Ben-Gurion University of the Negev

Research Proposal for Ph.D.

Thesis proposal

‘DESIGN STRATEGIES TOWARDS MORE ENERGY EFFICIENT SKYSCRAPERS’

אסטרטגיות תכנוניות לקראת גורדי שחקים יעילים יותר אנרגטית

By: Tanya Saroglou Student number: 850210840

Under the Supervision of:

Prof. Isaac A Meir Prof. Emeritus Baruch Givoni

8th of March 2016

Department of Man in the Desert

Advisor's name and signature: Head of Departmental Committee's name and signature:

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ABSTRACT

Considering the fact that since 2007 more than half of the world’s population is living in urban areas (this figure is expected to rise to 60% by 2030) the livability of high-density city is gradually becoming a central point of focus. The skyscraper as a successful model of urban planning provides the possibility to increase city-space vertically as opposed to a continuous expansion outwards that has environmental consequences. Today, population migration towards the cities and the typology of the skyscraper characterize many of the big cities around the world.

However, current high-rise examples do not present a sustainable solution to an increasing population or as models of economical prosperity, as they are linked to high-energy demands, environmental and social imbalances. These statements describe most of 20th century’s architecture that portrays a deviation from climatic considerations and reliance on mechanical means for the building’s operations. However, skyscrapers are very large buildings and their impact in the urban fabric is much greater.

The design of the skyscraper as a positive addition within the urban fabric needs further research and experimentation. Currently there are a number of green-skyscrapers that celebrate a high status of environmental strategies, combined with a high rank in green certification, but there is no transparency in their energy performance. In addition, there seems to be a gap between green certification and operation energy, meaning that a highly certified building may still be consuming high amounts of energy and producing greenhouse gas emissions.

This thesis will study the energy efficiency of the skyscraper by forming a climatically responsive design. The focus is on three parameters: first, a design strategy according to the building’s immediate environment (meso and micro-climate); second, the thermal properties of the building envelope; third, the effect of height in energy performance. In this process, the building envelope is considered the most important mediator between the indoor and outdoor climate. It is anticipated that the relationships formed between these three variables will provide answers in the skyscraper’s energy performance.

EnergyPlus is used as the more widely accepted simulation engine to quantify the

energy consumption of a skyscraper model at 100m - 400m high. Energy efficiency will be calculated in line with indoor thermal comfort conditions according to ASHRAE Standard 55 and the local weather file. Tel Aviv, Municipality's Planning and Construction Committee has issued the 2025 city master plan supporting the construction of new sky-rise development, thus will serve as the case study.

This research considers the skyscraper as an urban phenomenon closely related to city living and investigates its environmental impact by quantifying its energy performance. It is anticipated that climatically responsive skyscraper design principles will promote its energy efficiency and, by so doing, reduce emissions and in effect, global warming.

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אנרגטית יותר יעילים שחקים גורדי לקראת וניותתכנ אסטרטגיות

תקציר

אחוז הצפוי לגדול (יותר ממחצית מאוכלוסיית העולם חייה באזורים עירוניים 2007בהתחשב בעובדה שמשנת

גורד השחקים כאב . מרכזית ביותר נעשיתהפיכת העיר הצפופה לנוחה למחייה ), 2030עד שנת 60%לכדי

אופקית אשר הבניגוד להתפתחות , שטח העירשל אנכית המספק פתרון להגדל טיפוס לפיתוח העירוני

וכן , כיום ערים גדולות רבות בעולם מאופיינות על ידי נהירת אוכלוסיות אליהן. השפעותיה הסביבתיות ידועות

.על ידי אימוץ טיפולוגית גורד השחקים

ותיכול ןואינ, בר קיימא לאוכלוסייה הגדלההדוגמאות הקיימות של גורדי שחקים אינן מציגות פתרון , ברם

פגיעה באיזון הסביבתי בו קשורים בצריכת אנרגיה גבוהה בניינים אלהמאחר ש, להוות דגם של סגסוג כללי

רוב האדריכלות של המאה הל רלוונטיותאמירות אלה אמנם . והחברתי המתאפיינת בסטייה משיקולים 20-

גורדי השחקים הנם בניינים גדולים , ובכל זאת. ם לתפעול הבנייןהסתמכות על אמצעים מכנייבאקלימיים ו

.והשפעתם על המרקם העירוני גדולה באופן משמעותי

כיום ישנם מספר גורדי שחקים . תכנון גורד השחקים כמרכיב חיובי במרקם העירוני מצריך מחקר וניסוי

דירוג גבוה של הסמכה ל זכוו, תיותאסטרטגיות סביב על סמךמי שבנויים כירוקים המתהדרים במעמד גבוה

נדמה כי יש פער בין הסמכה ירוקה , יתר על כן. אך חסרה שקיפות בנוגע לתפקודם האנרגטי בפועל, ירוקה

כלומר יתכן כי בניין בעל דירוג גבוה של הסמכה ירוקה עלול בכל , לבין השימוש בפועל באנרגיה אופרטיבית

לייצר כמויות גדולות של דוזאת לצרוך כמויות גדולות של אנרגיה ו .תחמוצת הפחמן-

המיקוד יהיה על . תזה זו תחקור את פוטנציאל היעילות האנרגטית של גורד השחקים על ידי תכנון מוטה אקלים

מסו( אסטרטגיה תכנונית הכפופה לסביבת הבניין המידית , ראשית: שלושה משתנים ומיקרו - ); אקלים-

, בתהליך זה. השפעת הגובה על התפקוד האנרגטי, שלישיתו; הבנייןהתכונות התרמיות של מעטפת , שנית

מצופה כי היחסים בין . מעטפת הבניין נחשבת כמתווך החשוב ביותר בין אקלים פנים הבניין לבין זה שבחוץ

.שלושת המשתנים האלה יספקו תשובות אודות תפקודו האנרגטי של גורד השחקים

ש ככלי העיקרי לכימות צריכת האנרגיה של אב טיפוס של גורד תשמ EnergyPlusתכנת ההדמיה התרמית

100שחקים בגובה בין היעילות האנרגטית תחושב בהתייחס בתנאי הנוחות התרמית בפנים המבנה '. מ 400-

הועדה המקומית ש מאחר, תשמש אירוע חקר תל אביב . ובכפוף לאקלים המקומי ASHRAE 55לפי תקן

.המעודדת את הקמת גורדי שחקים 2025מתאר לשנת לתכנון ובנייה השיקה תכנית

וחוקר את השפעתו , מחקר זה מתייחס לגורד השחקים כתופעה עירונית הקשורה קשר הדוק לחיים העירוניים

מצופה כי יישום של עקרונות . כמת את התפקוד התרמי של הבנייןילשם כך המחקר . מנקודת מבט סביבתית

ועל ידי כך , הגדול של נפח גורד השחקים יאפשר לקדם יעילות אנרגטיתתכנון מוטה אקלים בקנה המידה

.לצמצם את ההשפעה הסביבתית השלילית של טיפוס בניין זה

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TABLE OF CONTENTS

A. INTRODUCTION............................................................................................................2

B. ENERGYCONSUMPTION&BUILDINGS..........................................................................7

C. THETYPOLOGYOFTHESKYSCRAPER...........................................................................11

D. RESEARCHQUESTION:................................................................................................23

D. METHODOLOGY.........................................................................................................24

E. DESIGNRESEARCHTOOLS...........................................................................................27

F. TIMESCALE.................................................................................................................30

REFERENCES.......................................................................................................................31

LIST OF FIGURESFigure1:Populationgrowthfrom1800stotodaywithprojectionsto2100

(UnitedNationsDepartmentofEconomicandSocialAffairs/PopulationDivision)p.2

Figure2:Distributionofskyscrapersof200m.<High(CTBUHResearchReport2014) p.3Figure3:BankofAmericasiteenergyusedFeb.2013-Jan.2014.

