The Role of Service Cores in Optimising Heating Energy of Tall Buildings in Temperate Climate

THE ROLE OF SERVICE CORES IN OPTIMISING HEATING ENERGY IN TALL OFFICE BUILDINGS IN TEMPERATE CLIMATE ABHISHEK CHAKRABORTY1 M. Arch. Sustainable Architectural Studies, Reg. No. 090138292, University of Sheffield, 2009-10

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Guided by: Dr. Steve Fotios

“Each and every building is unique in its own way and, for no lesser a reason, the design of the service cores should be so too.” - Yeang

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Acknowledgement

I owe my deepest gratitude to my supervisor Dr. Steve Fotios from the School of Architecture, University of Sheffield for his constant supervision and analysis of this work. I am grateful to Dr. Dario Trabucco from University IUAV, Venice, Italy for his invaluable advice and help throughout my research process. I would also like to thank Oscar Preciado from School of Architecture, University of Sheffield, for his timely help and technical support. I would like to dedicate this dissertation to my family for their encouragement and support without which this project would not have been possible.

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Abstract

This dissertation examines the role of the service core in tall buildings and its significance as a passive design tool to optimise heating energy consumption of tall buildings in U.K. It evaluates the effect of altering the location of service core in a tall building on the heating energy consumption of the office space. Seven models of tall buildings with different service core location are tested to investigate the variation in space heating energy consumption using Energyplus thermal simulation program for the coldest day in Sheffield. The double side east-west external core model is found to have the lowest heating energy consumption among the seven variations of tall buildings with different service core locations.

Keywords: Service core, tall buildings, heating energy, temperate climate, thermal simulation, Energyplus.

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Table of Contents 1. Introduction………………………..………..………………………………………07

2. The Service Core – Redefined……………………………………………………...10 2.1.Conventional Definition…………………………..………….…..…..…….…….10 2.2.Ecological Definition…………………………………………………...….…….11 2.3.Significance of Service Core in Design of Tall Buildings……………..………...12 2.4. Evolution of Service Core Configurations – A Historical Perspective……..…...13

3. Bio Climatic Approach To Service Core Design.....................................................21 3.1.The Case for Central Cores…………………………………………….…..…….21 3.2.Service Core and Operational Energy Consumption…………………….……....22 3.3.Case Studies………………………………………...……………….….…..……24 3.4.Conclusion from Case Studies…………………..……………………….………31

4. Service Core Design for Tall Buildings in Temperate Climate…………..……...32 4.1.Investigating Service Core Design Alternatives in U.K. ……….…...…………..32 4.2.Aims and Objectives……………………………………………………….…….35

5. Research Methodology…………….…………………………..…………………...37 5.1.Thermal Simulation Method……………………..………….………….…..……37 5.2.Choice of Simulation Program ……………………………….…………...…….38 5.3.Simulation Strategy………………………………………………………...……39

6. Thermal Simulation of Building Prototypes……………………………..…..…...44 6.1.Modelling Process ……………………….. ………………………….……..…...44 6.2.Setting Input Parameters…………………………...…………………..………...46 6.3.Output Variables……………………….....….……….………………………….54 6.4.Assumptions………….…………………..………….…………………………...55

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7. Results and Analysis……………………………………………………………….57 7.1.Stage 1 – Passive Zone Thermal Outputs……………………..…….……..…….57 7.2.Stage 2 – Zone Heating Energy Consumption (without internal gains)…...….....62 7.3.Stage 3 – Zone Heating Energy Consumption with Internal Gains……….…......65

8. Conclusion………………………………………..…………………………………69 8.1.Conclusion……………….……………..…….…………....…………………….69 8.2.Scope for Further Research……………………………………………….……...70

References…………..……..…………………………..………………………………...75

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Chapter 1 - Introduction

Tall buildings are not only a necessity for our ever growing cities but also the pride and image of technological advancement and economic prosperity. 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. 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. 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,

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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). An example of this would be existing studies on energy usage optimisation of elevator systems in tall buildings by Dr. Barney. The latter two issues of operational and embodied energy are related to each other and 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. 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, passive design strategies, naturally ventilated service core areas such as lift lobbies, toilets and staircases, carefully planned openings and suitable use of materials and insulation. Optimising operational energy of habitable or office spaces in tall buildings would involve investigating certain design decisions pertaining to building orientation, location of service cores, floor plate configuration, appropriate structural system, material choice, façade treatment and resulting issues such as scope for natural lighting, ventilation, heat dissipation, fire safety and human psychology. This research focuses on the issue of optimising heating energy consumption in tall office buildings in the temperate climatic conditions of Sheffield by altering the location of the service core. Chapter two explains the role and significance of service cores in the design of tall buildings followed by the historical evolution of the core in tall buildings which gives an idea about the factors that influenced its predominant central location. In chapter three, the advantages of central core configuration is explained in terms of higher NRA (net rentable area)/GFA (gross floor area) ratio and lower embodied energy consumption. Subsequently, the operational energy optimisation benefits of external service core configurations are elaborated with reference to Yeang’s theories. The research presents two previous simulation studies on tall buildings where the solar shading effect of external core configuration is demonstrated by optimising cooling loads in warmer climate. In chapter four, based on the

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conclusions of literature review and case studies, a hypothesis is developed that altering the location of service core in a tall office building can act as a buffer from cold in temperate climate and help in optimising space heating energy in the office area. The study is carried out in three stages, where the thermal conditions of a passive office zone is studied in the first stage to account for the passive heat loss or gain followed by the introduction of heating loads and internal gains in the subsequent two stages. In chapter five, the research methodology and the tools used for the study are explained and justified. Chapter six explains the computer simulation process in Energyplus and the assumptions that have been considered for the study. The simulation test results are elaborated and discussed in chapter seven which answers the hypothesis that external service core location helps in optimising heating energy in tall buildings. The conclusion drawn from the research is presented in chapter eight along with recommendations for future scope of work in the field of tall building service core design and energy balance between operational and embodied energy consumption in temperate climate. This research aims to make a contribution by adding to the existing knowledge database on sustainable tall buildings, but with a special emphasis on service cores and temperate climatic conditions.

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Chapter 2 - The Service Core - Redefined

The service core is built up of a number of individual components such as lifts, staircases, pumps, service lines, lobbies, toilets etc. and each having a different function to perform.. 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 linking the various floors with vertical service linkages. The most appropriate word for this part of the building is perhaps mentioned by Yeang in the title of his book ‘Service Cores’, 2000 (Trabucco, 2008).

2.1. Conventional Definition The service core could be simply described as that part of the building that consists of 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: 1. 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). 2. 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.

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3. Toilet areas, janitor’s store, fire egress lobbies, lift lobbies and pantry in some cases (especially single tenement buildings).

2.2. Ecological Definition 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. From an ecological point of view, the service core can be described as that inseparable volume of the building which houses the vertical service linkages and could be used as a passive design tool to buffer the habitable/usable volume from harsh sun or cold winds through thoughtful planning and design incorporated right at the concept development stage. Depending on the placement of service cores, there are two types of configurations (Yeang, 1996) (see figure 1). 1. Internal/Central Service Core – most common practice mainly due to aesthetic and structural reasons. 2. External/Peripheral Service Core – not a common practice. However, few buildings feature this configuration but most of them are due to structural reasons while few have climatic design considerations as well. They can be further categorised as a. Single Core at one side – Single Sided Core/End Core b. Double Cores at opposite ends – Double Cores

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Central Core

Split Core

End Core

Atrium Core

Figure 1: Types of Service Core Configurations (Image Source: Author; Image Data: Yeang, 2000, Service Cores)

2. 3. Significance of Service Core in Design of Tall Buildings The successful performance of tall building requires complete integration of architecture and engineering in the early stages of the design process because they require co-ordination of complex interdependent systems (Ali & Armstrong, 2008). It is imperative for designers to include considerations about the service core design and placement right at the beginning of the design process not only for economical benefits but also for obtaining a less energy intensive building model. It could be argued that during the design process of a tall building, the location of a service core is a prime consideration for designers as they can help in planning an efficient circulation pattern, providing accessibility to office spaces depending on occupancy scenario such as single, double or multiple tenants, maximising utilisation of floor plate and moulding the shape and form of the building. Today, designers should include an additional parameter or prerequisite of the ‘energy consumption’ factor while designing service cores for tall buildings. Decisions made at an early stage in the design process regarding the service core location can have a long and permanent impact on the energy consumption pattern over its life cycle.

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2.4. Evolution of Service Core Configurations – A Historical Perspective 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. Tall buildings, over the past 120 years have undergone a series of transitions in terms of planning, structure, materials, economy and environmental impact. Since the beginning of human organisation, the height of buildings has been limited to a person’s ability to climb stairs (Yeang, 1996). The invention of a mechanised vertical transport system such as the elevator has been instrumental in igniting mankind’s desire to go high up in the sky. Similar to the tall building prototype, the current day service core is an output of an evolutionary design process that has taken more than hundred years and is still evolving (Trabucco, 2010). Based on the energy consumption characteristics, tall buildings can be classified into five energy generations (Oldfield et al, 2008). The evolution of service core is an inseparable part of the tall building’s historic journey through these five energy generations presented in the following sections. 2.4.1. Late 19th Century to 1916 In the late 19th century, when the tall building prototype first saw light in two American cities, New York and Chicago, the concept of a compact and defined service core did not exist. The layout of buildings depended on two factors - availability of natural light for workspaces and commercial value of space. At that time, electric and gas lamps had poor efficiency (Trabucco, 2010) and this was the major factor that resulted in placing the elevator shafts and other service shafts on the dark and less valuable commercially ‘dead’ spaces. Thus, having the entire outer perimeter of the building available for receiving natural light and placing the workspaces and cabins on the periphery meant that the vertical communication shafts eventually ended up in the centre. This central core arrangement was also viewed as advantageous in terms of accessibility, especially in cases of multiple tenancies.

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New York - The shapes of early tall buildings in New York were determined by the lot sizes which were between 20 to 30 metres wide and 60 to 70 metres deep (Trabucco, 2010). Buildings either occupied the entire depth of the plot or were split into two nearly square shaped blocks. In both cases, due to natural light requirements, elevator shafts occupied the central position. In case of buildings occupying the entire depth of plot, the elevator shafts, sometimes 12 to 14 in number were arranged in a single row in centre (see figure 2). In the latter case, a 2.5 metre wide corridor was flanked by 2.5 metre deep elevator shafts on both sides with core to wall distances between 8 to 9 metres as this was the optimum distance natural light could penetrate inside the building (Trabucco, 2010). The service core did not have any structural relevance as the rigid steel frame of the building resisted both vertical and horizontal forces (Trabucco, 2010).

Figure 2: The Trinity (top) and US Realty (bottom) Buildings have a long row of elevator and service shafts placed in centre (Image Source: Trabucco, 2010, Historical Evolution of Service Cores)

Chicago - Building designs in Chicago were governed by height restrictions and usually ended up being massive in plan, sometimes occupying a quarter of a 100 m x 100 m lot (Trabucco, 2010). These massive square blocks had a central atrium court such that offices could be arranged in concentric squares served by a doubly loaded corridor. The elevator shafts in this case could not assume a distinct central position and were placed together at one

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side to serve an adjacent building in the event of expansion on the inner lot line (Trabucco, 2010). The staircases were placed at the corners of the inner ring offices. Thus, the elevator shafts and staircases had a staggered arrangement on a typical floor plan (see red markings in figure 3). Thus, in both cases, it can be clearly seen that the location of the elevator and service shafts were not influenced by structural or climatic reasons and were purely based on non availability of efficient artificial lighting fixtures, ease of circulation and flexibility to expand in future.

