga, Malaysia, 1989-1992, Ken Yeang (Source: Pank, 2002)
3. SKYSCRAPERS AND SUSTAINABLE DEVELOPMENT Sustainability is a concept that involves taking a long term view of environmental, economic and social issues. Its agenda varies across the world and evolves to reflect political, economic, and business priorities. Sustainable, green and environmentally friendly is a movement which appeared in 1970. All buildings, high-rise and low-rise could be more sustainable in terms of their design, the construction process, their operation and the impact on the community. Sustainability can be achieved in buildings by using renewable energy sources such as wind turbines and photovoltaic, designing very low energy demand buildings and the economic and social issues associated with developments. There is no doubt that sustainability considerations need to be incorporated into building design for both legislative and moral reasons. However, tall
buildings are required, for sound commercial reasons, to embrace sustainability as a requirement for more space accommodation, efficiency, respect to land use, and the occupier demands. Sustainable development can be defined as "meeting the needs of the present without compromising the ability of future generations to meet their own needs." However, a better quality of life should be provided for everyone, now and for future generations to come. The main objectives of sustainability are: 1. 2. 3. 4.
Maintain high and stable levels of economic growth and employment. Protecting the environment effectively. Carful use of natural resources. Recognizing the needs of everyone to achieve social progress.
Cities are becoming the engines of national economic growth and the destination for new residents, whose activities have a huge impact on the environment. Cities are the places where the extreme interaction between humans and their environments takes place. The development of urban areas in cities, significantly affect the ecosystems, the waterways, the land, and the air quality, and consequently affect the quality of both peoples’ life, and the living environment. 7 Green skyscrapers represent a critical component of sustainable urban development. They consume enormous amounts of energy and materials and pose very complex design challenges as compared to low and medium-rise buildings. From an energy consumption standpoint, more than 45% of energy used in the United States goes to buildings and that nearly 25% of landfill volume is related to construction waste.8 Green Skyscrapers can be evaluated for their sustainable suitability by applying four principles of the sustainable urban development. 1. 2. 3. 4.
Reducing energy use as it pertains to transportation. Adequacy and accessibility of parks and public spaces within green skyscrapers. affect the urban fabric. Affect social and ethical issues
3.1 Green Skyscrapers and Transportation Building green skyscrapers, remains a controversial issue regarding its ability to promote sustainable urban development. It is believed that skyscrapers can reduce the energy consumption per inhabitant related to transportation. This assumption can be examined by looking at how skyscrapers, green or not, affect a city’s energy use. The energy consumption in a city can be recognized in two categories, immobile uses and mobile uses. immobile uses, includes residential, commercial, industrial, and public, while mobile uses includes all motorized transportation related activities, such as rail, bus, tram, and automobile. Transportation is very often considered as the largest sector of energy use in a city, and is highly related, both to land use policies and the use of mass transit. It is important to look at how the built environment, specifically green skyscrapers can reduce the consumption of energy in a city. The patterns of transportation energy use of a city reflect its degree of automobile use and its relation to population density. Skyscrapers are large structures that occupied by a large number of people in one place. Therefore, cities with a large number of skyscrapers are more energy efficient with regards to transportation than cities with fewer skyscrapers, depends on the total
per-capita transportation energy use. The figures in (table.1) show significant variation in the degree to which cities are dependent on automobiles. The comparison shows that US cities are higher in their total use of transportation energy than their international counterparts.9 Table (1) Skyscrapers and total transportation energy use
(Source: Newman and Jeffrey, 1999)
3.2 Green Skyscrapers and Public Space Public and open space is always of prime importance to city planners and urban designers. Parks represent an integral parts of human’s physical, social, emotional, and spiritual landscapes. Nowadays, the provision of public spaces is not the only aim of planners, but the accessibility of the parks to the citizens, as well as how far these parks are to the citizens who use them. However, the distance to a park is more important measure than the total amount of park space in a city and can affect its use. The spaces in green-skyscraper are not always comparable to the street-grade variety. Green and public space in the street level allows citizens to interact with the space and other citizens, while in a green skyscraper, they lose their connection to the broader public space network. However, designers of green skyscrapers take advantage of this point and strive to integrate public spaces into the building in new and imaginative ways. 10 The Transbay Transit Center, San Franciscans (fig.3), is an illustrative example of introducing and integrating public spaces into the design of skyscraper. The project consists of a graceful glass tower paired with an elegantly sweeping transit center topped with a five-and-a-half acre public park.