(HPBHighPerformingBuildings2014:VentilationinWonderland),p.52p.5

Figure4:Impactofspirallingenergycostsoverthenextdecade,asstatedbyprivateorganizations (Gensler,2006.FaultyTowers:istheBritishOfficeSustainable?,London),p.6

p.7

Figure5:ASHRAE’sEnergyUseTargetsforNZEBs(ASHRAE,2008.ASHRAEVision2020:ProducingNetZeroEnergyBuildings,Atlanta,GA)p.13

p.8

Figure6.BankofAmerica,BryantPark1,NewYork,streetleveldesign(http://inhabitat.com) p.11

Figure7:Decreasesinefficiencybetweenofficelow-riseandhigh-riseconstruction (Barton,J.&Watts,S.,2013.Officevs.residential:Theeconomicsofbuildingtall.CTBUHJournal,(2),pp.38–43.),p.43

p.14

Figure8.HongKongskyscraperbeachfrontconstruction,viewofskyscraper‘walleffect’(Source:HongKong,Aug.2007,http://www.globalphotos.org)

p.15

Figure9.(a)2Dstreamlineanddistributionofverticalvelocityiny=B(b)Turbulentkineticenergy(TKE)iny=B.(Hang,J.&Li,Y.,2010.Ventilationstrategyandairchangeratesinidealizedhigh-risecompacturbanareas.BuildingandEnvironment,45(12),pp.2754–2767),p.2762

p.15

Figure10:TotalEEconsumedbytheentirestructurefordifferentframesandfloortypesinrelationtotheheightofthebuilding.(Foraboschi,P.,Mercanzin,M.&Trabucco,D.,2014.Sustainablestructuraldesignoftallbuildingsbasedonembodiedenergy.EnergyandBuildings,68(PARTA),pp.254–269.),p.259

p.18

Figure11.AnanalysisoftheEmbodiedEnergyofOfficeBuildingsbyHeight,inMelbourne(Treloar,G.J.etal.,2001.Ananalysisoftheembodiedenergyofofficebuildingsbyheight.Facilities,19(5/6),pp.204–214),p.210

p.19

Figure12.AverageEUIinkBtu/ft2/yrofallNewYorkofficebuildings.(Leung,L.&Ray,S.D.,2013.NewYorkCityEnergyBenchmarkingDataPaperType :Low-energyTallBuildings ?RoomforImprovementbyNewYorkCityEnergyBenchmarkingData.InternationalJournalofHigh-RiseBuildings,Volume2,,pp.285–291),p.287

p.20

LIST OF TABLESTable1:WindSpeedProfileCoefficients(ASHRAEFundamentals2005),p.3 p.17

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A. INTRODUCTION

World population is

not spread evenly across the

globe, with Europe and Asia

having the highest

population density: 300 -

1000< people/km2. World

population is growing at a

very fast pace. Statistics

show (Fig.1) that population

rose from 1 billion at the

peak of the industrial

revolution in the mid-1800’s,

to 2 billion by 1930, 3 billion

in 1959, 4 billion in 1974, 5

billion in 1987 and that more

than 7 billion people are living in the world today (UN DESA 2014a). The rapid increase

in world population affected the growth and density of the urban environments with

cities like Hong Kong and Mumbai having very high densities of 20,000 people/km2,

London 5,100 and New York 1,750 (Ng 2010).

Considering the fact that since 2007 more than half of the world’s population is

living in urban areas, this figure is expected to rise to 60% by 2030 (UN DESA 2014b), the

livability of high density city is gradually becoming a central point of focus. Thus, it is

possible to predict that high-density urban environments will soon be the norm and will

dictate an increase in building demand. Rapid urbanization has given rise to the

phenomenon of megacities, cities whose population exceeds 10 million people. Today

there are 21 megacities that consume 80% of the worlds’ energy use and produce 80% of

greenhouse gas emissions (FIG 2010). In addition, according to UN data, a new city with

1.3 million inhabitants will be built every week for the next four decades (Wei et al. 2016).

Figure 1. Population growth from 1800s to today with projections to 2100 (Source: United Nations Department of Economic and Social

Affairs/Population Division)

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Population

migration towards the

cities on a worldwide

basis, has promoted the

typology of the

skyscraper as an

important high-density

living solution to the

already dense urban

centers. According to a

research report by the

Council of Tall buildings and Urban Habitat (CTBUH) (Fig.2) the distribution of

skyscrapers of 200m and more around the globe to date is as follows: China (348), South

Korea (48), Rest of Asia (140), Australia (27), Europe (37), Middle East (120), USA (169)

(Safarik & Wood 2015). Except for the USA, where skyscraper construction is distributed

evenly across the 20th century, China’s boom on skyscrapers was initiated in the 1990’s,

reflecting the country’s fast pace of urbanization, and in the Middle East from 2000

onwards as a tool for advancing economic and political influence.

As world population is becoming progressively urbanized, a sustainable

approach needs to be established that lessens the environmental impact of cities. Current

high-rise buildings do not present an all-around successful solution either to an

increasing population or as examples of economic prosperity, as they are linked to high-

energy demands, environmental and social imbalances (Girardet 2006). This is a general

observation of 20th century’s architecture that is characterized by a deviation from

climatic considerations and reliance on mechanical means for the building’s operation, a

reflection that does not only affect the typology of the skyscraper. However, skyscrapers

are very large buildings and their impact on the urban fabric is much greater.

Sustainability of the urban development is defined as the process of integration

and co-evolution of economic, social, physical and environmental subsystems. The

carrying capacity of a city is another aspect of sustainability within the city (Wei et al.

2016). The aim of sustainable development is to enhance population wellbeing without

Figure 2. Distribution of skyscrapers of 200m. < High (Source: CTBUH Research Report 2014)

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compromising development possibilities. In terms of city infrastructure and building

technology, these need to display technological progress and environmental design

principles in order to successfully sustain the growing population.

Currently, the building industry is regarded as the most energy intensive sector

with buildings accounting for close to 50% of carbon dioxide (CO2) emissions, created

through the combustion of fossil fuels for the extraction of raw materials, the production

of building materials and components, their transportation and the construction of

buildings (Embodied Energy – EE), and for heating, cooling, lighting and other building

operations (Operational Energy – OE). Sustainable development and green building

design strategies have been gradually introduced into National Planning Policies, i.e.,

green building certification procedures, with special attention given to the estimation of

energy consumption. Consequently, in the process towards sustainable urban

environments the gradual independence from fossil fuels becomes vital.

The skyscraper as a successful model of urban planning provides the possibility to

grow city-space vertically as opposed to a continuous expansion outwards that has

environmental consequences, e.g., increase in air pollution due to higher vehicle traffic,

loss of agricultural land, natural habitats and land reserves. Also, the energy and

environmental demands for growing infrastructure can be huge. Skyscrapers, on the

other hand, also affect the environment by putting stress on the local infrastructure

mainly with the consumption of high-energy levels per city area unit; however, achieving

energy efficiency in high-rise structures is a challenging demand. The design of the

skyscraper as a positive addition within the urban fabric needs further research and

experimentation. This thesis considers the skyscraper as an urban phenomenon closely

related to city living and will investigate design strategies towards reducing its energy

consumption levels.