Figure 3: The Straus Building in Chicago shows a typical distribution of Quarter Block Building (Image Source: Trabucco, 2010, Historical Evolution of Service Cores)

2.4.2. The Zoning Law of 1916 The random growth of tall buildings in New York drove civic officials to limit the volume of these buildings by specifying setback criteria according to height of buildings. Twenty five percent of the plot area was allowed to be developed without any height restriction (Trabucco, 2010). The building rose in steps with the central part of the tower rising as high as then existing technology could support. This zoning law of 1916 gave rise to the famous ‘wedding cake’ prototype of tall buildings in New York (Oldfield et al, 2008) (see figure 4). 15

Two famous examples of this prototype are the ‘Empire State’ and ‘Chrysler’ buildings in New York. As a result of this pyramidal form, the deep dark central space was occupied by the elevator shafts and other mechanical ducts. This is also perhaps the first time when the service rooms, elevator shafts and staircases were placed at the centre forming a single core. In very tall towers, the service core was placed in the centre while towers built on smaller lot dimensions had cores on one side as its central location would hamper efficient space utilisation (Trabucco, 2010). The lighting technology had not made much progress and buildings still heavily relied on natural lighting. Thus, it could be ascertained that the service core location was still influenced by lighting limitations and effective space utilisation which was ultimately related to commercial value of property. (b)

(a)

Figure 4: (a) Impact of zoning law of 1916 (b) Empire State Building, New York – a famous example of the ‘wedding cake’ building typology affected by 1916 zoning law (Image Source: (a) Oldfield et al, 2008, Five Energy Generations of Tall Buildings: A Historical Analysis of Energy Consumption of High Rise Buildings (b) Google Images)

2.4.3. Post World War II – The International Style In the 1950s, advances in technology and changes in architectural ideology liberated the tall building from its dependence on nature and site (Willis, 1995). Buildings were designed as to fit in anywhere in the world with little or absolutely no regard of the site and climatic

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context. The introduction of glass curtain walls to maximise views outside resulted in locating the structural bracing system and service core towards the centre of the building (Trabucco, 2010). The single glazed curtain wall resulted in excessive heat loss in winter and required increased mechanical systems to heat the office interiors and vice-versa during summers. This led to a significant increase in sizes of ventilation shafts which were then eventually combined with the central elevator and staircase shafts to form a compact and solid central core. Buildings in this era were much taller than their pre world war era counterparts and thus required the service core to act as a structural member, resisting lateral loads and its dimension was dictated by structural requirements (Trabucco, 2010). Thus, in this era, the service core assumed its characteristic central position. Examples: Seagram Building (see figure 5) and Lever House in New York, Lakeshore Drive Apartments in Chicago and The Arts Tower in Sheffield. (a)

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Figure 5: (a) Glass Curtain wall façade of Seagram Building, a typical practice of ‘International Style’ (b) Plan of Seagram Building showing central Service Core location (Image Source: (a) www.rrhobs.com (b) www.moma.org)

2.4.4. New Generation of Service Core Design – Energy Efficient Approach The energy crisis 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 last few years, a new wave of innovations in service core 17

design has been related to sustainability issues and architects have been the frontrunners in promoting this trend rather than end users, industry or developers (Trabucco, 2010). Architects like Yeang have focussed exclusively on the role played by the service core in the design of tall buildings and how a simple decision about their placement can affect the energy consumption of buildings. Yeang’s extent of work stretches over two decades on a number of his own projects in the hot and humid tropical climate where he demonstrates a multitude of advantages gained from an external service core configuration and justifies the need to have an integrated and holistic approach to tall building and service core design. It is clear from his work that the future trend would be to displace the service cores from their central position and have them on external sunny sides for shading and thermal buffering effect (Trabucco, 2010). The mix use office and retail Poly International Plaza in Guangzhou, China, developed by SOM Architects features an external service core which defines an energy efficient design and embraces local climate (SOM website) (see figure 7). Examples: IBM Plaza in Malaysia (see figure 6), Menara Boustead in Malaysia, One Bush Street in San Francisco, Inland Steel Building in Chicago and Poly in China (see figure 7).

2.4.5. Future Service Cores In the recent years, some of the new generation tall buildings such as the Swiss Re Tower in London and Commerzbank Tower in Frankfurt by Foster, redefine the outlook and functionality of service cores and display innovative ways of substantially improving energy performance (Oldfield, et al., 2008). The Swiss Re Tower features spirally rising voids on its external surface meant for naturally ventilating the office spaces. The spiral voids in Swiss Re Tower which are completely open to the floor volume, in effect, could be compared to the compact and enclosed vertical ventilation shafts of Thomas Herzog’s Messe Tower in Hanover which were a physical part of the service core as they are based on the same principle (see figure 8). Architects are now encouraged to ‘think outside the box’ throughout the design process and develop more complex possibilities for the design of service cores (Yeang, 2006). A smarter design is the path to follow to build good quality, low budget skyscrapers and advanced service cores could be a good starting point (Cox et al, 2002).

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(a)

(b) Figure 7: Poly International Plaza in Guangzhou, China (2007) features an external service core (Image Source: SOM website)

Figure 6: (a) Naturally lit lift lobby of IBM Plaza in Kuala Lumpur, Malaysia (b) Plan of IBM Plaza showing service cores on the hot south west side (Image Source: Yeang, 1994, Bioclimatic Skyscrapers)

2.4.6. Conclusion It is evident from the historical evolution of the service core in tall buildings that its predominant central position was due to the quest for achieving greater commercial value for the rentable office space, technological limitations in artificial lighting equipments and sometimes structural ramifications. It is only after the energy crisis of 1970s that the building industry started paying attention to the importance design decisions pertaining to various components of the tall buildings including the service core, to optimise energy consumption of tall buildings.

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(b)

(a)

(c)

Figure 8: (a) Natural ventilation through central atrium in Commerzbank, Frankfurt (b) Natural ventilation through spiral voids in Swiss Re Tower, London (c) Conventional enclosed natural ventilation shaft in Messe Tower in Hannover by Herzog, in effect, has the same principle as the Commerzbank and Swiss Re Towers (Image Source: (a) Arend et al, Commerzbank Tower (b) & (c) Trabucco, 2009, The strategic role of service core in energy balance of tall buildings)

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Chapter 3 - Bio Climatic Approach to Service Core Design

The historical evolution of service cores highlights the reasons as to why and how the service core assumed its predominant central position in a tall building. It is important to understand that it was only after the energy crisis of 1970s that building industry professionals started paying greater attention to sustainability and energy efficiency issues in tall buildings with a thought on the design strategy for service cores being one of the secondary considerations. Careful thought applied towards service core design strategy 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 and as discussed before, this trend is emerging in modern day practice. This section discusses the case for and against central cores and the role played by the location of service cores in helping to reduce energy consumption of tall buildings through Yeang’s work which largely focuses on tropical high rises.

3.1. The Case for Central Cores Hill, an authority on commercial real estate, explained in ‘The Architectural Record’ that an office building’s prime and only objective is to earn the greatest possible return for its owners’ (Willis, 1995). This statement clearly reflects the tendency to treat tall buildings as revenue generating machines which eventually governs the design decisions. 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 GFA that gives the NRA available on each floor. The extent of NRA and GFA are determined during the initial stages of design and it is at this time, that the typical and atypical floor-plates are generally configured (Yeang, 1996). 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

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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 (Trabucco, 2008). This is one of the major reasons that traditionally, building industry professionals have always preferred a central core configuration for tall buildings. In early 20th century, buildings in New York had long and thin tower floor plans which had a compact central service core and the plan produced an impressive ratio of sixty eight percent rentable areas (Willis, 1995). With the sophistication in elevator technology and concept of sky lobbies, floor plate efficiencies for central core tall buildings have improved over time. As in the case of external core configuration, 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. However, an argument could be placed that the benefits generated out of an unconventional service core design over the lifespan of the structure could outweigh the factor of additional embodied energy spent in constructing it is an interesting research topic in itself and is beyond the scope of this research. Thus, it could be said that, the topic of NRA/GFA ratio assumes importance not only from an economic point of view but also on the energy consumption pattern of tall buildings.

3.2. Service Core and Operational Energy Consumption 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 (in hot climate) or heat loss (in cold climate) and maximise energy efficiency and improve indoor thermal comfort (in case of naturally ventilated buildings). This is the first and most simple step towards a bioclimatic approach to tall building design. The location of the service core

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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: a. 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). b.The service core could be naturally ventilated and natural light could be incorporated to light the lift lobbies, staircases and toilets. This would minimise, if not eliminate, the need for artificial lighting and mechanical ventilation in these areas. c. 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). This might also reduce the area of service cores and increase floor plate efficiency. d.In addition to acting as solar buffer, external service cores also have a shading effect on the rest of the building which furthermore helps in optimising the cooling load (Trabucco, 2008). e. Heat generated by lifts and lighting in the service cores could be easily dissipated to the outside which would be ideal for reducing cooling loads in warmer climates (Trabucco, 2008). f. 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. g.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).

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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 & Ip, 2006). 3.3. Case Studies As discussed in the previous sections, there seems to be a theory regarding the advantages gained out of an external core design for a tall building especially in warmer climates. The following two research studies demonstrate the effectiveness of external service cores in optimising cooling and overall energy consumption of tall buildings in different climates.

3.3.1. Case Study 1 - IBM Plaza, Kuala Lumpur, Malaysia – Testing Yeang’s Theory in a Tropical High Rise Kuala Lumpur is situated at 3.12° N latitude and 101.55° E longitude and has tropical climate. As could be seen from figure 9, the annual average temperature ranges from a minimum of 22.5° C to a maximum of 33.2° C. Cooling degree hours is quite high at 8718 hours which suggests that buildings require air conditioning for about 99.5% of the year. Thus, buildings in this region would be predominantly cooling intensive and would naturally require sun shading and solar buffers to minimise solar heat gains. The energy consumption of a building is greatly affected by the placement of its service cores and it depends on a multitude of factors such as geographical location, local climate and type of building (Yeang, 2000). There is a correlation between the service core and the cooling and heating loads of the building, the former being most influenced by the core position (Yeang, 2000). Yeang’s theories suggest that, in tropical countries, a split-core design with the cores facing east and west and glazing facing north and south would have lesser cooling load than a central core design. The effectiveness of split-core design heavily relies on orientation of the building where north-south oriented building can have cooling loads nearly one and half times higher than buildings oriented longitudinally from east to west (Yeang, 2000).

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(a)

(b)

Figure 9: (a) Exterior view of IBM Plaza building by Yeang in Kuala Lumpur, Malaysia (b) Typical office floor plan of IBM Plaza showing service cores on the hotter sides east & West (Image Source: (a) Google Images (b) Yeang, 1994, Bioclimatic Skyscrapers)

Yeang’s theory of the effectiveness of double core configuration has been tested using IES-VE (Integrated Environmental Solutions – Virtual Environment) software (Jahnkassim and Ip, 2006); on his IBM Plaza building in Kuala Lumpur, Malaysia to understand how much cooling load could be reduced by altering the service core placement. Five configurations were tested – Generic, single side-east, single side-west and two options for double cores. The study shows that the double core configuration has a significant impact of about 8 to 10 percent reduction in terms of total and cooling energy use (Jahnkassim and Ip, 2006).

