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BAHRAIN WORLD TRADE CENTRE

DEPARTMENT OF CIVIL ENGINEERING

Presented by:-Sugandha Singh

ID No.:-36282Civil Engineering

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TABLE OF CONTENTS

S.No. TOPIC PAGE No.I. Abstract 3

II. Introduction 5

III. Background 6

IV. Wind Tunnel Testing 6

V. Wind Turbines 7

VI. Wind Analysis 7

VII. Wind Turbine Components 8

A. Nacelle & Rotor 8

B. Bridges 8

C. Control, Monitoring & Safety System 9

D. Energy Building Interface 10

VIII. Wind Turbine Details 10

IX. Environment Friendly Building 10

X. Conclusion 12

Acknowledgement 13

References 14

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Sugandha Singh

Id No.:-36282

Civil Engineering

College Of Technology, Pantnagar

Department Of Civil Engineering

Bahrain World Trade Centre

Structural Engineering

ABSTRACT

The Bahrain World Trade Centre, also known as the Power Tower is a 240m (787ft) high 50-floor twin tower

office complex located in Manama, Bahrain. The towers were built in 2008 by the multi-national architectural

firm Atkins. It is the first skyscraper in the world to integrate wind turbines into its design. It currently ranks as

the second tallest building in Bahrain and has received various awards for its sustainability.

The two towers of the building are joined by three sky bridges of 30m span holding a 225KW wind turbine each

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totaling a 675KW wind power production. All of these wind turbines has a diameter of 29m (95 ft), weighing a

substantial 65 tonnes each and are aligned in the north direction from where wind from Persian Gulf is supposed

to blow in. The shape of the towers is sail-shaped are designed so as to funnel wind through the gap to provide

accelerated wind passing through the turbines. This was confirmed by wind tunnel tests, which showed that the

buildings create an S-shaped flow, ensuring that any wind coming within a 45 angle to either side of the central

axis will create a wind stream that remains perpendicular to the turbines. This significantly increases their

potential to generate electricity. Furthermore, the difference in the vertical shape of the towers helps reduce the

pressure difference between the bridges, which, when combined with an increased wind speed also provides an

equal velocity amongst the turbines. All this provides for an even greater efficiency in the powering of

generators.

On performing various ground tests, it is supposed that these wind turbines will be providing 11-15% of the total

energy requirement of both the towers. There are various other features that make it environment friendly such

as reducing carbon emission, providing kinetic insulation, etc.

Keywords-kinetic insulation, wind tunnel test, reflection pools, airflow, aerofoils

I. INTRODUCTION

The Bahrain World Trade Centre located in Manama, Bahrain, a huge project to rejuvenate an existing hotel and

a shopping mall. It is located near the Arabian Gulf where a huge wind load acts on the buildings. The building

is a twin tower skyscraper of height 240m and 50 storeys and are harmoniously integrated on the top of a three

storey sculpted podium and basement which accomodates various malls, residential houses, offices, etc,. The

two towers are made of the shape of a sail and are connected through three skybridges of 30m span consisting of

a wind turbine each of diameter 29m and weighing 65 tonnes. Each wind turbine produces 225KW electricity

totalling 675KW. This fulfills 11-15% requirement of the building. On an average, it produces 1.1-1.3 GWhr

electricity a year. In addition to producing electricity the building is also very environment friendly and is

designed in such a way that it reduces carbon emission.

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The elliptical plan form and sail like profiles acts as aerofoil, funneling the wind between them as well as

creating the negative pressure behind, thus accelerating the wind velocity between the two towers. Also, the

sculpting of the towers is a function of airflow dynamics. As the tower taper upwards, the aerofoil section

reduces which when combined with the effect of increasing velocity at increasing heights create nearly equal

wind velocities around each wind turbine. Such a relationship between shape and spatial arrangement of towers

and the effect of wind was confirmed by the wind tunnel testing confirming that creating an S-flow whereby the

centre of the wind stream remains nearly perpendicular to the blades of turbines being within the 45 to the

central axis of the turbine.

Earlier, there was a problem of high cost which was reduced to about 3.5% of the total cost of the project due to

use of off-the-shelf technology for the turbines. There are various other features that make it environment

friendly such as reducing carbon emission, providing kinetic insulation, etc.