Figure (3) Transbay Transit Center, San Franciscans, Pelli Clarke Pelli (Source: www.artdaily.org)
3.3 Green Skyscrapers and Urban Design Urban design is concerned with the pedestrian quality of streets. In her “The Death and Life of Great American Cities.”, Jane Jacobs explained that to have a vibrant street-life, blocks must be short so that streets and opportunities can meet. She argued that isolated street neighborhoods with long blocks damage the urban fabric of the city and have a negative economic impact to the neighborhood. Jacobs’ theory holds that people who live on long streets can form a pool of economic use only where their long, separated paths meet and come together in one stream.11 This physical segregation of the regular users of one street from the regular users of the next is often amplified in the presence of skyscrapers. Skyscrapers tend to occupy big blocks, and as they get taller, its base gets wider.12 With short streets, citizens can reach their destination, while long blocks reduce the ability of citizens to interact and mix with each other. However, before planners embrace green skyscrapers as a solution to the environmental impacts of urban developments, they must consider what the quality of life might be in a high-rise city as well as how green skyscrapers affect the city’s social network. Jacobs argued that in streets containing buildings where things could start up and grow, places for buying, eating, seeing things, getting a drink should be considered.13 Therefore, planners may attempt to mitigate the disturbed urban fabric of the skyscraper by placing retail on the street level. A representative prototype is the City-Center project (fig.4), which include a huge base for retail and other services. The center brings sustainability to the forefront, and earned the tag of one of the world’s largest environmentally sustainable urban communities.
Figure (4) City Center, Las Vegas, Pelli Clarke Pelli, Foster + Partners, and Rafael Vinoly (Source: www.skyscrapers.org)
3. 4 Green Skyscrapers and Social and Ethical Issues Sustainability has an obvious ethical aspect towards communities. During the construction phase of any tall building, the social needs of the building’s neighbors should be highly considered. High-rise building can provide facilities for the surrounding community, such as employing and, if necessary, training the local workforce, to contribute both in the construction phase, and in delivering the building’s primary work function. Health and safety is another important issue to be considered during the construction period of a high-rise building, to serve both the building’s occupants and visitors, and neighbors. There are many important issues associated with the construction of tall buildings, including falls both from a building and onto someone, and peoples’ escape following the threat of actual fire or earthquake. In fact, feeling unsafe in working or visiting a high-rise buildings is a new issue for designers to face and to find appropriate solution to it.14
4. RENEWABLE ENERGY TECHNOLOGIES There are number of important aspects that help reducing the carbon footprint in building including, energy efficiency HVAC, lighting, transportation systems, and small power use equipment within buildings (computers etc) and fabric measures that protect against excessive solar gain or high thermal transfer through the fabric. In this regard, the European Commission (EC), introduced a series of mandatory building energy labels (fig.5) and requirements for regular inspection of the “carbon footprint”.15
Figure (5) Building energy labels
(Source: Dalton and John, 2008) Low energy use is a fundamental key to sustainable development, but energy demand is not the main issue within a sustainable building; it is how this energy has been generated. The major driver in tall buildings is to reduce greenhouse gas emissions. However, number of renewable energy technologies can be included as part of site development including, combined heat and power, photovoltaic, wind energy, and fuel cells.
