THE ROLE OF SERVICE CORES IN OPTIMISING HEATING ENERGY IN TALL

OFFICE BUILDINGS IN TEMPERATE CLIMATE

ABHISHEK CHAKRABORTY

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1M. Arch. Sustainable Architectural Studies, Reg. No. 090138292, University of Sheffield, 2009-10

Guided by: Dr. Steve Fotios

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“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).

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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.

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

(a) (b)

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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.

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

(a) (b)

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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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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.

Figure 7: Poly International Plaza in Guangzhou,

China (2007) features an external service core (Image

Source: SOM website)

(a)

(b)

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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)

(a) (b)

(c)

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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).

25

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).

(a) (b)

26

(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)

(a)

27

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

(a)

(b)

28

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

29

(b)

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).

Figure 13: (a) Psychrometric Chart – San Francisco (b) Temperature Range – San Francisco (Image

source: Climate Consultant Software; Image Data: Energy Plus Weather Data Website)

(a)

30

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)

Difference from Glazed Box

per year

One Bush adiabatic 3.4 -1 GW

Actual One Bush building 4.1 -0.3 GW

Equivalent ‘glazed box’ of same

floor area

4.4 -

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

31

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.

32

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

33

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)

34

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)

35

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

36

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.

37

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

38

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

39

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.

40

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 m

2. 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.

41

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.

42

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)

Office Zone (Thermal Zone)

Service Core Zone

(a) (b)

(c) (d)

(e) (f)

(g)

N

43

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.

44

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

45

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.

46

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

47

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 Description Value

North Axis 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.

0 degrees.

Terrain The surrounding built environment was set to mimic city

terrain for a more realistic simulation environment.

City.

Loads convergence

tolerance value

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.

0.04*

Temperature

convergence

tolerance 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.

0.4*

Solar Distribution 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**.

Full Interior

and Exterior

Maximum number

of warm-up days

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.

25*

Table 3: Input parameters: Location of the building models

Latitude 53.5° N

Longitude 1° W

Elevation 11 m from sea level

Time zone GMT 0.00 hrs

48

Table 4: Input parameters: Simulation run period (* indicates Energyplus default values; ** indicates

reference to definition from USDOE, 2010)

Field Description Value

Begin Month Starting month for simulation (in this case it is January) 1

Begin Day of Month Starting day of the month for which simulation is to be carried

out (starting at 00.00 hrs on 12th January)

12

End Month End month for simulation (January) 1

End Day of Month End day of the month for which simulation is to be carried out

(ending at 24.00 hrs on 12th January)

12

No. of times run

period to be repeated

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.

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.

49

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

Name Exterior

wall

(periphe

ral

columns)

Exterior

Core Wall

(external

core

models)

Interior

wall

(central

core

wall)

Exterio

r

glazing

Exterio

r floor

(ground

floor

slab)

Interio

r floor

(12th

floor

slab)

Exterior

roof

(terrace

on top of

building)

Interior

ceiling

(12th

floor

ceiling)

Outsid

e layer

300 mm

heavy-

weight

concrete

50 mm

wood

200 mm

concrete

block

Grey

12 mm

50 mm

insulatio

n board

Acoust

ic tile

200 mm

heavy-

weight

concrete

Carpet

Layer

2

- Insulation:

polyiso-

cyanuratej

Insulation

expanded

polystyre

ne -

extruded

Argon

gas 13

mm

200 mm

heavy-

weight

concrete

Ceiling

air

space

resista

nce

Ceiling

air space

resistance

100 mm

light-

weight

concrete

Layer

3

- Insulation:

expanded

polystyrene

- extruded

200 mm

concrete

block

Clear

12 mm

- 100

mm

light-

weight

concret

e

Acoustic

tile

Ceiling

air

space

resistanc

e

Layer

4

- Wall air

space

resistance

- Argon

gas 13

mm

- Carpet - Acousti

c tile

Layer

5

- 300 mm

heavyweigh

t concrete

- Clear

12 mm

- - - -

Table 6: U values of exterior building surfaces

Surface Name Description U-value with Film (W/m2-K)

