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Double skin façades performance: effects on daylight and visual comfort in office spaces

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Double skin façades performance: effects on daylight and visual comfort in office spaces

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Content DOUBLE SKIN FAÇADES PERFORMANCE: EFFECTS ON DAYLIGHT AND VISUAL COMFORT IN OFFICE SPACES by Elham Motevalian A Thesis Presented to the FACULTY OF THE USC SCHOOL OF ARCHITECTURE UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF BUILDING SCIENCE August 2014 Copyright 2014 Elham Motevalian II Acknowledgements My thanks and sincere gratitude go to my thesis chair, Professor Douglas Noble, whose continued support, precious guidance and encouragement made this project possible. His wide knowledge and constructive feedbacks have been of great value to me. I would like to express my profound gratitude to Professor Marc Schiler, for his scientific advice and knowledge and many insightful discussions and suggestions. My special acknowledgements go to Professor Karen Kensek, who always share her knowledge with me, and guide me with her valuable suggestions to the right direction. Thanks to Jeffery Vaglio, who helped me at the early stages of this work. I am also thankful for the assistance and support given by Professor Anders Carlson for keeping me on track. I would also like to thank my family for all of their love and support without which I could not have managed to complete my thesis. I would like to thank my husband, Ali, who supported me unconditionally all along the way. And last but not least I would like to thank all my classmates from the Building Science program for encouraging me to continue on and finish up my thesis. III Table of Contents Acknowledgements ......................................................................................................................... II List of Figures ............................................................................................................................... IX List of Tables ............................................................................................................................... XII Abstract ........................................................................................................................................... 1 Chapter1: Introduction .................................................................................................................... 3 1.1 Research Problem .................................................................................................................. 3 1.2 Terms of Study ...................................................................................................................... 4 1.2.1 Daylighting and Architectural Design ............................................................................ 5 1.2.2 Double-Skin Façade (DSF) ............................................................................................ 7 1.3 Hypothesis ............................................................................................................................. 9 1.4 Research Objectives .............................................................................................................. 9 1.5 Scope of Work ....................................................................................................................... 9 1.6 Chapter Structure................................................................................................................. 10 Chapter 2: Literature Review on Daylight and Visual Comfort Studies ...................................... 11 2.1 Daylight Design................................................................................................................... 11 2.1.1 Static Daylight Metrics ................................................................................................. 11 2.1.2 Dynamic Daylight Metrics ........................................................................................... 12 2.2 Visual Comfort Design........................................................................................................ 13 2.2.1 Glare Metrics ................................................................................................................ 13 2.2.2 Relation between Daylight Illuminance Metrics and Glare Metrics ............................ 15 2.3 Daylighting and Glazed Facades ......................................................................................... 15 2.4 Daylight and Visual Comfort Simulation............................................................................ 16 2.4.1 Daylight Simulation Algorithms and Glare Simulation Method .................................. 17 IV 2.4.1.1 Radiosity ................................................................................................................ 18 2.4.1.2 Backward Ray-Tracing .......................................................................................... 18 2.4.1.3 Glare Simulation Method ....................................................................................... 18 2.4.2 Daylight and Glare Simulation Software Overview ..................................................... 19 2.4.2.1 Radiance ................................................................................................................. 19 2.4.2.2 Daysim ................................................................................................................... 19 2.4.2.3 DIVA...................................................................................................................... 19 2.4.2.4 IES VE Daylight simulation .................................................................................. 20 2.5 Daylight and Visual Comfort Multi-Objective Analysis .................................................... 21 2.5.1 Multi-Objective Analysis Previous Studies .................................................................. 21 2.5.2 Pareto Solution ............................................................................................................. 23 2.6 Daylight Standards for Commercial Space Design ............................................................. 24 Chapter 3: Literature Review on Double Skin Façade ................................................................. 27 3.1 Double-Skin Façade History ............................................................................................... 27 3.2 Double-Skin Façade Definition ........................................................................................... 28 3.3 Ventilated Double Skin Façade Types ................................................................................ 29 3.4 Double Skin Facade Design Elements ................................................................................ 32 3.4.1 Cavity............................................................................................................................ 33 3.4.2 Envelope Layers ........................................................................................................... 33 3.4.3 Shading device .............................................................................................................. 34 3.5 Double Skin Façade Performance Review .......................................................................... 37 3.6 Previous Double-Skin Façade and Daylight Studies........................................................... 39 Chapter 4: Methodology ............................................................................................................... 41 4.1 Defining Fixed Parameters .................................................................................................. 41 4.1.1 Reference Model ........................................................................................................... 41 V 4.1.2 Model Component ........................................................................................................ 42 4.2 Defining Variables .............................................................................................................. 43 4.3 Simulation Approach........................................................................................................... 45 4.3.1 Simulation Setting ........................................................................................................ 45 4.3.2 Custom Material for Simulations ................................................................................. 49 4.3.3 Simulation of Shading Device ...................................................................................... 53 4.3.4 Simulation Limitations and Considerations ................................................................. 55 4.3.4.1 Simulation Limits with Correlations to Modeling Software.................................. 55 4.3.4.2 DIVA Simulation and Target Setting Considerations ........................................... 55 4.4 Testing Simulation and Model Setting ................................................................................ 56 4.4.1 Testing the Internal Reflection ..................................................................................... 56 4.4.2 Testing Two Layers Façade .......................................................................................... 58 4.5 Solution Analyzing Using Evolutionary Algorithms .......................................................... 