II. BACKGROUND

Bahrain World Trade Centre is situated in the Middle East near the Arabian Gulf, designed by the multinational

company Atkins chief architect Shaun Killa. The concept portrays that Bahrain is committed to options that

reduce demand on fossil fuel energy reserves and will move urban and building design in desert climates in a

more sustainable direction. The wind climate in the Arabian Gulf with its dominant sea breeze characteristics is

conducive to harnessing wind energy. As BWTC is a high rise building, the wind load on it would have been

very high, thus in order to avoid such a problem, the designers designed the building in such a way that it acts as

an aerofoil and the sea breeze from the Gulf when enters in between the two towers gets funnelled and

accelerated creating an S-flow. This accelerated wind acts on the horizontal wind turbines perpendicularly

resulting in their revolution around the horizontal axis thus generating electricity. The premium on this project

for including the wind turbines was less than 3% of project value.

III. WIND TUNNEL TESTING

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It is a technique used for modeling of wind effects on buildings and structures designed to produce turbulent

boundary layer models of the natural wind. Wind tunnel tests currently being conducted on buildings and

structures can be divided into two types-

a. The first is concerned with the determination of wind loading effects to enable the design of a

wind resistant structure.

b. The second is concerned with the flow fields induced around the structure.

The type of test used to determine wind loading effects can be further divided into those which are quasi-steady

and those which model dynamics of both wind and structure. The quasi-steady type of test usually involves the

measurement of mean, also called static pressure distribution of force on a structure. In the dynamic approach

test we model the velocity profile and turbulence characteristics of the natural wind correctly.

The process is conducted by modeling the natural wind accurately. The minimum requirements for this are

similarity of velocity profile (Vz /VG), turbulence intensity (v/Vz) and power spectral density of the longitudinal

component.

Velocity measurements are made using a hot wire or hot film anemometer. The hot wire anemometer is named

so because it measures velocity fluctuations by detecting electrically the change in temperature of a heated wire

caused by the change in fluid velocity.

Air is blown or sucked through a duct equipped with a viewing port and instrumentation where models or

geometrical shapes are mounted for study. Usually a series of fans is used to blow the air as it is not practical to

use a single large fan for a single large wind tunnel. Various techniques are used to study the actual airflow

around the geometry and compare it with theoretical results, which must also take into account the Reynolds

number and Mach number for the regime of operation.

IV. WIND TURBINES

Wind turbines, on the basis of their axis, can be classified as:-

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A. Horizontal axis

B. Vertical axis

In horizontal axis wind turbines are uni-directional i.e., they turn to face the direction of the wind whereas the

vertical axis wind turbines are omni-directional. Although in Bahrain World Trade Centre, horizontal wind

turbines are used due to the fact that vertical turbines are not available for the building operations. But the

horizontal wind turbines face the drawback of only being able to operate with wind from a limited azimuth

range if the problems with b lade deflections and stressing through excessive skew flow are to be avoided. Thus,

leading to large scale integration of the wind turbines in the building.

V. WIND ANALYSIS

Three horizontal wind turbines are pole mounted on three sky bridges in order to generate electricity and utilize

the wind load which could have had destructive impact on the skyscraper. These turbines deploy the principle of

a fixed turbine. Extensive wind tunnel modeling have shown that the incoming wind is in effect deflected by the

towers in the form of an S-shaped stream line which passes through the space between the towers at an angle

within the wind skew tolerance of the wind turbine. These wind turbines can be operated only when wind with

angle between 270 and 360 but as a factor of safety its operation is limited to a range of 285 and 345. If wind

direction is outside this range then the wind turbines will attain a standstill mode i.e., they will not rotate.

The funneling of the towers has the effect of amplifying the wind speed at the turbine location of up to 30%. A

building permits flow around a free end and the incident free stream is a turbulent boundary layer with mean

velocity increasing with height and turbulence intensity decreasing with height. The amplification due to

funneling, in conjunction with the shape of the tower (large effect at the ground) and the velocity profile of the

wind lowest at the ground has the effect of balancing the energy yield to the extent that the upper and lower

turbines will produce 109% and 93% when compared to 100% for the middle turbine.

VI. WIND TURBINE COMPONENTSThe wind turbines used in this project consists of the following key components:-

A.Nacelle and Rotor

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A nacelle is a term used for cowling containing gearbox, brake, controls, etc., and in addition there is a

rotor attached to it. The nacelle is so designed that it is placed on the top of the bridge rather than inside

it. The rotor blades are bolted onto the hub at a fixed angle and the profile has been designed to ensure

that the moment the wind speed becomes too high. It creates turbulence on the leeward side of the rotor

blade and prevents lift, stalling the blade so that the power output stabilizes at a maximum output.