Service Core Wall Exterior concrete shear wall of service

core in external core models

0.344

Glazing Triple glazing with two layers of 12 mm

argon gas filling

1.547

Table 7: Input parameters: Boundary conditions for zone surfaces

Name Office zone

exterior wall

Office

zone floor

Office

zone roof

Service core

zone

exterior wall

Service core zone

interior wall

Construction

Name

Exterior wall Interior

wall

Interior

ceiling

Exterior core

wall

Interior wall

Zone Name Office zone Office zone Office zone Service core

zone

Service core zone

Outside

Boundary

Condition

Outdoor Adiabatic Adiabatic Outdoor Office zone

Outside

Boundary Object

Sun and wind

exposed

- - Sun and wind

exposed

Office zone wall

surface

50

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 Description Object 1 Object 2

Name 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.

Fraction

(unit varies)

Temperature

(unit varies)

Lower limit value Lowest possible value for the schedule type

(real or integer)

0 -60

Upper limit value Highest possible value for the schedule type

(real or integer)

1 200

Numeric type Either continuous (all numbers within min.

and max. are valid) or discrete (only integer

numbers between min. and max. are valid)

continuous continuous

Table 9: Input parameters: Operation schedules for lights, office equipments, people occupancy in

office zone and heating thermostat

Name Office Lights

Schedule

Office Equipment

Schedule

Office Occupancy

Schedule

Heating Setpoint

Schedule

Schedule type

limits

Fraction Fraction Fraction Temperature

Field 1 Until 08:00 Until 08:00 Until 08:00 Until 08:00

Field 2 0 0 0 0

Field 3 Until 18:00 Until 18:00 Until 18:00 Until 18:00

Field 4 0.9 0.9 0.95 21

Field 5 Until 24:00 Until 24:00 Until 24:00 Until 24:00

Field 6 0 0 0 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

51

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 Description Object 1 Object 2

Name Unique reference name

for object

Office people Service core people

Zone Zone name for which

people gain is to be added

Office zone Service core zone

Schedule Name Name of schedule to be

followed for occupancy

pattern (same for both

zones)

Office occupancy

schedule

Office occupancy

schedule

Calculation Method Calculation method for

setting people gains

Number of people Number of people

Number of People Number based on 1

person per 10 m2

60 8

Fraction Radiant Characterises the type of

heat given out by people

in a zone.

0.5 0.5

52

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 Description Object 1 Object 2

Name Unique reference name

for object

Office lights Service core lights

Zone Zone name for which

lighting gain is to be

added

Office zone Service core zone

Schedule Name Name of schedule to be

followed for lighting

pattern

Office lighting schedule Office lighting

schedule

Design Level

Calculation Method

Calculation method for

setting lighting gains

Watt/m2 Watt/m

2

Watts Per Zone

Floor Area

Lighting level per floor

area of zone

12* 12*

Return Air Fraction Used for sizing

calculations if return air

fraction coefficients are

mentioned

0** 0**

Fraction Radiant Fraction of heat from

lights that goes into the

zone as long wave

radiation

0.37** 0.37**

Fraction Visible Fraction of heat from

lights that goes into the

zone as short wave

radiation

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 Description Object

Name Unique reference name for object Office equipments

Zone Zone name for which office equipment

gain is to be added

Office zone

Schedule Name Name of schedule to be followed for

equipment usage pattern

Office equipment schedule

Design Level Calculation

Method

Calculation method for setting equipment

gains

Watt/m2

Watts Per Zone Floor Area Equipment power consumption per floor

area of zone

15*

Fraction Latent 0**

Fraction Radiant 0**

Fraction Lost 0**

53

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 set-

point 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.

54

Table 13: Input parameters: Air infiltration rate in office zone (* indicates reference to CIBSE, 1986;