59 4.6 Multi-Objective Analysis Objective’s Target ..................................................................... 62 4.7 Multi-Objective Trade off Chart ......................................................................................... 65 Chapter 5: Results ......................................................................................................................... 67 5.1 Depth of Cavity Effect on Daylight and Visual Comfort.................................................... 69 5.2 Envelope Material Effects on Daylight and Visual Comfort .............................................. 75 5.2.1 Testing the Visual Transmittance and Sequence of Layers Effect on Daylight and Visual Comfort-Clear Glass .................................................................................................. 75 5.2.2 Testing the Effect of Coated and Clear Glass Combinations on Daylight and Visual Comfort .................................................................................................................................. 77 5.2.3 Testing the Effect of Coated Glass Combinations on Daylight and Visual Comfort ... 79 5.2.3.1 Coated Glass Effect on Daylight and Visual Comfort-Set 1 ................................. 79 5.2.3.2 Coated Glass Effect on Daylight and Visual Comfort-Set 2 ................................. 81 5.2.3.3 Coated Glass Effect on Daylight and Visual Comfort-Set 3 ................................. 82 VI 5.2.3.4 Coated Glass Effect on Daylight and Visual Comfort-Set 4 ................................. 84 5.2.4 Testing the Effect of Translucent Panel and Glass Combination on Daylight and Visual Comfort .................................................................................................................................. 86 5.2.5 Testing the Effect of Frit Glass on Daylight and Visual Comfort ................................ 87 5.2.5.1 Frit and Clear Glass Effect on Daylight and Visual Comfort- First Set of Pattern 87 5.2.5.2 Frit and Clear Glass Effect on Daylight and Visual Comfort- Second Set of Pattern ............................................................................................................................................ 89 5.2.5.3 Frit and Clear Glass Effect on Daylight and Visual Comfort- Third Set of Pattern ............................................................................................................................................ 89 5.2.5.4 Frit and Clear Glass Effect on Daylight and Visual Comfort- Fourth Set of Pattern ............................................................................................................................................ 90 5.3 Walkway Parametric Design Effect on Daylight and Visual Comfort ............................... 92 5.3.1 Walkway Position inside the Cavity Effect on Daylight and Visual Comfort ............. 92 5.3.2 Walkway Material Effect on Daylight and Visual Comfort ......................................... 93 5.3.3 Walkway Perforation Effect on Daylight and Visual Comfort .................................... 95 5.4 Shading Device Parametric Design Effect on Daylight and Visual Comfort ..................... 96 5.4.1 Position of Shading Device inside the Cavity .............................................................. 97 5.4.1.1 Position of Shading Device inside the Cavity-Solid Walkway ............................. 97 5.4.1.2 Position of Shading Device inside the Cavity-50% Perforated Walkway ............. 98 5.4.2 Shading Device Material .............................................................................................. 99 5.4.2.1 Shading Device Material- Solid Walkway ............................................................ 99 5.4.2.2 Shading Device Material- 50% Perforated Walkway .......................................... 100 5.4.3 Shading Device Size and Spacing .............................................................................. 101 5.4.3.1 Shading Device Size Effect- Solid Walkway ...................................................... 102 5.4.3.2 Shading Device Size Effect- 50%Perforated Walkway ....................................... 102 5.4.4 Dynamic Shading Device Simulation ......................................................................... 103 VII 5.4.5 Multi Variable Analysis Shading Device (Size, curvature, position and rotation) .... 105 Chapter 6: Analysis and Discussion ........................................................................................... 108 6.1 Variables Effect Summary ................................................................................................ 108 6.2 Trade-Off Charts ............................................................................................................... 111 Chapter 7: Conclusions and Future Work ................................................................................... 116 7.1 Conclusion ......................................................................................................................... 116 7.2 Limitations of Study .......................................................................................................... 117 7.3 Future work ....................................................................................................................... 117 7.3.1 Objective Studies ........................................................................................................ 117 7.3.2 Variable Studies .......................................................................................................... 118 7.3.3 Validation ................................................................................................................... 118 7.3.4 Glare Simulation Plug-in for Grasshopper ................................................................. 118 Bibliography ............................................................................................................................... 119 Appendix A ................................................................................................................................. 125 Nomenclature .......................................................................................................................... 125 Appendix B ................................................................................................................................. 127 Effect of depth of cavity on annual glare-Different walkway projection ............................... 127 Effect of depth of cavity on annual glare-Fixed 72” walkway ............................................... 129 Effect of depth of cavity on annual glare-Multi-story closed cavity ....................................... 129 Appendix C ................................................................................................................................. 131 Effect of envelope material on annual glare-Clear glass......................................................... 131 Effect of envelope material on annual glare-Coated glass ...................................................... 132 Effect of envelope material on annual glare-Frit and clear glass ............................................ 135 Effect of envelope material on annual glare-Translucent and clear glass ............................... 138 Appendix D ................................................................................................................................. 139 VIII Effect of walkway design on annual glare-Walkway position ................................................ 139 Effect of walkway design on annual glare-Walkway material ............................................... 140 Effect of walkway design on annual glare-Walkway perforation ........................................... 140 Appendix E ................................................................................................................................. 141 Effect of shading device design on annual glare-Shading device position ............................. 141 Effect of shading device design on annual glare- Shading device material ............................ 142 Effect of shading device design on annual glare- Shading device size ................................... 143 IX List of Figures Figure 1: US Zero energy building goals by organizations ............................................................ 3 Figure 2: Eli and Edythe Broad Center double-skin facade, Los Angeles ..................................... 4 Figure 3: Daylight effect on human performance ........................................................................... 5 Figure 4: Architectural parameters with direct effect on daylighting ............................................. 6 Figure 5: Right- Banco Ciudad Office by Foster Left- Adidas Office by Kinzo Architecture ...... 7 Figure 6: Energy consumption comparison for a conventional façade and a double façade .......... 8 Figure 7: Visible transmittance and solar heat gain coefficient in single and double skin façade 16 Figure 8: Elements to be defined for daylight simulation............................................................. 17 Figure 9: DIVA plug-in with different simulation engines .......................................................... 20 Figure 10: Multi-objective facade analysis ................................................................................... 