In recent years there have been a number of built skyscrapers aiming at achieving

energy efficiency. A good example of a skyscraper that demonstrates the efforts and

complexities of sustainable high-rise construction is ‘The Bank of America’ by Cook +

Fox Architects in New York, at 366 m height to architectural top, completed in 2010. The

tower has approximately 47,000 m2 of trading floors and nearly 10,000 occupants a day.

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Figure 3. Bank of America site energy used Feb.2013-Jan.2014.

(Source: Donnolo et al. 2014)

Bank of America received ‘Core and Shell’ LEED Platinum certification from the US

Green Building Council (USGBC n.d.), which is the highest level of LEED certification,

and was awarded the 2010 ‘Best Tall Building Award - Americas’ by the Council of Tall

Buildings and Urban Habitat (CTBUH 2014).

The skyscraper was designed to set new standards on high-performance of high-

rise buildings, both for the people occupying the spaces and for the city a whole. The

tower reduces CO2 transport related emissions by providing no car parking spaces, while

including in its design bicycle parking facilities. It is also worth mentioning that its total

budget incorporated a number of public facilities with the aim of giving something back

to community through its presence. The most notable of them is the reconstruction of

Henry Miller’s Theatre to become the first “green” Broadway Theater, the LEED Gold

certified Stephen Sondheim Theater. Moreover, with its transparent façade and corner

entrance that overlooks Bryant Park opposite, it enhances a visual and physical

connection with its surroundings at street level.

Examples of the advanced technologies used in the tower are a 5.0 MW gas

turbine cogeneration plant in the basement that provides 65% of the annual electricity

required as well as lowering daytime peak demand by

30%. In terms of materials used, the tower incorporated

75% recycled steel and concrete made from cement

containing 45% blast furnace slag, and low-VOC

emitting interior finish materials. High indoor air

quality (IAQ) was achieved with a zone-by-zone

ventilation system, while the curtain wall of the

envelope provides abundant natural light and with the

use of low-E glass, heat-reflecting ceramic frit that

reduce energy consumption by 10% (Donnolo et al.

2014; CTBUH 2014).

Bank of America specifications make the building a highly sophisticated, top-

quality structure in terms of design and technologies used. However, in 2013 New York

City released a public report (Fig.3) on the building operations revealing that in 2012 the

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tower had a site energy use intensity of 665 kWh/m2/yr, higher than any comparably

sized office building in Manhattan (Donnolo et al. 2014). Scot Horst, the senior vice

president of LEED at the USGBC supported the building’s design by drawing attention

on the fact that the structure produces most of its required electricity, and by so doing

reduces its impact on infrastructure. It took more than a year for the architects and

engineers of the project to start pin-pointing the “faults” and come up with the

conclusion that a big part of the high energy consumed was due to the over-sized

ventilation system used. The combined intentions of meeting sustainable rating system

requirements, dealing with local jurisdictional interpretation, and using design industry

standard practice resulted in the over-performing of the system (Donnolo et al. 2014).

However, in the example of the Bank of America the total energy consumption is not

only governed by the design strategies and specifications used, but also by the building’s

use (trading floors with high computing energy requirements) and the occupants’

behavior, which were not taken into consideration (Calhoun & Torbert 2013).

The high-energy rates of the building also made obvious the gap between what

LEED as a certification procedure is able to achieve regarding the environmental

performance of the structure as a whole, and what the building’s actual energy

performance is. Unfortunately, the level of information that New York City released on

Bank of America is missing for all other skyscrapers. Even the most recent ones that

celebrate a high status of environmental strategies, combined with a high ranking in

green certification, do not provide transparency in their energy data. This lack of

information hinders the understanding of how a skyscraper operates, towards

quantifying its energy performance and forming a body of successful green-design

guidelines in high-rise construction.

The process of minimizing the impact of the skyscraper both in regards to energy

consumption and carbon emissions is of high importance, considering the number of

skyscrapers that are being built across the world annually (Safarik & Wood 2015) and are

in planning for the near future. China is leading with the highest number of new

skyscrapers built every year. Other places like Tel Aviv, in Israel, changed their planning

policies to allow for future skyscraper construction. More specifically, Tel Aviv’s

Planning and Construction Committee issued the 2025 city master plan that has set new

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guidelines on skyrise development. With Israel advancing its green building standards it

is expected that the new skyscraper development will also be an opportunity to put green

building guidelines into practice (Fox 2011). The impact of a skyscraper on infrastructure

and its popularity on a worldwide basis dictate the need for a new insight on its design

and operation. In order to advance the energy efficiency of the structure it is important to

study the skyscraper’s form from a climatically responsive perspective and focus on

quantifying its energy requirements.

B. ENERGY CONSUMPTION & BUILDINGS

Energy consumption is divided in three sectors: Industry, Transportation and

Building Construction. The building industry has become the most energy intensive

sector that consequently produces the highest amounts of greenhouse gas (GHG)

emissions. These are produced throughout the building process, i.e., extraction,

transportation and use of materials, the building’s construction and operation, and the

dismantling or demolition at end of the building’s life (EE). However, emissions

produced from the energy used to operate the building (OE), form the largest source of

building-related GHG emissions that is approximately 80-90% of the whole building

process, according to UNEP SBCI (La Roche 2012).

Badly designed, inefficient

buildings that put short-term profit

before long-term sustainability are now

left empty creating the growing

phenomenon of the ‘dead building

syndrome’ (Roaf et al. 2009).

Lightweight constructions, with usually

large amounts of glazing are designed to

operate purely on fossil fuels, as they completely ignore the climatic conditions of their

location. However, since the start of the 2008-9 economic recession they are gradually

abandoned because they have become too expensive to operate. Gensler’s Faulty Towers

2006 study of UK’s commercial properties makes the connection between business and

environmental issues by considering the energy efficiency of buildings in relation to their

Figure 4. Impact of spiralling energy costs over the next decade, as stated by private organizations (Source: Gensler 2006)

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operational costs. The study revealed that both property developers and tenants believe

that the escalating operating energy costs over the following decades will be a major

factor in tenants’ choice of property and that this will force developers to make more

energy efficient structures that will reduce operation costs to more than a quarter. The

above statements clearly indicate that both property developers and managers are

looking for a more sustainable future with reduced operational (cost efficient) and

environmental (carbon emissions) rates on construction (Gensler 2006).

Faulty Towers study also revealed the developers’ belief that change will happen

through government legislation, regulation and penalties. EU legislation, the Energy

Performance of Buildings Directive (EPBD), first published in 2002, required all countries

to develop their building regulations in line with energy certification schemes for

buildings (Concerted Action (CA) EPBD 2014). The implementation of the legislation was

mainly based on the introduction of energy performance certificates (EPCs). EPCs are set

to become an essential performance initiative towards raising the building standards in

the coming years. This implies that the capital value of the poorly graded stock will fall

dramatically affecting greatly property managers. As a result, property market choices

will be either disposal of the existing stock, the least preferable solution in terms of EE

waste, an upgrade where possible, and a demand for higher energy efficiency of new

buildings (Gensler 2006).

In addition, the political and

economic uncertainties of the oil and gas

markets (U.S. Energy Information

Administration 2015; Profit Confidential

2015) in tandem with the catastrophic

consequences on climate that a reliance on

these types of energy will bring, as well as

the difficulties relating to nuclear power

production(WNA 2015), have paved the road for the development of sustainable

technologies for the production of energy. We are at a critical point where we have to

start designing our way out of fossil fuel dependence and aim towards a more

sustainable way of living. In order to achieve this, our resources supply levels have to be

Figure 5. ASHRAE’s Energy Use Targets in kbtu/square foot/year towards NZEBs

(Source: ASHRAE 2008)

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re-calculated to a critical supply-and-demand model, as well as investigate strategies for

reducing GHG emissions. An important aspect of this process is to advance the energy

efficiency of buildings.

