INTELLIGENTTERRITORY
A responsive cooling tower and shading system for arid environments
ALINA HRAMYKA1, NEIL GREWAL2, MOHAMMED MAKKI3 and BRITTNEY DILLON4 1,2,3,4The Architectural Association 1,2{alinegromyko|neildsgrewal}@gmail.com 3,4{Mohammed.Makki| brittney.dillon}@aaschool.ac.uk
Abstract. Climatic change coupled with desertification processes impacting cities located around the Mediterranean, has raised serious questions for the capability of the affected cities to adapt to the rapidly changing environmental conditions. This research aims to design small-scale tower structures and shading devices in Nicosia, Cyprus through employing environmental analyses within a generative design process to create an intelligent, adaptive system. Guided by Bernoulli’s principles, geometrical design parameters acquired from fluid simulations, alongside solar analyses of the existing city fabric, were used to generate an evolutionary algorithm for design. The research develops a methodology to facilitate environmental flows in urban architectural systems, generating cooling processes in arid environments that facilitate the adaptation of cities to changes in climatic and environmental conditions. Keywords. CFD Simulation; Generative Design; Desertification; Passive cooling system.
Figure 1. Tower and shading system in Nicosia, Cyprus.
Intelligent & Informed, Proceedings of the 24th International Conference of the Association for Computer-Aided Architectural Design Research in Asia (CAADRIA) 2019, Volume 2, 571-580. © 2019 and published by the Association for Computer-Aided Architectural Design Research in Asia (CAADRIA), Hong Kong. 572 A. HRAMYKA ET AL.
1. INTRODUCTION Desertification, a process that transforms fertile land into desert as a result of rising temperatures, has driven the built infrastructure of affected cities towards being better equipped to respond to the changes in climatic conditions (Shoukri, E. and Zachariadis T., 2012). Small-scale structures have been used in both urban and rural environments to lower temperatures and increase airflow. However, while these interventions have helped cities adapt to climate change, the geometry of the structure has proven to be highly influential in how efficient they are in mitigating the changing environmental conditions (Weinstock, M., 2011). The research presented in this paper is part of a larger body of research, conducted by Brittney Dillon and Alina Hramyka, on both urban and rural conditions in Cyprus. Specifically, the content presented will focus on the design of a responsive urban environment (Figure 1) while contributing a computational methodology for architects and designers involved in urban planning. The research aims to create a responsive architectural ecological system for border conditions susceptible to desertification that can collect, store, distribute water, provide shade, lower temperatures, and decrease evaporation levels along the United Nations (UN) Border. A generative process is developed to design a tower structure and shading system that is driven by data gathered through solar analysis (using Ladybug, a grasshopper add-on) and computational fluid dynamics (CFD). Additionally, an evolutionary algorithm (the Strength Pareto Evolutionary Algorithm - 2 (SPEA-2) used in the grasshopper add-on Octopus) is used to develop the design of infrastructure in four impacted zones within the walled city of Nicosia through tackling a multi-objective design problem; whose solutions and relationships are catalogued and can be implemented in future responsive design interventions. The impact of desertification in Cyprus will be explained, as it played a key role in the selection of affected zones within the city. In addition, a brief summary of the developments in the field of environmental systems will also be engaged, as its key principles play a significant role in providing a proper foundation to design small-scale tower structures and shading devices.
2. NICOSIA, CYPRUS 2.1. DESERTIFICATION In its latest estimate, The Department of Environment in Cyprus projects that 50% of Cyprus will become a desert by 2050 (Shoukri, E. and Zachariadis T., 2012). This will result in temperatures that exceed 55 degrees Celsius (Figure 2) and a significant shortage of water (Sofroniou, A. and Steven, B., 2014). As temperatures rise, evaporation increases resulting in long-lasting droughts, especially during the summer months. Current climatic and environmental analyses being conducted have demonstrated that temperatures above 35 degrees Celsius have had a detrimental impact on the island (Shoukri, E. and Zachariadis T., 2012). Mortality rates due to higher temperatures could increase by 30,000 deaths annually by 2030 and 50,000 to 110,000 deaths annually by 2080 (Bank of Greece, 2011). Such changes directly influence the ecological system and INTELLIGENT TERRITORY 573 human habitation in both urban and rural environments. Agricultural production in rural environments is reduced due to low precipitation, leading to severe land degradation, while urban environments suffer from both production loss and inhabitability due to rising temperatures (Ministry of Agriculture in Cyprus, 2013). This is further amplified due to the urban heat island effect. The use of high thermal absorbing building materials in Nicosia, such as Yellowstone and asphalt, as well as a lack of water bodies and vegetation results in heat waves that can last up to several weeks.