22 Figure 11: Design process using inverse method ......................................................................... 23 Figure 12: Sample of Pareto frontier plot ..................................................................................... 24 Figure 13: Occidental Chemical Corporation, NY ....................................................................... 28 Figure 14: Types of double skin façade ........................................................................................ 29 Figure 15: Partitioning of the DSF façade .................................................................................... 30 Figure 16: DSF different air flow type ......................................................................................... 31 Figure 17: Double-skin facade component ................................................................................... 32 Figure 18: Different types of walkway design in DSF building cavities ...................................... 33 Figure 19: 110 Degree glass louver transfer more light deep to the space ................................... 40 Figure 20: Research workflow ...................................................................................................... 41 Figure 21: Reference model .......................................................................................................... 42 Figure 22: Grasshopper parametric design and DIVA plugin ...................................................... 45 Figure 24: Radiance parameters setting for simulation model ..................................................... 46 Figure 23: Working plane and sensors.......................................................................................... 46 Figure 25: The effect of parameters on the way simulation works ............................................... 48 Figure 26: Glass optical properties, Radiance script can be exported from Optic 6 .................... 50 Figure 27: Making multi-layer glazing system with Window 7 ................................................... 52 Figure 28: OptictoGlazedb, input for writing a frit glass script. ................................................... 53 Figure 29: Dynamic shading device with DIVA-automated control based on glare .................... 54 Figure 30: Annual automatic shading diagram in comparison to annual glare chart ................... 54 X Figure 31: Model to Test the Internal Reflection.......................................................................... 56 Figure 32: Testing the material setting ......................................................................................... 57 Figure 33: Point in time illuminance for different reflection ........................................................ 58 Figure 34: Single and Double Skin Model ................................................................................... 59 Figure 35: Different genes, and genomes in Galapagos component ............................................ 61 Figure 36: Galapagos connected to the average DA ..................................................................... 61 Figure 37: Galapagos finding the best fitness to maximize daylight autonomy ........................... 62 Figure 38: Daylight autonomy result sample, showing the sensors position ................................ 63 Figure 39: The occupant viewport looking at the monitor for glare analysis .............................. 63 Figure 40: Annual glare result ...................................................................................................... 64 Figure 41: Annual glare result- Showing month, day, hour and DGP .......................................... 65 Figure 42: Sample of trade-off chart ............................................................................................. 64 Figure 43: Research methodology summary ................................................................................ 66 Figure 44: Comparing the result from the previous research with same model and setting ......... 67 Figure 45: Point in time illuminance results-Right: IES VE, Left: Diva ...................................... 68 Figure 46: Diva and IES VE point in time glare simulation ......................................................... 69 Figure 47: First test modeling approach ....................................................................................... 70 Figure 48: Effect of cavity depth on daylight autonomy .............................................................. 70 Figure 49: Los Angeles - Daylight autonomy distribution (different depth of cavity) ................. 71 Figure 50: New York - Daylight autonomy distribution (different depth of cavity) .................... 71 Figure 51: Houston - Daylight autonomy distribution (different depth of cavity) ....................... 71 Figure 52: Effect of depth of cavity on visual comfort ................................................................. 72 Figure 53: Depth of cavity -Second test modeling approach ........................................................ 72 Figure 54: Effect of cavity depth on daylight autonomy (Second modeling approach) ............... 73 Figure 55: Effect of cavity depth on annual glare (Second modeling approach) ......................... 73 Figure 56: Multi-story closed cavity modeling-Without walkway ............................................... 74 Figure 57: Depth of cavity effect on daylight autonomy-Multi-story closed cavity DSF ............ 74 Figure 58: Effect of cavity depth on annual glare for multi-story DSF ........................................ 75 Figure 59: Effect of changing Vt of inner layer glass on daylight autonomy............................... 76 Figure 60: Effect of changing Vt of outer layer glass on DA ....................................................... 76 Figure 61: Effect of changing Vt of inner layer glass on annual glare ......................................... 77 XI Figure 62: Daylight autonomy distribution on working plane- First set ...................................... 80 Figure 63: Daylight autonomy distribution on working plane- Second set .................................. 82 Figure 64: Daylight autonomy distribution on working plane- Third set ..................................... 84 Figure 65: Daylight autonomy distribution on working plane- Fourth set ................................... 85 Figure 66: Cavity depth effect on daylight autonomy difference ................................................. 87 Figure 67: Frit and clear glass combination-First set of pattern ................................................... 88 Figure 68: Frit and clear glass combination -Second set of pattern .............................................. 89 Figure 69: Frit and clear glass combination -Third set of pattern ................................................. 90 Figure 70: Difference of modeling from third set to fourth set of simulation .............................. 91 Figure 71: Modeling to test the effect of walkway position on daylight autonomy and glare ..... 92 Figure 72: Effect of walkway position on daylight autonomy distribution .................................. 93 Figure 73: Effect of walkway material on daylight autonomy distribution .................................. 94 Figure 74: Walkway perforation models for the simulations ....................................................... 95 Figure 75: Effect of walkway perforation on daylight autonomy distribution ............................. 96 Figure 76: Position of shading device for DA and glare simulation............................................. 97 Figure 77: Effect of shading device position on daylight autonomy distribution......................... 99 Figure 78: The effect of shading device material reflection on daylight autonomy distribution 101 Figure 79: Shading device size and spacing change modeling for DA and glare simulation ..... 102 Figure 80: Automatic shading device effect on daylight and visual comfort ............................. 105 Figure 81: Trade-off chart- Los Angeles .................................................................................... 112 Figure 82: Trade-off chart- New York ........................................................................................ 113 Figure 83: Trade-off chart- Houston ........................................................................................... 114 XII List of Tables Table 1: Case studies of glazing types and shading devices in double-skin façade ..................... 35 Table 2: Advantage and disadvantages of DSF ............................................................................ 37 Table 3: Reference model materials ............................................................................................. 43 Table 4: Variables and range of possible values ........................................................................... 43 Table 5: Radiance parameter definitions and ranges .................................................................... 47 Table 6: Parameter setting number for simulation ........................................................................ 49 Table 7: The result for opaque and transparent material by 50% reflection ................................. 57 Table 8: The results for opaque and transparent material with 50% reflection ............................ 57 Table 9: Single and double-skin facade comparison .................................................................... 