Parametric BIM-based Energy Simulation for Buildings with Complex Kinetic Façades

Transcription

1 Parametric BIM-based Energy Simulation for Buildings with Complex Kinetic Façades Hyoungsub Kim 1, Mohammad Rahmani Asl 2, Wei Yan 3 1,2,3 Texas A&M University, College Station 1,2,3 {gudtjq81 mrah wyan}@tamu.edu This paper aims to investigate a new methodology for analysing energy performance of buildings with complex kinetic façades. In this research, the flexible movements of individual kinetic façades in a building is determined by the façades' opening ratios and the sun path. The platform development is conducted through a visual programing environment in BIM, and the process is presented with a case study. Finally, the building's energy performance is compared with a building having static façades using whole building energy analysis tool. Keywords: Parametric Modeling, BIM, Kinetic Façades, Energy Simulation INTRODUCTION Performance-based building design methodologies have been investigated to deal with diverse decision variables and design objectives in various environmental issues (Machairas et al., 2014). Simultaneously, designers are responsible for designing buildings and their urban context to provide inhabitants with better spaces. The development of technologies in Architecture, Engineering, and Construction (AEC) and building energy simulation software enables architects to assess and visualize the building performance of various design alternatives. Currently, Building Information Modeling (BIM) has the potential to serve for the investigation of buildings' sustainability (Yan et al., 2013). In addition, BIM's capability of parametric modeling helps architects examine various design alternatives (Rahmani Asl et al., 2014). To this extent, BIM-based parametric design methods can be integrated with kinetic architecture in order to suggest a systematic design decision process that enables buildings to respond to specific seasonal climate changes including the variations of solar radiation and wind direction (Wang et al., 2010). This research studies buildings with complex kinetic envelops and responsive shading devices to analyze the kinetic envelop system's influence on reducing cooling loads by comparing with a static envelop. LITERATURE REVIEW BIM provides a virtual environment of all the building components, including specific data sets such as geometric and material components to generate a building product model (Eastman et al., 2008). BIM's parametric modeling capabilities enable the generation and management of the building information (Sacks et al., 2004). In addition, Application Programming Interface (API) allows BIM to be integrated with various analyses such as daylight and building thermal analyses (Kim et al., 2015, Kota et al., 2014). As one of high performance building design methods, the installation of stationary vertical or horizontal shading devices could function for not only providing occupants with an appropriate daylight BIM - Applied - Volume 1 - ecaade

2 condition, but also reducing the energy consumption of buildings (Palmero-Marrero and Oliveira, 2010). To be more efficient, adaptable kinetic façades could be one of the ideal approaches to respond to seasonal change of the environment (Kasinalis et al., 2014). The application of kinetic façades has a great potential to reduce energy consumption by integrating with diverse performance issues such as glare, daylighting, and heating and cooling loads (Tzempelikos, 2007). For instance, an office building with dynamic louvers located in Abu Dhabi consumes less energy in comparison with a building using fixed louvers (Hammad and Abu-Hijleh, 2010). To control the moveable façades, a motorized shading modular sys-tem, (Konstantoglou et al., 2013) and parametric camshaft system (Sjarifudin and Justina, 2014) are created. Even though the building forms and façades become more complex in contemporary architectural design, existing studies about shading devices only focus on the simple geometric variables such as width, length, and angles of vertical and horizontal shading devices. In terms of energy analysis of a building with complex kinetic façades, two possible issues exist. First, a new approach is required to trace the movement of the sun instead of only considering the solar altitude angle. Second, unlike buildings with fixed shading devices, complex kinetic components have to be updated to reduce the heating and/or cooling loads of buildings. Thus, it is necessary to develop a methodology to analyze the influence of complex kinetic façades on the heating and cooling loads of the buildings. This study examines the methodology with a case study to integrate the sun path and a complex moveable façade for energy analysis through a visual programing environment in BIM and whole building energy simulations. METHODOLOGY KINETIC FAÇADES CONTROL SYSTEM The Vertical Shadow Angle (VSA) and Horizontal Shadow Angle (HSA) of a given location are required to compute the appropriate size of the overhang and vertical fin (Grondzik et al., 2011), using various existing software or hand calculation. However, when it comes to complex façades, the only consideration of VSA and HSA cannot provide the proper size of a shading device. In addition, the complexity of the relationship between the façades and VSA / HSA results in a difficult application of those angles to the façade design. Figure 1 illustrates the differences between simple and complex shading devices, and the limitation of the applying VSA and HSA to complex shading devices. To solve this problem, this paper develops a new method to define the appropriate movement system of complex kinetic shading devices and the solar incidence angle in a parametric model. The incidence angle is the angle between the Sun's direction vec- Figure 1 The use of VSA and HAS and its limitation in complex façades. 658 ecaade 33 - BIM - Applied - Volume 1

