Utilization of Wind Energy in Fast Developing High-Rise Buildings A Case Study of the Pearl River Tower, Guangzhou, China Rasha Mazen*1, Magdy Radwan2 and Mohamed Abdel-Samiea2 1 Architectural Department, Sohag University, University, Sohag, Egypt Egypt 2 Architectural Department, Assiut University, University, Assiut, Egypt * Corresponding Author:
[email protected] [email protected] Abstract: This paper is aimed at estimating the possible energy generation by wind in high rise buildings. The 71-strory, 310m height Pearl River Tower in Guangzhou, China is selected as a case study. The tower being designed as office building for Chinese National Tobacco Company (CNTC) headquarters has a 2 2 total gross area of 210,000 m of which 40,000 m for 5-story basement. The energy demand of the tower including the office spaces as well as the technical systems such as water pump system, elevators, control and IT system, fire protection system, etc. is assessed also in the paper. This estimates how high the energy generation by wind contributes significantly to the energy demand of the tower. Keywords: Energy Demand, High-Rise Buildings, Renewable Energy, Wind Energy.
1 . In In t r o d u c t i o n
One of the largest companies, in Guangzhou, is the Guangdong Tobacco Company, which is part of the Chinese National Tobacco Company (CNTC). In 2005, SOM (Skidmore, Owings & Merrill) was hired to design a headquarters tower for CNTC. The tower is located on the Pearl River and its name in China is Pearl City. The Pearl City covers an area of 10636 m2 and includes an office tower and podium with a floor area ratio of 16. The tower was developed into a 71-story building with height of 310 m and total gross area of 210,000 m 2 of which 40,000 m 2 for 5-story basement for f or parking garage. The podium with associated conference facilities is a 3-story building with height of 27 m (Extravagant Network, 2009), Fig. (1).
1. Operable skylight 2. Business Club 3. Typical Office Floor 4. Integrated Wind Turbine 5. Podium 6. Cafeteria 7. Double-decker Double-decker Elevator 8. Parking Garage
Fig (1): The Pearl City.
This tower takes advantage of both high energy-efficiency building design and solar and wind power to generate energy for its consumption. Therefore, this tower is considered the first one in the world to integrate different technologies, being capable of significantly reducing the amount of energy consumption when compared with a building of this size and type. 1
This paper is aimed at assessing the energy demand of the Pearl River Tower including electrical energy for lighting, cooling and energy for equipment, air conditioning energy as determined by internal and external loads as well as services loads (elevators, fire fighting systems,…etc). This is in addition to the estimation of the energy generated by wind turbines, one of the renewable energies utilized in the tower. 2 . W i n d E n e r g y u t i l i z at i o n i n t h i s t o w e r :
Wind energy is a clean fuel source and doesn't pollute the air unlike power plants that rely on combustion of fossil fuels with a subsequent production of atmospheric emissions that cause acid rain or greenhouse gasses. Consistent with the high performance approach to building design, the use of wind turbines on the Pearl River Tower is significantly enhanced by their integration with building architecture. In Pearl River Tower, eight wind turbines are located (Hansen, 2007) at openings of dimension 6 x 6.8 m 2 on two mechanical floors between the three main sections of the tower. Confining the turbines to the mechanical floors reduces the noise and vibration and also simplifies maintenance (Stewart, 2006). The Pearl River tower implements vertical axis Darreius wind turbines, Fig. (2), as they are capable of harnessing winds from prevailing wind directions with minor efficiency loss. The turbines are located on both the north and south sides of the tower in order to take advantage of prevailing southern winds (Fortmeyer, 2007, Wong, 2007). The wind causes a large build-up of positive pressure on the windward side of the building. Vortex shedding around the sides and over the top of the building creates a large negative pressure on the leeward side of the building. In allowing air to pass through the building openings, the differential pressure from front to back is reduced and the forces on the building are, in turn, reduced (Stewart, 2006, Fortmeyer, 2007), Fig. (3). This approach from the structural point of view allows for a reduction in the quantity of steel and concrete to maintain building's stability (Frechette and Gilchrist, 2008). The shape of the building's façade accelerates (Stewart, 2006, Fortmeyer, 2007) the wind through the turbines. SOM engineers initially estimated that the wind speed would increase to 1.5 times the actual ambient wind, but the funnel shape of the structure at the mechanical floors resulted in increase of the wind speed by a factor as high as 2.5 (Koerner, 2006, Hansen, 2007).