** indicates Energyplus default values)

Field Description Object 1

Name Unique reference name for

object

Office zone infiltration

Zone Zone name for which infiltration

is to be added

Office zone

Schedule Name Name of schedule to be followed

for equipment usage pattern

Always On

Design Flow Rate Calculation

Method

Calculation method for setting

infiltration rate

Air changes/hour

Air Changes Per Hour Standard air change rate for

office building as per CIBSE

guide

1*

Constant Term Co-efficient Constant under all conditions

and not modified by

environmental effects

1**

Temperature Term Co-efficient This parameter is modified by

the temperature difference

between outdoor and indoor air

dry-bulb temperature

0 –C**

Velocity Term Co-efficient This parameter is modified by

the speed of wind being

experienced outside the building

0 s/m**

Velocity Squared Term Co-

efficient

This parameter is modified by

the square of speed of wind

being experienced outside the

building

0 s2/m**

Table 14: Input Parameters: Defining HVAC thermostat name and operation schedule

Field Setting

Name Constant Setpoint

Heating Setpoint Schedule Name Heating setpoint schedule

Table 15: Input parameters: Ideal loads air heating system in office zone

Field Setting

Zone Name Office zone

Template Thermostat Name 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:

55

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

56

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.

57

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

58

Transmitted Solar Radiation Through External Glazing

0

200

400

600

800

1000

1200

1400

1600

9 10 11 12 13 14 15 16

Time of Day (Hrs)

So

lar

Ra

dia

tio

n (

W)

Central Core Double Core North-South Double Core East-West Single Core North

Single Core South Single Core East Single Core West

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.

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

Transmitted solar radiation in office zone in watts

Time of

Day (Hr)

Central

Core (W)

Double

Core North-

South (W)

Double

Core

East-

West (W)

Single

Core

North

(W)

Single

Core

South

(W)

Single

Core East

(W)

Single

Core

West (W)

9:00 274.4 195.0 195.9 240.9 175.4 175.0 240.3

10:00 1449.2 919.6 1095.1 1297.0 918.7 881.4 1188.9

11:00 1393.8 834.4 1080.4 1197.9 952.3 911.8 1046.2

12:00 1340.9 734.6 1076.4 1146.5 933.9 901.4 935.8

13:00 1163.7 656.0 924.1 980.8 822.4 815.6 799.4

14:00 857.8 537.6 651.8 707.4 614.7 637.0 600.7

15:00 339.4 237.5 244.5 264.9 256.1 260.6 254.7

16:00 36.12 25.7 25.7 27.7 27.71 27.7 27.7

Total (W) 6855.7 4140.7 5294.2 5863.5 4701.44 4610.9 5094.15

59

Heat Gain/Loss Through Glazing

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

3000

3500

4000

4500

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)

Heat

Gain

/Lo

ss (

W)

Central Core Double Core North - South Double Core East -West

Single Core North Single Core South Single Core East

Single Core West

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.

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

60

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

Solar heat gain/loss through glazing in watts

Time of

Day (Hr)

Central

Core (W)

Double

Core North

– South

(W)

Double

Core East

–West

(W)

Single

Core

North

(W)

Single

Core

South

(W)

Single

Core East

(W)

Single

Core

West (W)

1:00 -1057 -606 -695 -727 -636 -609 -688

2:00 -907 -501 -589 -609 -519 -493 -570

3:00 -1046 -602 -685 -717 -628 -604 -678

4:00 -1160 -687 -770 -807 -721 -695 -771

5:00 -785 -417 -502 -515 -422 -402 -473

6:00 -612 -288 -373 -380 -280 -268 -330

7:00 -753 -390 -474 -491 -392 -380 -442

8:00 -1166 -690 -772 -816 -724 -707 -773

9:00 -207 -20 -93 30 122 -105 63

10:00 3804 2473 2997 3661 2411 2293 3331

11:00 3818 2350 3111 3456 2735 2625 2985

12:00 3679 2104 3097 3287 2722 2649 2679

13:00 3045 1819 2549 2693 2311 2329 2190

14:00 2048 1428 1657 1800 1625 1737 1539

15:00 124 316 225 240 332 369 291

16:00 -791 -405 -511 -547 -434 -411 -475

17:00 -852 -456 -557 -589 -484 -458 -526

18:00 -1013 -575 -673 -712 -615 -584 -658

19:00 -1233 -736 -832 -886 -791 -760 -835

20:00 -1679 -1056 -1156 -1240 -1144 -1113 -1189

21:00 -1938 -1251 -1344 -1444 -1354 -1322 -1399

22:00 -1844 -1186 -1279 -1370 -1280 -1249 -1327

23:00 -1541 -696 -1060 -1126 -1030 -1007 -1086

24:00 -1135 -674 -766 -808 -712 -688 -761

Total (W) -3201 -746 505 1383 92 147 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

61

Heat Gain/Loss - Zone Surface Air Convection Rate

-300.0

-200.0

-100.0

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

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)

Heat

Gain

/Lo

ss (

W)

Central Core Double Core East - West Double Core North - South

Single Core North Single Core South Single Core East

Single Core West

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.