The full power of 225KW is achieved at the speed of 15-20m/s. At the time of high wind speeds, in the

operating or standstill modes, the tip of the blade extends under the centrifugal force and rotates to act as

self governing brakes.

B. Bridges

The three sky bridges join the two towers and also support a wind turbine each. These bridges are 30m in

span. The lowermost bridge is at a height of 60m, middle one at 98m and the uppermost one at 136m.

For designing the bridge, it is important to determine loads on the rotor through the nacelle and then onto

the bridge and buildings so that the structure can be analyzed for strength and fatigue. Prior to designing

of these bridges, a total of 199 different load conditions were modeled for each turbine, and it was shown

theoretically that it is safe and that the bridge and turbine would survive without excessive fatigue.

The bridges are ovoid in section for aerodynamic purposes. The bridges that span 31.7m and support a

nacelle with a mass of 11 tones have been designed to withstand and absorb wind induced vibration and

vibrations induced by both an operating and standstill turbine. Further precautions for vibration

included in the design to allow the bridge to be damped, if the practice vibrations are found to be

problematic. These precautions include the facility in the design to add spoilers to the bridge and to

adjust the tuned mass dampers.

It is shallow V-shaped in plan (173) to take account of blade deflection during extreme operating

conditions and to afford adequate clearance and thus avoid blade strike. The blade clearance to bridge is

1.12m. The worst scenario is with blade tips extended giving a factor of 1.35 safety margin, and under

this condition adequate clearance is still achieved. Additionally a laser blade position monitoring system

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is incorporated that will set the turbine to standstill if deflections become excessive.

C. Control, monitoring and safety system

These are various systems installed in the turbines to control and monitor them so that they work

properly as they have an automatic shutting down system of the wind turbine when the conditionsbecome worse. There are three key features of this:-

1) Wind turbine control system (WTCS) that directly controls and monitors the turbines

2) Extended wind turbine monitoring system (EWTMS) that is a separate monitoring system developed

for this project to provide monitoring and calibration system

3) Building monitoring system (BMS) used as a means of providing connectivity from remote sensors

to WTCS and EWTMS.

D. Electrical building interface

Each nacelle has a 225kW nominally rated, 400V, closed, 4 pole induction, 50Hz, asynchronous

generator that is connected to a generator control panel inside each tower. From each generator control

panel, separate low voltage feeders connect to the interfaces on the main low voltage switchboard at

three substations. These substations supply electricity to the landlord areas of the World Trade Center

development.

TABLE I

WIND TURBINE DETAILS

Nominal electrical power

generated

225KW

Power regulation Stall

Rotor diameter 29m

Rotor speed at full load 38rpm

Air brake centrifugally activated

feathering tips

High speed mechanical

brake

fail safe type disc brake

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Low speed mechanical

brake

caliper type

Generator closed, 4 pole

asynchronous induction,

50Hz

Maximum wind speed for

blades

80m/s (any direction)

Cut in wind speed 4m/s

Cut out wind speed 20m/s (5 minute rolling

average) reduced from

25m/s for this

application

VII. ENVIRONMENT FRIENDLY DESIGN

The Bahrain World Trade Centre, aside from including wind turbine, is also an environment friendly

building. It considerably reduces the carbon emission in comparison with the other buildings in the

Middle East. Some of such design characteristics are as follows:-

1) Buffer spaces between the external environment and air conditioned spaces to reduce air temperature

and conductive solar gain. Deep gravel roofs in some locations that provide kinetic insulation.

2) Significant proportion of projectile shading to external glass facades.3) Balconies to the sloping elevations with overhang to provide shading.

4) Where shading is not provided to glazing, a high quality solar glass is used with low shading

coefficient to minimize solar gains.

5) Low leakage windows- Building air leakage denotes the passage of air through the outer structural

components of the building including the walls, windows, doors, roofs and floors. Wind pressure is

positive on the upwind side of a building and is negative on the downside, so air leakage caused by

wind tends to flow through the building. The magnitude of negative pressure on the downwind side

of the building is much less than the magnitude of the positive pressure on the upwind side. This is

because the kinetic energy of the wind is dissipated in turbulence on the downward side.

6) Enhanced thermal insulation for opaque fabric elements.