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(a)

(b)

Figure 10: (a) Pshycrometric Chart – Kuala Lumpur (b) Temperature Range Chart – Kuala Lumpur (Image Source: (a) & (b) Climate Consultant Software; Image Data: Energyplus Weather Data Website)

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(a)

(b)

Figure 11: (a) Impact of core placement on total and cooling energy (b) Impact of core placement on peak cooling load (Image Source: (a) & (b) Jahnkassim and Ip, 2006, Linking bioclimatic theory and environmental performance in its climatic and cultural context – an analysis into the tropical high rises of Ken Yeang)

3.3.2. Case Study 2 - One Bush Street, San Francisco, U.S.A. This study was carried out on the 20 storey One Bush Street Building, completed in 1969, by Trabucco (2008). The study was carried out for assessing the impact of alternate service core design strategies on both operational and embodied energy of the building. The building features an external service core facing south that shades the office block. San Francisco is

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situated at 37.62° N latitude and 122.4° W longitude and has a Mediterranean climate with warm to hot summers and mild winters. The annual average temperature ranges between a minimum of 8° C and maximum of 25° C. Figure 12 suggests that annually, buildings would require heating for 4229 hours which is about 48.2% of the year. However, the chart also suggests that there is no conventional air conditioning requirement.

(a)

(b)

Figure 12: One Bush Street, San Francisco, USA (1969) has an external service core on the south side which shades the building. (a) Service Core on South side acts as solar buffer and shades the building. (b) Aerial View of One Bush Street. (Image Source: Google Images)

The test was carried out using three models including the actual building prototype so as to determine the impact of service core design strategy on both operational and embodied energy of the building. However, as far as the scope of this paper is concerned, only the operational energy results are discussed. Three models were made – one similar to the real building, one standard glazed box of the same net rentable area and a third one similar to the actual building but with a naturally ventilated adiabatic service core and the analysis was carried out using Energyplus thermal simulation software integrated within Design Builder Evaluation Version 1.2.2. (Trabucco, 2008). All three models were simulated on a typical summer day and the heat produced by the electrical lighting, solar radiation and cooling loads were analysed. The test results show that the uncooled adiabatic service core model has the best performance for two main reasons – as the service core is naturally ventilated, the volume of space to be air conditioned is less and the external core acts as a thermal buffer

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and shading body. Also, a naturally ventilated service core dissipates its heat gains, using its thermal inertia to keep its temperature at comfort level (Trabucco, 2008).

(a)

(b)

Figure 13: (a) Psychrometric Chart – San Francisco (b) Temperature Range – San Francisco (Image source: Climate Consultant Software; Image Data: Energy Plus Weather Data Website)

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Table 1: Comparison of three different design strategies for One Bush building, San Francisco (Data: Trabuco, 2008) Building

Total energy consumption for cooling per year (GW) One Bush adiabatic 3.4 Actual One Bush building 4.1 Equivalent ‘glazed box’ of same 4.4 floor area

Difference from Glazed Box per year -1 GW -0.3 GW -

Figure 14: Simulation results for three different strategies of service core design for One Bush Street building on hottest summer day in San Fransisco, U.S.A. (Image source: Trabucco, 2008, An analysis of the relation between service cores and embodied running energy of tall buildings)

Table 1 suggests that a naturally ventilated external service core placed on the hot side of the building could result in a significant saving of 1 GW in a single year as compared 30

to a standard central service core glazed box design. However, one of the interesting points to be noted here is that even though the climatic data suggests that cooling is not required for buildings in this location, which would suggest that it never gets so hot that air conditioning would be required, the test results show that significant savings could be made by having an external service core to the south and using it as a solar buffer. 3.4. Conclusion from Case Studies From the first case study on IBM Plaza building, Yeang’s principles on the advantages gained out of an external and that too double sided split core service core configuration is quite clear. However, the paper does not clarify the details of the two double sided core models namely 1 and 2. It is not clear as to whether these two models have different orientation such as east-west and north-south or are the cores naturally ventilated. Although the test results show that these two double sided core configurations have lower cooling loads, it would have been helpful to know the exact difference between these models. In case of the second case study on the One Bush Street building, a further investigation could be made into the possibility of reducing heating loads, which could be considered as a priority in the climate of San Francisco, by a different design strategy where the service core could act as a heavy mass of insulation on the colder side (north) of the building and reduce heat loss from building. Further, a double (split) core design option with cores facing east and west could be tested to evaluate its significance in comparison to the single south side and single north side core configurations. It would be interesting to find out the reductions in both heating and cooling loads to conclude as to which strategy has greater significance in such climatic conditions. This would allow making more informed decision at the design stage to adopt the most effective design strategy for service cores in tall buildings.

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Chapter 4 - Service Core Design for Tall Buildings in Temperate Climate

The advantages of external and especially double core east-west oriented configuration of tall buildings in the tropical climate are evident from the studies and thermal simulations which are in line with Yeang’s theories. However, there could be an extension of this study to analyse as to which service core design strategy would work best in temperate or colder climates.

4.1. Investigating Service Core Design Alternatives in U.K. The theories about operational energy optimisation in external service core buildings that work well in hot tropical climates may or may not be as effective in temperate climate which is perhaps the most varied type of climate in the world. For example, in the U.K., which largely has a maritime temperate climate, heating loads might form a significant part of energy consumption as compared to cooling, which in many cases is not required at all. This might give a hint that in this case, adopting a design strategy with service cores facing the colder north-east and north-west sides can help buffering the building from cold winds and minimising heat loss and thus optimising heating loads (Yeang, 1996). However, the heating energy savings from such a configuration remains untested and leaves scope for further study and investigation of other external core strategies as well. Regions falling between 30° N and 60° N latitude and between 30° S and 60° S latitude have temperate climate (see figure 15). There are two main types of temperate climate – maritime and continental (Geographical Association, 2009). U.K., Europe and most of North America fall under the temperate climatic zone. U.K. has predominantly maritime temperate climate as summers are cooler than Europe, which has continental temperate climate and in winters, temperature in U.K. easily falls well below 0° C. Adopting the most effective design strategy for tall building service core in temperate climate can be a challenge owing to variations between and within countries. This necessitates basing the study on a particular country and city so as to achieve more reliable results which would allow drawing conclusions in terms of strategies that could be applied to that particular region. Figure 16 suggests that in temperate climate, the service core could be located on the North (cold side) (highlighted area in red). However, as the theories for hot

32

tropical climate have been tried and tested, this idea for the temperate climate still remains as a mere suggestion and needs to be assessed to determine the impacts of different core design strategies on the heating energy consumption of tall buildings.

Figure 15: Climatic regions of the world (Image source: Yeang, 1994, Bioclimatic skyscrapers)

Figure 16: Strategies for building form, orientation and service core location in different climates (Image source: Yeang, 1994, Bioclimatic skyscrapers)

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4.1.1. The C.I.S Solar Tower, Manchester, U.K. The C.I.S. solar tower in Manchester is an example of a tall building with an external service core on the south side (see figure 17). However, in this case, the intention of having an external south side service core does not seem to be linked to the thought of optimising space heating energy. The primary focus, in this case, is to use the dead walls of the exterior service core for mounting photovoltaic panels and generate electricity. Originally, the exterior walls of the service core were clad with grey mosaic tiles which were replaced by 7244 80W photovoltaic modules to harness the sun’s energy (Solar Century, 2010). Thus, apart from subconsciously contributing to significant savings in the heating energy consumption of the building, this is a classic example where the external core provides the necessary base for mounting PV panels which considerably reduce reliance on grid connected electricity and carbon emissions.

(a)

(b)

Figure 17: (a) The south side exterior service core of the CIS solar tower in Manchester clad in grey mosaic tiles before refurbishment (b) Photovoltaic panels clad on the south facing exterior service core (Image source: Google Images)

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4.2. Aims and Objectives of Research As discussed in the literature review and case studies, the design decision pertaining to location of service cores in a tall building can have significant impact on the overall energy consumption pattern of tall buildings. The effectiveness of a service core design strategy largely depends on the geographical location and climatic conditions of a place. The energy consumption priorities change with the change in location. For example, in hotter climates, optimising cooling energy would be the priority and in a colder climate, heating energy optimisation would be the primary concern. The conclusions developed from the literature review and case studies suggest that there is a significant savings in cooling and overall energy consumption of tall buildings when the service core location is altered. This has been proved by studies done on buildings in tropical or warmer climates with a focus on optimisation of cooling loads. The research proposes to question the effectiveness of such alternate design strategies for the service core in a tall building in U.K.’s temperate climate where heating energy forms a significant portion of energy consumption in buildings. As discussed earlier, for acquiring reliable test results, it is necessary to base the study at a particular location which is representative of the climatic condition of that region. This study is based on the climatic condition of Sheffield in U.K. Sheffield is located at 53.5° N latitude and 1° W longitude and has a maritime cool temperate climate. Sheffield’s weather is characterised by strong cold winds predominantly from the west for most part of the year (U.S. Department of Energy). According to the weather data on the U.S. Department of Energy website, heating is required for 7500 hours annually, which is almost 85% of the year with no requirement for mechanical cooling, if adequate natural ventilation is provided. Thus, it would be worthwhile to assess the heating loads for the coldest day of the year and total annual energy consumption. In this study, the example of Arts Tower is used to relate the research to an existing building in terms of its size, shape and height. The Arts Tower in Sheffield features a central service core wrapped around by a single skin glass curtain wall. The building resembles a near perfect scaled down imitation of the Seagram Building in New York. The Arts Tower, completed in 1966 (Schneider, 2008), seems to be heavily influenced by the ‘Post World War International Style’ and disregards any climate sensitive design considerations whatsoever. A major refurbishment project is underway to add a double skin façade to the building to

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address problems of internal spaces getting too cold or too hot and excessive energy consumption. The phase two of the project intends to solve problems related to the service core such as providing additional toilets and improving fire egress (University of Sheffield, 2010). However, in order to create an ideal typical office building that would be relevant to any location in the U.K., the material specifications of exterior facades were adjusted to meet current building regulations in the country which were then kept constant for all the variations of tall building prototypes during simulation. This can help in generalising the study for a standard tall office building in the U.K. and just not limit the study to a particular building in Sheffield. Thus, it could be said that the example of Sheffield and Arts Tower were used for the research study purpose and is representative of similar location and typical standard office building in the temperate climate of U.K. The research aims to address the following hypotheses: 1. The service core location in a tall building affects the space heating energy required by the office area in the temperate climate of Sheffield. 2. The external service core configurations can help in optimising the heating energy requirement of an office space as compared to the standard base case central core ‘glazed box’ typology. 3. Adding internal gains and infiltration rate in addition to heating equipment might bring about a change in the rank order of the seven models at the three different stages. The objective is to study the variations in the passive indoor thermal conditions and heating energy consumption pattern for an office zone in seven tall building models with different service core positioning. The study does not include assessment of heating energy consumption by the service cores. The following chapters elaborate the research strategy, simulation study process and discuss results of the study. The outcome of this study could be adopted as a base case for locations in the U.K. having similar climatic conditions and built upon for further research in this field.

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Chapter 5 – Research Methodology

The research methodology uses computer simulation tools to answer the hypotheses. The chapter illustrates the appropriateness of using computer based simulation programs for this particular study, validation and choice of computer simulation program and the overall strategy of the study in terms of the limitations and assumptions defining the boundary conditions for the simulation work.

5.1. Thermal Simulation Method The effects of different service core locations on the heating energy consumption of a typical office floor in a tall building could be done by either performing an experimental study using scaled or full size physical models or by carrying out a thermal simulation using computer based programs. Performing an experimental thermal study by actually building physical scaled or full size model would not only be time consuming but also economically not feasible. It might not be practical or technically possible to accurately evaluate room temperatures, heating loads with internal gains and air infiltration using scaled models. Using scale correction in this case might prove to be difficult and perhaps inaccurate. Testing full size models might give accurate results; however, the testing parameters cannot be changed easily and can prove to be costly (Burton, 2001). In this case, if the physical parameters of the building model are implemented to the exact specifications under laboratory conditions, the results obtained from such a study would be quite accurate. However, the idea of building an actual model and performing a live study seems unpractical in a time where comprehensive computer based programs are available which can evaluate the thermal conditions to near accurate estimates. Computer simulation is less time consuming than analysis using physical models and the boundary conditions can be varied quite easily. The computer simulation programs are pre loaded with numerous default input parameters and also provide the opportunity to make custom adjustments as per requirements like materials, adiabatic zones or surfaces and equipment or machinery operation schedules. Certain advanced simulation programs also provide detailed surface, zone and equipment outputs which, in some cases would be difficult and cumbersome to obtain from an experimental analysis. However, a drawback of using

37

simulation programs is that its accuracy depends on the validity and testing of the program and it would tend to give near approximation as against an accurate output in a live experimental work which would be close to the real world situation (Magri, 2006). Also, the accuracy of results largely depends on setting of input parameters, assumptions and estimations which defines the boundary conditions for the simulation. Thus, it is important to validate the choice of simulation program from previous studies which include similar simulation analysis and also understand the settings and working of the program to be able to clearly define the parameters and make any valid conclusions.