59 Table 10: Effect of coated glass on outer layer of DSF (Inner layer: clear 65%Vt)..................... 78 Table 11: Effect of coated glass on inner layer of DSF (Outer layer: clear 65%Vt) .................... 78 Table 12: Daylight autonomy and annual glare results- First setting ........................................... 80 Table 13: Daylight autonomy and annual glare results- Second setting ....................................... 81 Table 14: Daylight autonomy and annual glare results- Third setting.......................................... 83 Table 15: Daylight autonomy and annual glare results- Fourth setting ........................................ 85 Table 16: Effect of translucent and glass material on Daylight autonomy and annual glare ....... 86 Table 17: Effect of frit and clear glass on daylight autonomy and visual comfort-First set......... 88 Table 18: Effect of frit and clear glass on daylight autonomy and visual comfort-Second set .... 89 Table 19: Effect of frit and clear glass on daylight autonomy and visual comfort-Third set ....... 90 Table 20: Effect of frit and clear glass on daylight autonomy and visual comfort-Fourth set ..... 91 Table 21: Effect of walkway position on daylight autonomy and glare ....................................... 93 Table 22: Effect of walkway material on daylight autonomy and visual comfort ........................ 94 XIII Table 23: Effect of walkway perforation on daylight autonomy and visual comfort ................... 95 Table 24: The effect of shading device position inside a double skin facade cavity .................... 97 Table 25: The effect of shading device position inside a double skin facade cavity .................... 98 Table 26: The effect of shading device material on daylight and visual comfort ....................... 100 Table 27: The effect of shading device material on daylight and visual comfort walkway ....... 100 Table 28: The effect of shading device width on DSF daylight autonomy and visual comfort . 102 Table 29: The effect of shading device width on DSF daylight autonomy and visual comfort . 103 Table 30: Multi-variable shading device design ......................................................................... 105 Abstract The demand for fully glazed, highly transparent façades has increased in recent decades as architects and clients embrace the style, and modern construction methods and materials have made them economically viable. Double-skin façades are also becoming more common as a system that can be highly transparent and if designed appropriately more energy efficient than conventional systems. As a relatively new system, there is still limited data about energy performance and occupant comfort of the different variants of double skin facades. Designing the façade elements of the building to make a well daylit space is a challenging issue for designers. A well daylit office space will reduce the energy consumption of the building and will make a comfortable, healthier, and productive work environment for users. Too much daylight can introduce glare, heat gain, and other negative impacts. As a multi-objective analysis, the tradeoffs between daylight quantity and visual comfort in the office spaces are complex, but it is possible for a designer to find an appropriate balance. Daylight autonomy (DA) metric of 300 lux (~30 fc) has been chosen as a target for measuring daylight quantity based on IESNA 2012 recommendation and daylight glare probability (DGP) as the metric for measuring visual comfort. Using a virtual office test cell of 27 by 12 by 9 feet, five façade parameter effects have been studied: depth of cavity; double skin façade type; facade material including different types of glass and translucent materials; shading device design considering their size, material and position in the cavity; and walkway design within the cavity. 2 Computer simulations with Rhino, Grasshopper, and DIVA (with Radiance engine) were used to determine how the design of each façade element affects the goals in three different geographic locations: Los Angeles, New York and Houston. The results have been plotted on trade-off charts for each city. By using the simulation results and trade-off charts, designers will be able to find an appropriate balance between visual comfort and daylight availability while designing a double-skin façade. Hypothesis: Design parameters of double skin façades have significant direct effects on the daylighting levels and visual comfort inside the space. Key Words: Double-Skin Facade, Daylight, Visual Comfort, DIVA Daylight Simulation, Trade- Off Chart. 3 Chapter1: Introduction The research investigates daylight performance and visual comfort in double-skin façade office buildings. The importance of the subject, the research hypothesis, the study objectives and limitations are explained in the following section. 1.1 Research Problem The demand for fully glazed, transparent façades has increased during the past decades as architects and clients embrace the style and construction methods have made it possible. The sustainability of these types of facades continues to be in question. As the energy codes are becoming stricter, it will be increasingly important and perhaps even required to improve the performance of glazed facades to keep them desirable in the future (Figure 1). Figure 1: US Zero energy building goals by organizations (Torcellini, NREL, presentation slide, 2007) 4 The double-skin façade (DSF) can be integrated in buildings to increase the transparency of the buildings (Figure 2). Researchers and practitioners have mixed opinions as to whether these systems decrease the energy consumption of a building and provide for tenant’s comfort. Daylight performance of DSF has received less attention compared to the ventilation and thermal performance, and there are a few studies completed in this area. The effect of different elements of the double-skin façade design on daylight and visual comfort were not studied comprehensively. Previous research criticized the daylight performance of DSF. Researchers argue that due to the extra layer of glass and depth of cavity, these buildings receive less daylight when compared to a single-skin fully glazed façade. Further studies on combination of envelope material choice and shading device design were suggested by previous researchers (Oesterle et al, 2001). 1.2 Terms of Study Effect of architectural design on daylight and visual comfort and definition of double-skin façades have been explained in the following section. Figure 2: Eli and Edythe Broad Center double-skin facade, Los Angeles 5 1.2.1 Daylighting and Architectural Design Daylighting is the use of sunlight or skylight to provide an appropriate lighting level for a specific task in an interior space. Designing the façade elements for the building to make a well daylit space is always a challenging issue for designers. A high performance façade design should provide appropriate daylight in to the space, reduce the energy consumption of the building (cooling and heating load), and make a comfortable, healthier, and more productive work environment for users (Figure 3). Figure 3: Daylight effect on human performance (Boyce, 2003) Architectural parameters that have direct effect on daylighting include aperture design (size, opening to wall ratio, position of the aperture), glazing selection, shading device, light redirecting elements, interior surface and finish, building form and orientation (Figure 4). Previous studies show that good architectural design for different climates can also balance between energy consumption and lighting load (Wu, 2012). 6 Figure 4: Architectural parameters with direct effect on daylighting In all stages of the building design and construction, daylighting strategies should be considered with different levels of detail. In the conceptual design stage, the position of the building in relation to adjacent buildings and landscape should be studied very carefully. The orientation, form and proportions of the building have also direct effect on daylighting a space. In the schematic and design development phase, the aperture of facade, along with the materials and finishes that are going to be used in the façade and interior space are going to be chosen. In these design stages, the designer also should make decisions about shading devices, and if they are going to use any daylight re-directing elements for the building or not. Lighting control devices like daylight and occupancy sensors can be chosen to reduce electricity consumption of building as well. Daylight System aperture design Opening to wall ratio Opening size Opening position Glazing Selection Visible transmitance Visible light reflectance Shading and light redirecting device design Color-Reflection Position Size Shape Building form and oreintation Interior finish Color-Reflection 7 After the building has been constructed and occupied by tenants, checking the lighting controls performance and maintenance of daylighting systems to verify that the building performs as designed is the building manager’s task (IEA, 2000). Figure 5: Right- Banco Ciudad Office by Norman Foster (http://www.fosterandpartners.com, 1/20/2014) Left- Adidas Office by Kinzo Architecture (http://www.archiii.com, 1/20/2014) 1.2.2 Double-Skin Façade (DSF) The term double skin façade includes a variety of façade systems and designs; there can range from a wide air tight cavity façade to very narrow natural ventilated cavity. There is not a single unique universally accepted definition of double-skin façades. Kragh defines DSF as a system that includes an internal and external layer and a ventilated cavity in between. The layers can be single or double glazed. Solar shading devices can be placed inside the cavity. Depth of the cavity and ventilation type should be defined based on the environmental conditions (Kragh, 2000). Saelens describes the double-skin facades as an envelope that includes two transparent layers placed in a way to create an air flows in the intermediate cavity (Saelens, 2002). 