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.

62

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

Heat Gain/Loss in Office Zone air under passive conditions in watts

Time of

Day (Hr)

Central

Core (W)

Double

Core East

– West

(W)

Double

Core

North –

South

(W)

Single

Core

North

(W)

Single

Core

South

(W)

Single

Core East

(W)

Single

Core

West (W)

1:00 5.0 6.4 10.5 7.7 11.3 12.9 5.7

2:00 14.9 9.8 13.3 10.5 14.6 15.2 11.7

3:00 -47.2 -36.9 -33.3 -41.1 -36.2 -35.8 -37.9

4:00 -42.4 -40.5 -37.2 -45.3 -42.1 -41.3 -38.0

5:00 46.7 30.9 34.2 32.7 37.4 36.3 36.5

6:00 22.0 19.6 24.0 20.6 27.4 26.0 20.7

7:00 -31.2 -24.5 -19.8 -27.7 -21.5 -21.8 -24.3

8:00 -100.6 -83.9 -80.1 -92.9 -89.3 -88.1 -84.4

9:00 150.3 102.0 100.1 130.2 81.1 81.3 130.9

10:00 637.6 567.1 456.1 681.7 462.0 436.8 559.7

11:00 237.7 266.3 181.2 251.5 278.1 272.1 156.3

12:00 61.7 105.9 38.3 84.5 113.1 117.0 24.9

13:00 -30.7 -15.3 4.1 -21.3 8.9 26.0 -23.5

14:00 -126.8 -120.9 -39.0 -120.4 -82.1 -61.5 -80.4

15:00 -268.5 -240.4 -171.8 -262.3 -211.6 -219.8 -189.6

16:00 -212.7 -186.6 -159.3 -204.7 -181.1 -184.3 -164.1

17:00 -75.4 -83.9 -72.0 -90.9 -81.2 -81.3 -68.0

18:00 -64.5 -62.5 -58.7 -66.9 -64.6 -64.0 -54.3

19:00 -71.1 -65.5 -62.4 -71.5 -68.4 -68.3 -60.4

20:00 -127.3 -110.0 -106.0 -121.7 -117.6 -117.4 -107.4

21:00 -95.5 -89.3 -88.7 -100.2 -98.3 -98.2 -85.6

22:00 -28.9 -33.4 -30.9 -38.2 -35.2 -35.0 -28.3

23:00 22.5 11.9 16.0 12.7 16.3 16.9 16.8

24:00 54.8 42.0 46.3 45.0 50.4 49.8 45.2

Total (W) -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

63

Office Zone Heating Energy (Without Internal Gains)

8.0

13.0

18.0

23.0

28.0

33.0

38.0

43.0

48.0

53.0

7 8 9 10 11 12 13 14 15 16 17 18 19 20

Time of Day (Hrs)

Heati

ng

En

erg

y (

KW

h)

Central Core Double Core North - South Double Core East - West

Single Core North Single Core South Single Core East

Single Core West

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.

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.

64

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)

Central Core

(KWh)

Single Core East

(KWh)

Single Core

South (KWh)

Single Core

North (KWh)

Single Core West

(KWh)

Double Core

North-South (KWh)

Double Core East-West

(KWh)

9:00 50.0 45.0 44.9 44.7 31.4 41.2 41.0

10:00 29.6 26.4 26.3 25.4 26.0 24.2 23.7

11:00 28.0 24.6 24.5 23.9 24.7 22.8 22.2

12:00 26.8 23.4 23.3 22.7 23.6 21.8 21.1

13:00 26.0 22.4 22.4 21.9 22.8 21.0 20.3

14:00 25.5 21.8 21.8 21.4 22.1 20.4 19.9

15:00 25.7 21.6 21.6 21.4 21.9 20.2 19.9

16:00 25.6 21.4 21.4 21.2 21.6 19.9 19.7

17:00 25.0 20.8 20.8 20.6 21.0 19.4 19.2

18:00 24.5 20.2 20.2 20.1 20.5 18.9 18.7

Total (KWh)

287.1

247.6

247.1

243.2

235.6

229.9

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.