In 2007, the American Society of Heating, Refrigerating and Air-Conditioning

Engineers (ASHRAE), created the vision that by 2020 buildings will produce as much

energy as they use when measured on site, to be called the Net Zero Energy Buildings

(NZEBs). They believe such buildings can be market-viable by 2030 (Fig.5) (ASHRAE

2008). ASHRAE is also involved with Architecture 2030, a non-profit think tank for the

‘2030 Challenge’ that is essentially a ‘carbon free’ future for all buildings by 2030

(Architecture 2030 2002). The European Commission (EU) has set similarly ambitious

targets for 2020 (20-20-20), that aim at 20% reductions in Greenhouse Gas (GH) emissions

from 1990 levels, a 20% increase to energy produced by renewable sources and 20%

increase in energy efficiency. In June 2013, EU published a report update towards Nearly

Zero-Energy Buildings (NZEB) by the end of 2020 (EU 2013).

In order to attain a carbon free future, a robust transition to energy from

sustainable sources, e.g., sun and wind, is vital. Policy settings to support renewable

energy, e.g., solar panels, mini-wind turbines and other renewable energy sources, have

helped set priorities in the development of such clean forms of energy in the coming

decades. The challenges set on a worldwide basis state that a renewable energy economy

will be an important part for future energy reserves, with the only constraints being how

quickly and efficient the transition from fossil fuels will be. However, the most

economical and environmentally friendly solutions to a building’s energy consumption

and energy efficiency, exist while the building is still on the drawing board, forming a

design strategy according to the special climatic and regional conditions and taking

advantage of passive heating and cooling techniques to satisfy the building’s needs. Any

additional technologies used at a later stage, ideally should be there to assist the

building’s thermal equilibrium in extreme weather conditions. Low energy consumption

as a result combats climate change and atmospheric pollution, by reducing the

production of GHG emissions.

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Climatically responsive architecture analyzes each location’s specific data, e.g., air

temperature, humidity, wind speed and intensity of solar radiation, and develops

strategies providing solutions towards more energy efficient, healthier and comfortable

environments. So, building design should be relevant to the area’s macro- meso- and

microclimate characteristics. Latitude, solar azimuth and altitude (time of year and time

of day) play a very important role in the climatic conditions of a location. In addition,

landscape heterogeneity, e.g., presence of significant water bodies, topography,

vegetation or a forest, can influence greatly the local climate by affecting wind patterns,

changes in temperature and humidity (Givoni 1981) and in the intensity of solar radiation

on a surface (Mazria 1979). The building envelope also becomes important in relation to

the building’s thermal behavior according to the climate and microclimate around it

(Trefil 2003). Its special physical properties, i.e., the thermal resistance and heat capacity

of the materials used, must interact appropriately with the ambient climatic conditions to

reach healthy, comfortable indoors (Givoni 1969). The morphology of the “proposed”

building site is also significant as the environmental conditions differ between a low

density (countryside, villages), a medium density (towns, city outskirts) and a high

density built environment (city center). Within a dense city fabric, the average height of

the surrounding buildings affects the specific climatic conditions of the urban section as

height impacts on solar exposure (daylight levels, solar heating), as well as wind patterns

(ventilation) and the Sky View Factor (SVF), which determines the potential of urban

cooling by long wave outgoing radiation that is restricted in urban canyons.

Undesirable climatic modifications brought about by urbanization need to be

mitigated through the implementation of sustainable development and building design

strategies. ‘Sustainable building’s’ aims are to increase energy efficiency and, by doing so,

reduce air and noise pollution, waste, and use of toxics, integrate vegetation and green

open spaces within design area, while enhancing healthy social relationships (Samiei

2013). Climatically responsive architecture works with the particular features of its

location and adapts the building to its surroundings. This means that OE used in

buildings is minimized by taking advantage of passive cooling and heating techniques.

11

C. THE TYPOLOGY OF THE SKYSCRAPER

Reaching great heights changed the aesthetics of the city. Fascination with

skyscraper design is very common, and cities are rated on how impressive their skyline

is. The skyscraper is seen as symbol of the city’s power and wealth. A list of the world’s

most impressive skylines sees Hong Kong first with 380 skyscrapers. Third on the list is

New York, even though skyscraper construction there started much earlier, with a total

of 250 skyscrapers. The list includes Shanghai, Chicago, Singapore and many more

(Kaushik 2012). Edward Glaeser, an urban economist at Harvard University, in his book

‘Triumph of the City’ talks about the history of the skyscraper and its importance in the

fast evolving cities towards the beginning of the twentieth century. He argues that high

rise Manhattan is not just a commercial center, but also a successful neighborhood with a

very vibrant street action with stores and restaurants. Commenting on the diversity of

people’s preferences he points out that such high-density levels may not be the majority’s

preferable living arrangements, but many people do like tall buildings (Glaeser 2011).

However, buildings don’t just stand up

high, they have a very strong presence on the

ground. They may contribute positively to their

environment or add up to the noisy, congested

experience of the street. How a building meets

the ground becomes very important and helps to

bond the structure with its surroundings,

however high it might be. Visibility, accessibility,

openness and the possibility to provide multisensory experiences throughout the day are

very important characteristics of a successful public realm. Street level designs of recent

skyscrapers, like the Shard in London and Bank of America in New York (Fig.6), have

shown great progress in that respect. The towers have also contributed in a number of

ways within their urban context by connecting to existing public transportation routes,

constructing a number of public facilities, as well as incorporating construction works for

the wider city as part of their total budget.

Figure 6. Bank of America, Bryant Park 1, New York, street level design (Source: http://inhabitat.com)

12

There is a difference between high-rise design and skyscrapers. Skyscrapers are

very tall buildings. What used to be a very tall building some years ago today is not as

impressive. In addition, the way skyscrapers look and are designed today is completely

different from the early skyscrapers of the 20th century, and will most probably be so, too,

in comparison to the future ones. The changing fashion is reflected in the continuous

evolution in building materials and construction methods. In the beginning of 20th

century tall building construction was characterized by excessive use of building

materials due to the absence of advanced structural analysis techniques (Milana et al.

2006). In 1965, the structural engineer Fazlur Khan created a whole new range of

structural systems, like framed tubes, braced tubes and super-frames that created a new

architectural vocabulary and advanced the structural possibilities for DeWitt-Chestnut

Apartments in Chicago ( Ali 2006). Super tall buildings, like the Petronas Towers and

Taipei 101, use the method of outrigger-and-core systems, where belt trusses or mega-

columns are employed at the perimeter, creating big openings for windows on the

facades. The use of diagrid node connections or megabrace can be seen as the next step to

tall building construction that allows for complete elimination of vertical columns and

the design of even taller structures (Milana et al. 2014). Freeing parts of the façade from

structural burdens has given rise to a new set of possibilities of innovative façade

technology that, combined with HVAC systems, may aim for energy efficiency and

indoor thermal comfort. Their combined design properties may reduce both initial and

operating costs, as well as opt for higher system performance altogether ( Ali 2006). This

is a step forward in the design of the skyscraper as a more climatically responsive

building where the façade and the mechanical systems can be designed to complement

each other.