4.1 Combined Heat and Power (CHP) Combined heat and power is considered as a highly efficient energy source, mainly to densely built-up areas. CHP, known as co-or tri-generation, is the simultaneous production of power, heat and, sometimes, chilled water for air-conditioning. It mainly avoids transmission losses because electricity is generated close to point of use. The simultaneous production of electricity and heat in a useable form enables overall thermal efficiencies of up to 80 per cent to be achieved. This means that less fuel is used for a given amount of work and a substantial reduction in CO2 produced. Electricity is produced by a prime mover such as a gas turbine, or a steam turbine which exhausts heat in the form of hot air, steam or hot water. CHP system is common in many European cities, such as Stockholm, Helsinki and Copenhagen.16
4.2 Photovoltaic (PV) Over the last two decades, photovoltaic systems (PV) have evolved rapidly and proved to be an efficient system and practical solution for the sustainable supply of energy in buildings. It mainly converse the solar energy to electricity, which is a potential opportunity for future skyscrapers. PV technology is proven and available and its performance can range from 50-50 W/m² of the PV area depending upon the type of cell, which allows the transmission of daylight. The application of PV can be significant for high-rise buildings since they provide an opportunity for a clear path of direct sunlight above other buildings, as well as collecting energy in diffuse light. In addition, solar PVs can provide an excellent opportunity for aesthetic and environmental
innovation. Panels can replace roofs, and wall cladding systems can cover existing unsightly concrete buildings, provide rain coverings and act as roof lights (fig.6).17 A good example is the Lighthouse, an innovative green skyscraper in Dubai (fig.7). It will have 4000 photovoltaic panels on the south facing façade in addition to three enormous 225 kilowatt wind turbines (29 meters in diameter). It aims to reduce its total energy consumption by up to 65% .
Figure (6) PV Panels in Operation in London
Figure (7) The Lighthouse,Dubai, Atkins Group
(Source: Pank, 2000) (Source: www.skyscrapers.org) (Table 2) provides indicators of output for mono crystalline panels used in major cities in descending values of energy yield in kWH/m²/year, and the panel optimum tilt angle. Table (2) International Energy Agency, 1999 (Source: Pank, 2000)
4.3 Wind Energy Energy can also be generated by a wind turbine, which benefits from the relatively high wind speeds at altitude. Turbines could be an integral part of the building Fabric or be mounted between buildings, or even to be placed on the top of buildings. In all instances the central economics of either losing space and / or having to reinforce structure need to be considered as well as the other costs and benefits of using a wind turbine system. The idea is to capture a huge wind resource for generating electricity by on-site wind turbines. Wind turbines can exploit higher wind speeds around tall buildings or at the top and can be designed for low noise emissions.18 Burj al-Taqa (Energy Tower), Dubai (fig.8), is a super green skyscraper, which includes 200-foot wind turbine that will sit atop the building.
Figure (8) The Burj al-Taqa (Energy Tower), Dubai (Source: www.skyscrapers.org)
4.4 Fuel cells Fuel cells is typically the conversion of hydrogen to electricity. A fuel cell consists of two electrodes sandwiched around an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water and heat with a very high operating efficiency, and their waste heat can also be used in CHP systems (fig. 9). They have advantages over other cogeneration systems in that they are more efficient in producing electricity, produce fewer emissions, and make less noise. Research is currently under way to develop a second-generation fuel cell system with advanced technology, lower cost, longer life, and greater adaptability to cogeneration. Fuel cells are currently very expensive, and can usually only be justified if a wide range of other value benefits are considered. Because of their economics, there are only a handful of significantly sized fuel cell systems currently in use globally.19
Figure (9) Showing efficiency of commercial fuel cell in the USA (Source: Pank, 2002)
5. SUSTAINABLE SKYSCRAPERS A sustainable skyscraper is the building, whose design team have achieved a balance between environmental, economic and social issues at all stages, including design, construction, and operation. This may involve greater emphasis on different aspects at different stages in the building’s life for example, energy for building services and transport of building users and occupants and associated CO2 emissions. A sustainable tall building can also be defined as the one which emits no pollution to air, considers its land and water, and can contribute positively to the local community whilst be economically occupied throughout its time-life. However, incorporating sustainable aspects in tall buildings is a challenge.20
5.1 Orientation on Plan: Daylight and Passive Solar Tall buildings are less constrained than low-rise buildings by the shape of land plots or the layout of streets. The orientation of the building and the shape of its plan allow the maximum advantage of using daylight. The fabric of the façade and the area given to windows are also of ultimate concern both in determining the thermal insulation of the exterior walls, and in gathering light. While an individual tall building can be ideally suited to capturing the heat and light energy of the sun, a second or a third tower constructed in its shadow would be adversely affected.21 For example, the dark shadows cast across the Bow building, Calgary, Canada (fig.10), in the morning by the surrounding buildings, may affect its running costs. However, optimizing its orientation is essential to its sustainable development.
