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During the past few decades, skyscrapers have gained considerable importance in most of the cities around the world. Rapid commercialisation, increasing business needs, scarcity of land and advancement in technology are some of the factors that have forced us to look towards the sky and go vertical. It is projected that by 2030, 5 billion people will live in urban areas, which means that about 60% of the world population will live in urban areas (Ali & Armstrong, 2008). Considering the rising demands arising out of increasing rural to urban migration and resulting need for expansion within limited land area, the skyscraper is looked upon as a built form that would be the only option in meeting this crisis. However, with skyscrapers dominating the skyline of cities, concerns about their impact on environment and vice-versa has been a popular area of study since 1970s. Tall buildings are massive consumers of energy and a major liability on the urban infrastructure due to their scale and purpose and should be the focus of sustainable design (Ali & Armstrong, 2008). The sustainability of tall buildings can be achieved through a multidisciplinary approach since it involves the integration of various complex services and expertise like infrastructure, planning, structure, M&E, elevators, economical and social development. There are many aspects related to tall building design that need to be given a thought from the energy efficiency point of view, to achieve an environmentally sensitive design output. The service core, which is often regarded by architects as a technical element to be tackled by structural, lift and HVAC engineers, is one of the major aspects of tall buildings that could significantly contribute in optimising energy consumption (Trabucco, 2008). It is important for architects to understand service cores not just as distinct block in the building but as an inseparable part of it, that needs due consideration during the initial design phase and has a substantial impact on the building's both operational and embodied energy.
Powell & Yeang (2007) state that, "the tall building typology is the most 'unecological' built form. The tall building when compared to other built typologies uses three times more energy and material resources to build, to operate and to demolish. In reality, the tall building cannot be made completely green and having realised this, architects should try to mitigate its negative impacts on the environment". Thus, it could be said that every effort should be made to look at the different components of such tall buildings and modify them so as to achieve an environmentally sustainable building. The service core is one such component of tall buildings.
2. AIMS AND AREA OF RESEARCH
The importance of service core increases with the increase in height and it contributes significantly to the energy consumption of buildings. There are three specific issues to be tackled in achieving energy efficiency for tall building through service core design. First, optimising the energy consumed by the service core itself. Second, adopting a suitable design strategy for the service core which helps in optimising the operational energy of the entire building. The second case gives rise to the third issue related to embodied energy consumption. As for the first case, there have been several studies carried out to lower the energy requirements of the individual components of the service core (Trabucco, 2008). The latter two issues of operational and embodied energy require in-depth study as to understand the importance of careful consideration of the service core design while developing an architectural concept for environmentally sustainable tall buildings.
The research shall address the following:
- Passive means of optimising the energy consumption of the service core itself.
- Optimising running/operational energy consumption of the building through various passive design strategies for service cores and address the impact of such design decisions on the embodied energy.
The above mentioned two points are related to each other. Certain design strategies which might be beneficial for optimising operational energy also have a positive impact on the energy consumption pattern of the service core itself. However, the same cannot be said about the embodied energy which cannot be optimised using the same design principles.
Optimising energy consumption of the service core itself could help in optimising the overall energy consumption of the building. This would usually involve using the most efficient and low energy systems for elevators, HVAC and other mechanical and electrical services which have been dealt with in the past by various studies and research work. However, this research shall address some of the passive design techniques such as natural lighting and ventilation for lift lobbies, toilets, staircases which could significantly reduce the energy consumption of service cores and in turn reduce the energy consumption of the building as a whole.
The research shall also assess the impact of different design strategies for service cores on the operational energy performance of the building and demonstrate the ideal service core design adaptation. This would involve investigating certain design decisions pertaining to building orientation, placement of service cores, floor plate configuration, appropriate structural system, material choice, facade and resulting issues such as scope for natural lighting, ventilation, heat dissipation and fire safety. The research shall also demonstrate how atriums and sky lobbies could be considered as an integral part of service cores and influence energy efficient design. In addition to this, certain psychological aspects related to design strategies of service cores shall also find a brief mention in the research. In the concluding chapter, the research shall highlight some of these drawbacks as far as embodied energy consumption is concerned; arising out of such designs and suggest possible measures that could be considered to minimise such negative impacts.