Fig (2): The vertical axis Darreius wind turbine.
Fig (3): Air flow through building openings.
3. Energy Demand o f Pearl River Tower
The same as for any building, the energy requirement of Pearl River Tower being an administrative building can be classified as electric energy, air-conditioning energy and energy for service loads. The electric energy includes that for cooling, equipment and lighting. The air conditioning energy is to cover internal and external loads requirements. The internal loads are due to office equipment, office lighting and heat given off by people in the office. The external loads depend greatly on the surface p roportion of the glazing as well as the sun-protection tools on the facades of the tower. Thus, the transmitted sun irradiance through the tower façade and associate space heating represent an extra load
2
on the air-conditioning system. The service loads of the tower include power demand for basement, water pump system, fire-fighting system, control & IT system and kitchenettes. 3.1 Design Considerations: A survey on 6000 buildings in the USA showed a range of total electricity consumption for offices and commercial buildings between 165 and 220 kWhm -2a-1. If about 60 kWhm-2a-1 is subtracted for lighting and 50 kWhm -2a-1 for cooling, this corresponds to average electricity consumption for equipment between 55 and 110 kwhm-2h-1 (Eicker, 2009). About 50% of internal loads are caused by office equipment such as PCs (typically 150W including the monitor), printers (190 W for laser printers, 20 W for inkjets), photocopiers (1100 W), etc., which leads to an area-related load of about 10 – 15 Wm-2. Modern office lighting has a typical connected load of 10-20 Wm -2 at an illuminance of 300 - 500 lx. The heat given off by people is around 5-7 Wm -2 in an office (Eicker, 2009). External loads depend on the ratio between window and floor surface area and the chosen shading system. For ratios between 0.1 and 0.7, the transmitted external loads are between 8 and 60 W m -2 of average surface area of the building (Eicker, 2009). The elevators in the building are so fast with an average speed of 9 m/s and about 1.6 ton load. The power demand of such elevator is 178 kW (Mizuguchi, et.al, 2005). The average power demand of the basement was assumed 10 Wm -2 (Siemens, 2008). For a building with 11-stories and floor area of 1350 m2, the average power demands for water pump system, fire fighting system, control & IT system and kitchenettes are 30, 6, 55 and 3 KW, respectively (Siemens, 2008). 3.2 Estimation of Different Loads 3.2.1 Electric Energy: Assuming the number of working hours per day is 10 averaged over the week days. The building has total gross area 170,000 m 2. 3.2.1.1 Cooling Energy: The specific energy consumption for cooling is selected at 50 kWhm-2a-1. Therefore, the power required to fulfill the building demand of cooling energy is estimated as 50 x 170,000 / (10 x 365) = 2329 kW or 2.3 MW. 3.2.1.2 Equipment Energy: The specific energy consumption for equipment is selected at the maximum value which is 110kWhm -2a-1. Therefore, the power required to fulfill the building energy demand for equipment is estimated as 110 x 170,000 / (10 x 365) = 5123 kW or 5.1 MW. 3.2.1.3 Lighting Energy: The specific energy consumption for lighting is selected at 60kWhm-2a-1. Therefore, the power required to fulfill the building demand of illumination energy is estimated as 60 x 170,000 / (10 x 365) = 2795 kW or 2.8 MW. Therefore, the total power to meet the cooling, equipment and lighting energies is equal to 2.3 + 5.1 + 2.8 = 10.2 MW. 3.2.2 Air Conditioning Energy: 3.2.2.1 Internal Loads: As the building has total gross area 170,000 m 2, then office area is assumed 0.75 x 170,000 = 127,500 m 2 for 75% occupation of offices from the building area.