Figure (10) The Bow, Calgary, Canada, completion 2010, Foster + Partners (Source: www.skyscrapers.org
5.2 Building Shape and the Effects of Wind The shape and profile of a tall building determines its performance in wind. Shape not only affects the loading on the structure, but also has an impact on conditions in the surrounding streets and buildings. Good aerodynamic design has a beneficial impact on the structural frame of a tower in terms of materials, and on the comfort of pedestrians at ground level. For new towers in the City, wind analysis and modelling are valuable design tools in optimising the shape and form of the exterior.22 The shape of the World Trade Center Towers, Bahrain (fig.11) will create an accelerated airflow for the jumbo blades to generate electricity with wind turbines and to reduce the consumption of fossil fuels.
Figure (11) The World Trade Center Towers, Bahrain
(Source: skyscrapers.org)
5.3 Floor Plate Depth and Ceiling Height The width of a building, usually referred to as floor plate depth, has a critical impact on its economic, social and the environmental performance. The ratio of net internal area to gross internal area can be increased with a deep floor plan. This ratio decreases with height as a greater area is given to cores in tall buildings. In terms of running costs, however, energy for lighting, can be greatly reduced by the use of daylight. Useful daylight penetrates 3-6 m inside a building from the windows, and shallower floor plates maximize the use of daylight. The width of the building and the height of the ceiling also affect the level of lighting. However, businesses are now more aware of the effects of ceiling height, ventilation and distance from windows upon the output of the employees. A tall building can have fewer constraints on floor height and a narrower floor plate than a low-rise office block which can lead to an increased rentable value.23
5.4 Floor Slab Thickness and Thermal Mass Daylight entering a building arrives with a degree of passive solar heat gain. The structure of a building can be arranged to absorb and drive away that heat energy by its thermal mass characteristics. In principle, this involves direct absorption of heat into the floor slabs when there is sunlight and a release at cooler periods. While passive solar gains can be exploited to avoid the need for heating a buildings in winter, gains in summer can create the need for cooling. Through design, fabric energy stored in the building structure can be removed at night by natural ventilation, reducing energy consumption in cooling systems. Control over the radiant heat entering or leaving the building can be provided by external moveable shutters (fig.12). Use of this type of mechanically operated shading has become more common in London, where it has replaced more conventional internal blinds.24
Figure (12) Holloway Circus Tower Principles of Environmental Design
(Source: Pank, Girardet & Cox, 2002)
5.5 Faรงade Engineering Another area where the fabric of a building can be used to control the internal conditions is the faรงade. Double glazing with argon-filled cavities, triple-glazing and glass coatings can decrease energy consumption. Air tightness of the faรงade is a major issue for tall buildings where pressure differentials from higher winds at the top of a building can cause problems with controlling
internal temperatures and draughts. Double skin facades offer several advantages, such as acting as buffer zones between internal and external conditions, and reducing heat loss in winter and heat gain in summer. Natural ventilation can be drawn from the buffer zone into the building by opening windows in the inner façade. This type of double skin glazed façade used in the RWE Headquarters (fig.13), which is encased in a double glass skin. Outside is a single layer of strengthened safety glass, while the inner glazing is heat-insulated white glass, allowing daylight to be maximized. A 500mm void between the layers of glass acts as a thermal buffer.25
Figure (13) RWE Headquarters (Source: Pank, Girardet & Cox, 2002)