5.2. Choice of Simulation Program A number of simulation programs are available to perform thermal simulations of built environment, ranging from simple ones to very complex computer programs. The complexity of a simulation program largely depends on the extent of input parameters that can be adjusted for the building model. Such complex programs demand in depth knowledge on the subject area of building physics and heat transfer to be able to set appropriate values for the input parameters which define the boundary conditions of the model. Simulation tools dealing with energy efficiency and indoor quality in buildings can be classified into two categories (Burton, 2001): 1. Global computational tools – Such tools are used to evaluate the overall performance of a building and are based on empirical or statistical algorithms and are valid only under certain conditions (Burton, 2001). 2. Specific computational tools – Such tools are used to evaluate the performance of specific parts of building or certain design techniques such as natural ventilation in a space or air flow through atriums or specific equipments such as HVAC system etc. Most of the specific computational tools are validated against real measured data from experimental buildings and/or test cells (Burton, 2001). A good example of a simple computer based simulation program is Ecotect. The program can perform a wide range of building simulation functions ranging from thermal analysis, lighting analysis and even whole building energy analysis. It is a single program that allows creating 3D models and run simulations and gives interactive outputs in form of graphs. However, the program uses a large number of assumptions and provides very few options to

38

change any advanced input parameter. Also, the options for output variables are not as wide as some more advanced programs such as Energyplus or IES (Integrated Environmental Solutions). This simulation study uses Energyplus which is an energy analysis and thermal load simulation program. The program is developed specifically for calculating heating and cooling loads in a building in addition to sizing HVAC equipment and optimising energy performance. Energyplus works like a link between an external building modelling program like Openstudio where the 3D building models are made and the IDF editor where the input and output parameters are set. The program has options to set custom people occupancy, electric lighting, office equipment and air infiltration operation schedules along with detailed performance parameters for the same. Energyplus allows for detailed surface and zone air passive thermal condition outputs and is a more complete thermal load simulation program than Ecotect. A similar thermal simulation study using Energyplus has already been discussed in the One Bush Street case study. This is one of the major reasons for using Energyplus for this simulation study as the results could be validated from a previous study undertaken with the same computer program. Thus, this study uses Energyplus to simulate the passive thermal conditions and heating energy loads in seven tall building models with different service core positioning.

5.3. Simulation Strategy The heating energy requirements for a tall building can be calculated by simulating a typical floor of the building. The office volume for which the simulation results are recorded is referred to as the ‘office zone’ and the service core volume is referred to as the ‘service core zone’. The thermal simulation results depend on the boundary conditions and input parameters such as building geometry, choice of location which influences climatic data, generic alternatives of service core positions, heat transfer between the thermal zone and outdoor environment depending on the cardinal orientation of the building and core positioning, heat transfer between two zones (office and service core), material specification, internal gains and air infiltration rates. It is important to identify the limitation of any simulation study and define the boundary conditions before proceeding further. The overall simulation strategy addressing the above mentioned issues are explained in this section.

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5.3.1. Choice of Building Geometry In order to assess the effects of changing the service core position in a tall building on the heating energy consumption, a typical single floor midway through the height of a tall building is studied. Choosing a floor midway through the height of the building would give an idea of the average scenario of any thermal or climatic effects caused by the overall height of the building (Magri, 2006). The study uses the example of Arts tower for data regarding the physical geometry such as the size, shape, usable and net rentable floor areas and building height. The Arts Tower model is considered as a standard 20 storied rectangular parallelepiped office building prototype and simulation is carried out for the 12th floor of the building. This is referred to as the ‘office zone’ throughout the study. For the office zone, the GFA is 692.25 m2. Out of this, the service core area is 107.25 m2. Thus, the NRA of the office zone is 585 m2. The floor to floor height (slab top level) is considered as 3.5 m. The area and volume parameters of office and service core zones are kept constant for all the seven models but the external dimension of the office block varies for the external service core models so as to accommodate an effective span. Following are the variations in sizes of office zone: 1. Central Core Model – 35.5 m x 19.5 m (includes 19.5 m x 5.5 m service core in centre) 2. External Core Models – 39 m x 15 m (excluding split or combined external cores)

5.3.2. Choice of Climatic Data It is important to base the study at a particular geographical location to be able to apply the relevant and accurate climatic data in the simulation process. The choice of weather file in the simulation program affects the reliability of the output. In this study, the Sheffield weather file is obtained from the U.S. Department of Energy website which also happens to be the developers and distributors of Energyplus simulation program. The weather file is available in .epw format and is recognised by Energyplus. The simulation is carried out for winter design day, i.e. 12th of January, which is the coldest day in Sheffield as per the data available from Energyplus climate summary file.

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5.3.3. Generic Alternatives of Service Core Configurations The choice of generic tall building alternatives with various service core positions is crucial for the study and thus, as many as seven alternatives are simulated to determine the best case scenario. When performing an analysis that involves comparing various design alternatives, one should have a prototype, referred to as the base case, to compare the results with (Magri, 2006). According to Hamza (2004), there are two types of base case definitions: 1. An existing base case – an existing building whose performance is compared against that of the design alternatives. 2. A hypothetical base case – This would be a hypothetical building model compiled from statistical data, surveys, building standards and previous studies. This study uses the physical geometry of an existing building but creates a hypothetical base model by altering the material specification to match the minimum standards of Part L Building Regulations for the U.K. The reason for creating an ideal model is to demonstrate the effect of changing the service core positioning on the heating energy consumption in a building which meets the prescribed requirements of the Building Regulations in terms of material U-value specifications and also make the building a standard typical office building that could be anywhere in the U.K. This should eliminate any discrepancies in the study which would arise by using the original material specification of the Arts Tower which uses a single glazing (until the recent ongoing refurbishment project) at present and does not meet the Part L Building Regulation requirements. The following seven tall building models were tested (see figure 18): 1. Central core (base case ‘glazed box’ typology) 2. External Core - Double Side East-West 3. External Core – Double Side North-South 4. External Core – Single Core North 5. External Core – Single Core South 6. External Core – Single Core East 7. External Core – Single Core West The simulation program varies only the service core positioning, while the weather file, material specification and other physical parameters such as floor areas and volumes remain constant.

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(a)

(b)

(c)

(d)

(e)

(f)

N

Office Zone (Thermal Zone) Service Core Zone

(g) Figure 18: (a) Central Core (b) External Double Side East-West Core (c) External Single Side North Core (d) External Single Side South Core (e) External Single Side West Core (f) External Single Side East Core (g) External Double Side North-South Core (Image source: author)

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5.3.4. Stages of Simulation The primary objective of the research is to analyse the effect of changing the service core location in a tall building on the indoor thermal conditions and the heating energy consumption of the office zone. The simulation study is carried out in three stages: 1. In the first stage, the office zone is considered as a passive zone i.e. without any space heating supply, to assess the thermal conditions in the zone by recording transmitted solar radiation, heat gain/loss through glazing via conduction and heat gain/loss in the office zone air via convection with the external surfaces/facades. 2. In the second stage, an ideal loads air heating system is introduced in the models to determine the space heating loads in the office zone. At this stage, the office zone is considered as an ideal air tight box neglecting any air infiltration rate and internal gains. 3. In the third stage, people, lights and office equipments are added for internal gains in both the office and service core zones. Also, an air infiltration rate is introduced in all the models to observe its effect on the overall heating energy consumption pattern of office zone.

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Chapter 6 - Thermal Simulation Process

The thermal simulation process involved creating 3D models for seven tall building design alternatives for different positions of service cores. The second phase involved setting the input parameters to define the boundary conditions of the simulation study. The final phase involved choosing the appropriate output variables before running the simulation and managing output data to answer the hypotheses.

6.1. Modelling Process Energyplus is only a thermal loads calculation program and is linked to various other 3D modelling programs for creating virtual 3d models. This study uses openstudio 3D modelling program which is available as a plug in for Google sketchup version 7. The openstudio program could be described as a semi-independent program within sketchup. It uses the same user interface and drawing commands of sketchup but the models are created in a thermal zone which has certain unique commands which are recognised only by openstudio. All building components are modelled as individual thermal zones which can be edited using openstudio commands. The ‘create new file’, ‘open file’ and ‘save file’ options are unique for openstudio operations and are independent of sketchup. The model files are saved as .idf format which is recognised by Energyplus and can be edited using the IDF editor link in Energyplus launch window which will be explained later in this chapter. The surface properties of the model created in openstudio can be edited in IDF editor and any changes or modifications made in either program updates the model to reflect the changes in both the programs.

6.1.1. Creating Thermal Zones In openstudio, each and every building volume was modelled as a thermal zone. The building was divided into separate zones in such a way that the thermal properties of each zone could be modified to be unique. For example, in the case of double core east-west model, the 12th floor office area was modelled as the ‘office zone’ and the two service cores on the east and west were modelled separately as ‘east core’ and ‘west core’ (see figure 19). Thus, it was possible to set the zone input parameters for the office and service core zones independent of

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each other. As the office zone is located on the 12th floor, the lower office floors were modelled as a single block having a height equivalent to 11 floors. Similarly, the upper floors were modelled as a single block having a height equivalent to 8 floors. The same modelling principal was applied to all the seven models and saved as separate files.

Figure 19: The 12th floor office zone, east and west service core zones adjoining the office zone, lower office floor block, upper office floor block and respective service core zone blocks (Image source: author)

6.1.2. Modelling Office Zone Facade The external façade of the office zone was modelled in a way to resemble the original façade of a typical floor of Arts Tower in terms of the window size, shape and placement. However, the windows were modelled as full floor height windows as opposed to the low sill height windows in the original building (see figure 20). The idea of modelling full floor height windows was to generalise the facade as a typical glass curtain wall surface. The windows were placed 0.2 m apart, separated by peripheral columns as existing in the original building. However, the original building has steel columns with concrete casing around for fireproofing which was simplified and substituted by concrete columns 0.2 x 0.3 m in size.

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The façade design was kept exactly the same for all seven models except in those places where an external service core overlaps on the exterior façade. The material specifications are explained in detail in the construction section. Also, the building surface properties were adjusted such that the office zone floor and ceiling slabs had outside boundary condition as adiabatic to neglect any heat transfer to and from the floors above and below the office zone. This is explained in detail in the assumptions section later in this chapter.

Figure 20: The 12th floor office zone showing triple glazed full floor height windows spaced at 200 mm apart in all the seven models (Image source: author)

6.2. Input Parameters Once the model was completed in openstudio, the input parameters were fed into the model using IDF editor link through Energyplus launch window. The simulation environment, equipment operation schedules, material specifications, zone surface properties, internal gains and infiltration rates were defined using this program. This section gives a detailed account of the input parameter settings for each of the criteria mentioned above.