8 Double-skin façades is as a system of two skins placed in a way that air flow inside the cavity. The glass skins can be single or double glazed with a distance from 20 cm to 2 meters, and the ventilation can be natural, fan supported or mechanical. Often, there is a shading device inside the cavity (Poirazis 2004). In this study, a double-skin façade is defined as an active system that covers the constructed building by multiple glazed skins. The cavity between skins can be air tight or open and naturally or mechanically ventilated (Belgian Building Research Institute, 2002). Studies show that a well-designed double-skin façade system design can reduce the energy consumption of the building when compared to a single skin façade (Figure 6) (Stribling, 2003). Figure 6: Energy consumption comparison for a conventional façade and a double façade (Stribling, 2003) Previous study also shows acoustical insulation increasing when using DSF, which make them an appropriate design for busy cities (Kragh, 2000). London Los Vegas WINNIPEG New York Miami Rome Munich 0 50 100 150 200 250 300 SS DS SS DS SS DS SS DS SS DS SS DS SS DS Heating Cooling Fans Pumps 9 1.3 Hypothesis Design parameters of double skin façades have significant direct effects on the daylighting levels and visual comfort inside the space. 1.4 Research Objectives The three main objectives of this research are: 1. To find out the effect of extra layer of glass on daylight and visual comfort in the space 2. To determine the design elements that has most effects on the daylighting performance of double-skin facade buildings (Depth of cavity, walkway design, shading device…) 3. To find DSF design solutions that can get an improved results in lighting performance 1.5 Scope of Work As a multi-objective analysis research, the study has investigated the trade-offs between daylight quantity and visual comfort in the space. Computer simulations have been done to determine the design elements affect on each goal. The final result of the study includes a decision support chart for designers that facilitate exploration of double-skin façade design choice effects on illuminance and /or glare. The effect of design elements on natural ventilation, thermal and acoustical performance of double-skin façade is not considered. 10 1.6 Chapter Structure In first chapter, the problem, hypothesis, main terms of study, scope of the work and limitations were explained. Chapter 2 of the study focuses on daylight and visual comfort literature review. In this chapter, daylight and visual comfort metrics, simulation tools and standards are explained. This chapter continues by reviewing two case studies of multi-objective researches on daylight and visual comfort. Chapter 3 is about double-skin façades. In this chapter, the definition, different types of DSF and their performance are described. Two previous research projects that have been completed on daylight performance of double-skin façade are reviewed in this chapter. Chapter 4 is about research methodology, and includes definitions of the reference model, variable and constant assumptions of the study, and descriptions of the software that was selected for the research. Chapter 5 includes the simulation results. The results show the effect of each variable on daylight and visual comfort in the reference model. Chapter 6 contains the resulting analysis and conclusions from the simulations. In this chapter, all the results are plotted in a trade-off chart. Chapter 7 explains limitations of the study and future possible works. 11 Chapter 2: Literature Review on Daylight and Visual Comfort Studies Daylight and visual comfort metrics, simulation tools and standards are explained and two case studies of multi-objective research on daylight and visual comfort are reviewed. 2.1 Daylight Design In order to quantify the daylight level and visual comfort, many daylight and glare metrics have been defined by researchers. In the first section of this chapter some of these metrics are explained. 2.1.1 Static Daylight Metrics Static metrics define a single condition calculation method (point in time calculation). The following section describes some of the static daylight simulations metrics.  Single Point in Time (SPT) working plane illuminance. Single point in time calculation simulates the illuminance level at a specific time of the day. Sky condition, working plane and sensor positions, day, month and hour for each simulation are defined. This method considers orientation and shading techniques of the design.  Uniformity: This metric is the ratio of maximum to minimum illuminance on the working plane. It shows the balance of illuminance level on the working plane (Energy Design Resources, 2008).  Daylight Factor: this metric have been described as the ratio of the illuminance level of a sensor point on a working plane inside the building to the external horizontal illuminace of un shaded point under a CIE overcast sky. Orientation, location, shading device (as it is defined for overcast sky) of the building and sky conditions, season or time of the day 12 are not taken in to account for daylight factor simulations. Building materials and geometry are the elements that have effect on DF simulations (Hensen et al, 2011). 2.1.2 Dynamic Daylight Metrics Dynamic metrics define an annual calculation method, describing the variability of daylight over a year. As opposed to static metrics, dynamic metrics account for operating schedule and varying sky conditions. “Perez all weather sky models,” which consider different sky conditions during the year, are used in the most dynamic daylight simulations. In this section, some of the dynamic daylight simulations metrics are explained.  Daylight Autonomy: This metric is one of the first dynamic metrics that has been defined. Daylight autonomy is described by percentage of annual daytime working hours that a specific point in the space is above a defined illuminance level. The hours that the specified illumninace level is not met, the user needs electrical light. As opposed to daylight factor, daylight autonomy considers façade orientation, occupancy schedule and all sky conditions based on the location (Hu et al, 2013).  Continuous Daylight Autonomy: The concept is like daylight autonomy, but it also gives partial credit to the illuminance values that are below the specified one (Rogers 2006).  Useful Daylight Illuminance (UDI): Illuminance levels have been divided into three ranges to define this metric; 0-100 lux, 100-2000 lux and above 2000 lux. Different credits will be given to each range. A horizontal illuminance level between 100-2000 lux 13 is defined as the useful range for full credit. The other ranges below 100 lux and above 2000 lux do not grant any credit (Mardaljevic et al, 2005). 2.2 Visual Comfort Design Visual comfort data is usually based on occupant surveys and feedback. “Glare is a measure of the physical discomfort to an occupant caused by excessive light or contrast in a specific field of view” (Jakubiec and Reinhart, 2010). This overall sensation of glare is then subdivided into two major types: disability glare and discomfort glare. “Disability glare is defined as the effect of stray light in the eye whereby visibility and visual performance are reduced. Discomfort glare is glare that produces discomfort. It does not necessarily interfere with visual performance or visibility” (Rea, 2000). The major factors that affect people’s perception of discomfort glare are: the luminance of the light source, the luminance of the background, the visual size of the light source, and the relative position of the light source (in relation to the observer’s point of view) (Boyce 2003). 2.2.1 Glare Metrics Although discomfort glare remains a relatively subjective metric, researchers have developed formulas to quantify it. There are several glare indexes which include: VCP, BGI, DGI, and DGP (as defined below). Comparison of these metrics by each other using computer simulation and HDR image results taken from a building confirm that the evaluation of glare from these five glare metrics and HDR images are not consistent (Suk et al, 2013). Daylight Glare Index (DGI): DGI was developed by Hopkinson, this metric consider the large glare sources like bright sky through a window. (Jakubiec and Reinhart, 2010). 