As previously reported on Carboun, Masdar City – the $22 billion project of the Abu Dhabi Future Energy Company (Masdar) – is currently under construction and is due to be completed in 2016. As the the first zero-carbon emissions and zero-waste city, the master plan for Masdar City integrates many passive design and planning strategies with renewable energy production to achieve its ambitious sustainability goals.
At the center of Masdar City lies its first building, the Masdar Headquarters, which will become the new home of Abu Dhabi’s Future Energy Company, as well as the secretariat of the International Renewable Energy Agency (IRENA). The building - together with other key building -will act as an anchor and a catalyst for the development of the city.
The Masdar Headquarters building -which is part of the first phase in the city’s phased development and is due for completion at the end of 2010- is also meant to set an example to following development in the city by raising the bar above the Masdar City’s goals for individual buildings. These goals can be summarized as reducing energy use and waste production in each building to appropriate levels so that they can be handled by the city’s clean renewable energy systems and its waste-to-energy plants.
For Masdar Headquarters (Masdar HQ henceforth) to become this example, an international design competition was held in 2008, challenging architects to produce the highest level of sustainable design. The competition, which was managed by the Louis Berger Group – the project manager- drew more than 150 design proposals, which narrowed down to 15 architecture and design firms. The criteria for selection of the 15 included building functionality, water and wastewater efficiency, indoor environmental quality, zero carbon emission, carbon footprint reduction and firm experience. A jury of world renowned experts on sustainable design selected four global leaders to submit final proposals, of which the scheme designed by the architecture office of Adrian Smith + Gordon Gill was ultimately chosen.
The winning design of the Masdar HQ is a seven-story, 135,000 square meter building (including landscaped areas) which will include commercial and residential spaces, retail and public gardens, as well as a prayer hall and direct access to the city’s transportation systems (Figure 2).
The design is also set to become the world’s first mixed-use, positive-energy building. A number of sustainable design strategies and systems would be integrated into the very form of the structure to create a building that would achieve the lowest impact in terms of energy, water, and waste, while maintaining occupant comfort. The building is designed to have a record-low energy intensity for its class in hot/humid climates, produce more energy than it consumes, produce zero solid and liquid wastes, and reduces its water needs by 70% (Figure 1).
Passive design strategies
The design of the Masdar HQ follows the successful formula of combining passive design strategies with active systems strategies and renewable energy to achieve its energy savings goals. But unlike other projects where sustainable strategies appear to be an after thought, the building’s basic forms appears to have been derived from these strategies.
One of the main form-making strategies is a ventilation strategy derived from the region’s traditional ventilation elements. Before the recent discovery of oil in the gulf region’s, its hot and humid climate led to the development of a traditional architecture that encourages air movement in order to improve comfort conditions. One of the ventilation elements used in this environmentally responsive architecture was the wind tower.
The design of Masdar HQ is dominated by 11 cone-shaped adaptations of traditional wind towers which act as outlet wind towers drawing hot air upwards during the day. The optimized form of these cones (also called wind cones) uses stack ventilation as well as the wind above the building to create a negative pressure at the top of the cones, which in turn creates air movement in the interior courtyard spaces at the base of the cone and draws cooler air up through the subterranean levels of the city below. At night, the wind cones reverse roles acting as inlet wind towers drawing cool night air downwards to cool the building structure (Figure 3). Computational Fluid Dynamics (CFD) studies were used to analyze the effect of outside wind on air movement inside the wind cones and to optimize the location of the air inlets for more uniform ventilation (Figure 4).
The building’s form was also driven by the need to shade the entire building structure to reduce its solar heat gain. A seven-acre large canopy with a substantial overhang dominates the building’s roof and is structurally integrated with the cones that support it to create a super structure around which the building spaces and functions are arranged. The operable windows around the cones gives the occupants around them the option to naturally ventilating interior spaces and to benefit from the air movement inside the cones. A shaded sky garden at the roof level is also created under this canopy with a microclimate that includes landscape of indigenous vegetation as well as water features. In addition to its role in shading, the roof canopy also incorporates one of the world’s largest photovoltaic and solar thermal arrays, simultaneously producing electricity solar energy and providing thermal energy for solar cooling (Figures 5).
The concept of the shading canopy is arguably inspired by local and regional traditional buildings where screens and shading played a dominant role. And while the building’s super structure appears to be a novel design idea developed exclusively for the project (Figure 6), the ‘oasis-like’ interior courtyards at the base of each cone -which benefit from controlled daylighting through the opening at the top and serve as flexible outdoor assembly spaces- resonates with the role and comfort conditions provided by the traditional courtyards of the Middle East (Image 2).
In addition to these form-giving passive strategies, the building also features many passive strategies that are less obvious to the casual observer, such as the use of high-thermal-mass exterior glass cladding to reduce heat gain while keeping transparency to preserve views. Under the building, earth ducts were also used to reduce the building temperature through contact with the almost constant temperature of the earth below. The ducts also act as underground pedestrian passages that connect the building with the proposed mass transit system. Like local traditional architecture and except for exterior curtain walls, the buildings walls are to have a heavy construction of masonry with a 30% glazing ratio to achieve a high thermal mass and reduce the indoor heat gain.