6.2.1. Boundary Conditions for Simulation The boundary conditions defining the overall limitations and scenario for the simulation such as building’s geographical orientation, surrounding physical/built environment are important

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factors in the process of setting up the stage for running thermal simulations. Table 2 gives the details of the boundary conditions for the buildings. Table 3 gives the details that were used to determine the geographical location of Sheffield. Table 4 indicates the simulation period i.e. the day for which the simulations were performed. Table 2: Input parameters: Boundary conditions for building models (* indicates Energyplus default values; ** indicates reference to definition from USDOE, 2010) Field North Axis

Terrain Loads convergence tolerance value

Temperature convergence tolerance value Solar Distribution

Maximum number of warm-up days

Description The direction of north was set by default along the Y axis in the model space in openstudio. Thus, the building model was already aligned as per north and this value was set to zero degrees. The surrounding built environment was set to mimic city terrain for a more realistic simulation environment. This value represents the number at which the loads values must agree before ‘convergence’ is reached**. This is an advanced setting and thus, it was set to Energyplus default value. This value represents the number at which zone temperatures must agree (from previous iteration) before ‘convergence’ is reached**. This is an advanced setting and thus, it was set to Energyplus default value. This parameter determines how Energyplus treats solar beam radiation and reflectances from exterior surfaces that strike the building, and ultimately, enter the zone. This setting calculates the amount of beam radiation falling on each surface in zone such as floor, walls and windows by projecting the sun’s rays through exterior windows, taking into account the effect of exterior shadowing objects and shading devices, if any. It also calculates how much beam radiation falling on the inside of an exterior window (from other windows in the zone) is absorbed by the window, how much is reflected back into the zone and how much is transmitted to the outside**. This parameter specifies the number of ‘warmup’ days that might be used in the simulation before ‘convergence’ is achieved**. This is an advanced setting and thus, it was set to Energyplus default value. Table 3: Input parameters: Location of the building models

Latitude Longitude Elevation Time zone

53.5° N 1° W 11 m from sea level GMT 0.00 hrs

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Value 0 degrees.

City. 0.04*

0.4*

Full Interior and Exterior

25*

Table 4: Input parameters: Simulation run period (* indicates Energyplus default values; ** indicates reference to definition from USDOE, 2010) Field Begin Month Begin Day of Month End Month End Day of Month No. of times run period to be repeated

Description Starting month for simulation (in this case it is January) Starting day of the month for which simulation is to be carried out (starting at 00.00 hrs on 12th January) End month for simulation (January) End day of the month for which simulation is to be carried out (ending at 24.00 hrs on 12th January) This parameter indicates the number of times (usually years) the simulation is to be carried out in a multi run period simulation**. The Energyplus default value of 1 was used.

Value 1 12 1 12 1*

6.2.2. Input Parameters for Building Model The data regarding surface properties of the building, especially the office and service core zones, construction types, materials and U-values play an important role in setting up the boundary conditions for the building models. Table 5 details out the type of construction used for the various zone surfaces such as walls, floors, ceilings and glazing. The construction types were custom made to achieve a certain U-value within the range specified in the Part L Building Regulations for U.K. Table 6 specifies the U-values achieved in the model for exterior surfaces of the zones in accordance with the Building Regulations, 2006 for U.K., where U-values for solid opaque walls should be within 0.35 W/m2-K and for triple glazing metal frame windows with 12 mm argon gas filling, it should be within 2.0 W/m2-K. Table 7 specifies the outside boundary conditions that were set for the zone surfaces. This input parameter helps in defining the nature of heat transfer between zones and also with the outside environment. For example, the ceiling and floor surfaces of the office zone was set as ‘adiabatic’ so that there is no heat transfer between the office zone and floors above and below it. Thus, these settings help in controlling the heat transfer pattern for the zones which in result have an impact on the heating energy consumption figures.

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Table 5: Input parameters: Type of construction for building surfaces Name

Exterior wall (periphe ral columns) 300 mm heavyweight concrete -

Exterior Core Wall (external core models) 50 mm wood

Interior wall (central core wall) 200 mm concrete block

Insulation: polyisocyanuratej

Layer 3

-

Insulation: expanded polystyrene - extruded

Insulation expanded polystyre ne extruded 200 mm concrete block

Layer 4

-

-

Layer 5

-

Wall air space resistance 300 mm heavyweigh t concrete

Outsid e layer

Layer 2

-

Exterio r glazing

Exterio r floor (ground floor slab) 50 mm insulatio n board

Interio r floor (12th floor slab) Acoust ic tile

Argon gas 13 mm

200 mm heavyweight concrete

Clear 12 mm

-

Argon gas 13 mm Clear 12 mm

-

Ceiling air space resista nce 100 mm lightweight concret e Carpet

-

-

Grey 12 mm

Exterior roof (terrace on top of building) 200 mm heavyweight concrete Ceiling air space resistance

Interior ceiling (12th floor ceiling) Carpet

Acoustic tile

Ceiling air space resistanc e

-

Acousti c tile

-

-

100 mm lightweight concrete

Table 6: U values of exterior building surfaces Surface Name Service Core Wall Glazing

Description Exterior concrete shear wall of service core in external core models Triple glazing with two layers of 12 mm argon gas filling

U-value with Film (W/m2-K) 0.344 1.547

Table 7: Input parameters: Boundary conditions for zone surfaces Name

Office zone exterior wall

Office zone floor

Office zone roof

Construction Name Zone Name

Exterior wall

Interior wall Office zone

Interior ceiling Office zone

Office zone

Outside Outdoor Adiabatic Boundary Condition Outside Sun and wind Boundary Object exposed

Adiabatic

-

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Service core zone exterior wall Exterior core wall Service core zone Outdoor

Service core zone interior wall Interior wall Service core zone Office zone

Sun and wind Office zone wall exposed surface

6.2.3. Input Parameters for Equipment and People Occupancy Operation Schedules The occupancy schedule for people and operation schedule for lights and office equipments such as computers, printers and fax machines determine the time duration and pattern of internal heat gains in the office and service core zones. Table 8 shows the values that were set to define the minimum and maximum limits of people occupancy and equipment operation schedules. Table 9 describes the hours and level of people occupancy and equipment operation pattern.

Table 8: Input parameters: Minimum and maximum limits for types of operation schedules Field Name

Lower limit value Upper limit value Numeric type

Description Name of schedule limit value. This is unique and used to set operational properties of schedule types such as people occupancy, lights, equipment, thermostat on/off etc. Lowest possible value for the schedule type (real or integer) Highest possible value for the schedule type (real or integer) Either continuous (all numbers within min. and max. are valid) or discrete (only integer numbers between min. and max. are valid)

Object 1 Fraction (unit varies)

Object 2 Temperature (unit varies)

0

-60

1

200

continuous

continuous

Table 9: Input parameters: Operation schedules for lights, office equipments, people occupancy in office zone and heating thermostat Name Schedule type limits Field 1 Field 2 Field 3 Field 4 Field 5 Field 6

Office Lights Schedule Fraction

Office Equipment Schedule Fraction

Office Occupancy Schedule Fraction

Heating Setpoint Schedule Temperature

Until 08:00 0 Until 18:00 0.9 Until 24:00 0

Until 08:00 0 Until 18:00 0.9 Until 24:00 0

Until 08:00 0 Until 18:00 0.95 Until 24:00 0

Until 08:00 0 Until 18:00 21 Until 24:00 0

6.2.4. Input Parameters for Internal Gains The heating energy requirement for a space does not solely depend on the relationship between the outdoor atmospheric conditions and the thermal zone in question, but also on internal conditions such as heat transfer between two or more thermal zones and heat dissipated by people, lights and equipments. The addition of people, lights, pumps, elevators

50

and gas lines within the service core would further complicate the inter zone heat transfer pattern as the amount of heat dissipation from the core to the office zone would be a deciding factor for the overall heating energy load on the heating system. The amount of heat dissipation would vary for the different building configurations owing to the physical location of the service core as well. For example, in case of a central core model, all the heat generated by people, light and other equipments within the service core will be eventually dissipated to the surrounding office area unlike in an external core model where only a part of the heat generated within the core will diffuse into the office space while most of it might be lost to the outside environment.. Thus, the overall space heating load on the heating system in the office space might be lesser for a central core model than for an external core model. The internal gains were set for both the office and service core zones. Table 10 describes the input parameters that were set for people occupancy level in the office and service core zones. Table 11 gives a detailed account of the input parameters that were set for internal gains from recessed lights in office and service core zones whereas table 12 describes the settings for internal gains from office equipments only in the office zone. Table 10: Input parameters: People occupancy settings in office and service core zones Field Name Zone Schedule Name

Calculation Method Number of People Fraction Radiant

Description Unique reference name for object Zone name for which people gain is to be added Name of schedule to be followed for occupancy pattern (same for both zones) Calculation method for setting people gains Number based on 1 person per 10 m2 Characterises the type of heat given out by people in a zone.

Object 1 Office people

Object 2 Service core people

Office zone

Service core zone

Office occupancy schedule

Office occupancy schedule

Number of people

Number of people

60

8

0.5

0.5

51

Table 11: Input parameters: Internal gains due to artificial lighting in office and service core zones (* indicates reference to Bordass & Fordham, 1995; ** indicates reference to ASHRAE, 2009 for values of recessed lighting system) Field Name Zone

Schedule Name

Design Level Calculation Method Watts Per Zone Floor Area Return Air Fraction

Fraction Radiant

Fraction Visible

Description Unique reference name for object Zone name for which lighting gain is to be added Name of schedule to be followed for lighting pattern Calculation method for setting lighting gains Lighting level per floor area of zone Used for sizing calculations if return air fraction coefficients are mentioned Fraction of heat from lights that goes into the zone as long wave radiation Fraction of heat from lights that goes into the zone as short wave radiation

Object 1 Office lights

Object 2 Service core lights

Office zone

Service core zone

Office lighting schedule

Office lighting schedule

Watt/m2

Watt/m2

12*

12*

0**

0**

0.37**

0.37**

0.18**

0.18**

Table 12: Input parameters: Internal gains due to office equipments in office zone (* indicates reference to Bordass & Fordham, 1995; ** indicates Energyplus default values) Field Name Zone Schedule Name Design Level Calculation Method Watts Per Zone Floor Area

Description Unique reference name for object Zone name for which office equipment gain is to be added Name of schedule to be followed for equipment usage pattern Calculation method for setting equipment gains Equipment power consumption per floor area of zone

Fraction Latent Fraction Radiant Fraction Lost

Object Office equipments Office zone Office equipment schedule Watt/m2 15* 0** 0** 0**

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6.2.5. Input Parameters for Air Infiltration Rate Infiltration is the flow of outdoor air into a building through cracks, other unintentional openings and through the normal use of external doors for entrance and egress (ASHRAE, 2009). Introducing infiltration rates makes the design conditions more realistic and can have significant negative impact on the optimisation of heating energy consumption of the thermal zone in question. Heating energy consumption of a zone could be affected by heat loss through minor gaps or cracks in window frames. It could be argued that higher percentage of glazing surface can attribute to higher heat loss due to infiltration as there could be higher possibility of cracks and gaps in glazing framework i.e. between the glass and frames than a solid concrete core wall. Thus, it could be possibly argued that the central core typology might have higher heat loss due to infiltration through cracks and fissures around glazing framework present on all four sides than the external core typology with the double core models being least affected. It would be interesting to observe the changes, if any, in the heating energy consumption of office zone in stage 3 after introducing infiltration rate. Table 13 describes the input parameters that were set for introducing air infiltration rate in the office zone.

6.2.6. Input Parameters for Heating System In order to determine the optimisation in space heating energy of the office space in a tall building, an ideal loads air heating system was introduced only in the office zone. It can be seen from table 14, the heating schedule pattern for the thermostat was set to ‘heating setpoint schedule’ which was defined previously in the operation schedule. Thus, the heating system follows the preset operation schedule by switching on at 8:00 hours and shuts down at 18:00 hours. Also, the HVAC thermostat was given a unique reference name of ‘constant setpoint’. It can be seen from table 15, the heating system was introduced for the office zone only and the previously defined ‘constant setpoint’ thermostat was selected as the heating system.