14 Visual Comfort Probability (VCP): This metric is valid for electric lighting. The light source should be surface mounted and have uniform luminances. This metric indicates if a lighting system would have direct glare problems. VCP estimates the percentage of people that would accept a lighting arrangement as visually comfortable. Variables included in this metric are: field of view, luminaire mounting height, size, luminance, room size and surface reflectance (Jakubiec and Reinhart, 2010). British Glare index (BGI or BRS): This glare metric has been evaluated by the following ranges: noticeable, acceptable, uncomfortable and intolerable. This index, assumes that the glare source is small and determined by the background luminance only (Clear, 2012). Daylight Glare Probability (DGP): “Daylight glare probability (DGP) is a recently proposed discomfort glare index that was derived by Wienold and Christoffersen from laboratory studies in daylit spaces using 72 test subjects in Denmark and Germany. In the experimental setup, two identical, side-by-side test rooms were used. In one of the rooms a CCD camera based luminance mapping technology was installed at the exact position and orientation as the head of the human subject in the other room” (Reinhart and Wienold, 2010). DGP is based on the vertical eye illuminance and on the glare source luminance, its solid angle and a position index (Suk and Schiler, 2012). DGP Comfort Ranges are based on this ratio: DGP < 35% imperceptible 35% < DPP < 40% perceptible 40% <DGP < 45% disturbing DGP > 45% intolerable. DGPs: is a simplified method to calculate the DPG. In Wienold and Christoffersen (2006) study, it is shown that the “vertical illuminance at eye level shows a reasonable correlation to the glare perception”. DGPs could be defined as: 15 “DGPs = 6.22 x x Ev + 0.184 where Ev is vertical illuminance at eye level. This equation neglects the influence of individual glare sources. Therefore the DGPs can be applied only if no direct sun or specular reflection of it hits the eye of the observer.” (Wienold, 2009). 2.2.2 Relation between Daylight Illuminance Metrics and Glare Metrics Useful Daylight Illuminance (UDI) as described section 2.2.1 is defined as horizontal illuminance level between 100-2000 lux. This range is subdivided into two parts: UDI- supplementary and UDI-autonomous. Horizontal daylight illuminance in the range 100 to 300 lux is called UDI-supplementary. In this case additional electrical lighting might be needed to reach the desired level of illuminace for specific tasks like reading. Horizontal daylight illuminance in the range 300 to 3000 lux is called UDI- autonomous. In this range usually the daylight is sufficient.UDI metric indicates the upper illuminance limit that may have direct relationship with glare. Previous studies on residential buildings show that there is the potential to compute measures of daylight glare probability using UDI (Mardaljevic et al, 2012). 2.3 Daylighting and Glazed Facades Selecting the best material for the façade is a process of trading off between higher daylight level quantity and glare or solar heat gain. Therefore it needs a careful evaluation of the material properties. Glass materials in relation to daylight and energy performance can be defined by these properties: Visible Transmittance: This property defines the percentage of light that pass through the glass. Higher Vt usually means clear look and more daylight in the space, however it may cause glare. In this case, the tradeoff is between the daylight and glare. Visible transmittance can range from about 90% for uncoated clear glass to 10% for tinted and highly reflective glass (Figure 7). 16 Visible reflectance: This property defines the percentage of light that will reflect back in the visible portion of the spectrum. Glass manufacturers usually provide exterior and interior reflectance of the glass material. Metallic coatings on the glass will increase their visible reflectance, and will decrease visible transmittance of the glass property. Solar Heat Gain Coefficient (SHGC): This property is the ratio of solar radiation admitted through the glass. SHGC is range from 0 and 1. The higher solar heat gain coefficient can reduce heating load in winter, although lead to overheating in summer. As a result in this case, the trade-off is between heating and cooling load. Solar heat gain is influenced by the glass type, the number of panes, and glass coatings (www.commercialwindows.org). Figure 7: Visible transmittance and solar heat gain coefficient in single and double skin façade (Redrawn based on: www.commercialwindows.org) 2.4 Daylight and Visual Comfort Simulation Designing a well daylit space based on the different standards like the LEED rating system or IES standard has become essential for all the sustainable buildings. The complex design 17 strategies make it difficult to evaluate the quality and quantity of daylight in space with rules of thumb or physical models. Due to these difficulties, daylight computer simulations have become more popular. Four important setting before staring the daylight or visual comfort simulation are: Making the model and surrounding environment, specifying the grids and viewports, defining the building type and lighting requirements, and choosing the right sky model based on the objectives (Figure 8). Figure 8: Elements to be defined for daylight simulation (http://ocw.mit.edu, 11/14/2013) 2.4.1 Daylight Simulation Algorithms and Glare Simulation Method The two most common approaches for the daylight simulations have been backward ray tracing and radiosity methods, which have their own strengths and weaknesses. 18 2.4.1.1 Radiosity Radiosity algorithm concept comes from heat transfer theory. Surfaces consider as diffuse reflectors, and a hemisphere which defines the sky is centered on the scene center. The virtual sky it is divided into a set of patches, and a radiosity value for each sky patch is assigned according to the luminance value of the sky model. Radiosity move to the virtual scene from the different sky patches. (Müller et al, 1995). Autodesk Viz is one of the software using radiosity algorithm. 2.4.1.2 Backward Ray-Tracing Backward ray-tracing algorithms trace the light rays back from the view point or point of measurement to the light source. This method is used with many lighting simulation software like Radiance (Reinhart et al, 1999). 2.4.1.3 Glare Simulation Method The glare metric used in this research is Daylight Glare Probability (DGP). To calculate DGP, high dynamic range imaging techniques and Evalglare software can be used. Using CCD camera, the luminance quantity on the occupant viewport is measured and recorded. “For automatic glare evaluation of the luminance images, computer-based software, Evalglare, has been developed. Evalglare is used for evaluating glare originating from daylight solutions. It can also be used to calculate glare from HDR photographs. Glare sources can also be identified based on a threshold value, which can be specified by the user manually as a fixed luminance value or computationally determined based on average luminance in the field of view, or computationally determined based on a user specified task location” (Suk, Schiler, 2012). 19 2.4.2 Daylight and Glare Simulation Software Overview There are different daylight simulation software programs that are being used by designers and architects including: Radiance, DaySim, DIVA and IES VE. 2.4.2.1 Radiance Radiance is a lighting visualization engine, which was developed at the Lighting Systems Research group at Lawrence Berkeley Laboratories. It is a validated research tool (in previous studies Radiance results have been compared to scale model measurements and real spaces data) for simulating visible radiation in a space. This software uses backward ray-tracing algorithms and has the ability to handle diffuse inter-reflections between objects. Gensky is the Radiance program that can create CIE standard sky scene description. Using this program, users can define any time of the year, any location and any sky condition for their simulation (clear or overcast). 2.4.2.2 Daysim Daysim is using the Radiance engine to perform annual and dynamic simulations (Reinhart, 2010). The daylight coefficient method provided by Radiance engine is giving an accurate illuminance results for individual time steps and averaged annual one (McNeil, Andrew et al, 2012). 2.4.2.3 DIVA DIVA is an acronym for Design Iterate Validate Adapt, is a plug-in for Rhinoceros 3D modeling program and Grasshopper plug-in. This program uses Radiance and Daysim engine for daylight simulation, and can do both dynamic and static daylight analysis. For glare study, DIVA uses the Evalglare; point in time and annual glare study can be done with this software. In addition to all 20 Rhino Geometry Modeling Grasshopper Parametric Design Diva Simulation Radinace Visualization/ Static Daylight Simulation Daysim Dynamic Daylight Simulation Evalglare Glare Simulation variety of simulation that can be done with DIVA, being able to use Grasshopper and Rhino for modeling, helps DIVA user to do a parametric study on their design. Figure 9: DIVA plug-in with different simulation engines 2.4.2.4 IES VE Daylight simulation IES VE (Virtual Environment Integrated Environmental Solutions software) uses the Radiance engine for daylight simulation as well. This software gives the user ability to do static simulations like point in time illuminance at working plane, daylight factor, or daylight uniformity. The glare metrics that IES VE can define are visual comfort probability, CIE glare index, unified glare rating, BRS glare index and daylight glare index (The definition of these metrics have been explained in section 2.2.1). 21 2.5 Daylight and Visual Comfort Multi-Objective Analysis Multi-objective analysis (MOA) is studying the trade-offs between usually different conflicting objectives. Daylight availability and glare are considered as the analysis objectives, and the trade-off between these two objectives have been studied. 