65

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

Heating Energy

Consumption on 12th

January (KWh)

Percentage Reduction in

Heating Energy

Consumption from Central

Core Model (%)

1 Double Core East-West 225.9 21.31

2 Double Core North-South 229.9 19.92

3 Single Core West 235.6 17.90

4 Single Core North 243.2 15.29

5 Single Core South 247.1 13.93

6 Single Core East 247.6 13.75

7 Central Core (Base Case) 287.1 -

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

66

Office Zone Heating Energy (With Internal Gains)

20.0

30.0

40.0

50.0

60.0

70.0

80.0

7 8 9 10 11 12 13 14 15 16 17 18 19 20

Time of Day (Hrs)

Heati

ng

En

erg

y (

KW

h)

Central Core Double Core North - South Double Core East - West

Single Core North Single Core South Single Core East

Single Core West

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.

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.

67

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)

Central

Core

(KWh)

Double

Core

North -

South

(KWh)

Double

Core East

- West

(KWh)

Single

Core

North

(KWh)

Single

Core

South

(KWh)

Single

Core East

(KWh)

Single

Core

West

(KWh)

9:00 72.7 67.7 67.6 69.7 69.9 70.0 66.8

10:00 44.2 38.8 38.5 39.3 40.2 40.3 38.9

11:00 40.5 35.4 34.8 35.7 36.3 36.4 35.3

12:00 38.0 33.0 32.2 33.1 33.7 33.8 32.9

13:00 36.6 31.4 30.8 31.6 32.1 32.2 31.3

14:00 35.5 30.0 29.6 30.4 30.8 30.8 30.0

15:00 35.3 29.4 29.2 30.1 30.3 30.3 29.4

16:00 34.7 28.6 28.4 29.3 29.5 29.5 28.5

17:00 33.5 27.4 27.3 28.1 28.2 28.3 27.3

18:00 32.9 26.8 26.6 27.4 27.5 27.6 26.6

Total

(KWh)

404.4 348.9 345.5 355.3 359.1 359.5 347.3

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.

68

It is interesting to note that the single core west outperforms the double core north-

south 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

Heating Energy

Consumption on 12th

January (KWh)

Percentage Reduction in

Heating Energy

Consumption from Central

Core Model (%)

1 Double Core East-West 345.538 14.55

2 Single Core West 347.336 14.11

3 Double Core North-South 348.997 13.70

4 Single Core North 355.306 12.14

5 Single Core South 359.121 11.19

6 Single Core East 359.532 11.09

7 Central Core (Base Case) 404.401 -

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.

69

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

70

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.

71

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

72

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

73

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.

74

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.

75

References

Ali, M. M., 2003. Integrated design of safe skyscrapers: Problems, Challenges and Prospects. In:

Proceedings of the CTBUH (Council on Tall Buildings and Urban Habitat) Conference on Tall

Buildings, Malaysia, 20-23 October 2003, CIB Publication no: 290.

Ali, M. M., Armstrong, P. J., 2008. Overview of sustainable design factors in high-rise buildings. In:

Proceedings of the CTBUH (Council on Tall Buildings and Urban Habitat) 8th World congress,

Dubai, 2008.

ASHRAE, 2009. American Society of Heating, Refrigerating and Air Conditioning Engineers

(ASHRAE) handbook of fundamentals (SI edition).

Bordass, B., Fordham, M., Willis, S., 1995. Avoiding or minimizing the use of air-conditioning – A

research report from the EnREI programme. Watford, U.K.: BRECSU and ETSU

Building Regulations, 2006. Approved Document L1A Conservation of Fuel and Power. [Online].

Available at: www.planningportal.gov.uk/uploads/br/BR_PDF_ADL1A_2006.pdf

[Accessed 5 July 2010]

Burton, S. ed., 2001. Energy efficient office refurbishment. London, U.K.: James & James (science

publishers) Ltd.

CIBSE, 1986. CIBSE Guide, Vol. A, Design data. London, U.K.: The Chartered Institution of

Building Services Engineers.