Figure 2. Land surface temperature map (left); Areas sensitive to desertification processes over the next 30 years (right).
Stagnant air is a result of the dense city fabric both within and outside the walled city, further impacting rising temperatures; resulting in significant increases of energy consumption (primarily for cooling). Moreover, it is projected that the areas shown in Figure 2, are the first patches of land that will see the impacts of desertification within the next 30 years (Ministry of Agriculture in Cyprus, 2013). These areas indicate the starting points for design intervention and played a crucial role in site selection.
3. AN INTELLIGENT URBAN SYSTEM 3.1. OVERVIEW
Figure 3. Proposed hyperbolic tower structure designed using Bernoulli’s principle of fluid dynamics. 574 A. HRAMYKA ET AL.
While many strategies reduce urban heat island formation, this research addresses two main factors; urban geometry and reduced vegetation. The objective is to alter the dimensions and spaces between built infrastructure and generate tower structures that will provide shade to lower temperatures, encourage vegetation growth, and promote convective air movement. Guided by Bernoulli’s principle of fluid dynamics (Hydrodynamica, 1738), tower structures were designed to prevent air stagnation. Tall, chimney-like geometries allow for air movement between high temperatures and low temperatures. Even slight interventions can impact how air is exhausted, consequently, increasing air extraction efficiency. The geometry of the tower plays a significant role. A tower with negative Gaussian curvature (Figure 3) is more stable against external pressures than straight towers (Asadzadeh, E. and Alam, M., 2014). In order to satisfy all design ambitions, an evolutionary algorithm was used to optimize a multi-objective design problem. Environmental data, solar exposure and existing wind flow conditions were collected and used as an input to drive the evolutionary simulation. In addition, urban surfaces were analysed during extensive heat periods to highlight areas needed for increased shading and air flow. Locations that have a low solar and wind performance index highlighted the areas where the tower infrastructure would impact the micro-climate towards reducing the urban heat island effect. Even a shading device can reduce surface temperatures up to 7°C (Armson, D., 2012). Solutions are generated to increase performance, and an iterative process of design and environmental analysis is performed to create an intelligent, responsive urban system.
3.2. SITE Although the complete body of research tackles both the urban and rural environments, the research presented herein focuses on the urban condition, specifically within Nicosia’s walled city. Characterized by long, narrow streets (3-6 meters) and open public squares, the city was analyzed both functionally and environmentally. In July, a day can last 14 hours and reach temperatures up to 45°C. A lack of shading on pedestrian walkways, coupled with very little vegetation throughout, make it difficult to occupy public spaces during the day. Although the city is relatively dense (almost 2,500 inhabitants per square kilometer), public spaces are predominantly empty due to lack of relief from heat. As such, four plazas were selected (Figure 4) to represent areas within the city most affected by desertification processes. Each plaza is defined by its overall area, the ratio of hard-scape to soft-scape, location of existing vegetation, public and private space, existing street network, existing wind flow conditions, and amount of shadow.
Figure 4. Four selected sites within Nicosia walled city. INTELLIGENT TERRITORY 575
3.3. GENERATIVE ALGORITHM 3.3.1. OVERVIEW As each site needs to adapt to both environmental and functional implications, a generative algorithm was used to provide solutions to a design problem with multiple conflicting objectives. The aim is to create a responsive, urban system that strives to maximise air movement and maximise shaded area within each selected plaza through the design of a tower structure and shading system. An evolutionary solver allows the designer to edit, assess, and select a set of solutions rather than a single solution that only satisfies one objective. This gives a broader understanding of how design parameters can affect the solution’s geometry.
Figure 5. Genetic algorithm workflow.