53

Table 13: Input parameters: Air infiltration rate in office zone (* indicates reference to CIBSE, 1986; ** indicates Energyplus default values) Field Name Zone Schedule Name Design Flow Rate Calculation Method Air Changes Per Hour

Constant Term Co-efficient

Temperature Term Co-efficient

Velocity Term Co-efficient

Velocity Squared Term Coefficient

Description Unique reference name for object Zone name for which infiltration is to be added Name of schedule to be followed for equipment usage pattern Calculation method for setting infiltration rate Standard air change rate for office building as per CIBSE guide Constant under all conditions and not modified by environmental effects This parameter is modified by the temperature difference between outdoor and indoor air dry-bulb temperature This parameter is modified by the speed of wind being experienced outside the building This parameter is modified by the square of speed of wind being experienced outside the building

Object 1 Office zone infiltration Office zone Always On Air changes/hour 1*

1**

0 –C**

0 s/m** 0 s2/m**

Table 14: Input Parameters: Defining HVAC thermostat name and operation schedule Field Name Heating Setpoint Schedule Name

Setting Constant Setpoint Heating setpoint schedule

Table 15: Input parameters: Ideal loads air heating system in office zone Field Zone Name Template Thermostat Name

Setting Office zone Constant setpoint

6.3. Output Variables Selection of output variables is crucial in answering the research hypothesis. There are a wide range of output variables that can be obtained from Energyplus. Output data that explain the thermal conditions of the indoor environment under passive conditions and the heating energy consumption of the office zone were selected and are explained below: 54

a. Transmitted Solar Radiation – This is the sum of direct solar radiation through external glazing and diffuse radiation owing to reflections from floor, wall and ceiling surfaces. It would be interesting to note the variations in the transmitted solar radiation received by the external core models as this could give a fair idea about the possible day lighting and thermal behaviour of the office zones in winter and summer months. b. Solar Gain/Loss Through External Glazing – This output parameter gives an idea about the conduction heat gain or loss from the office zone through external glazing only owing to temperature differences between the zone and outdoor environment. These values have close relevance to the percentage of glazing in the office zone of different core models and also on the relative location of the service core with respect to the office zone. Again, in this case, it should be worthwhile to observe the differences amongst the external core models and with the central core typology. c. Zone Surface Air Convection Rate – This is the sum of heat transferred from the exterior surfaces of the office zone to the zone air through convection. This is largely influenced by temperature differences between the zone air and the surfaces and also the relative location of the service core with respect to the office zone. The set of output data obtained for this parameter shall give a good prediction about the heating energy consumption pattern of each model. d. Zone Heating Energy – This data was recorded in the second and third stages of the simulation study. It is the heating energy supplied by the heating system. In other words, it indicates the heating energy consumed by the office zone. The simulation uses an ideal heating loads air heating system which calculates the heating load in the office zone. This parameter is the most complete criteria in determining the variations in heating energy demand for the seven different models and takes into account all the advanced input parameters such as heating energy requirement that might be offset by internal gains or enhanced by infiltration. The values obtained for all the external core models were compared against the base case central core model.

6.4. Assumptions In the process of carrying out the simulation study, certain assumptions were made which might have an impact on the end result of the study. It is important to specify the assumptions

55

clearly so that any future work based on this study can include them to determine the variation in output.

6.4.1. Adiabatic surfaces The floor and ceiling surfaces of the office zone were considered as adiabatic surfaces i.e. no heat transfer was considered to be taking place between the office zone and the floors above and below it through these surfaces. This particular assumption was made considering that the floors immediately above and below the 12th floor office zone would have similar thermal conditions and thus, any heat transfer between from these floors could be neglected.

6.4.2. Energyplus Default Values As far as possible, while defining the boundary conditions for the simulation, values for input parameters such as air change per hour, lighting level per office floor area and occupancy level were added as per norms and standards referred from CIBSE guide and ASHRAE handbook of fundamentals. However, certain pre loaded Energy Plus default values were set for parameters such as radiant gain and latent gain in case of people occupancy and the air flow rate due to changing wind speed in case of infiltration rate as explained in the tables in input parameters section. These default values could be calculated as per instructions in ASHRAE handbook of fundamentals and Energyplus user manual to relate the simulation to real environmental scenario and achieve more accurate results.

6.4.3. Heat Dissipation from Electro-Mechanical Equipments in Service Core Heat dissipation from machinery such as lifts were neglected as most of the heat is generated in the lift machine room which is usually at the top or basement floor and is not likely to affect the 12th floor office zone under consideration. Any heat generated due to the friction between the lift car and the rails while passing by the 12th floor service core shaft was neglected to simplify the simulation process. Also, the heat given out by service lines such as hot water risers, gas risers and any pumps were not considered as their effect on the overall heating energy requirement of the office zone would be negligible. However, these smaller values could be included in further work to establish more accurate results.

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Chapter 7 - Results and Analysis

This chapter presents the results of the computer thermal simulations and analyses the trend of heating energy consumption of each service core configuration model and discusses further additional work that could have possible effects on the simulation results. The results are discussed in three distinct stages: 1. Passive thermal output variables without any heating system in the office zone. 2. Heating energy consumption by office zone where the zone is considered as an ideal airtight box without any internal gains. 3. Heating energy consumption by office zone with internal gains in both office and service core zones and air infiltration in office zone only.

7.1. Stage 1 – Office Zone Passive Thermal Outputs In this first stage, the office zone was treated as an ideal air tight box and studied for its passive thermal performance. The simulation was run for 12th January without any heating system and the output parameters such as transmitted solar radiation, solar heat gain/loss through glazing and surface air convection rate were recorded to give a fair prediction about the possible heating energy consumption of different service core configuration models.

7.1.1. Transmitted Solar Radiation Transmitted solar radiation is the sum of direct and diffuse solar radiation and could be an useful parameter in determining which configuration will have a better day lighting prospects and also heating energy requirements. Availability of sufficient natural light is related to electricity consumption by artificial lighting equipment which is however beyond the scope of this study. As can be seen from figure 21 and table 16, the central core model has the highest transmitted solar radiation owing to the presence of glazing on all four sides. As far as heating energy requirements are concerned, this could be a problem as there could be severe heat loss from the office zone. Among the single core models, the single core north model has the highest radiation levels as it has glazing on the sunny sides of east, west and especially south. The single core west model shows an interesting trend as the solar radiation

57

level drops down in afternoon owing to the shading effect of the service core on the west side. The double core north-south model has the lowest transmitted solar radiation that can be explained as the presence of service core as a solar buffer on the north and south sides. Transmitted Solar Radiation Through External Glazing 1600

1400

Solar Radiation (W)

1200

1000

800

600

400

200

0 9

10

11

12

13

14

15

16

Time of Day (Hrs) Central Core

Double Core North-South

Double Core East-West

Single Core South

Single Core East

Single Core West

Single Core North

Figure 21: Hourly transmitted Solar Radiation in office zone through external glazing between 9 am and 4 pm for seven permutations of service core location on 12th January in Sheffield Table 16: Hourly transmitted solar radiation in office zone through external glazing between 9 am and 4 pm for seven permutations of service core location on 12th January in Sheffield

Time of Day (Hr)

9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 Total (W)

Transmitted solar radiation in office zone in watts Central Double Double Single Single Single Core (W) Core NorthCore Core Core Core East South (W) EastNorth South (W) West (W) (W) (W) 274.4 195.0 195.9 240.9 175.4 175.0 1449.2 919.6 1095.1 1297.0 918.7 881.4 1393.8 834.4 1080.4 1197.9 952.3 911.8 1340.9 734.6 1076.4 1146.5 933.9 901.4 1163.7 656.0 924.1 980.8 822.4 815.6 857.8 537.6 651.8 707.4 614.7 637.0 339.4 237.5 244.5 264.9 256.1 260.6 36.12 25.7 25.7 27.7 27.71 27.7 6855.7 4140.7 5294.2 5863.5 4701.44 4610.9

58

Single Core West (W) 240.3 1188.9 1046.2 935.8 799.4 600.7 254.7 27.7 5094.15

7.1.2. Heat Gain/Loss through Glazing The heat gain (solar gains) or loss through glazing via conduction is a good estimate of the thermal performance of the office zone in the various service core configurations. It can be predicted that models having lesser solar heat loss are likely to have lesser heating energy requirement and vice versa. It can be seen from figure 22 that almost all models have similar heat gain and loss pattern across the 24 hour cycle. Table 17 shows the hourly as well as total solar heat gain or loss values for all the seven models. It can be seen that the central core model has the highest heat loss while the single core north model has the highest heat gain which could be explained as the presence of service core on the colder north side which prevents heat loss while glazing on the sunny south, east and west sides allow for high solar heat gains through glazing via conduction. It is interesting to observe that all external core models except the double core north-south model have higher solar heat gain. In the double core north-south model, although the service core on the north prevents heat loss, the core on south prevents heat gain through solar radiation and thus experiences heat loss. Heat Gain/Loss Through Glazing 4500 4000 3500 3000

Heat Gain/Loss (W)

2500 2000 1500 1000 500 0 -500 -1000 -1500 -2000 -2500 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

Time of Day (Hrs) Central Core Single Core North Single Core West

Double Core North - South Single Core South

Double Core East -West Single Core East

Figure 22: Solar heat gain/loss through glazing via conduction for office zone in seven permutations of service core location in tall office building on 12th January in Sheffield

59

Table 17: Comparison of solar heat gain/loss values through glazing via conduction for office zone in seven permutations of service core location in tall office building on 12th January in Sheffield

Time of Day (Hr)

Central Core (W)

1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 24:00 Total (W)

-1057 -907 -1046 -1160 -785 -612 -753 -1166 -207 3804 3818 3679 3045 2048 124 -791 -852 -1013 -1233 -1679 -1938 -1844 -1541 -1135 -3201

Solar heat gain/loss through glazing in watts Double Double Single Single Core North Core East Core Core – South –West North South (W) (W) (W) (W) -606 -501 -602 -687 -417 -288 -390 -690 -20 2473 2350 2104 1819 1428 316 -405 -456 -575 -736 -1056 -1251 -1186 -696 -674 -746

-695 -589 -685 -770 -502 -373 -474 -772 -93 2997 3111 3097 2549 1657 225 -511 -557 -673 -832 -1156 -1344 -1279 -1060 -766 505

-727 -609 -717 -807 -515 -380 -491 -816 30 3661 3456 3287 2693 1800 240 -547 -589 -712 -886 -1240 -1444 -1370 -1126 -808 1383

-636 -519 -628 -721 -422 -280 -392 -724 122 2411 2735 2722 2311 1625 332 -434 -484 -615 -791 -1144 -1354 -1280 -1030 -712 92

Single Core East (W)

Single Core West (W)

-609 -493 -604 -695 -402 -268 -380 -707 -105 2293 2625 2649 2329 1737 369 -411 -458 -584 -760 -1113 -1322 -1249 -1007 -688 147

-688 -570 -678 -771 -473 -330 -442 -773 63 3331 2985 2679 2190 1539 291 -475 -526 -658 -835 -1189 -1399 -1327 -1086 -761 97

7.1.3. Surface Air Convection Rate The surface air convection rate is the sum of heat transferred to the office zone air from all the exterior surfaces enclosing the zone through convection. This parameter is a direct indicator of possible heating energy requirement in the office zone for different models as it indicates the heat gain or loss of the office zone air. It can be seen from figure 23 that all seven core configurations have similar heat gain and loss trends and the hourly values are quite close to each other except between 10 am and 4 pm when the difference between the highest and lowest values is in the range of 100 to 250 watts. This graph has similar trend as compared to the graph showing heat loss and gain

60

through glazing except that the single core north model experiences maximum heat gains at around 10 am as compared to the central core model which could be due the solar gains transferred from the glazing surface on the warmer east and south sides. Table 18 shows hourly and total heat gain/loss figures for the seven models where the single core east model has the lowest heat loss from the zone air to the external surfaces closely followed by single core north and south models. Heat Gain/Loss - Zone Surface Air Convection Rate 700.0 600.0 500.0

Heat Gain/Loss (W)

400.0 300.0 200.0 100.0 0.0 -100.0 -200.0 -300.0 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

Time of Day (Hrs) Central Core Single Core North Single Core West

Double Core East - West Single Core South

Double Core North - South Single Core East

Figure 23: Heat gain/loss in office zone air from external facades via convection in seven permutations of service core location in tall office building on 12th January in Sheffield

The double core east-west model has lower overall heat loss than its north-south counterpart which could be possible explained by the fact that in the latter case, the solar gain from the south side, which is available for most of the day, is significantly reduced by the dead service core walls. The single core west has the maximum heat loss among the single side external core models which could be due to the higher heat loss from the office zone air through the west facing service core walls in addition to the glazing all around on other three sides.