Quantifying the energy requirements of the skyscraper becomes very important in

todays’ energy troublesome era. Its design and construction is at a critical point where it

needs to catch up with regulations on sustainable design and energy efficiency that apply

to all other new development. According to an article published by High Performing

Buildings (HPB) in 2009 (Hinge & Winston 2009), calculating a building’s energy use

intensity (EUI) is an easy task: sum up all the energy used and divide it by the floor area

to obtain the building’s EUI (usually expressed in kBtu/ft2/yr or kWh/m2/yr). The figure

13

can then be compared to the estimated EUI through the design process. However, the

HPB article also states that although modeling seems to be improving, there are

substantial inconsistencies between the EUI estimated through design and the actual EUI

when the building is occupied, meaning that even high performance buildings are using

much more energy than predicted, as in the example of Bank of America, New York. So,

even though green certification is able to provide significant environmental benefits, e.g.,

environmentally friendly products into the marketplace, the issue of energy efficiency is

still problematic. Only by rating buildings according to their energy consumption,

estimated by utility bills, a building can be said to have achieved energy efficiency – or

not. Having an effective energy rating system, like one based on utility bills, may start to

produce concrete results on the building’s energy efficiency that relate to carbon

emissions and these, in turn, to climate change (Gifford 2008). Ashraevision 2020

(ASHRAE 2008) proposes two energy performance indicators: one is the ‘design rating’,

and the other is the ‘operations rating’. One way to present this information would be

with the production of Green Building Energy Consumption Surveys (GBECS).

In regards to the energy efficiency of the skyscraper, the building industry’s

concerns have advanced relative to the number of built and proposed skyscrapers built

today. CTBUH conducted the ‘Roadmap on the Future Research Needs of Tall Buildings’

(Oldfield et al. 2014), at the Illinois Institute of Technology, Chicago. The research is put

together from responses of practicing professionals and academicians in the building

industry all over the world, and identifies 11 different fields to be investigated for

advancing skyscraper design in the following years. The section ‘Research on the

integration of passive design strategies and technologies into tall buildings to reduce

energy requirements and improve occupant comfort’ scored the second highest rating of

7.6 out of 10 points. CTBUH’s 11 research fields revealed that there is little knowledge so

far on skyscraper design and that there is a growing concern to advance the industry’s

expertise on this building type.

Given the difficulties discussed above to accurately estimate building energy

performance, especially after being occupied, a focus on energy efficiency should be

given to the reductions produced through design alone, more specifically, to improve the

form and fabric of the building to such an extent that minimizes considerably the impact

14

of energy consumption on heating and cooling. For the example of the skyscraper, in

order to achieve such results a holistic understanding of its pros and cons is vital. This

means a detailed understanding of the issues that this building type instigates, as well as

what makes it exceptional. This process in effect creates the basis upon which changes

towards the sustainable future of the skyscraper can occur.

A skyscraper is the product of a fruitful cooperation between a number of parties

involved. Complex forms of coordination are formed between the clients and the

architects of the project, in collaboration with the engineers and the developers, in line

with the building regulations by the City Council, and numerous consultations with the

important neighboring developments. Further issues that need to be taken into

consideration, when designing such a building type, are its connection with the local

transportation systems, as well as its impact on infrastructure and the ecology of the site

(Yeang 2008).

When considering the

construction of a skyscraper within a

dense urban fabric, initial drawbacks

come from an economic point of view.

The increased construction costs of

typical high-rise buildings are

approximately 40% higher in

comparison with the typical low-rise

ones. In addition, regarding typical

floor area efficiencies (Fig.7), gross internal area (GIA) for low-rise is between 68%-75%,

while for the high-rise 60%-70% (Watts & Langdon 2010). Net internal area is also smaller

in high-rise buildings, as more area is used by plant and risers. The result is a 15%-25% of

the high-rise floor area being taken over by circulation alone.

The skyscraper’s excessive height is also an important issue, as long shadow lines

obstruct the solar rights of the surrounding areas; this includes both the overshadowing

of public open spaces and of adjacent buildings. Solar access has become closely linked to

life quality, and to energy efficiency by valuing the sun as an important source of energy.

Figure 7. Decreases in efficiency between office low-rise and high-rise construction

(Source: Barton & Watts 2013)

15

The incorporation of a solar envelope in building design as a zoning device, is a way to

assure urban solar access for both energy and life quality standards (Knowles 1999). For

example, solar envelope regulations between two or more adjacent buildings, is that the

volume of one compliments the design and volume of the other, meaning that shadows

are cast in a way that all buildings enjoy ‘adequate sunlight’ for the design of passive and

low-energy architecture; the characteristics of the solar envelope are relevant to land size,

shape as well as the climate and microclimate of the location, for example, the minimum

recommended requirement for solar access in a ‘Mediterranean’ climate is four hours

(Knowles 2000).

Furthermore, the large-scale volume of the

skyscraper affects a city’s natural ventilation potential.

This is especially valid in places of the world where

skyscraper construction is intense. Cities like Beijing,

Hong Kong and Tokyo, where there is a high

concentration of skyscrapers, have serious issues of

pollution. In Hong Kong, high-rise beachfront

construction is a leading example of what is know as

the ‘wall effect’ where skyscrapers along the coast block the ingress of sea breezes (Fig.8).

This phenomenon enhances poor city air quality and the Urban Heat Island (UHI) effect,

due to the compromised natural ventilation rates (Yim et al. 2009).

Learning from the mistakes of the past, it becomes essential to avoid creating

similar conditions, while investigating solutions on how to remedy existing problems. A

study made on ventilation strategies and air

change rates in high-rise compact areas

revealed that variations between low-to-

medium and high-rise structures improved

ventilation by increasing vertical mean

airflow. The structures were aligned on a

main street, parallel to the approaching wind.

The ventilation and air exchange for both the

Figure 8. Hong Kong skyscraper beachfront construction, view of skyscraper ‘wall effect’ (Source:

Hong Kong, Aug. 2007, http://www.globalphotos.org)

Figure 9. (a) 2D streamline and distribution of vertical velocity in y = B (b) Turbulent kinetic

energy (TKE) in y = B. (Source: Hang & Li 2010)

16

main streets and the secondary streets was improved, but the lateral inflow or outflow

rates of the secondary streets were especially improved (Fig.9) (Hang & Li 2010).

The effect of wind on the skyscraper also needs careful consideration. Its shape

and volume have to take into account the wind loads imposed on the structure. Due to its

tallness, strong wind forces up above, have the power to rock the structure if it is not

designed appropriately to withstand such forces, while also create wind vortexes on

ground level that need to be calculated so that damages on the structure can be avoided.

When a strong wind hits the building, it is pushed up, down and around the sides,

creating what is known of as the ‘downdraught effect’ and ‘channeling effect’. One

design solution around this problem, is the use of various types of dampers along the

envelope as well as varying the structure’s cross section with height in order to ‘confuse’

the wind and make the vortices lose their coherence (Irwin 2010).

Complaints on strong winds at the bottom of skyscrapers within dense urban

environments have prompted the municipalities of a number of cities to start demanding

an Environmental Impact Assessment (EIA) as part of Planning Application, with a

special emphasis on site wind analysis. The City of London Corporation prompted for

the requirement for an EIA, after concerns on strong winds and radiation reflection

around the “Walkie Talkie” tower in the Square Mile (Clark 2016). The tower became the

precedent for an EIA prerequisite for a number of high-rise projects in the UK, opening a

new era in the relationships formed between the skyscraper and the urban environment.