Mumbai, as the business capital of India and a global financial hub, is rapidly developing and is currently the most populated city proper of the world (Wikipedia, 2004). With huge foreign investment in business and finance sectors and depleting land resource, Mumbai is now looking to conquer the sky. As the construction for India's tallest and greenest skyscraper, the 301 metre high India Tower by FXFOWLE Architects is underway, one can expect more of these mega structures being built in the island city (Wikipedia, 2004). Thus, it would be necessary to have a holistic and multidisciplinary approach towards this new endeavour for a new city from the very beginning. This paper aims to make a humble contribution to the existing knowledge database on sustainable tall buildings but with a special emphasis on service cores and tropical climatic conditions.
Thus, the primary research questions to be answered is 'What are the appropriate passive design considerations/guidelines for service cores to optimise its self and overall operational energy performance of tall office buildings in the context of Mumbai?'
The research shall answer the following sub questions in order to fulfil the primary aim:
- What are the best suited physical parameters in tall building design related to built form orientation and location of service cores?
- How does the suitable built form for tall buildings negatively affect the NRA/GFA ratio? What are the ways to mitigate such negative impacts?
- What is the range of benefits derived from an unconventional approach to service core design?
- How service core designs can improve fire safety and instil positive psychological impact along with energy efficiency benefits?
- What structural benefits does the ideal service core option enjoy over conventional designs in terms of structural system of the total building?
- What are the best material specifications coupled with mentioned structural system to optimise thermal performance of service cores?
- What are the positive or negative impacts of each of the discussed advantages of a suitable service core design on the embodied energy consumption of the building?
- How can such negative impacts be mitigated to derive overall optimised energy performance?
The primary aim of research is to devise a set of design guidelines for service cores to achieve low energy tall buildings tailored specifically for the tropical climate and also demonstrate the issues of embodied energy in relation to service core design and how it could have an impact on the overall energy consumption pattern of tall buildings and suggest topics for further research.
3. NEED FOR RESEARCH
Tall buildings, over the past 120 years have undergone a series of transitions in terms of planning, structure, materials, economy and environmental impact. The very first tall building, The Home Insurance Building, Chicago, dating back to 1885, gave rise to an era of high rise construction in North America, which soon became a symbol of pride and economic prosperity (Oldfield, et al., 2008). Ever since, the tall building has been a popular prototype and grown in number as well. The energy crises of 1970s forced the building industry professionals to rationalise their design strategies and come up with buildings that use less resources and create a pleasant indoor working environment. In the past decade, some of the new generation tall buildings such as the bioclimatic skyscrapers by Dr. Ken Yeang and Commerzbank Tower, Frankfurt by Sir Norman Foster, display innovative way of substantially improving energy performance (Oldfield, et al., 2008). In an era where environmental sustainability is gaining greater importance, the issue of addressing matters of energy efficiency concerning tall buildings is inevitable.
Service Cores account for about one third of the energy consumed by a tall building owing to the mechanical services housed in it. However, apart from their self operational energy consumption, they can play a positive role in improving the building's overall energy performance through a careful design approach. A great deal of effort is made in dealing with natural ventilation, day lighting and façade design for tall buildings to optimise the energy consumption. However, very little thought has been applied towards service core design that could help in optimising the operational energy of tall buildings in addition to natural ventilation, day lighting, glazing, structure, materials etc. The idea of making an integrated, conscious and holistic approach towards service core design to achieve energy efficiency in tall buildings is relatively recent. Some work has been done in the past related to individual components such as elevators, HVAC and other M&E services. This is evident in Dr. Gina Barney's and many others work dealing exclusively with energy efficient elevator models and few papers on evaluation of appropriate HVAC systems for tall buildings. However, little work has been done in general to reduce the energy consumption of the service core itself through passive design features by considering the benefits generated out of adopting a suitable design.