3
3.2.2.1.1 Internal load due to office equipment: The energy consumption for internal load due to office equipment is selected at the maximum value, which is 15 Wm -2. Therefore, the power required to meet the internal load (due to office equipment) on the air-conditioning system is estimated as 15 x 127,500 = 1,912,500 W or 1.9 MW. 3.2.2.1.2 Internal load due to office lighting: The energy consumption for internal load due to office lighting is selected at the maximum value which is 20 Wm-2. Therefore, the power required to meet the internal load (due to office lighting) on the air-conditioning system is estimated as 20 x 127,500 = 2,550,000 W or 2.6 MW. 3.2.2.1.3 Internal load due to persons in office: T he energy consumption for internal load due to presence of persons in the office is selected at the maximum value which is 7 Wm -2. Therefore, the power required to meet the internal load (due to people in the office) on the air-conditioning system is estimated as 7 x 127,500 = 892,500 W or 0.9 MW. Therefore, the total power to meet all internal loads on the air-conditioning system is 1.9 + 2.6 + 0.9 = 5.4 MW. 3.2.2.2 External Load The energy consumption for external load is selected at the maximum value which is 60 Wm -2 of building surface area. As the tower has total gross area 170,000 m 2, then the area per story is 170,000 / 71 = 2394 m 2 as the Pearl River Tower consists of 71 stories. Assuming the floor area is rectangular in shape with length to breadth ratio equals to 5 : 1. Therefore, the length is 109.4 m and the breadth is 21.9 m. Subsequently, the surface area of the building is expressed as 2 x (length + breadth) x building height. The building height is 310 m and the surface area is 81,406 m 2. The power required to meet the external load on the air-conditioning system is estimated as 60 x 81,406 = 4,884,360 W or 4.9 MW. Therefore, the power required to meet the internal and external loads on the air-conditioning system is 5.4 + 4.9 = 10.3 MW. 3.2.3 Energy Demand of Service Loads: 3.2.3.1 Elevators load: The Pearl River Tower has 1 escalator, 12 passenger elevators and 4 freight elevators. Assuming the power demand is the same for all elevators and escalator, i.e., = 178 kW. Therefore, the total power for operation of the building elevators and escalators is 178 x 17 = 3026 kW = 3 MW. 3.2.3.2 Basement load: The gross area of the 5-story basement is 40,000 m 2 and the average power demand is 10 Wm -2. Therefore, the power required for the basement load is 40,000 x 10 = 400,000 W = 0.4 MW. 3.2.3.3 Water pump load: The power demand for the pump system is assumed to be proportional to the building height and the floor area. The power demand for a building with 11-story and floor area of 1350 m 2 is 30 kW. Therefore, the power demand for pump system in the pearl tower is 30 x (2394 / 1350) x (71 / 11) = 343 KW = 0.34 MW. 3.2.3.4 Fire fighting load: Similar to the water pump load, the power demand for the fire fighting load is 6 x (2394 / 1350) x (71 / 11) = 68 KW = 0.07 MW. 3.2.3.5 Control & IT system load: Also, the power demand for the Control & IT system load is 55 x (2394 / 1350) x (71 / 11) = 630 KW = 0.63 MW.
4
3.2.3.6 Kitchenette load: In analogy to the control & IT system load, the power demand for the Kitchenette load is 3 x (2394 / 1350) x (71 / 11) = 34 KW = 0.03 MW. Therefore, the power requirement for all service loads is 3 + 0.4 + 0.34 + o.o7 + o.63 + 0.03 = 4.4 MW Therefore, the total power demand to serve all the loads as listed above is 10.2 + 10.3 + 4.4 = 24.9 MW. 4. Renewable Energy Sourc es
The Pearl River Tower utilizes the wind and solar energy seeking "high performance building". This paper is focused on the utilization of the wind energy in the tower. 4.1 Wind speed at turbine location The ambient wind speed in Guangzhou at 10 meters height lies in the range 9 - 16 km/hr, i.e., 2.5 - 4.5 m/s. The wind speed increases with height according to Hellman's equation (Hier, 2005): vw (h) = vw(10) (h / 10) α
(1)