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7) Dense concrete core and floor slabs presented to the internal environment in a manner that will level

loads and reduce peak demand with associated reductions in air and chilled water transport system. A

chilled water applied system uses chilled water to transport heat energy between the airside, chiller

and the outdoors. These systems are more commonly are found in large HVAC installations given

their efficiency advantages. Another benefit of a chilled water applied system is refrigerant

containment. Having the refrigeration equipment installed in a central location minimizes the

potential for refrigerant leaks, simplifies refrigerant handling practices and typically makes it easier

to control the leak if wonders occur.

8) Variable volume chilled water pumping that will operate with significantly less pump power at part

loads than conventional constant volume pumping

9) Low pressure loss distribution for primary air and water transport systems that reduces fan and pump

power requirements

10) Total heat energy recovery heat wheels of fresh air intake and exhausts to recover coolth from the

vitiated air and recover it to the fresh make up air

11) Energy efficient, high efficacy, high frequency fluorescent lighting

12) Dual drainage systems that segregate foul and waste water and allow grey water recycling to be

added at a later date

13) Connection to the district cooling system that will allow an order of magnitude improvement on

carbon emissions since in Bahrain efficient water cooled chillier are not allowed due to water

shortage, whereas the district cooling solution will involve sea water cooling / heat rejection andmuch improved levels of energy conversion efficiency

14) Reflection pools at building entrances to provide local evaporative cooling

15) Extensive landscaping to reduce site albedo, generate C02 and provide shading to on grade car parks

16) Solar powered road and amenity lighting

VIII. AWARDS

Various awards have been awarded to the Bahrain World Trade Centre for its innovation and sustainability.

Some of such prestigious awards are NOVA award for innovations, The 2006 LEAF Award for Best Use ofTechnology within a Large Scheme and The Arab Construction World for Sustainable Design Award.

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IX. CONCLUSION

The Atkins designed the Bahrain World Trade Centre, made history today as the turbines on this

pioneering project turned together for the first time. It is an iconic landmark to integrate wind turbines on

such a scale into a commercial development.

The building has been so designed that it serves the need of the hour. It reduces the consumption of fossil

energy which is a non renewable source and utilizes the renewable source that is wind. It takes urban and

building design in desert climate in a more sustainable direction. The towers have been sculpted according

to airflow dynamics. A key benefit from this project is the knowledge and experience gleamed which can

be disseminated to design teams globally. In this project, the use of wind turbines costs less than 3% of the

project value.

Its an environmentally responsive design. It produces technically viable solutions and balances energy

yield. In this building, each nacelle operates independently and thus is not affected by the failure of

another nacelle. Thus, if any nacelle gets failed, the system will keep on functioning properly and thus the

functioning of the whole building would not be disturbed. While designing bridges, various precautions

have been taken such as bridge gets damped if vibrations are found to be problematic.

As this World Trade Centre incorporates new and innovative technology into its design, there are various

limitations associated with it. This design concept of wind turbines can be used only where the wind load

is enough to move wind turbines. The concept of wind turbines cannot be used at places where wind

direction is varying frequently and comes for a very short time into its azimuth range. This design will not

be economical and would not serve the purpose for which it is designed.

In this project, horizontal wind turbines have been used which functions within a particular azimuth range.Therefore, while designing the towers, the direction and flow of the wind is taken into care. In this, if wind

falls outside this range, the turbines attain a standstill mode. This protects the building from the probable

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harm due to wind load but if the range of operation would have been larger, we could have taken more

energy output out of it. The vertical wind turbines could be used which is Omni-directional, and thus

works for a wider range thus could have been used in the place of horizontal wind turbine. But it is not

used here as vertical turbines are not available for building applications.

The achievements of this project will probably encourage other designers and developers to consider more

innovative design solutions to reduce their buildings energy and water consumption and ultimately reduce

their carbon emission. Thus, it is a remarkable project.

ACKNOWLEDGEMENT

I would like to convey my special thanks to all who supported and helped me in making this paper. I thank

for the support extended by my family, faculty of department of civil engineering and my friends. I also

thank the authorities who provided us with the various facilities due to which I am able to present this

paper.

REFERENCES

[1]http://www.e-architect.co.uk/bahrain/bahrain_wtc_wind_turbines.htm

[2] http://en.wikipedia.org/wiki/Bahrain_World_Trade_Center

[3] Energy Efficiency Manual- Donald R. Wulsinghoff

[4] Architectural Aerodynamics- R.M. Aynsley, M. Melbourne, B.J. Vickery

[5] Simplified Building Design Fro Wind & Earthquake Forces- James Ambrose, Dimitri Vergun

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