There are limited resources such as Dr. Ken Yeang's work that mainly deal with the ideal location of the core and how it assists in minimising the energy consumption of the building. However, it is necessary to have an unconventional outlook towards service cores than just a block containing vertical service lines and carry out a detailed study of how a holistic approach towards its design could encompass areas such as atriums, sky lobbies and wind scoops as an integral part of it and have positive impact on the operational energy of tall buildings. Thus, the study of designs of service cores in optimising the self and operational energy of tall buildings is an area of research which is new, relatively unexplored to a great extent, has a potential to be viewed from a different perspective and needed to contribute in developing a sustainable model for future tall buildings.
Due to the vast and unexplored nature of the subject, it is difficult to base the research on a single methodology. The research shall use a combination of three distinct methods. A literature review will assess available information on the subject matter and put forward arguments and findings. A few concepts on future service cores shall be introduced as a personal interpretation and viewpoint on the subject. Such arguments shall be demonstrated through a book case study of IBM Plaza Tower in Malaysia. The arguments put forward in the literature review and case study findings shall be justified by carrying out an energy simulation of a virtual study building and its design alternatives.
4.1 Literature Review
There is very little information available on the subject which makes it difficult to base the research largely on literature review. Information pertaining to advantages arising out of an unconventional design of service cores in optimising operational energy could be investigated from resources such as books and published journals in related disciplines, where we could find mention about passive features in such designs and that they help in improving the energy efficiency of the building. Advantages of appropriate structural systems and choice of materials for an unconventional service core could be demonstrated through this method. The issue of negative impact on embodied energy of tall buildings arising out of design of service core as justified being instrumental in optimising operational energy performance shall be illustrated through literature review of the few research papers available in the subject area.
4.2 Case Study
A case study of the IBM Plaza building in Kuala Lumpur, Malaysia shall be used for demonstrating the advantages arising out of a bioclimatic approach towards service core design in the context of tropical climate. This would be a book case study where relevant information will be collected and analysed from the research work of Puteri Shireen Jahnkassim who is also the author of 'Linking bioclimatic theory and environmental performance in its climatic and cultural context - an analysis into the tropical high rises of Ken Yeang' presented at the 23rd Conference on Passive and Low Energy Architecture, Geneva, Switzerland in 2006. The findings of the case study shall support the arguments put forwards in literature review.
4.3 Energy Simulation Models
The findings of the literature review and case study will form a base for building a hypothetical virtual model. This model along with two other design alternatives shall be tested for thermal performance through Ecotect energy simulation program in the climatic context of Mumbai. The simulation study will analyse data such as the heat from solar radiation and cooling load for the different building prototypes. The simulation program will only vary the building configuration for the various prototypes keeping the location, orientation, climatic conditions, materials and other physical parameters constant.
5. THE SERVICE CORE
The service core is built up of a number of individual components, each having a different function to perform and highly technical in nature. It is important to understand each of these different parts and their interdependency so as to achieve a low energy design option (Trabucco, 2008). There are several words that could be used to describe this part of the building which houses all the major components of services, vertical transportation and utilities serving as the lifeline of the building. In some cases it also serves as the spine of the building acting as a primary support or member of the support system in addition to fulfilling the previously mentioned functions. The most appropriate word for this part of the building is perhaps mentioned by Ken Yeang in the title of his book 'Service Cores', 2000 (Trabucco, 2008).
The service core could be simply described as that part of the building that consists the lift shafts with lift cars and supporting mechanism, lift lobbies, staircases, vertical M&E riser ducts toilets and air handling units in some cases (Yeang, 2000). Due to ease of maintenance, accessibility and economic factors these elements are almost always placed together forming a vertical core like structure ideally connecting the floors vertically. In some cases, the structure of the service core can also contribute in the structural framing and stability of the building.
The service core typically consists of the following:
- Vertical transportation - This would typically include the lift shafts with lift cars and related mechanism and the staircases. There could be a main staircase and a separate fire escape staircase. However, in tall buildings all staircases might be designed to serve during emergencies (depending on local bye laws).