The set of solutions are numerically assessed, where the evaluation is based on the solutions ability to either encourage airflow or provide shade; design relationships are derived and used as inputs for a second iteration of geometric optimisation (Figure 5). The generated feedback loop makes this methodology an intelligent one, allowing the designer and evolutionary solver to generate an air-cooling, shade-promoting design, responsive to any arid environment
3.3.2. SELECTION STRATEGY The iterative process generated a population of solutions that respond to the environmental and climatic context for each selected plaza. Design solutions were selected based on three criteria; 1. distance between design intervention and existing infrastructure to provide pedestrian pathways; 2. placement and orientation of towers to provide maximum shadow; 3. and solutions that provide a cooler micro-climate that facilitates increased vegetation growth. The selection process employs methods that are independent from the ones used to develop and run the evolutionary simulation. As such, the generated solutions were evaluated a second time according to static pressure, air velocity, and shadow, on the ground (Figure 6).
Figure 6. Selected individuals. 576 A. HRAMYKA ET AL.
3.4. EXPERIMENTAL SETUP The experiment uses both fluid simulations and solar analysis as inputs for a generative algorithm (Figure 7). The use of these tools allow for recursive experimentation that are difficult to simulate physically. Several parameters are used to facilitate airflow movement and shading techniques.
Figure 7. Solar radiation analysis; Dividing plaza surfaces into cells for calculation (left); Initial CFD simulation testing existing condition (Plaza 1): Air velocity = 10 m/s (right).
3.4.1. COMPUTATIONAL FLUID DYNAMICS (CFD) The Bernoulli Effect can be observed through air mass movement in CFD simulations. These simulations provide quantifiable data for informed geometric manipulation of tower infrastructure. A three-dimensional analysis is computationally demanding (˜2 hours per simulation), therefore, a two-dimensional analysis was conducted using a section perpendicular to the prevalent wind direction (Figure 7). A velocity of 10 m/s was tested to simulate the maximum wind velocity in the southwest direction in July. A preliminary CFD simulation was conducted on the existing urban fabric on a simplified 3D model of the city. Tower structures were added to the model to test a range of geometric configurations that maximise air movement through the plaza. The towers’ distance from the ground was incrementally adjusted to increase fluid speed. The distance between multiple tower edges were tested to control static pressure, where each edge was assigned an angle between 20 and 45 degrees to maximise wind velocity. Note that the CFD simulations show the relative difference between existing atmospheric pressure and proposed excess pressure, the values indicated in the figures are not absolute.
3.4.2. SOLAR ANALYSIS In addition to CFD, solar analysis was used as an input for the generative process. In order to analyse solar radiation, a 3D model of the existing city fabric was divided into a series of cells (Figure 7). Each cell was assigned a sun vector and calculated the amount of sun hours exposed in July; a month that consists of long-lasting days and intensive heat. A shading device was added to the digital model to test a range of curvature and perforations on the surface to create shadow on the ground plane. Each cell was restrained in the x and y direction and could move in both INTELLIGENT TERRITORY 577 directions. Perforations were added to the surface, where the diameter of each opening could range between 0.25 meters and 4 meters. The angle of each cell and the size of the opening worked to limit the sun exposure and maximise the shaded area within the selected plaza.
Figure 8. Tower structure parameters for generative algorithm.
The tower’s placement, height, and distance above the ground facilitate global wind flow, while the shading surface curvature and porosity facilitate both local wind flow and shadow on the ground plane (Figure 8). In addition, the research conducted assumed that materials used in all experiments were of low thermal conductivity, as to ensure excess heat is not absorbed and released by the used materials, thus impacting airflow through the proposed tower structures.
3.5. RESULTS
Figure 9. CFD Simulation of proposed tower and shading system measuring static pressure, air movement, and air velocities on four selected plazas.
3.5.1. AIR MOVEMENT The results indicate that the height of the tower structure, presence of a shading surface, and the distance of the intervention from existing infrastructure, play a key role in controlling air movement. Mainly, if the height of the proposed tower exceeds existing infrastructure the tower acts as a screen resulting in global 578 A. HRAMYKA ET AL. pressure differentiated zones. The air velocity in these zones are controlled by the tower’s geometry where hyperbolic geometries created zones optimal for air mass movement. As seen in Figure 9, when A < B, and C < D, the tower intakes air. However, if the height of one side of the tower exceeds the other and both sides have congruent geometry facing wind direction, then a gradient of static pressure from high to low along the prevalent wind direction is created. Where A < B, A < D, and C < D, a lower static pressure is observed within the tower. Note that the results show the difference between existing atmospheric pressure and pressure created by an object, otherwise known as excess pressure. The figure indicates that when a taller tower is placed at farther distance from its smaller counterpart in the prevalent wind direction, turbulence between both towers is increased. The hyperbolic shape of towers accelerates the influx of air, improving cooling efficiency. In contrast, when A > B, C < D, and the diameter is increased, the tower extracts air. However, it is observed that when the distance between towers exceeds 18 meters, any design intervention minimally impacts the plaza’s ability to increase air flow and provide more shade. The proposed tower structures are raised above the ground plane to increase air movement within habitable zones. All experiments revealed that a gap between the ground plane and bottom of the structure less than 2 meters, may have increased air velocity by 10 m/s, beyond human comfort level (Stathopoulos, T., 2009).