3 tor and the normal vector of a surface (Figure 2a). For example, 0 of incidence angle means that the Sun's direction is aligned with the surface's normal (Figure 2b), and 90 means that the Sun's direction and the surface's normal are perpendicular (Figure 2c). The opening ratio α of any surface of incidence angle θ can be projected onto the plane of incidence angle 0, and the projected opening ratio can be calculated as follows: F (θ) = α cos (θ) (1) where F(θ) is the opening ratio toward the sun, α is the opening ratio of a given surface, and θ is the incidence angle of a given surface. F(θ) is the actual opening ratio towards direct sun light entering the room through the opening when the incidence angle is θ. Thus, the incidence angle on a given surface is employed to define the opening ratio through the movement of the complex kinetic façade. PAPAMETRIC MODELLING OF COMPLEX KINETIC FAÇADES Using an example of complex kinetic façades, this study examines a responsive façade system applied to the Al Bahr Towers in Abu Dhabi, designed by Aedas UK (CTBUH, 2013). In this study, the complex façades vary by manipulating the opening ratio of each curtain panel in order to adjust solar heat gain. Figure 3 demonstrates how the incidence angle can be incorporated with the opening ratio of the complex façades. 0 of incidence angle on a surface means that the surface's normal is parallel with the Sun's direction, then the panel is fully closed. When Figure 2 The angle of incidence on a given surface (a) θ (b) 0 (c) 90. Figure 3 The variation of complex kinetic façades based on the incidence angle. BIM - Applied - Volume 1 - ecaade

4 the incidence angle is equal to or larger than 90 which means there is no direct solar radiation, the complex kinetic façades is fully open. The variation of the façades is gradually changed based on the incidence angle of each panel. As shown in Figure 4, a BIM-based parametric curtain panel family for the complex kinetic façades is developed. Three parametric changes of the curtain panel can be seen from the figure. The values to define the opening ratio range from 0.1 to 3.0, which makes the panel fully closed to fully open, respectively. Thus, the opening ratio in this case can be calculated by the following formula: F (θ) = 2.9 cos (θ) IMPLEMENTING CONTROL COMPLEX (2) GEOMETRY In this study, a new complex kinetic façades control system is developed by utilizing Dynamo, an open source visual programing environment for parametric modelling in Autodesk Revit. Visual programing allows architects to easily experiment with various design alternatives without professional knowledge of programing or scripting, and there exist several visual programing environments in CAD tools such as Bentley Generative Components and Grasshopper for McNeel Rhinoceros (Boeykens and Neuckermans, 2009). The overall workflow of the system is demonstrated in Figure 5, and consists of the following two parts: parametric modelling and energy simulation. First, the parametric curtain panel is loaded into a conceptual model of the building (two floors of the building as a simplified case study) with the opening ratio variable. The Sun path of a given building location and time is provided through the BIM tool Revit. The incidence angle, which is calculated using the Sun vector and the normal of each panel, controls the opening ratio. Through the process, each individual panel can have different opening ratios, automatically updated based on the change of time. For example, as shown in Figure 6b, in the morning, the panels on the east are closed because the incidence angle on the east façades are close to 0, and on other directions become open gradually at that time. Figure 4 BIM-based parametric modelling for the complex façades. Each shading unit is hosted by a façade. Figure 5 The overall work flow of parametric modelling and energy simulation. 660 ecaade 33 - BIM - Applied - Volume 1

5 Figure 6 A visual programing environment and the resulting BIM model with parametric curtain panels. Second, for a geometry model based parametric simulation study, we may use DIVA with Rhino/Grasshopper. For the present BIM-based study on the Revit platform, we choose to use Green Building Studio (GBS), Autodesk Revit Energy Analysis tool, in order to convert the BIM model to the energy model for the case study. However, GBS cannot recognize the complex panel as a shading device. Thus, the complex panel geometry has to be simplified, maintaining the same opening ratio. The simplified panels are generated automatically based on the complex pan- els and are illustrated in Figure 6b. The opening ratios of the simplified panels are equal to their complex counterparts. In addition, GBS does not provide the hourly energy analysis result, thus the energy model is exported as DOE2.2 input file to obtain energy simulation result using equest, a widely used building energy simulation tool. To obtain hourly performance results of the kinetic building, simulation based on hourly curtain panel scenarios is conducted through the whole year, then the selected results of each hour scenarios are combined. Figure 7 BIM - Applied - Volume 1 - ecaade