According to information published by the CTBUH, there are five steps in

determining wind loads. First, is the wind regime, i.e., wind speed and direction in the

building’s location; second, is the influence of the terrain, e.g., surface roughness and

topography; third, the aerodynamics of the building and influence from nearby

structures; fourth, the building’s wind-induced response and aero-elastic effects; fifth, the

criteria used to assess the relationship between the building and the wind. The guidelines

for the final step are that the building should be over 120m. tall, its height should be

greater than four times its average baν (building width normal to the wind direction over

the top half of structure), the lower frequency movement of the building to be less than

0.25Hz for the well-being and comfort of its occupants (Michaels et al. 2009), and that the

17

reduced velocity at extreme conditions be greater than 5 (Irwin et al. 2013), calculated

with the following relationship:

𝑈/(𝑓!𝑏!")

Where:

U, is the mean hourly wind velocity at the top of the building

f1, is the lowest natural frequency of the building

bαν, is the average width of building

The microclimate of the skyscraper, that is the environmental factors like

temperature, barometric pressure and wind speed, changes with altitude. Wind speed

increases with altitude. Since the typical height of meteorological station anemometers is

10 meters above ground, it becomes critical to conduct further calculations for wind

speeds at higher altitudes, when designing tall buildings. According to ASHRAE 2009

(ASHRAE 2009), Chapter 24: Air flow around Buildings, the hourly average wind speed

UH of an uninterrupted wind approaching a building in its local terrain can be calculated

from the following equation:

𝑈!! 𝑈!"# 𝛿!"#𝐻!"#

!!"#

𝐻𝛿

!

Where:

UH , the hourly average wind speed

Umet , is the height above ground

αmet and δmet can be calculated from the following table

Table 1. Wind Speed Profile Coefficients air layer thickness δ and exponent α (ASHRAE Fundamentals 2005)

Terrain Category Description Exponent α Layer Thickness

δ, m

1 Large city centers, in which at least 50% of buildings are higher than 21 m, over a distance of at least 2000 meters upwind

0.33 460

2

Urban, suburban, wooded areas, and other areas with closely spaced obstructions compared to or larger than single-family dwellings (over a distance of at least 2000 meters upwind)

0.22 370

3 Open terrain with scattered obstacles generally less than 10 0.14 270

18

meters height, including flat open country typical of meteorological station surroundings

4 Flat, unobstructed areas exposed to wind flowing over a large water body (no more than 500 meters inland)

0.10 210

The following example describes the relationship between wind, air temperature

and height. Based on ASHRAE 2009 calculations and the Typical Meteorological Year

TMY2 weather file for Central Park in New York City, at 40 m high (10th floor) a local

wind speed of 5.5m/s escalates to 7.0 m/s at 120 m high (30th floor), a 27% increase, and

then advances to 7.8 m/s at 200 m high (50th floor) (Leung & Ray 2013). Furthermore, in

simulations performed for a high-rise building of 60 floors, it was revealed that the effect

of wind speed change was dominant for the first 10 floors. Higher up, at floor 25, the

effect due to drop of air

temperature became equal with

the effect of wind speed. Even

higher up, above floor 25, the

effect of air temperature was

overriding, making it an

important consideration to

estimate the reduction of air

temperature with altitude when

simulating tall buildings

(EnergyPlus 2015a).

Increased wind speeds on high altitudes necessitate the increased use of materials

in order to strengthen the structural system of the skyscraper. This boost of building

materials between a high-rise and a low-rise structure has given shape to the conception

that tall buildings are unsustainable due to their high consumption of resources. The

amount of extra materials required in high-rise construction is relative to the wind-load

resisting system. One method to measure and compare the impact between high-rise and

low-rise construction, in terms of additional materials used, is through the energy

consumption during the production and construction of materials, or else their EE. Even

though EE of materials holds only a small percentage of total energy consumption

Figure 10. Total EE consumed by the entire structure for different frames and floor types in relation to the height of

the building. (Source: Foraboschi et al. 2014)

19

throughout a building’s life cycle (approximately 15%) in comparison with the

operational energy (at about 85%), opportunities to reduce EE should be taken into

consideration.

A study of the “Inventory of Carbon and Energy” (ICE), which is the cradle-to-

gate database including all activities from materials extraction, manufacturing,

assembling and transportation to fabrication processes, of reference structures

dimensioned between twenty (80m high) to seventy stories high (280m high), provided

an insight on the relative EE increases with height. The upper limit of seventy stories

high is considered a threshold in this study, after which the wind-load structural

resisting system necessitates greater

use of materials, especially for the

core, implying a greater consumption

of EE (Foraboschi et al. 2014), due to

the greater wind loads and increased

needs for an anti-seismic design

requirements (belt trusses, super

columns, mega brace etc.).

The report assesses the

increases of the Embodied Energy

(EE) of the different height structures

with the use of a Reinforced Concrete

(RC) central core, and either RC or steel rigid frames. For the floors three different

structural combinations were used; reinforced concrete, steel and a lightweight flooring

system. It was revealed that the floors almost always consume most of the EE, whatever

combination is adopted, but with an emphasis on the increased EE of the lightweight

materials. The results showed that considering the relationship of EE with height, the

consumptions of EE were within reason for the RC frames, while the EE of steel frames is

higher (Fig.10). The report concludes that it is possible to construct sustainable tall

buildings with the EE of materials as an indicator, by studying the relationships between

the unitary EE and the building height (Foraboschi et al. 2014).

Figure 11. An analysis of the Embodied Energy of Office Buildings by Height, in Melbourne

(Source: Treloar et al. 2001)

20

Another study conducted on data possessed from five case studies of office

buildings of the following heights: 3, 7, 15, 42 and 52 stories high, gave a different insight

into the relationship of EE with height (Treloar et al. 2001). An important characteristic of

this study is the difference of geometry and construction systems between the buildings

in question. The analysis of and comparison between the buildings showed that the EE in

the columns and internal walls of the high-rise buildings was significantly higher than in

the low-rise, due to the increased use of materials related to the structural requirements

of wind and vertical loads. In total, the EE results showed a 60% increase in the EE/m2

between the 3 stories and 52 stories buildings (Fig.11). The results of the above studies

form an understanding on the use of building elements and their variations in a

building’s embodied energy as height increases.

Higher wind speeds on upper levels may also create variations in the EE of other

building components, like windows and insulation, but the effect of these was not

included in the above examples. However, the use of materials with low EE and high

thermal properties, like for example materials with high thermal insulation capabilities

and low EE, result in reductions in both embodied and operational energies (Kua &

Wong 2012). In addition, a skyscraper consumes higher amounts of OE due to its large-

scale volume compared to low-rise development. A main reason for the higher energy

consumption is the energy used by elevators, which is often negligible in low-rise

construction. It is estimated that depending

on height and program, elevators can

consume from 5-15% of the total energy

consumed in tall buildings. This is due to the

higher travel distances and the faster speeds

used (Leung & Ray 2013).

Since 2009 the New York City requests

from all buildings with gross areas greater

than 50,000 ft2 (4,645 m2) to publicly release

their energy consumption data. The height of

the buildings is not included in the reports,

Figure 12. Average EUI in kBtu/ft2/yr of all New York office buildings reported by The City of

New York as a function of total number of floors. (Source: Leung & Ray 2013)

21

but the number of floors is, which provides a good indication of height. Leung and Ray

in their study on the energy consumption of tall buildings, collected energy

benchmarking data of office buildings, with at least 80% of their total area used as office

space. This eliminated possible discrepancies created with different building uses. 706

buildings were studied. Results show the difference in energy consumption between

buildings of 9 to 50+ floors, measured in energy usage intensity (kBtu/m2 /yr). The

analysis revealed that lower buildings consume less energy on average than taller

buildings (Fig.12). Results show a steady increase in EUI between 1-29 floors, with a

rapid escalation at 30-39 floors, after which a plateau is reached for tall building

construction. An important consideration in the EUI escalation between the 30th and 39th

floor and the EUI balance that followed, is that buildings of that height to date are mostly

exposed to the sky and don’t experience wind or sun shading from other structures

(Leung & Ray 2013).