The design also features the use of integrated renewable energy generation, such as integrated wind turbines and the world’s largest integrated Photovoltaic systems, both mounted on the roof canopy. The installation of these renewables would help bring the building from a net energy user to a net energy producer that produces 3% more than it consumes, thus creating a building that is not only carbon neutral but carbon negative (Figure 7).
As previously noted on Carboun, the Middle East’s water scarcity makes the need to implement water conservation strategies just as important as energy conservation. At Masdar HQ, a water conservation strategy is employed to save 70% of the building’s water use compared to a typical mixed use building of the same size. This reduction in water demand consequently reduces the city’s energy demand, since most of the Emirate’s potable water comes from energy -intensive desalination plants.
Rainwater and condensation are collected, stored, and used -together with grey water from showers, laundries, and lavatories- to irrigate the shaded roof garden. Grey water is also used to flush toilets. Black water from toilets and kitchens is also used as a biofuel for diesel engines after treatment at the city’s black water treatment center (Figure 9).
Masdar HQ’s designers plans to reduce the building’s foot print were not limited to reducing its use of energy and water, but also extended to addressing the energy embodied in the materials used to construct it.
Materials used in the building were considered in terms of their environmental impact. Recycled materials and rapidly renewable materials were specified around the building. Materials were also to be sourced from locations no further than 800km from the building site. Flexible, modular, prefabricated materials and furniture were also specified to make the process of recycling them easier, and in many cases the structure was used as the finish material to reduce the use of finish materials.
In addition, project team calculated the embodied energy of the different building elements. According to the architects, the exterior walls were calculated to constitute 22% of the building’s embodied CO2, the frame and upper floors 39%, and the roof canopy and cones superstructure 17%. It is unclear as to how these values where obtained and whether a full Life Cycle Analysis (LCA) was carried out for each building element to establish these ratios.
Furthermore, assembly alternatives were also compared in terms of their embodied CO2. For example, the external facade assembly was determined by analyzing 6 facade alternatives in terms of their embodied CO2 as well as their their U-value and thermal performance. The embodied energy (or CO2) score of each alternative was weighed against its use performance score to determine the most sustainable assembly. Likewise, the feasibility of the canopy roof and its incorporated photovoltaics was also analyzed not in terms of their financial payback but in terms of their CO2 emissions payback, given the energy and CO2 embodied in their manufacturing process. The analysis showed that the CO2 payback of the canopy and PV was rather short, at approximately 5 years, which can be attributed to the high solar insolation in Abu Dhabi.
The Masdar HQ building is designed to be a highly sustainable, energy and water efficient building not only after occupancy but also during its construction phase. For example, the building’s super structure of cones and overhanging canopy roof would be built first, to create a cooler shaded environment underneath for the remainder of the construction to take place within.
The roof canopy will also be covered with solar photovoltaic panels from the outset so as to serve as a source of electricity providing energy for the construction of the rest of the building.This simple phasing strategy has the potential to substantially reduce the carbon footprint of construction by using clean energy while having minimal implications on construction costs.
This sequence of phasing corresponds with the structural phasing, where the nature of the the superstructure makes it most logical that the cones and canopy roof get built first (Image 5. shows the early stages of construction with the cones bases the first to get built).
The first interesting thing about the Masdar HQ project is the design integration of passive sustainable design strategies into the fabric and form of the Masdar HQ building. But perhaps more interestingly is the role that these passive strategies’ play and their significant contribution to the building’s energy use as a percentage of the total energy saving.
In many green buildings in Europe and the United States, the role of passive design strategies is shadowed by that of efficient energy systems. This is partly caused by the climatic conditions in many european and american cities where buildings have considerably more heating loads than in he Middle East. This has resulted in the growth of the scope of mechanical and electrical engineers in the design process which came at the expense of the architect whose role has been relegated to a coordinator of these active systems.
In the Middle East, for climatic and socio-economic reasons, the role of passive design becomes substantially larger. With much of the sustainable design process geared towards blocking heat away rather than generate it efficiently, and without the a large industrial base to support complicated mechanical and electrical systems, the contribution of passive strategies into overall energy saving in Middle Eastern green buildings is larger than its contribution to energy savings in European and American green building practices.
At Masdar HQ, passive design strategies alone are estimated to contribute 52% of energy savings. The remaining portion of the 103% in energy savings (including the 3% of positive energy generation) is achieved through efficient active systems (20%) and renewable energy generation (31%).
The designers’ attempts to balance embodied energy (or CO2) in materials with their associated use energy is commendable as it reflects an increased sophistication in the design process. By weighing the simulated energy savings of using a material or an assembly to its assumed embodied energy, designers can make design decisions that are informed with the true emvironmental impact of their decisions.
Karim Elgendy is an architect and a sustainability consultant based in London. He can be contacted at: Karim [AT] Carboun [DOT] com
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