61

Table 18: Comparison of heat gain/loss values in office zone air from external facades via convection in seven permutations of service core location in tall office building on 12th January in Sheffield

Time of Day (Hr)

1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 24:00 Total (W)

Heat Gain/Loss in Office Zone air under passive conditions in watts Central Double Double Single Single Single Single Core (W) Core East Core Core Core Core East Core – West North – North South (W) West (W) (W) South (W) (W) (W) 5.0 6.4 10.5 7.7 11.3 12.9 5.7 14.9 9.8 13.3 10.5 14.6 15.2 11.7 -47.2 -36.9 -33.3 -41.1 -36.2 -35.8 -37.9 -42.4 -40.5 -37.2 -45.3 -42.1 -41.3 -38.0 46.7 30.9 34.2 32.7 37.4 36.3 36.5 22.0 19.6 24.0 20.6 27.4 26.0 20.7 -31.2 -24.5 -19.8 -27.7 -21.5 -21.8 -24.3 -100.6 -83.9 -80.1 -92.9 -89.3 -88.1 -84.4 150.3 102.0 100.1 130.2 81.1 81.3 130.9 637.6 567.1 456.1 681.7 462.0 436.8 559.7 237.7 266.3 181.2 251.5 278.1 272.1 156.3 61.7 105.9 38.3 84.5 113.1 117.0 24.9 -30.7 -15.3 4.1 -21.3 8.9 26.0 -23.5 -126.8 -120.9 -39.0 -120.4 -82.1 -61.5 -80.4 -268.5 -240.4 -171.8 -262.3 -211.6 -219.8 -189.6 -212.7 -186.6 -159.3 -204.7 -181.1 -184.3 -164.1 -75.4 -83.9 -72.0 -90.9 -81.2 -81.3 -68.0 -64.5 -62.5 -58.7 -66.9 -64.6 -64.0 -54.3 -71.1 -65.5 -62.4 -71.5 -68.4 -68.3 -60.4 -127.3 -110.0 -106.0 -121.7 -117.6 -117.4 -107.4 -95.5 -89.3 -88.7 -100.2 -98.3 -98.2 -85.6 -28.9 -33.4 -30.9 -38.2 -35.2 -35.0 -28.3 22.5 11.9 16.0 12.7 16.3 16.9 16.8 54.8 42.0 46.3 45.0 50.4 49.8 45.2 -69.8 -31.8 -35.2 -28.2 -28.7 -26.8 -37.8

7.2. Stage 2 – Office Zone Heating Energy Consumption – Without Internal Gains In this case, the office zone was considered as an ideal airtight box without any air infiltration. There were no internal gains in terms of people, lights or office equipments. Heating was supplied to the zone by an Ideal Loads Air Heating System, which was used to determine the heating loads of the office zone. A constant thermostat setpoint temperature of 18° C was adjusted i.e. the heating equipment starts supplying heat when the zone’s operative temperature drops below 18° C so as to maintain a constant temperature throughout its hours of operation. The heating system was assumed to operate for 24 hours and this

62

setting is kept constant for all seven models. The heating energy consumption pattern for the office zone was recorded between 8 am and 6 pm on 12th January. Office Zone Heating Energy (Without Internal Gains) 53.0

48.0

Heating Energy (KWh)

43.0

38.0

33.0

28.0

23.0

18.0

13.0

8.0 7

8

9

10

11

12

13

14

15

16

17

18

19

20

Time of Day (Hrs) Central Core Single Core North Single Core West

Double Core North - South Single Core South

Double Core East - West Single Core East

Figure 24: Results of thermal simulation showing hourly heating energy consumption (KWh) pattern for an ideal air tight office zone without internal gains on the 12th floor of a 22 storey office building on 12th January for seven permutations of service core location in Sheffield.

From figure 24, it can be seen that all the seven models have very similar heating energy consumption pattern. Most of the major differences in heating energy requirements could be observed between 9 am and 3 pm. This is due to the differences in passive solar gains which differ for all models owing to the cardinal location of the service core with respect to the office zone. The sharp rise in the heating requirement between 8 am and 9 am could be explained as higher load on the heating system as the office zone air is cold owing to no heating overnight. All the single core models have negligible differences in their heating energy consumption except for the North core model which has a considerably lower consumption between 10 am and 6 pm as the heavy mass of the service core on the north acts as a buffer from cold and prevents excessive heat loss to the north. The single core west model has the lowest heating requirement between 8 am and 9 am which could be explained as the effect of higher solar heat gain from the morning sun falling on the east façade glazing.

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Also, the west side core buffers the office zone from the cold westerly winds of Sheffield and thus, outperforms the single side north core model in this aspect. Among the double core models, the double core east-west model has significantly lower heating consumption as compared to north-south model between 10 am and 2 pm. A possible explanation could be that the service core on south side of the north-south model actually blocks a large part of solar radiation from the south and thus has lower solar gains resulting in higher space heating energy requirements.

Table 19: Results of thermal simulation showing hourly and total heating energy consumption (KWh) figures for an ideal air tight office zone without internal gains on the 12th floor of a 22 storey office building on 12th January for seven permutations of service core location in Sheffield. Heating energy consumption of office zone without internal gains and air infiltration in KWh Time of Day (Hr)

9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 Total (KWh)

Central Core (KWh)

Single Core East (KWh)

Single Core South (KWh)

Single Core North (KWh)

Single Core West (KWh)

Double Core NorthSouth (KWh)

Double Core EastWest (KWh)

50.0 29.6 28.0 26.8 26.0 25.5 25.7 25.6 25.0 24.5 287.1

45.0 26.4 24.6 23.4 22.4 21.8 21.6 21.4 20.8 20.2 247.6

44.9 26.3 24.5 23.3 22.4 21.8 21.6 21.4 20.8 20.2 247.1

44.7 25.4 23.9 22.7 21.9 21.4 21.4 21.2 20.6 20.1 243.2

31.4 26.0 24.7 23.6 22.8 22.1 21.9 21.6 21.0 20.5 235.6

41.2 24.2 22.8 21.8 21.0 20.4 20.2 19.9 19.4 18.9 229.9

41.0 23.7 22.2 21.1 20.3 19.9 19.9 19.7 19.2 18.7 225.9

From table 19 it can be seen that the base case central core model has the highest heating energy consumption of about 287 KWh and the double core east-west model has the lowest consumption of about 225 KWh over a period of 10 hours between 8 am and 6 pm on the simulation day i.e. 12th January. The difference between the two double core models is in the range of 4 KWh while that between the highest and lowest energy consuming single core models is in the range of 12 KWh. Table 20 shows the heating energy ranking of the different service core configuration models based on their percentage reduction in the heating energy consumption as compared to the base case central core model.

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Table 20: Energy ranking of seven different service core configuration models based on percentage reduction in heating energy consumption of office zone on 12th January as compared to central core model Ranking Service Core Configuration Model

1 2 3 4 5 6 7

Heating Energy Consumption on 12th January (KWh)

Double Core East-West Double Core North-South Single Core West Single Core North Single Core South Single Core East Central Core (Base Case)

225.9 229.9 235.6 243.2 247.1 247.6 287.1

Percentage Reduction in Heating Energy Consumption from Central Core Model (%) 21.31 19.92 17.90 15.29 13.93 13.75 -

The results of stage 2 were almost in line with the author’s expectations, except for the single core west performing better than the single side north core which is due to better wind buffering on the windy west side in the former case. It would be interesting to note the changes in the ranking of these service core configuration models when the office zone is simulated after introducing air infiltration rate and internal gains in the third stage of the study.

7.3. Stage 3 – Office Zone Heating Energy Consumption with Internal Gains In this case, people, lights and office equipments were added for contributing towards internal gains and an air infiltration rate of one air change per hour (CIBSE, 1986) was introduced to mimic near real life situation. The heating thermostat was scheduled to operate between 8 am and 6 pm and was kept the same for all seven models. People occupancy, lights and office equipment schedules were also set to operate from 8 am to 6 pm and these input parameters were maintained constant for all seven models. The simulation was carried out for 12th of January and the hourly and total heating energy consumption by the office zone were recorded for all seven models. It is interesting to note the changes in the heating energy ranking of the seven models on introducing air infiltration rates and internal gains. Figure 25 and table 21 show hourly heating energy consumption by the office zone. From figure 25 it can be seen that almost all the models have a similar heating energy consumption trend. One of the key points to be noted is the closeness in the heating energy

65

consumption figures between the external double and single core models as compared to results from stage two where there was a significant difference in the consumption figures. Office Zone Heating Energy (With Internal Gains) 80.0

Heating Energy (KWh)

70.0

60.0

50.0

40.0

30.0

20.0 7

8

9

10

11

12

13

14

15

16

17

18

19

20

Time of Day (Hrs) Central Core Single Core North Single Core West

Double Core North - South Single Core South

Double Core East - West Single Core East

Figure 25: Results of thermal simulation showing hourly heating energy consumption (KWh) pattern including internal gains and infiltration rate for the 12th floor office zone of a 22 storey office building on 12th January for seven permutations of service core location in Sheffield.

The heating energy consumption value rises to a maximum between 8 am and 9 am and is similar for all models. This rise could be possibly explained by the fact that the heating equipment starts operating at 8 am and experiences a maximum load at this hour as it has to heat the indoor volume air in the office zone which is cold due to constant heat loss with the outdoor environment as observed from figure 25. The values drop down drastically between 9 am and 10 am as the office zone air gets heated up by both the heating equipment and internal gains from people, lights and office equipments. This value then gradually keeps dropping throughout the day until the system is switched off at 6 pm after which the office zone rapidly loses all the heat and drops to zero at around 7 pm.

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From table 21 it can be seen that the central core model has the highest heating energy consumption at 404.4 KWh in total and the double core east-west model has the least heating energy consumption at 345.5 KWh which is in line with the author’s expectations. The heating energy consumption of the double and single core models are quite similar with the maximum difference of about 15 KWh between the double core east-west and single core east and south models.