6 illustrates an example of the data processing based on the results on the summer solstice. ENERGY ANALYSIS FOR COMPLEX KINETIC FAÇADES To test the proposed method, an energy model for a two-story office building is created based on the concept of Al Bahr Towers in Abu Dhabi, as shown in Figure 8. Abu Dhabi, the United Arab Emirates is chosen as the building location because it is possible to earn comfortable hours to 32.5% of a whole year by installing Sun shading for windows (Milne et al., 2007). In this study, the building cooling load on summer solstice June 21st from 8 am to 6 pm is analyzed and compared between the kinetic and fixed façades. The kinetic façades operate using Equation (2), visualized using Figure 3 and 4. First, Figure 9a shows the results of complex façades and fixed shading devices range from opening ratio 10% to 90%. The complex facades consume similar energy as the fixed facades with 60% opening, less energy compared to fixed facades with more than 60% opening, and 9% less energy than without shading devices. Second, the hourly result comparison between complex façades and fixed façades with 80% opening ratio is shown in Figure 9b. The complex façades case consumes totally 4% less than the fixed one during 8am to 6pm. The interesting finding is that even though the outside dry-bulb temperate at 1 pm in Abu Dhabi is 40.5 C, which is the second highest during the day, the cooling load at that time is the lowest. The reason could be that the solar incidence angles of all curtain panels with different normals are all close to 90 meaning that the amount of direct solar radiation on the façades is minimum at that time. This implies that direct solar radiation plays a significant role in increasing the cooling load rather than the outside dry-bulb temperature in this case study. 662 ecaade 33 - BIM - Applied - Volume 1 Figure 7 An example of the hourly data processing for kinetic façades energy model. Figure 8 The energy model for a two story office building.

7 Figure 9 Building cooling load (a) Static façades with different opening ratio and kinetic façade (b) Hourly comparison of cooling load using kinetic façades and static facades with 80% opening ratio as a sample. CONCLUSION This study examines a new methodology to analyze energy performance of buildings with complex kinetic façades by integrating parametric BIM and energy simulation. First, to define the opening size of individual panels, a system is created by integrating the incidence angle in a visual programing environment in BIM. Second, to conduct the energy analysis, the hourly changed kinetic façades are automatically updated. The energy simulation results show that the building with complex kinetic façades consumes more or less energy depending on the opening ratio of the fixed façades. For example, it consumes 4% less energy than the base case that has static shading devices with 80% opening ratio. Smaller opening ratios in the fixed façades result in less energy consumption, but may cause daylighting performance problems potentially. This presents a limitation of the study. In other words, the amount of daylight can be critically affected by the opening ratio of the complex shading, and the fully closed façades might lead to the increase in usage of artificial light. Nonetheless, this current study only focuses on the relationship between the opening ratio and energy consumption but not daylighting performance. Furthermore, GBS does not provide the way to calculate complex shading geometry, therefore we had to simplify the shading geometry, though it's an automatic process. In addition, in this study, it should be noted that even though the complex façades have the shading components extruding along the panels' normal directions, for simplification, we only considered each façade as a flat surface with 2D shading components embedded in and aligned with the surface. In spite of the limitations, the main benefit of the proposed method is that the opening ratio can be easily defined based on incidence angle regardless of site location, time, direction of surface, and building form. This implies that the method enables architects to simply examine various design alternatives by integrating complex kinetic façades both visually and quantitatively. To improve the method, future research will be conducted with more complex building forms and multi-criteria optimization for daylighting, view analysis, and natural ventilation performance. REFERENCES Rahmani Asl, M, Bergin, M, Menter, A and Yan, W 2014 'BIM-based Parametric Building Energy Performance Multi-Objective Optimization', Fusion, Proceedings of the 32nd International Conference on Education and research in Computer Aided Architectural Design in Europe Boeykens, S and Neuckermans, H 2009 'Visual Programming in Architecture: Should Architects Be Trained As Programmers?', Proceedings of CAAD-Futures 2009 Eastman, CM, Teicholz, P, Sacks, R and Liston, K 2008, A Guide to Building Information Modeling for Owners, Managers, Architects, Engineers, Contractors, and Fabricators, John Wiley and Sons Grondzik, WT, Kwok, A, Stein, B and Reynolds, J 2011, Mechanical and electrical equipment for buildings, John BIM - Applied - Volume 1 - ecaade

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