- Mechanical & Electrical Services - These would include the electrical cables and telephone, internet cables placed in separate riser ducts. Water pipes, A.H.U. ducts, wet/dry riser ducts which are important for proper operation of the usable areas are included in this category. They usually take up less area and are arranged after placing the major utilities.
- Toilet areas, janitor's store, fire egress lobbies, lift lobbies and pantry in some cases (especially single tenement buildings).
Depending on the placement of service cores, there are three types of configurations (Yeang, 1996).
- Internal/Central Service Core
- External/Peripheral Service Core
- Single Core at the perimeter - Single Sided Core
- Double Cores at opposite ends - Double Cores
5.2. Impact of NRA/GFA Ratio on Energy Performance
The architectural design decision regarding the service core largely affects the success of a tall office building as a commercial venture. It is important to understand the relation between the service core positioning and its effect on the floor plate efficiency often referred to as the net-to-gross area ratio. The elements of the service core when combined, occupy an area which is excluded from the gross floor area (GFA) which gives the net rentable area (NRA) available on each floor. As the building height increases, the amount of services like number of elevators, supporting machinery also increase. This result in an increase in the area occupied by the service core and thus negatively affects the NRA/GFA ratio. Studies indicate that shorter buildings of about 15-20 floors have a higher NRA/GFA ratio of 0.85 - 0.9 as compared to 50 storey buildings that have ratios of about 0.8 and 0.75 for the tallest building till date (Trabucco, 2008).
The NRA/GFA ratio also depends on the placement of the service core, that is, the kind of service core configuration selected for the building. As mentioned earlier there are primarily two types of configurations - internal/ central service core and external/ peripheral service core placement. Buildings having peripheral service core placement have less floor plate efficiency as compared to their conventional central core position counterparts. This means that more built area will be required to achieve a floor plate efficiency of an equivalent central service core location building. This eventually means that the additional built area would require energy to lit, ventilate which directly affects the operational energy and materials for constructing which affects the embodied energy of the building. Thus, it is important to understand that the topic of NRA/GFA ratio not only has an impact on the economy of the tall building prototype but also on its energy consumption pattern.
5.3. Building Orientation and Service Core Placement
As per the climatic conditions of a particular zone and the sun-path chart, tall buildings could be oriented along the best possible cardinal axis to minimise solar heat gain and maximise energy efficiency and improve the indoor environment. This is the first and most simple step towards a bioclimatic approach to tall building design. Once the orientation of the building is decided, the location of the service core could be fixed to achieve best possible optimisation in terms of blocking solar gains in hot climates. The location of the service core affects a wide range of architectural design criteria such as floor plate efficiency, scope for natural ventilation, day light, indoor environment and structural decisions such as type of structural system, materials, amount of glazing and any requirement of cross bracing. Studies indicate that a peripheral service core location has more advantages than a conventional central core typology in terms of the following:
- Locating the service core on the hotter side of the building (as would be desirable in hot climates) would significantly reduce the amount of heat gained by the building as the service core would act as a solar buffer. In case of cold climate, the core could act as an effective wind buffer to protect from cold winds (Yeang 1996).
- The service core could be naturally ventilated and natural light could be incorporated to lit the lift lobbies, staircases and toilets. This would minimise (if not eliminate) the need for artificial lighting and mechanical ventilation in these areas.
- Natural ventilation to service core areas can eliminate the need of pressurisation shafts for staircases, lift lobbies and fire fighting pressurisation ducts. This helps in reducing the initial cost and subsequent operational costs (Yeang, 1996).
- In addition to acting as solar buffer, external service cores also have a shading effect on the rest of the building which helps in optimising the cooling load (Trabucco, 2008).
- Heat generated by lifts and lighting in the service cores could be easily dissipated to the outside (Trabucco, 2008).
