ctbuh.org/papers Title: New Solar Initiatives in Supertall Buildings: The Spire at Ras Al Khaimah Authors: Philip Castillo, Executive Principal, Murphy/Jahn Architects Meiring Beyers, Associate and Project Director, RWDI Subjects: MEP Sustainability/Green/Energy Keywords: Renewable Energy Sustainability Publication Date: 2010 Original Publication: CTBUH Journal, 2010 Issue III Paper Type: 1. Book chapter/Part chapter 2. Journal paper 3. Conference proceeding 4. Unpublished conference paper 5. Magazine article 6. Unpublished © Council on Tall Buildings and Urban Habitat / Philip Castillo; Meiring Beyers New Solar Initiatives in Supertall Buildings: The Spire at Ras Al Khaimah "The Great Solar Lake and the Solar Chimney are two ideas that merit further study and through this emerging technology extend the limits of sustainability and rethink the formal Philip Castillo Meiring Beyers typology of the tall building." Authors The Spire at Ras Al Khaimah, located in the United Arab Emirates, through its unique approach Philip Castillo, Executive Principal to building form and landscape offers opportunities to examine new sustainable strategies. Murphy/Jahn Architects, LLC. The design of this 875-meter multi-use tower with its spiraling form and absence of a 35 East Wacker Drive Chicago, Illinois, USA 60601 traditional core was the catalyst for the Integrated Solar Chimney. Proximity to the Arabian t: +1 312 427 7300 Gulf and an innovative landscape concept led to the development of the Great Solar Lake, a f: +1 312 332 0274 large-scale solar pond application. The solar pond acts as the solar collector required for the e: [email protected] www.murphyjahn.com solar chimney allowing the two concepts to work in unison as an energy provider for the tower. Meiring Beyers Associate and Project Director – Sustainability Rowan Williams Davies & Irwin Inc. The Spire at Ras Al Khaimah Al Khaimah Gateway City in the United Arab 650 Woodlawn Road West Guelph, Ontario, Canada N1K 1B8 "The solution to climate crisis isn’t far off in the Emirates. Our involvement was for the Gateway City Towers district of this new city t: +1 519 823 1311 future – it's in the buildings we inhabit, our f: +1 519 823 1316 civic infrastructure and the way we organize (see Figure 1). Gateway City Towers is planned e: [email protected] with 14 towers ranging in height from 275 www.rwdi.com our lives.” [1]. The consequence is that as architects and engineers, we will have to meters up to 400 meters organized within a Philip Castillo shallow, 2 kilometers long sustainable water Throughout his 35 year career, Philip has been involved re-evaluate how our cities are planned and with large-scale urban developments and complex feature (see Figure 2). building typologies. Most notable in his association at how we design our buildings and take Murphy/Jahn, is his work with Helmut Jahn on Sony responsibility, not only for our actions but also The uses within Gateway City Towers include Center in Berlin, Germany, the Suvarnabhumi International Airport in Bangkok, Thailand and the for educating our clients so that the result is an commercial, office, hotel and residential with a Tokyo Station Development in Japan. Philip has improved environment. total area of approximately 2.5 million square embraced the ideal of Integrated Building Design; a concept that includes meaningful collaboration with In 2008, Murphy/Jahn was invited to meters. The centerpiece of the development key consultants at the outset of the design process, is the 875-meter Spire at Ras Al Khaimah, a advancing technology in building components and participate in the planning and design of Ras systems and promoting new concepts in sustainability on a larger urban scale include proposals for Gateway City Towers in Ras Al Khaimah and Jeddah Free Trade City in Saudi Arabia. Meiring Beyers Meiring Beyers obtained his PhD in Mechanical Engineering from the University of Stellenbosch in South Africa and is currently Project Director – Sustainability and Associate at Rowan Williams Davies and Irwin. He is responsible for technical leadership and consulting on a wide variety of integrated solutions for sustainable design, renewable energy and energy efficiency, comfort and urban habitability. He has specialist experience in analysis and interpretation of environmental fluid dynamics using Computational Fluid Dynamics (CFD) and physical wind tunnel modeling. Meiring has also carried out various field investigations of Aeolian transport phenomena in Antarctica and the Arctic and contributes to ongoing research in Aeolian transport. He has published and presented a number of technical papers in internationally peer-reviewed publications and conferences and leads and contributes to sustainable projects