Table 21: Results of thermal simulation showing hourly and total heating energy consumption (KWh) figures including internal gains and infiltration rate for the 12th floor of a 22 storey office building on 12th January for seven permutations of service core location in Sheffield. Heating energy consumption of office zone with internal gains and air infiltration in KWh Time of Day (Hr)

9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 Total (KWh)

Central Core (KWh)

72.7 44.2 40.5 38.0 36.6 35.5 35.3 34.7 33.5 32.9 404.4

Double Core North South (KWh) 67.7 38.8 35.4 33.0 31.4 30.0 29.4 28.6 27.4 26.8 348.9

Double Core East - West (KWh)

Single Core North (KWh)

67.6 38.5 34.8 32.2 30.8 29.6 29.2 28.4 27.3 26.6 345.5

69.7 39.3 35.7 33.1 31.6 30.4 30.1 29.3 28.1 27.4 355.3

Single Single Core Core East South (KWh) (KWh) 69.9 40.2 36.3 33.7 32.1 30.8 30.3 29.5 28.2 27.5 359.1

70.0 40.3 36.4 33.8 32.2 30.8 30.3 29.5 28.3 27.6 359.5

Single Core West (KWh) 66.8 38.9 35.3 32.9 31.3 30.0 29.4 28.5 27.3 26.6 347.3

The difference between the two double core models is significantly less, at about just 3 KWh with the east-west core having lesser consumption. In the single core category, the west core model scores better than its counterparts with least heating energy consumption. One of the interesting points is that the difference between single core east and single core south models is negligible. Thus, it could be said that under the specified boundary conditions of the simulation, the double side east-west core model consumes about 14.5% less heating energy than the central core model. Table 22 gives a rank order of the seven service core configurations with the least heating energy consumer having the best rating and vice versa.

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It is interesting to note that the single core west outperforms the double core northsouth and single core north model in total heating energy consumption. This outcome could be related to the air infiltration parameter. A possible explanation to this could be that the predominant wind direction in Sheffield is west (Weather Tool, 2010) due to which a wind buffer in the form of service core on the west side blocks most of the westerly winds from leaking through the window gaps which in turn reduces the air exchange between the office zone and the outdoor environment and thus helping to retain the heat.

Table 22: Energy ranking of seven different service core configuration models based on percentage reduction in heating energy consumption of office zone on 12th January as compared to central core model Ranking Service Core Configuration Model

1 2 3 4 5 6 7

Double Core East-West Single Core West Double Core North-South Single Core North Single Core South Single Core East Central Core (Base Case)

Heating Energy Consumption on 12th January (KWh) 345.538 347.336 348.997 355.306 359.121 359.532 404.401

Percentage Reduction in Heating Energy Consumption from Central Core Model (%) 14.55 14.11 13.70 12.14 11.19 11.09 -

Note: The Arts Tower has an annual heating energy consumption of 160 KWh/m2 (Magri, 2006). The floor plate area of Arts Tower i.e. NRA which excludes the service core area is 585 m2. Thus, the total annual heating energy consumption would be about 93600 KWh. Considering that heating would be switched on from September to March i.e. seven months, the daily heating energy consumption could be calculated as 445 KWh. This is however an estimate where it is considered that the heating energy consumption pattern will be constant throughout the seven months. In reality however, the heating energy consumption during peak winter months, especially December and January is going to be much higher than other months. The simulated central core model which mimics the physical form and parameters of Arts Tower has a heating energy consumption of about 404 KWh on the coldest day in Sheffield which is near to the estimated figure of 445 KWh. The decrease in the value could be a result of the change in specification and U-values of glazing and opaque exterior building surfaces.

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Chapter 8 - Conclusion

8.1. Conclusion This research investigated the optimisation of heating energy consumption of tall office buildings in the temperate climatic conditions of Sheffield by altering the service core location and studying the differences in the results. Yeang suggested that service core location in a tall building affects cooling loads in tropical climates and thus this project investigated the impact on heating energy consumption in a temperate climate. It was proposed that placing the service core on the colder sides of a tall building in a temperate climate would reduce the heating energy consumption. This was investigated by carrying out thermal simulation using Energyplus computer program. A single storey of a multi-storey building was modelled using seven different service core locations including a central core and six external cores on different orientations. The thermal simulation was carried out in three stages. It was proposed that the service core location in a tall building would have an effect on the space heating energy of the office area in the context of Sheffield’s temperate climate. From the results of stage 1, by combining the values for heat loss/gain for the office zone via conduction and convection under passive conditions, it was found out that the single core north model had the lowest heat loss followed by the double core east-west model. Similarly from the results of stage 2 and 3 of the simulation, it was found that placing the service core on the exterior of a tall building and at different cardinal orientations affects the space heating energy consumption pattern of the office zone in the tall building. It was proposed that the external service core configuration can help in optimising the heating energy requirement of an office space when compared to the standard base case central core ‘glazed box’ typology. From the results of stage 2 and 3, it was found out that all the exterior service core configurations had lower heating energy consumption when compared to the central core configuration. Thus, it could be said that the exterior core configuration can help in optimising heating energy consumption of the office space in a tall building in temperate climate. It was proposed that adding internal gains and infiltration rate in addition to heating equipment might bring about a change in the rank order of the seven models at the three different stages. On comparing the results of stage 2 and 3, it was found out that although the double side east-west exterior core model had the lowest heating energy consumption in both

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stages, the single side west core outperformed the double core north-south in the third stage in terms of lower heating energy consumption. However, in both cases the single side north core remained at the fourth position. Also, in the third stage, the percentage reduction in heating energy consumption of the first four external core models when compared to the base case central typology, dropped by 5 to 6 % with respect to the results of stage 2. On an overall basis, it could be concluded that changing the service core location in a tall building could help in optimising heating energy consumption in a temperate climate. This research gave an insight into the importance of design decisions pertaining to the location of service cores in tall building design programs and their role in contributing to operational energy optimisation. The research, although, was not exhaustive, but gave a platform for future extension and additional work in the field to be built upon.

8.2. Scope for Further Research As previously discussed in the simulation strategy and assumptions section, this study considers certain assumptions to carry out the computer simulations. Also, due to constraints in terms of time and resources, the research is limited and has a scope for expansion. The following section elaborates the scope of further work that could be possibly done as an extension of this study.

8.2.1 Simulation Study for Extended Winter Periods The primary motive of this research is to evaluate the effect of different core locations on the thermal conditions of the interior office volume in the cold climate of Sheffield. Thus, in this study, the thermal simulations are carried out only for the coldest day in Sheffield, 12th January (Weather Tool, 2010). This leaves a scope for investigating any change or variations in heating patterns during the entire winter period. For example, running simulations for September to March period might give a more in depth and complete picture. However, the author believes that this may not make a significant change in the heating energy consumption pattern and as such the output from such a simulation might show similar trends in heating patterns.

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8.2.2. Simulations for Summer Period The study could be extended to check the thermal conditions of these building typologies during summer months and record any overheating periods. Extending the study over a complete annual cycle shall give a clear picture about the total number of heating design days for the different models and also any possible cooling design days during summer. As discussed earlier, currently, the Arts Tower does experience problems of overheating during summer months. It would be interesting to note what effects do these different service core locations have on the thermal conditions of the office space. However, it could be predicted that the central core ‘glazed box’ typology could be subject to higher solar radiation and likely to have higher heat gains during the day as compared to external core models. The conclusions drawn from studies on tropical tall buildings can be applied to this situation where the double core east-west model is likely to have lower solar radiation and heat gain due to solid thermal buffers in the form of service cores on the east and west sides blocking early morning and late afternoon sun. However, a comprehensive study on the same could be done so as to determine the actual effects of such core placement alterations on the indoor thermal conditions.

8.2.3. Total Energy Consumption This study takes into consideration the heating energy consumed by office zone in different tall building prototypes with varying core locations. It would be inappropriate to draw any concrete conclusions regarding the best suited service core location for tall buildings in U.K. solely based on the heating energy consumption. Thus, it would be appropriate to evaluate the total energy consumption by including an assessment of energy consumed by lighting equipments in addition to space heating equipment. A possible approach to this analysis could be to first assess the day lighting levels in the different building models by carrying out a lighting analysis to determine daylight factors and lux levels. This could give an insight into the possible level of artificial lighting requirements in the different models and thus leading to a more realistic analysis of the lighting energy consumption. It could be predicted that the central core typology, with exterior glazing surface to core wall distance of 6m and 8m on the south and north side respectively stands a better chance of having higher day light levels and thus, requiring less amount of artificial lighting arrangement. However, the

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benefits gained out of saving lighting requirements for the office area might be cancelled out by the fact that the centrally located service core areas would require constant use of artificial lighting. As explained in the modelling process, if the office floors in double core prototypes are designed with a span of 15m, this would allow for sufficient natural light penetration up to ideally 7.5m from opposite sides. Also, unlike the central core typology, in double core prototypes, the external location of the service core allows for use of natural light in staircases and lifts lobbies and thus reduces the requirement for artificial lighting. However, as far as day lighting in office area is concerned, the single core prototypes, especially the south side core might have certain disadvantage of blocking sunlight for most of the day but still with the advantages of lesser artificial lighting requirement in the external service core areas. Thus, it would be interesting to observe and compare the differences in the lighting and subsequently the overall energy consumption of these prototypes.

8.2.4. Use of Different Heating System In this study an ideal loads air heating system was used which actually is like an HVAC system and only determines the heating or cooling loads in the zone under simulation. It is like a dummy system which is physically non existent in the model but gives the same effect of using an air heating system. This kind of setting is used in Energyplus where the energy consumed by the system is not a concern and the sole purpose is to obtain heating loads for the zone in question. The study could be extended by setting up a different heating system such as a boiler which is a common practice in the U.K.

8.2.5. Infiltration Rate Sensitive to Change in Wind Speed This study assumed a constant volume flow of air infiltration under all conditions i.e. the volume of air flowing in and out of the zone is not affected by the wind speed which in reality varies with the climatic conditions. The three functions of environmental factors such as temperature term, velocity term and velocity squared term co-efficient could be modified to introduce the effect of varying wind speed on the heating energy consumption pattern of the office zone and this is likely to vary between different models. However, the amount of difference this setting might make is uncertain, unless tested, and should be included in further research on this topic. It would be interesting to observe the differences among the

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single core and double core models as the wind direction could play an important role in deciding the overall effect on the heating energy consumption pattern. For example, in case of Sheffield, where wind predominantly blows from the northwest and southwest region, the single core west and double core east-west models stand a better chance of being least affected losses due to infiltration as compared to singe core east and double core north-south models.

8.2.6. Naturally Ventilated Service Cores This study has considered the effect of external service core location on various sides of the tall building as a thermal and wind buffer. One of the ideas of having an external core is to naturally ventilate certain areas of the core such as the staircases, lift lobbies and toilets. Although the study considers the heat transfer between the service core and office zone, introducing natural ventilation or air flow parameter in the service core zone might affect the heating energy consumption pattern in the adjoining office zone owing to some heat loss from the office zone.

8.2.7. Introducing Lifts in Service Cores Active or moving equipments in the service core such as lifts, pumps, hot water/gas risers can contribute to the internal heat gains of the office zone. As discussed earlier in the assumptions section in chapter 6, majority of the heat is generated at the lift machine room which is usually at the top most of basement floor and thus, is not likely to affect the heating pattern of the office zone midway through the height of the building. However, some heat might be dissipated from the lift shafts due to the friction between the lift car and rails which could have an effect on the overall internal heat gain figure. Adding lifts in the service core zone as electrical equipments and considering that a fraction of it would be converted into heat could contribute to the internal heat gains not only in the core but also bring about some variation in the heating pattern of the office zone due to heat dissipation from the core to the office zone. This parameter, however small it might seem to be, could be considered in further scope of work to establish more accurate simulation results.

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8.2.8. Analysis of Embodied Energy Consumption As discussed in chapter 2, an argument could be made that the operational energy savings generated out of an unconventional service core design over the lifespan of the tall building could be minimised by the factor of additional embodied energy spent in construction of an exterior core which requires additional structural bracing and materials. However, it is unclear as to how serious is the consequence of embodied energy in an exterior core tall building when compared to a central core typology and does the embodied energy factor negate the operational energy benefits of an exterior core tall building. The point to be scrutinised is that whether the additional embodied energy in exterior core models going to be higher than the operational energy savings over the lifespan of the tall building. This certainly is a novel and interesting extension to this field of study demanding extensive research.

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