Bahrain World Trade Centre Name Mohamed Alsubaie MMU ID 09562211 Supervisor Dr. Mahera Musallam Assignment Wind Turbine Design Subject Renewable Power Systems Unit code 64ET3901 Course BEng (Hons) Computer and Communication Engineering
Table of Content TABLE OF CONTENT 1 TABLE OF FIGURES 2 TABLE OF TABLES 2 1. INTRODUCTION 3 1.1 ABOUT BWTC 3 2. BACKGROUND 4 2.1 WINDS IN BAHRAIN 4 3. TOWERS SHAPE 5 4. WIND TURBINE 7 5. BRIDGES 8 6. ECONOMIC ANALYSIS 8 7. CONCLUSION 9 8. REFERENCES 10 1
Table of Figures FIGURE-1: BAHRAIN WORLD TRADE CENTRE. 4 FIGURE-2: TOWERS EFFECTS ON CHANGING WIND SPEED AND DIRECTION. 6 FIGURE-3: CFD MODEL SHOWING AIRFLOW PATTERNS NEAR TOWERS. 6 FIGURE-4: WIND TURBINE COMPONENT. 7 FIGURE-5: THE POWER CURVE FOR NORWIN 225KW TURBINES. 7 FIGURE-6: THE V-SHAPE OF THE BRIDGE. 8 FIGURE-7: ANNUAL ENERGY YIELD FOR NORWIN 225KW TURBINES. 8 Table of Tables TABLE-1: WIND SPEED AND POWER DENSITY FOR YEARS 2003 2005 IN BAHRAIN AT DIFFERENT HEIGHT. 5 TABLE-2: WIND TURBINE DETAILS (NORWIN 225KW). 7 TABLE-3: ENERGY YIELD. 9 2
Bahrain World Trade Centre 1. Introduction Thousands of years ago, human beings learned how to use wind as an energy source. The first usage of the wind power was to sail ships on the ocean. Then, it was been used to grind grains and pump water. In addition, due to the development in the world wind power has been used to generate electricity, because it offers pollution-free solutions, excellent supplement and it is renewable source. Today, large wind-power plants are supplying an economical clean power in many part of the world. Wind turbines are normally located far from people who use it. However, Bahrain World Trade Centre is a modern project aims to benefit from the wind energy and convert it into useful energy to be used in skyscrapers or commercial buildings. This report covers the design aspect of BWTC project. It will describe the details of the building location, physical characteristics, economic and performance of wind power system showing how innovative ideas have come together to create this unique building. 1.1 About BWTC The Bahrain World Trade Centre was completed in 2008 costing about $150 million. It was the master-plan of rejuvenating an existing shopping mall and hotel on Bahrain s capital Al- Manama which is site at the edge of the Arabian Gulf. The concept design of the twin towers was inspired by the traditional Arabian Wind Towers in that very shape of buildings harness the unobstructed prevailing onshore breeze from the gulf, providing a renewable source for this project. Previous research and attempts at integration turbines were not successful because it very expensive. Such endeavours would raise cost of the project up to 30%. However, designers from Atkins Architects and Norwin turbine specialists were able to design an integrated turbine system that will only needs 3% on the project costs. This lowered construction costs and creative design make the BWTC a significant step toward innovated cost effective designs. Moreover, this project has generates a new standard for sustainable development by using the first horizontal axis wind turbines (Killa and Smith, 2008). The twin towers reach a height of 240m (787 ft) and support three 29m diameter large scale horizontal axis wind turbines. The two 50 storey sail shaped office towers provide a new shopping centres, accommodation, restaurants and business centres (Alnaser, 2008). 3
The Bahrain World Trade Centre generates a new standard model for innovation in sustainable design as the first skyscraper in the world to insert large scale wind turbines within its structure. This project received many awards in the area of sustainability, 2006 LEAF Award, The Arab Construction World for Sustainable Design Award, a 2008 Best Tall Building Award, and finally an honourable mention in the 2009 NOVA (Wu, 2009). Figure-1: Bahrain World Trade Centre. 2. Background 2.1 Winds in Bahrain Most of the studies show that the average wind speed in Bahrain is between 5 and 6 m/s with north to north west direction. In this case, the wind energy potential is not consider to be an economically viable because the full load hours of wind per year do not exceed 1360 h/y. Moreover, the electricity supply from the wind dose not exceeds 0.1 TWh/year which is very low comparing to all Middle East and North Africa region (Bachellerie, 2012). 4
However, another study was continued in investigating the wind power distribution at height of 10m, 30m and 60m. The study found that, the average annul wind speed 4.56 m/s for 10m height, 6.96 m/s for 30m height, and 8.65 m/s for 60m height. While, the average annul wind power density in 10m height is 114.54 W/m², in 30m height is 433.29 W/m², and in 60m height is 816.70 W/m² (Table-1). These results were showing good wind potential and strong winds of long duration which is suitable for wind power production (Jowder, 2009). Table-1: Wind speed and power density for years 2003 2005 in Bahrain at different height. 3. Towers Shape An important factor that makes this project successful is the towers physical characteristics. The shape and curves of the twin towers acts as an airfoil and funnels winds coming from the Arabian Gulf between them. Servicing as airfoils, the towers can reroute wind to amplify the wind speed at the wind turbine location of up to 30% (Killa and Smith, 2008). It can be clearly seen in figure-2, that the building is creating a negative pressure zone behind, which accelerate the velocity of wind towards the turbines. Since wind speed change with height, the higher turbine will spin faster and create more power than the lower turbines. The engineers found that the key of making the turbines work is the shape of the towers. Therefore, the building has a tapered shape in order to adjust for these changing wind speeds. The turbines will have approximately stable vertical velocity profile, where the lower, centre and higher turbines are almost equal at 93%, 100% and 109%, respectively, even with higher wind speeds at higher altitudes. The towers shape allows any wind coming with in 45º angle to either side of the central axis will generate a wind stream perpendicular to the propellers, considerably increasing the turbines ability to harness wind streams (Wu, 2009). 5