globally. Figure 1. Gateway City Tower 20 | The Spire at Ras Al Khaimah CTBUH Journal | 2010 Issue III new definition of the supertall high-rise; a framework wherein the different uses are suspended and optimized. A building like this requires a new way of thinking. It is the integration and synthesis of architecture and engineering and its approach towards sustainability (see Figure 3). This building extends Gateway City vertically and is flexible to accommodate commercial, office, hotel, residential, and special uses. This Vertical City, at 875 meters in height, can contain up to 136 floors of programmed uses in distinct, easily understood and visible components. This tower must address and deal with advanced concepts in structure, technical systems, vertical transportation and Figure 2. Arial View of Gateway City Towers and the Great Solar Pond green engineering. The prime generator is performance, not formal design, to create a low energy and comfortable building that will look and work better. The environmental strategies include those expected and standard (like building orientation as a strategy for solar loading and wind exposure, solar protection, water management, efficient mechanical and electrical systems) but push the boundaries with new concepts like the Great Solar Lake and Solar Chimney. The Client was receptive to the idea of using design features and architectural elements to improve a building's performance. On a preliminary basis, this appears achievable and will be continually tested as the design is advanced. The Great Solar Lake – A Large Scale Solar Pond Application Background Solar ponds capture and trap radiation from the sun by means of high concentration salinity gradients in large shallow salt water basins. A regular water pond with uniform or low salt concentrations would not trap solar radiation effectively because of heat losses associated with internal convective mixing. Other heat losses associated with wind exposure, evaporative losses or ground conduction can further reduce effective solar pond energy harvesting. In a solar pond, layers of varying salt Figure 3. The Spire at Ras Al Khaimah concentration are used to minimize convective mixing and heat transfer between shallow and deeper pond layers (see Figure 4). CTBUH Journal | 2010 Issue III The Spire at Ras Al Khaimah | 21 The bottom layer consists of a highly concentrated salt solution while the central layer consists of a salt concentration gradient (dense solution at the bottom and dilute solution at the top). The vertical concentration gradient in the central layer (non-convective zone) reduces convective currents induced by buoyancy effects as the pond is heated by radiation. This in turn reduces convective heat transfer between the bottom and top zones trapping radiation near the bottom and reducing environmental heat losses. Thermal Figure 4. Solar Pond Schematic energy is extracted from the bottom layer and used directly or converted to mechanical and electrical energy in Organic Rankine Cycles (ORC) (see Figure 5). Successful commercial application of solar pond power production has been demonstrated on ponds of between 0.3 hectares (70 kW, El Paso, Texas) and 25 hectares (5 MW, Beit Ha’Arava in Israel) [2]. Solar Pond Energy Conversion Efficiency and Economics Solar ponds convert, on average, 15% to 20% of the incoming beam and diffuse solar radiation into a steady supply of thermal energy. Higher extraction rates are available for Figure 5. Solar pond power production schematic: Solar radiation heats the pond bottom short intermittent periods without significantly saline layer (1). Thermal energy from the bottom layer is used to evaporate (2) a refrigerant affecting the stability and steady operation of (Organic Rankine Cycle) before returning to the pond (3). The refrigerant vapor drives a turbine (4) to produce electricity and is then condensed (5) before pumped back to the the ponds. Typically the bottom pond layers evaporator. The ORC cycle uses the cooler water from the top pond layers to condensing can achieve temperatures of around 90°C [3], the refrigerant (6). with the top layers of the ponds maintaining temperatures close to ambient conditions. Converting the thermal energy in an ORC with evaporator and condenser temperatures of 90°C and 30°C, respectively, can achieve a maximum Carnot conversion efficiency of 16.5%. Assuming an ORC turbine efficiency of 85% and condenser and evaporator heat exchanger efficiencies of 71%, yields an overall steady solar to electricity conversion efficiency of 1.5%. Solar pond conversion efficiencies are considerably lower than other renewable energy technologies, with photovoltaic cell technology converting between 10% and 20%, and concentrating parabolic trough solar