3.5.2. POROSITY The diameter of an opening on the surface, as well as the distribution between openings, plays a key role in both air movement and the resulting shadow on the ground plane (Figure 10). An indirect relationship is observed, where larger openings yield lower air velocities and higher solar exposure, while smaller openings yield higher air velocities and lower solar exposure. When the opening is less than 1.8 meters, the air velocity is increased and the air pressure above and below the surface is equalized. It is observed that in plazas smaller than 500 square meters, a dense grid of openings yields larger shadow coverage (Figure 13). In plazas larger than 500 square meters, the placement, size, and shape of an opening on the surface has a greater impact on overshadowing than the number of openings.
Figure 10. Solar radiation analysis measuring impact of porous canopy system on Plaza 3 (left) Density pattern of opening on curved shading surface - Plaza 3 (right). INTELLIGENT TERRITORY 579
4. ANALYSIS The results indicate that the geometry of the tower and openings on a shading canopy can create differentiated pressure zones, catalysing air movement as well as providing shaded environments for vegetation growth and human occupation. Though reasonable results were obtained, future work should focus on the implications of geometrical variations of the hyperbolic towers, and how building materials can impact the performance of the tower system. It is evident that the hyperbolic geometry of the tower can work to circulate air. A preliminary attempt to test varying degrees of curvature was taken. It should, however, be noted that geometrical refinement would impact air movement even more. In future, it is advised to create geometries that do not generate air velocities over 10 m/s on the ground, exceeding human comfort level. The materials used for the experiment assumed low thermal conductivity. Although not within the scope of this study, future work should test how to minimise heat absorption and promote air movement.
5. CONCLUSION This paper presents an ecological system that responds to climatic change and desertification processes. This topic is important for designers involved in urban planning, using environmental data and analysis as inputs for design. Using CFD simulations within the generative process mobilize precise geometrical adaption to control flows within urban environments. The strategy to design tower structures and shading devices that can adapt to rising temperatures, urban heat island formation, and stagnant air has significant potential for employing an intelligent system in areas prone to climate change. Incorporating geometrical parameters that will not only increase shadow in public spaces, but will also control the air flow for cooling within the existing city fabric, can influence the responsive system. By using hyperbolic tower structures and a connected curved, and porous shading surface, the desired environmental performance can be achieved. While the methodology presented in the paper showcases overall improvement from the existing condition, there is still possibility for further improvement. For example, the proposed intervention has created zones where air velocity exceeded the initial input of 10 m/s. As the research aims to create a comfortable, responsive urban system, habitability should be measured. In addition to human occupancy, the tessellation on the curved, porous surface should be geometrically adapted to provide optimal conditions for vegetation growth; as discussed, increased areas of vegetation helps reduce evaporation and can contribute to a productive urban landscape.
6. FURTHER INVESTIGATION Future research should focus on the rural conditions impacted by desertification in Cyprus (Figure 11). The methodology used to design tower structures will remain, however, the generative process will encompass water collection systems to respond to higher levels of precipitation outside the city to address water scarcity. The methodology should also consider not only built infrastructure, but also how 580 A. HRAMYKA ET AL. design can integrate with both the natural landscape and productive societies. The landscape should be evaluated based on existing topological conditions, vegetation patterns, water bodies, and interaction with local communities. This data will be quantified and used as input for the generative process outlined in this paper to provide resources for humans residing in dense city fabrics.
Figure 11. Water collection system within generative design process in rural conditions.
ACKNOWLEDGEMENTS We thank Michael Weinstock, Elif Erdine, Antiopi Koronaki, and George Jeronomidis for guiding the research at The Architectural Association School in Emergent Technologies and Design Master’s Programme. We also thank Andreas Papallas, Nadia Charalambous, Pavlos Schizas for their support on-site in Cyprus.
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