Figure-2: Towers effects on changing wind speed and direction. An extensive wind tunnel modelling has been validated using CFD modelling showing that the incoming is in effect deflected by the towers forming an S-shape streamline which passes between the towers, as it illustrated in figure-3. Engineers predict that the turbine will be able to work with wind directions between 270 and 360. However, caution has been applied by increasing the limits of the range of the operating turbine predictions and initial operating regimes between 285 and 345. The turbine will automatically adopt a standstill mode for all wind direction outside of this range (Killa and Smith, 2008). Figure-3: CFD model showing airflow patterns near towers. 6
4. Wind Turbine The towers are linked by three sky bridges with each holding a 29m diameter horizontal-axis wind turbine. They have been mounted at 60m, 120m and 180m high between the two towers. The three wind turbines, which have a 20-year life, were lifted into place in March 2007 and they turned together for the first time in April 2008. Each turbine has the capacity to generate 225kW power production of energy totally 674kW (Killa and Smith, 2008). A summary of the turbine details can be found on table-2 below. Table-2: Wind turbine details (Norwin 225kW). The turbine has rotor blades, nacelle, bridge, control, monitoring and safety systems and electrical building interface. The nacelle is the cowling containing break, gearbox, shafts, generator, cooling system and associated control systems. The generators are of a four-pole 400V asynchronous induction type, which require little maintenance and can be controlled by centres established in the towers (Wu,2009). The stall control is responsible for cuttingout wind speed of 20 m/s. With limiting the power of the turbine at high speed wind, turbulence on the leeward side of the blades prevents lift and stabilizes output to maximum. According the plot on figure-5, the turbine full power of 225kW is achieved at wind speed between 15 to 20 m/s, depending on air density (Alnaser, 2008). Figure-4: Wind turbine component. Figure-5: The power curve for Norwin 225kW turbines. 7
5. Bridges The structures of the bridges have been design to be strong enough to hold the 11 tonnes wind turbines. The bridges of 31.7m length are having curved shapes for aerodynamic purposes in order to absorb the vibration of wind and vibrations from operating and standstill of the turbine (Alnaser, 2008). Moreover, the bridge is having a V-shape, in order to deal with the blade deflection during extreme operating conditions and to have enough clearance and thus avoid blade strike. It can be clearly seen in figure-6, that blade clearance to the bridge of 1.12m is achieved with V- shape of 173 º angle. Even in worst scenario with extending the blades tips, the safety margin required will be 1.35m, and with this condition the clearance is still achieved (Killa and Smith, 2008). Figure-6: The V-shape of the bridge. 6. Economic Analysis The total cost of Bahrain World Trade Centre building is $150 million. Only 3% of the total cost is the price for the wind turbine system. The three wind turbines operate about 50% of the time. The planned energy yield from the turbines taking into account wind and availability data is summarised in table-3 below. Therefore, the total annual amount is Figure-7: Annual energy yield for Norwin 225kW turbines. 8
between 1,100 and 1,300 MWh per year. This is approximately 11% - 15% of the entire structures total power consumption, which is also enough to power up to 300 home. In carbon emission terms this equates to an average of 55,000 kgc. Since turbines are being placed over 60m above ground and between towers, the yield might even be higher (Killa and Smith, 2008). Table-3: Energy yield. Turbine # 1 Turbine # 2 Turbine # 3 340 to 400 MWh/year 360 to 430 MWh/year 400 to 470 MWh/year 7. Conclusion Categorizing the entirety of the BWTC as a true green initiative and project simply is not true. According to the European and other world-wide standard, this building is not intended to be a low carbon emission solution and only reduced the carbon emission comparing to other buildings. However, the design and construction of the building and the integration of large scale wind turbines into it has involved extensive research and development by probably some of the most capable specialists available. In addition, it should be appreciate and understand this project as a pioneering step toward sustainability design through the potentials of modern engineering and architecture. 9
8. References Alnaser, N.W., 2008. Towards Sustainable Buildings in Bahrain, Kuwait and United Arab Emirates. [pdf] Available at: <http://www.benthamscience.com/open/tobctj/articles/v002/30tobctj.pdf> [Accessed 10 January 2013]. Bachellerie, I. J., 2012. Renewable Energy in the GCC Countries Resources, Potential, and Prospects. [pdf] Available at: <http://library.fes.de/pdf-files/bueros/amman/09008.pdf> [Accessed 10 January 2013]. Jowder, F. A. L., 2009.Wind power analysis and site matching of wind turbine generators in Kingdom of Bahrain. [pdf] Available at: <http://ipac.kacst.edu.sa/edoc/1430/176905_1.pdf> [Accessed 10 January 2013]. Killa, S. and Smith, R. S., 2008. Harnessing Energy in Tall Buildings: Bahrain World Trade Center and Beyond. [pdf] Available at: <http://www.ctbuh.org/linkclick.aspx?fileticket=dgjd8kpuhrk%3d&tabid=1720&lan guage=en-gb> [Accessed 10 January 2013]. Wu, K., 2009. Bahrain World Trade Center. [pdf] Available at: <http://www.greendesignetc.net/buildings_09/bulding_wu_kevin_paper.pdf> [Accessed 10 January 2013]. 10