2.5.1 Multi-Objective Analysis Previous Studies There have been other studies done using genetic algorithms for optimizing of the façade design based on the daylight and glare. “Multi-Objective Façade Optimization for Daylighting Design Using a Genetic Algorithm” (Gagne et al, 2010). The research is based on a tool using a genetic algorithm (GA) that facilitates exploration of facade designs generated based on illuminance and/or glare objectives. In this method the original 3D model and performance goals have been defined by the user. The building form and overall massing have been considered the same, although the facade elements change to reach the performance goals. Glazing materials and geometric characteristics of apertures and shading devices have been considered as the variables of the study. The results of the study had been plotted on a Pareto frontier charts with visual references (Figure 10). 22 Figure 10: Multi-objective facade analysis (www.infoscience.epfl.ch) “Experience of light: the use of an inverse method and a genetic algorithm in daylight design” (Chutarat 2001). An inverse method problem-solving technique was used, which started with designer's goals and then identified a design to meet those goals. For this approach genetic algorithm (GA) has been used to find the optimal daylighting design solutions. The research presents a structured method for defining and evaluating multi objectives. Objective targets are defined as reaching to the preferred lighting conditions and increasing the visual comfort in the space (Figure 11). 23 Figure 11: Design process using inverse method (Chutarat, 2001) “Intelligent building skins: Parametric-based algorithm for kinetic facades design and daylighting performance integration” (El Sheikh, 2011). Using genetic algorithm to search for the best skin configuration at specific dates and times or under different sky conditions. On this thesis genetic algorithm helps to finding an optimal solution under certain parameters and conditions. Any changes in of the variable parameters make the simulation to run and find an optimal solution for the building facade to reach the desired luminous environment. 2.5.2 Pareto Solution In multi-objective analysis, sometimes goals are conflicting, and there is no best solution for the issue. In these cases Pareto optimality can be used for comparing the solutions. “A Pareto optimal set is a set of solutions that are non-dominated with respect to each other. While moving from one Pareto solution to another, there is always a certain amount of sacrifice in one objective to achieve a certain amount of gain in the other. Pareto optimal solution sets are often preferred to single solutions because they can be practical when considering real-life problems, since the 24 final solution of the decision making is always a trade-off between crucial parameters. Pareto optimal sets can be of varied sizes, but the size of the Pareto set increases with the increase in the number of objectives” (Konak et al, 2006). In the next step Pareto frontier chart can be used to visualize the data. A Pareto frontier is the plot of all Pareto, with the objectives plotted along each axis (Figure 12). Figure 12: Sample of Pareto frontier plot 2.6 Daylight Standards for Commercial Space Design A well-designed daylit office space typically considers the following principles:  Provide natural light to perform visual tasks without the need for supplementary lighting.  Provide visual comfort for occupant by indirect sunlight on the work surface, or let the occupant to adjust the lighting penetration. 25  Specifying the interior and workstations material in a way to reduce unwanted reflections (Schepers, Clintock and Perry, 1999). There are some rating systems that set quantitative definitions for a well daylit commercial space. LEED rating system and daylight credit: LEED (leadership in energy and environmental design), IEQ (indoor environmental quality) credit 8.1: “provide building occupants with a connection between indoor spaces and the outdoors through the introduction of daylight and views into the regularly occupied areas of the building.” Simulation: “Demonstrate through computer simulations that 75% or more of all regularly occupied space areas achieve daylight illuminance levels of a minimum of 25 footcandles (fc) (~250 lux) and a maximum of 500 fc (~5000 lux) in a clear sky condition on September 21 at 9 am and 3pm. Areas with illuminance levels above or below the range do not comply” (USGBC, 2009). Early versions of LEED (LEED2.1) rating system originally required a DF  2 for at least 75% of the critical visual task zones to achieve indoor environment credit 8.1. Standard 189.1-2009; Standard for the Design of High-Performance Green buildings: (ANSI/ASHRAE/ USGBC/IES, 2009): “The design for the building project shall demonstrate an illuminance of at least 30 fc (~300 lux) on a plane 3 ft (~ 1 meter) above the floor, within 75% of the area of the daylight zones area. The simulation shall be made at noon on the equinox”. 26 IESNA, 2012 Daylight Recommendation: “Spatial Daylight Autonomy300/50% (sDA 300/50%) is recommended as the preferred metric for analysis of daylight sufficiency. This metric uses an analysis illuminance threshold of 300 lux on horizontal surfaces to first assess the number of hours per year that each analysis point within a given analysis area meets or exceeds this value from daylight alone. Daylight conditions are based on typical meteorological year (TMY) data, with an analysis time period extending from 8am to 6pm local clock time (10 hours per day), which will hereafter be referred to as the analysis period”. 27 Chapter 3: Literature Review on Double Skin Façade This chapter is about background review of double-skin façade systems. In this part different definition of double-skin facades, their types and performance have been studied. Two previous research projects that have been completed on daylight performance of double-skin façade have been reviewed in this chapter 3.1 Double-Skin Façade History Double-skin façade systems were first used in low-rise buildings. In early 1990 these systems were implemented in high-rise building applications mostly in Europe. Few years after that - in 2000’s – these systems began to increase in the United States. The buffering zone in double-skin cavities was designed to reduce the energy consumption and heating load of the building. Natural ventilation inside the cavity reduces the energy needed for mechanical ventilation. The original concepts of these systems are still the same (Vaglio, 2010). Occidental Chemical Center (1981) is the first modern double-skin façade building in United States (New York). The square shaped, nine-story building is covered by a 4’ width double layer of green-tinted insulating glass. Due the high exposure wind on the side, the shading devices are placed inside the cavity. 28 Figure 13: Occidental Chemical Corporation, NY (www.cannondesign.com, 5/1/2014) 3.2 Double-Skin Façade Definition The double-skin façade definition in this research will follow the Belgian Building Research Institute definition: A double-skin façade is an active system which is covering the constructed building by multiple glazed skins. The cavity between skins can be air tight or open, and naturally or mechanically ventilated (Belgian Building Research Institute, 2002). Double-skin façades become popular in European countries mostly for:  The desire for a highly transparent façade  Requirement for improving the indoor environment quality  Requirement for improving the acoustics of buildings which are located in noise polluted urban area  Requirement for reducing of energy consumption of the building during the occupied hours (Poirazis, Harris. 2006) 29 3.3 Ventilated Double Skin Façade Types Double-skin facades can be categorized in three different areas, which are independent of one another. These areas are (Waldner et al, 2007):  Type of ventilation  Partitioning of the façade  Air flow type (Figure 14) Type of ventilation: This category of double-skin facades have been defined based on the ventilation of the cavity located between the two skins of the facade. “Each ventilated double skin facade concept is characterized by only a single type of ventilation”. There are three types of ventilation: natural, mechanical, and hybrid ventilation (Waldner et al, 2007). Double skin facade type Partitioning of the façade Box- window facade Corridor façade Shaft-box façade Multi-storey façade Type of ventilation Natural Ventilation Mechanical Ventilation Hybrid Ventilation Type of airflow Exhaust air Supply air Static air buffer External air curtain Internal air curtain Figure 14: Types of double skin façade 30 Partitioning of the façade type: This category of double-skin facades have been defined based on the partitioning of the cavity. The cavities are physically divided based on these partitioning layouts. This category has been subdivided as follow:  “Box window façade: In this case horizontal and vertical partitioning divide the façade in smaller and independent boxes.  Corridor façade: Horizontal partitioning is built for acoustical, fire security or ventilation reasons.  Shaft-box façade: In this case a set of box window elements are placed in the façade. These elements are connected via vertical shafts situated in the façade. These shafts ensure an increased stack effect.  