Cox, G., Girardet, H., Pank, W., 2002. Tall Buildings and Sustainability. [pdf] London: Corporation

of London.

Available at: http://www.cityoflondon.gov.uk/nr/rdonlyres/08a4077b-3199-442e-b4d1-

e7f9f2c68e15/0/sus_tallbuildings.pdf

[Accessed 20 April 2010]

Geographical Association, 2009. Temperate Climate. [Online] (Updated 2009)

Available at: www.geography.org.uk/download/GA_EYPSq2Temperate.doc

[Accessed 15 May 2010].

Hamza, N., 2004. The performance of double skin facades in office building refurbishment in hot arid

areas. PhD. University of Newcastle upon Tyne.

Jahnkassim, P. S., Ip, K., 2006, Linking bioclimatic theory and environmental performance in its

climatic and cultural context – an analysis into the tropical high rises of Ken Yeang. In: Proceedings

of the PLEA (Passive and Low Energy Architecture) The 23rd

Conference on Passive and Low

Energy Architecture, Geneva, Switzerland, 6-8 September 2006.

Magri, A., 2006. Envelope refurbishment of high-rise listed buildings with emphasis on double skin

facades and reference to the Arts tower, Sheffield. M.Sc. University of Sheffield.

Oldfield, P., Trabucco, D., Wood, A., 2008. Five Energy Generations of Tall Buildings: A Historical

Analysis of Energy Consumption in High Rise Buildings. In: Proceedings of the CTBUH (Council on

Tall Buildings and Urban Habitat) 8th World congress, Dubai, 2008.

76

Powell, R., Yeang, K., 2007. Designing the eco-skyscraper: premises for tall Building design. The

Structural Design of Tall and Special Buildings: CTBUH (Council on Tall Buildings and Urban

Habitat) 2nd

Special Edition: Tall Sustainability, 16, pp.411-427.

Schneider, T., 2008. This building should have some sort of distinctive shape: the story of the Arts

Tower in Sheffield. 1st edition. Sheffield, U.K.: PAR – Praxis for Architectural Research.

SOM (Skidmore, Owings & Merrill LLP.). Poly International Plaza. [Online]

Available at: http://www.som.com/content.cfm/poly_international_plaza

[Accessed 12 May 2010].

Solar Century, 2010. Business, housing developers and the public sector. [Online].

Available at: http://www.solarcentury.co.uk/Businesses-Housing-Developers-the-Public-

Sector/Commercial-Developments/Case-Studies/CIS-Tower%2C-Manchester

[Accessed 16 March 2010].

Trabucco, D., 2010. Historical evolution of the service core. CTBUH (Council on Tall Buildings and

Urban Habitat), 2010 (1), pp.42-48.

Trabucco, D., 2009. The strategic role of service core in energy balance of tall buildings. PhD.

Venice, Italy: University IUAV

Trabucco, D., 2008. An analysis of the relationship between service Cores and the embodied/running

energy of Tall buildings. The Structural Design of Tall and Special Buildings: CTBUH (Council on

Tall Buildings and Urban Habitat) 2nd

Special Edition: Tall Sustainability, 17 (5), pp.941-952.

University of Sheffield, 2010. Arts Tower Project. [Online] (Updated 13 April 2010)

Available at: http://www.sheffield.ac.uk/artstowerproject/

[Accessed 10 May 2010].

USDOE, 2010. EnergyPlus Documentation. Version 5.0. U.S.A.: U.S. Department of Energy.

USDOE, 2008, Weather Data. [Online] (Updated 26 November 2008)

Available at: http://apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm

[Accessed 3 May 2010].

Weather Tool, 2010. Autodesk Ecotect Analysis 2010. U.S.A.: Autodesk Inc.

Willis, C., 1995. Form follows finance – skyscrapers and skylines in New York and Chicago. 1st

edition. New York, U.S.A.: Princeton Architectural Press.

Yeang, K., 2000. Service Cores. 1st edition. Chichester, UK: Wiley Academy.

Yeang, K., 1996. The skyscraper bioclimatically considered: a design primer. London: Academy

Editions.

Yeang, K., 1994. Bioclimatic Skyscrapers: with essays by Alan Balfour and Ivor Richards. 1st edition.

London, U.K.: Artemis.