Where vw(h) = speed of wind at height h (m/s), v w(10) = speed of wind at height 10 m and α is Hellman's constant ( = 0.34 for neutral air above human inhabitated areas). The wind turbines are installed at the mechanical floors, which are assumed at heights 100 and 200 m. This assumes that the mechanical floors are located approximately at one-third and two-third of the building height (= 310 m). Based on an ambient wind speed of 3.5 m/s (average value) at height 10 m, the wind speed at height of 100 m is 3.5 x (100 / 10) 0.34 = 7.6 m/s and the wind speed at height of 200 m is 3.5 x (200 / 10) 0.34 = 9.7 m/s. Due the funnel shape of the openings where the turbines are located, the wind speed is increased 2.5 times its ambient value. Therefore, the wind speed, where turbines are located at the lower mechanical floor, is 2.5 x 7.6 = 19 m/s, and the wind speed, where turbines are located at the upper mechanical floor is 2.5 x 9.7 = 24.25 m/s. 4.2 Turbines' useful power The useful power developed by a wind turbine depends on the turbine radius R, wind speed at turbine location v, air density ρ (= 1.225 kg/m3) and turbine efficiency η as determined by the following equation (Dillon, 2010): P = 0.5π x ρ x R2 x v3 x η
(2)
The turbines employed in the tower are the Darreius turbines of efficiency 35% compared to 25% for the horizontal-axis turbines. The turbine radius is 5 m to suit the opening dimensions at the mechanical floors (Dillon, 2010). Therefore, the useful power developed by one turbine at the lower mechanical floor is 0.5π x 1.225 x 25 x 19 3 x 0.35 = 115,485 W = 0.12 MW. The useful power developed by one turbine at the upper mechanical floor is 0.5π x 1.225 x 25 x 24.25 3 x 0.35 = 240,104 W = 0.24 MW. The total useful power developed by the eight turbines, four at each mechanical floor is 4 x (0.12 + 0.24) = 1.44 MW. The above calculations are repeated over the wind speed range from 2.5 to 4.5 m/s in Guangzhou. 4.3 Wind energy contribution to building demand
5
Figure (4) shows the power generated by turbines and the percentage by which wind contributes to the tower energy for different values of wind speed. The figure indicates that the wind turbines contribute to the building's energy needs by about 2 - 12% which is slightly higher than the published value (Epstein, 2008). This is because the power demand of the podium was not considered as its dimensions are missing in the literature. 15
Generated Power (MW) Contribution Percentage (%)
10 5 0 2.5
3
3.5
4
4.5
Wind Speed, (m/s)
Fig (4): Wind power generated and energy contribution for different wind speeds. 5. Conclusio ns
1- The energy demand of the Pearl River Tower is estimated as equal to 10.2 MW for electric energy, 10.3 MW for air-conditioning energy and 4.4 MW for service loads. 2- The energy generation by wind turbines used in the tower lies in the range from 0.5 MW to 3 MW depending the wind speed in Guangzhou. 3- The wind energy contributes slightly to the tower energy requirements as reported in the literature. 6. Referenc es Dillon, Brendan (2010), "Pearl River Tower: Harvesting the wind for to make glorious building of natural energy", www.docstoc.com/docs/84042767/Pearl. Eicker, Ursula(2009), "Low Energy Cooling for Sustainable Buildings", J. Wiley & Sons, pp.1-20. Epstein, Kyra (2008), "How Far Can You Go?", Guangzhou High Performance Buildings, Winter, pp. 22 - 29. Extravagant Network (2009), "The world's first "zer energy" concept unveiled in Guangzhou office", http://re.chinaluxus.com/Bss/20091225/2076.html. Fortmeyer, Russel (2007), "SOM's Pearl River Tower", Architectural Record, http://archrecord.construction.com/features/digital/archives/0612casestudy-1.asp. Frechette, Rogers and Gilchrist, Russell (2008), "Towards Zero Energy - A case study of the Pearl River Tower, Guangzhou, China", CTBUH 8th World Congress, pp. 1-11. Hansen, Brett (2007), "China to construct "Zero Energy" Skyscraper", Civil Engineer, Vol. 77, No. 1, pp. 10-11. Hier, Siegfried (2005),"Grid Integration of Wind Energy Conversion Systems", John Wiley & Sons, Chic ester, USA, pp. 40-45. Koerner, Preston (2006), "Pearl River Tower, Guangzhou, China", Jetson Green, http://jetsongreen,typepad.com/jetson_green/2006/08/pearl_river_tow.html. Mizuguchi, Hiroaki, Nakagawa, Toshiaki and Fujita, Yoshiaki (2005), "Breaking the 1000mpm Barrier: High speed elevators", Elevator World, September, pp. 71-76. Siemens (2008), "Application Manual - Planning for a High-rise Building: Totally Integrated Power", www.siemens.com/tip. Stewart, Jude (2007), "Super tall and ultra green", MetropolisMag. Org; http://www.metropolismag.com/cda/stroy,php?arid=2227. Wong, Michelle (2007), " The Pearl River Tower: Skyscraping Innovations", California Engineer, Vol. 86, No. 1, pp. 13-15.
6