The tall structure of the skyscraper also affects energy consumption for heating

and cooling, in relation to altitude. The built environment is located within the

troposphere, which extends from sea level to sixteen kilometers high. However, the

typical height of skyscrapers is within the range of 300-400m high. Within the

troposphere, dry bulb temperature decreases with height at an almost linear rate, of

approximately 1 °C per 150m (EnergyPlus 2015b; U.S. Government Printing Office 1976).

Lotfabadi studied the decrease in temperature with altitude and its effects on energy

consumption for Tehran’s International Tower, in Iran, the highest residential tower in

the country up to 2012, with a height of approximately 164m. EnergyPlus simulation

program was used to estimate the reduction in cooling, while maintaining thermal

control setpoints, and it was revealed that 2.4% reduction was achieved just by changing

the variable of altitude that as a result decreased temperature in relation to height. The

study also revealed that 1.5% of the energy savings for ventilation were achieved by

lower air density alone at higher altitudes, as thinner outdoor-air requires less energy to

cool (Lotfabadi 2014), as well as to heat in that respect.

In regards to energy conserved all year round, the large-scale windows used

throughout the tower, sized: 1.4m x 3.0m with overhang shading devices of 1.2m deep,

22

result in energy efficiency in both cooling and heating, due to the different angles of the

sun between summer and winter, e.g. Mediterranean climate, where shading devices

prevent high-angle summer sun penetration, while allowing for low-angle winter sun

access. Passive heating is also enhanced by the location of the tower: a flat, unobstructed

site that receives both diffuse and direct beam radiation, and the fact that Tehran enjoys

approximately 300 days of sunshine per year. The large scale of the windows also allows

for increased natural day lighting, reducing energy consumed for artificial lighting.

In the example of the Freedom Tower in New York City (Ellis & Torcellini 2005), a

reduction of approximately 1.85°C was observed between the elevations of 1.5m to 284m

high. This decreased the energy consumption for cooling (summer) of the upper floors by

2.4%. Regarding annual variations for both cooling and heating energy consumption

according to height, a 9% net increase was found for both due to the decreased shading at

upper levels from other buildings. However, an analysis showed that the building

requires all-year cooling and minimum heating, which means that the annual energy

demand is essentially for cooling (Ellis & Torcellini 2005; Leung & Ray 2013). It is

important to note that that there is no provision for shading devices in the design of the

tower, and that the Freedom Tower is an office building with a number of other public

amenities, e.g. restaurants, and its internal heat gains are great, increasing thus the need

for cooling.

From the two examples above, Tehran’s International Tower and Freedom Tower

in Manhattan, we see that the considerations for estimating and reducing the energy

consumption in high-rise construction are based on a number of variables. So, the

reduction of ambient temperature with altitude can be a plus during the summer in a

warm climate, but it may create liabilities during winter, unless other design parameters

are considered, e.g., passive heating. In summary, design strategies like appropriate

orientation of the structure for blocking strong winds, while enhancing ventilation, as

well as the introduction of natural light through big glazed openings with the design of

shading devices for taking advantage of solar radiation without causing overheating,

become important elements in the final performance and appearance of the structure.

The wider impact of these ‘vertical cities’ has social, environmental, cultural and

23

economic consequences. Skyscrapers can accommodate diverse building services, a

combination of commercial and residential, and therefore advance the efficiency of the

land usage vertically. A good urban design strategy is able to deal with the above issues

and provide positive, vibrant places without compromising the need for development

and economic growth. The need to build high is growing as population is rising and

available land becomes scarce. The challenge is how this can be done in the most

sustainable way possible.

D. RESEARCH QUESTION:

This research intends to investigate what are the appropriate design strategies that can

promote more energy efficient skyscrapers

The typology of the skyscraper is gradually moving from the domain of the

special few cities to a widely recognized type of city development. A skyscraper located

within a dense urban fabric cannot avoid having a significant impact, but the effects of

this impact (positive or negative) are seen as important challenges towards 21st century’s

sustainable compact city. So, city density through high-rise architecture may be one

solution to sustainable development as long as these tall structures are also sustainable

and are able to reduce the burden of their resource demands in the wider infrastructure.

Malaysian architect Ken Yeang, has worked intensely on bridging the gap

between the skyscraper’s design and operation, through his ‘bioclimatic skyscraper’. By

combining his passion for tall buildings with vernacular architecture and environmental

strategies, he has created several tropical skyscrapers. His built projects are in the range

of 100-150m tall, while his conceptual designs can be over 300m. The projects show an

evolving process of bioclimatic design based on ecological principles: extensive

vegetation, sunshade, rainwater collection, natural ventilation, daylight etc. (Yeang &

Richards 2007). Yeang states that when designing tall buildings, the typology is very

different from traditional architecture, even though the climatic considerations remain

the same. He accepts that, in some respects, a skyscraper can never be truly ‘green’ due to

its size, but nevertheless he acknowledges the requirement for such a building type and

comments that green designers instead of negating it, should try to mitigate its negative

24

environmental impact and make it a good place for its habitants. He was the first to

address the issue of low energy in high-rise construction. This research focuses on the

energy consumption of the skyscraper and investigates design strategies towards its

energy efficiency by studying closely the skyscraper’s design in relation to its meso and

microclimate.

D. METHODOLOGY

DESING RESEARCH THEORY

The building envelope acts as a mediator between the indoor conditions and the

local climate. In climatically responsive architecture the envelope is designed in

accordance with the local environmental constraints and the building needs. In this

design process, it may be that differently oriented surfaces demand different design

approach. Ideas about spatial interior arrangement, location, size and depth of windows

as well as of shading devices also come to play. Analyzing the solar-climatic performance

of each façade will result in façade-design variations that relate to the specific energy

performance of each orientation.

Two important considerations in this process are the window-to-wall-ratio WWR

value (WWR = [window area/(outside wall area + window area)] × 100) and the design of

shading devices. A number of studies have focused on the relationship between WWR

and building energy consumption (Yang et al. 2015; Inanici & Demirbilek 2000). Depth,

size, shape and angle of the shading devices should ideally correspond to the building’s

location (latitude, altitude, elevation) and the orientation of the façade (Palmero-Marrero

& Oliveira 2010). The optimum length and height of the shading devices for advanced

energy efficiency of each orientation can be best calculated with the use of thermal

simulation programs (Ahmed & El Monteleb 2012). Similarly, the WWR value is also

relevant to the specific climatic conditions of the building’s location. In cold climates

where solar heat gain is needed, increased window sizes with S, SE and SW orientations

(in the Northern hemisphere) minimize heating requirements. In warm climates,

increased solar radiation advances the cooling energy requirements, so smaller WWR

values present better results (Yang et al. 2015). However, low WWR may compromise eye

25

contact with the outside and natural light. Highly sophisticated modern technology of

windows with low solar heat gain coefficient (SHGC), is able to reduce the intense

differences between window sizes and energy consumption (Kim et al. 2014). SHGC is

the degree of solar heat radiation through the window with values 0-1.