6. CONCLUSION Green skyscrapers imply dense urban development and should attempt to capitalize on this important asset. While green skyscraper proponents are stressing the importance of tall buildings, a more critical analysis suggests that the way towards sustainable urban development is more complex. The discussion over the energy efficiency of skyscrapers is just part of a wider debate over what sort of cities we want to inhabit in the future. It may be true that a skyscraper will consume more energy than a much smaller building, but within the wider context of urban design, the raw data of energy consumption does not tell the whole story. It is believed that taller buildings make more efficient use of urban space and existing infrastructure and provide one solution to the problem of urban sprawl. Proponents of urban planning believed that the city must build upwards in designated “activity centers”, rather than continually invade upon the surrounding countryside. Many cities around the world are taking the same approach and building up innovative buildings following the principles of green design to high rise buildings. However, the key issue of sustainability requirement for green skyscrapers revolves around the need for a common agenda between investors, developers, landlords, tenants, and their respective supply chains. Although, green skyscrapers can significantly reduce the consumption of energy, produce energy from renewable resources, reduce the production of wastewater and reduce material
wastes into landfills, they should also be measured by their impacts in other areas of concern to city planners. One such area of concern is whether green skyscrapers can provide public spaces that are accessible. Another area of concern is whether they can physically be integrated into the urban fabric of the city from the standpoint of building mass and height. In an urban environment, it is the combined effects of the buildings themselves and the collective supporting mechanisms that should be optimized in order to promote sustained urban development. Therefore the value of green skyscrapers and its utility will need to be viewed in this greater context. Green skyscrapers can never be viewed in isolation. Their contribution to the growth of a city, their impact on the cityscape, their relationship with neighboring buildings and their effects upon the people who use them are the ultimate test. In the design of the new generation of tall buildings, the best designers must strive for the highest quality and appropriateness to enhance the built environment and amenity in their designs. Sensitive design of tall buildings must create a positive sense of place by appealing on human scale to both occupiers and passers-by. This vision can succeed, if designers consider the city needs of better public spaces, improvements in air quality, and ecology and bio-diversity. The new generation of green skyscrapers should be memorable in appearance as well as resource efficient and people-friendly in function. They should be more permeable to people and more responsive to environmental conditions to embrace sustainable development. Whatever the future holds for green skyscrapers or tall buildings, their development must become more sustainable in a triple-bottom-line approach, environment, economy and people.
7. REFERENCES 1
EcoLibrium™ February 2005, pp.10-11 Will Pank, Herbert Girardet & Greg Cox, Tall Buildings and Sustainability. Report March 2002. 3 Ibid. 4 (www.whc.unesco.org/list/192) 5 Christl Dabu, Green super skyscraper. (www.chinadaily.com.) 6 Pank, Girardet & Cox, 2002. 7 Howard Bridgman, Robin Warner and John Dodson, “Urban Biophysical environments.” Oxford University Press, Melborne, 2000. 8 Ken Yeang, The Green Skyscraper: The Basis for Designing Sustainable Intensive Buildings. Prestel Verlag, Munich, Germany, 1999 9 Peter Newman and Kenworthy Jeffrey, Sustainability and Cities: Overcoming Automobile Dependence. Island Press, Washington D.C., 1999. 10 Peter Harnik and Jeff Simms, “Parks: How Far is Too Far?”, 2004. Planning: The magazine of the American Planning Association. Chicago, (Il. pp 8-11) 11 Jane Jacobs, The Death and Life of Great American Cities. New York, 1961. 12 Trefil, James, A Scientist in the City. New York, 1994. 13 Jacobs, 1961. 2
14
"Quality of Life Counts" Indicators for a strategy for sustainable development for the UK Dec 1999, HMSO. 15 Ken Dalton and Richard John, Towards More Sustainable Tall Buildings. CTBUH 8th World Congress 2008. 16 Pank, Girardet & Cox, 2002. 17 Ibid. 18 N. S. Campbell & S. Stankovic “Wind Energy for the Built Environment”. September 2001 (Project WEB).) 19 Pank, Girardet & Cox, 2002. 20 Brundtland Report “Our Common Future” World Commission on Environment and Development, 1987. 21 Pank, Girardet & Cox, 2002. 22 Ibid. 23 Ibid. 24 Ibid. 25 Ibid