- A naturally ventilated and lit service core is also friendly and safe in the event of an emergency like fire or power failure (Ali, 2003). It can have a great positive impact on the psychology of the people who might be trying to escape using the fire escape routes during such emergencies.
- Tall buildings having an external service core location have an exterior structural system which is more efficient than interior structural systems used in buildings having a central service core (Trabucco, 2008).
Majority of the tall buildings have a central service core configuration and this could be possibly explained as the advantage derived from the central solid core acting as a strong structural support. Thus the service core in these cases serves a dual purpose of providing vertical connections and also structural stability. However, from the environmental sustainability point of view, the peripheral service core would score better than the conventional central core typology (Jahnkassim and Ip, 2006).
6. DATA COLLECTION AND ANALYSIS
Information required for literature review shall be collected and assessed from sources such as books, especially those on bioclimatic skyscrapers by Dr. Ken Yeang. There are numerous papers on high rise buildings, most of them presented at seminars and conferences like CTBUH (Centre for Tall Buildings and Urban Habitat). These papers discuss topics ranging from overall view of sustainability issues in tall buildings, case study reports on few buildings by Dr. Ken Yeang to integrated design of safe skyscrapers extensively dealing with emphasis on role of service core design and placement for fire safety reasons. A paper by Puteri Shireen Jahnkassim and Kenneth Ip compares three buildings in terms of their bioclimatic performance and overall energy use. One of the buildings is the IBM Plaza Tower and the study demonstrates the impact of alternative core designs on the energy consumption. There is an unpublished PhD thesis by the same author and it has a post occupancy study of the above mentioned building to validate the findings. Information from this source shall be investigated and used to validate the findings of literature review. The energy simulation modeling will require geographic and climatic data for the chosen site, i.e. Mumbai, such as latitude, mean maximum temperature for the hottest day in summer (which will be used for simulation study), humidity etc. Physical parameters such as material specification shall be researched through assessing information on renewable and local materials (wherever possible) keeping the factor of embodied energy in mind. The conclusions from literature review shall inform the design of a hypothetical building model complete with the desired elements and location of the service core. Two other dummy alternatives shall be designed for comparing the simulation results and drawing conclusions. The data such as the heat from solar radiation and cooling load for the different building prototypes shall be analysed and compared. The last phase of the research dealing with emphasising the issue of embodied energy related to previously demonstrated service core design shall be analysed through information collected from Dario Trabucco's research which, at present, is the only extensive work done in this field. The recommendations as to minimise the negative effects generated out of such designs in context of Mumbai shall be a personal interpretation based on the above analysis.
7. WORK PROGRAMME
8. OUTCOME OF RESEARCH
The outcome of the research shall be recommendations in the form of an extensive design guideline for service cores that could optimise the self and operational energy of tall buildings. The following broad issues shall be addressed:
- Guidelines for the physical parameters for tall building design in relation to service cores..
- Contradictions of NRA/GFA ratio and ways to optimise the same.
- Benefits arising out of an unconventional design.
- Design for fire safety and positive psychological impact.
- Structural advantages and material specification to optimise thermal performance of service cores.
- Ways to mitigate negative impact on embodied energy consumption.
The research shall not only develop ideal guidelines as mentioned above but also demonstrate the impacts of service core design decisions on the embodied energy patterns of tall buildings and possible measures that could be devised to balance both the operational and embodied energy use. Thus, this research could be a stepping stone for further study in the wide and unexplored field of embodied energy use related to service cores in tall buildings within the tropical climate context.
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- Ali, M. M., Armstrong, P. J., 2008. Overview of sustainable design factors in high-rise buildings. In: Proceedings of the CTBUH (Council on Tall Buildings and Urban Habitat) 8th World congress, Dubai, 2008.
- Jahnkassim, P. S., Ip, K., 2006, Linking bioclimatic theory and environmental performance in its climatic and cultural context - an analysis into the tropical high rises of Ken Yeang. In: PLEA (Passive and Low Energy Architecture) The 23rd Conference on Passive and Low Energy Architecture, Geneva, Switzerland, 6-8 September 2006.
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