Energy consumption is calculated in relation to indoors thermal comfort

standards (Givoni 1981). Within this comfort zone the acceptable temperature range

according to the Predicted Mean Vote (PMV) model by Fanger, for winter, lies between

20-23°C, and between 23-26°C for the summer (ASHRAE 2004). Clothes control heat

exchange between the body and the exterior environment, by forming a barrier. Also, the

metabolic rate, that is the chemical energy a person frees from their body per unit of time,

or else the amount of heat produced according to activities conducted, influences the

requirements for thermal comfort. Moreover, the effect of weather conditions (climate),

both on a physical and psychological level of the individual, seems to be very important

even though it is not included in the PMV variables (Humphreys & Nicol 2002). De

Dear’s analysis of the ASHRAE database found that people were much more tolerant to

the thermal variations of naturally ventilated buildings (NV) than those of centrally

conditioned ones (AC) (Humphreys et al. 2013). Nevertheless, a building could be

operating in both modes during a year. It is worth noting that changes of climate have a

time lag before affecting indoor comfort temperatures and that this depends on the

thermal inertia of the building. The role of mechanical heating and cooling is to balance

out heat losses from the building. Achieving thermal comfort with minimum energy

consumption is an important principle of green architecture. The structure operates at a

higher-efficiency by consuming less energy without compromising interior comfort

conditions. In this process, the building envelope mediates between the interior

environment and the exterior climatic conditions in order to regulate the indoor

temperature.

Thermal conductivity or U-value is a material property vital in the assessment of

the thermal performance of building elements. In ASHRAE Standard 90.1 1989, ‘Energy

Standard for Buildings Except Low-Rise Residential Buildings’ HRAE 2013), the U-value

is described as the time rate or heat flow per unit area under steady conditions from the

fluid on the warm side of the barrier to the fluid on the cold side, per unit temperature

26

difference between the two fluids [W/(m²·°C)]. The U-value of a composite wall-section is

calculated from the sum of the thermal properties of the single layers. A low U-value

implies lower conductivity and higher insulation, and vise-versa. Thus, the choice of

materials and their combinations provide information on their thermal behavior. The

thermal properties of the building elements, as well as other characteristics like WWR,

type of windows and shading devices, and their variations according to orientation,

latitude and microclimate, could provide valuable insights on the optimum envelope

design for energy efficiency. Moreover, internal heat gains resulting from electrical

appliances, lighting fixtures and people occupying the space, alter considerably the

thermal requirements of a building, and they depend on the building type (residential,

office, public building etc.).

DESIGN RESEARCH METHODS

The above theoretical background will be tested with the use of thermal

simulations of reference models. Then energy consumption will be compared with data

on energy consumption of built skyscrapers. More specifically, the methods used in this

research are divided in four sections:

1. Establishing a ‘typical energy consumption per floor area kWh/m2

(residential and office buildings) by investigating existing case studies

2. Aiming to obtain data on the energy consumption of already built

skyscrapers (e.g. by placing monitoring equipment within the premises,

collecting energy bills etc.)

3. Simulating high-rise reference structures with the intention to form design

strategies towards energy efficiency

4. In the final step, the results of method 2 will be compared with the results

of the method 3, for certain typologies.

The above methods are sub-divided in further three categories:

• Residential

• Office

• Mixed use

27

E. DESIGN RESEARCH TOOLS

Energy use monitoring and benchmarking are becoming common worldwide

practices towards energy efficiency. Aiming at the reduction of carbon emissions related

to buildings, countries such as the US and Singapore have set up policies to track and

improve the energy efficiency of the built environment by monitoring the energy

performance of the building stock. As a first step, my target will be to retrieve such

information to use as reference on energy consumption in different building uses, in a

variety of climatic conditions. The tools used in the above countries, include an online

annual building energy submission system that records utility bills by the building

owners.

The second step aims at identifying real life examples of built skyscrapers located

in the greater Tel Aviv area, and undertaking interviews with their architects, contactors

and city planning officers. Data on completed and proposed skyscrapers will be collected

and specific examples will be chosen to analyze in more detail. The parameters for the

selection, in addition to the above three categories, are: the construction completion date

(ensuring that the construction methods are up to date and that the final design complies

with Green Building Standards, in Israel), the tower height is over 100m, and that its

energy performance data are accessible. A good source of information in this process is

CTBUH homepage, and their website and offices in Tel Aviv.

An additional analytical tool comprises of thermal simulations. These will allow

to test scenarios in relation to energy consumption, during the cooling and heating

seasons, in order to ensure indoor thermal comfort (as per ASHRAE 55) The results will

be quantitatively analyzed and inform design decisions on the best possible scenarios

that combine energy efficiency and thermal comfort. However, the level of sophistication

a program has in terms of data and details input for getting close-to-reality predictions,

varies, and so may the results. The accuracy of the calculations depends on the data

input, but one also needs to keep in mind that what is more important are the trends

rather than the exact figures, which can be affected even by marginal mistakes or changes

of input data. Weather data are also an essential variable of the simulation process. They

interrelate the structure with the climate of the proposed location. By operating complex

28

thermodynamic equations the simulation program estimates the building’s behavior in

relation to the local weather. The real-life data of the weather file work with the data

input of the simulated building. So, the more detailed and analytical the building input

data, the closer to reality the results can be. This method of analysis provides the

flexibility to evaluate different design alternatives of a building’s final form, in an

economical and quick fashion (Nimlyat et al. 2014).

Highly sophisticated thermal simulation programs, like EnergyPlus, evaluate the

thermal transmittance of a building component by the following characteristics: thickness

(m), density (kg/m3), heat conduction (W/m K) and specific heat (J/ kg K),. EnergyPlus

also includes a variable in its calculations that estimates wind acceleration with height,

according to ASHRAE (2009) equation in Chapter 24: Air flow around Buildings, and air

temperature drop by elevation (EnergyPlus 2015c), which is an important aspect of this

research, making EnergyPlus the more widely accepted simulation engine.

Models of skyscrapers of different heights, e.g., 100m/200m/300m/400m tall (400m

high is considered a threshold in today’s urban environments), will be simulated and

energy consumption will be tested according to the three main variables: first, a design

strategy according to the building’s immediate environment (orientation, prevailing

winds); second, the thermal properties of the building envelope; and third, the effect of

height in energy performance.

The climatic characteristics of Tel Aviv, Israel, will be selected as the main location

for the simulations. Tel Aviv Municipality's Planning and Construction Committee

issued the 2025 city master plan that supports the construction of new sky-rise

development. Studying skyscraper construction in the Mediterranean climate of Tel Aviv

will provide information for many other Mediterranean as well as other Middle Eastern

cities, undergoing a similar process.

Finally, the simulation results will be compared against data of real life buildings

obtained through on-site monitoring and/or energy bills. These comparisons will be

possible for buildings that share similar data, e.g. building use, building height,

(possibly) location etc. This process will help to link the design of the skyscraper with its

29

energy consumption and will assist in the process of forming design strategies that relate

to its energy efficiency.

The further sub-division between the different building uses relates to the effect

that internal heat gains have on energy consumption, a topic mentioned above, e.g.

example of Bank of America tower, in New York. More specifically, the increased internal

heat gains of an office building, stemming from considerably higher numbers of users,

lighting and electrical appliances, needs a different envelope design for energy efficiency,

when compared to a residential one. In addition, the envelope design of a typical office

building has a much higher WWR than a residential one. The higher window area, as a

result, reduces the thermal mass of the structure and affects negatively energy

consumption by limiting the temperature damping effect thermal mass usually has.

The study of the above building uses, residential and office, and their

comparisons, will be very important in forming design strategies for the skyscraper’s

energy efficiency. An increasing number of skyscrapers today have a mix of residential

and offices. How this distinction may affect the structures envelope design for energy

efficiency will be an important section in this thesis.

30

F. TIMESCALE

Table 2. Diagrammatic four Year Plan of Work for PHD studies

31

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