Multi-storey façade: In this case no horizontal or vertical partitioning exists between the two skins. The air cavity ventilation is realized via large openings near the floor and the roof of the building” (Poirazis, 2006) (Figure 15). Figure 15: Partitioning of the DSF façade (Vaglio, 2011) 31 The air flow type: This category of double-skin facades have been defined based on the air circulation inside the ventilated cavity. This category has been subdivided as follow: 1. “Outdoor air curtain: In this ventilation mode, air comes to the cavity from the outside. The ventilation of the cavity therefore forms an air curtain enveloping the outside façade. 2. Indoor air curtain: The air comes from the inside of the room and is returned to the inside of the room via the ventilation system. The ventilation of the cavity therefore forms an air curtain enveloping the indoor façade. 3. Air supply: The ventilation of the façade is created with outdoor air. This air is then brought to the inside room or into the ventilation system. The ventilation of the façade thus makes it possible to supply the building with air. 4. Air exhaust: The air comes from the inside of the room and is evacuated towards the outside. The ventilation of the façade thus makes it possible to evacuate the air from the building. 5. Buffer zone: This ventilation mode is distinctive; both of the skins are airtight in this mode. The cavity thus forms a buffer zone between the inside and the outside, with no ventilation of the cavity being possible” (Loncour et al, 2004) (Figure 16). Figure 16: DSF different air flow type (Redrawn based on Loncour et al, 2004) 32 3.4 Double Skin Facade Design Elements Design of the DSF involves decisions on geometric parameters, glass selection, ventilation strategy, shading, cavity, day lighting, aesthetics, wind loads, maintenance and cost expectations (Figure 17). Figure 17: Double-skin facade component (www.rawnarch.com, 11/17/2013) 33 3.4.1 Cavity A ventilated or closed cavity with a depth from about 4inch at the narrowest to 7 feet for the deepest are located between the two skins. The cavity can be naturally or mechanically ventilated or can have hybrid ventilation system. Cavities are usually designed with a grill walkway to provide space for cleaning and maintenance of the façade. In some cases, the walkway is designed solid or is covered with glass to prevent smoke spread between the levels (Figure 18). Figure 18: Different types of walkway design in DSF building cavities (Right: Eli Broad Center, Middle: Nokia China Center (www.arup.com, 1/05/2014), Left: Deutsche Messe Tower (www.betterbricks.com, 1/05/2014) 3.4.2 Envelope Layers The common pane types used for double-skin facades are: 34  For internal skin (façade): Usually the inner layer is thermal insulating double or triple glass. The glass are toughened and the gaps between them are filled with air, argon, or krypton. • For external skin (façade): Usually the external layer is tempered single glass, and in some cases it is a laminated glass. For a higher transparency, flint or low iron can be used as the exterior layer of double-skin façade (Lee et al, 2002). In double-skin facades system, number of layers and the thickness of panes are apparently greater than a conventional façade system; therefore the layers material should be chosen in a way to maintain a clear façade. Flint and low- iron glass can be used in the envelope to reach the desired transparency; the main disadvantage in this case is the higher costs of material. “Similar description of the panes used can be found in the existing literature. However, there is currently no literature connecting the pane types and the shading devices with the construction type (i.e. box window, corridor façade, etc) and the use of the double-Skin Façade” (Poirazis, 2006). 3.4.3 Shading device In order to design an effective shading device for a double-skin façade system, each properties of the façade should be studied carefully: glazing type of the double-skin façade, ventilation type, and partitioning of the cavity are some the important areas that might affect the design of shading device. (Poirazis, 2006) 35 Table 1: Case studies of glazing types and shading devices in double-skin façade Location Year DSF TYPE Cavity Depth Glazing Shading Device Art Institute of Chicago Modern Wing www.terrain.org Chicago, IL 2009 Corridor style 3 feet Horizontal aluminum solar shading Loyola University Chicago www.enclos.com Chicago, IL 2007 Multi- story 3 feet Monolithic and insulated glass 4 inch horizontal blinds inside the outer glass layer Riverhouse www.enclos.com New York NY 2008 Box- Window 5 inch exterior clear interior clear argon filled low-e glass Sun control blinds inside the cavity UMass Medical School, (Retrofit) www.payette.com Worcester MA 2004 Multi- story 3 feet Insulated glass inside and monolithic glass No shading device 36 outside layer Foundry Square www.studios.com San Francisco CA 2003 Multi- story 3 feet No shading device Cambridge Public Library www.gartnersteel.de Cambridge MA 2009 Multi- story 3 feet low-iron glass 12” Curved perforated operable aluminum louvers USC Eli and Edy Broad Center www.zgf.com/ Los Angeles CA 2010 Multi- story 2 feet Insulating glass inner layer, low iron glass outside layer Roller blind Düsseldorf city gate www.inhabitat.com Düsseldorfer Germany 1997 Corridor style 3 to 4 feet Low E glass inner layer, Fixed safety glass outer layer High- reflectance venetian blinds near the outer glazing layer 37 3.5 Double Skin Façade Performance Review Reviewing the advantages and disadvantages associated with double skin facades will help to determine the variables and parameters that should be considered. Table 2, is a brief review of multiple sources which define researchers ideas about the advantages and disadvantages of DSF in different categories. Table 2: Advantage and disadvantages of DSF (Vaglio, 2010) Arons (2000) Kragh (2000) Oesterle (2001) Compagno(2002) Lee et al (2002) BBRI (2002) Wigginton (2002) Saelens (2002) Herzog et al (2004) Poirazis (2006) Waldner (2007) Streicher (2007) Hausladen (2008) Advantages Acoustical insulation Winter thermal insulation Summer thermal insulation 1 Bligh Street www.urbanfile.org Sydney, Australia 2011 Corridor style 2 feet Double glass pane inner layer and clear glass outer space Internal automated venetian blind 38 Energy Saving Natural ventilation Thermal comfort Reduction of wind pressure Daylight Transparency- Aesthetic Fire escape Disadvantages Maintenance cost Overheating Increased airflow Poor cross ventilation Increased structural weight Daylight Increased electrical loads Acoustical insulation Fire protection Reduced floor area Overestimated energy saving 39 As shown in Table 2, researchers have different opinions about the performance of double-skin facades. The researchers that criticize daylighting performance of the double skin façade focus on two major areas:  Reduction of daylight by depth of façade and extra layer of glass  Limited view to outside 3.6 Previous Double-Skin Façade and Daylight Studies There have been few studies done on daylight performance of the double-skin façade.  “Daylight in Ventilated Double Skin Facades.The Berlaymont Building: a louvers façade” ( Deneyer et al, 2005). This paper presents the daylight performances of the Berlaymont building, a Ventilated Double Skin Façade building equipped with rotating glazed louvers in Belgium. It also presents a comparison between glazed louver performance and metallic louver façade performance. The louver outside face has a white multi-layer perforated film, which can reflect light and the inner faces are dark so people can see through them and reduce the contrast. The louver rotating is controlled by central management system, and it depends on the position of the sun (date and hour). The comparison of the daylight factor measurements on the glazed louvers and the metallic louvers shows that the best options are horizontal metallic louvers and 110° inclined glazed louvers under overcast sky. This option helps to reflect more light deeper in to the space (Figure 19). 40  “Investigations for Improving the Daylighting Potential of Double-Skinned Office Buildings” (Viljoen et al, 1997). In this paper the day lighting performance of a double skin façade office building was investigated based on the different walk way design options. Different size, color and perforation of the walkway has been modeled and simulated by Radiance in this study. The results show about 16% difference in daylight autonomy form a black solid walkway to white perforated one. The author suggested future studies on the effect of the design on visual comfort. Figure 19: 110 Degree glass louver transfer more light deep to the space 41 Chapter 4: Methodology The simulation process, setting, limitations, reference model definition, components, and all the simulation variables are described. The section is divided in four major parts ( Figure 20). First, the general fixed design parameters of a typical office model are considered. These are building geometry, dimensions, interior materials and schedules of occupancy. Second, the variable simulation parameters, such as the double skin façade depth of cavity, envelope material, walkway and shading device design parameters are compared. The third part is multi-objective simulation based on illuminance and glare. The final part is defining a trade- off chart based on the simulation results to help the designer decision-making. Figure 20: Research workflow 4.1 Defining Fixed Parameters Reference model dimension, geometry, orientation, interior material and working schedule have been considered as fixed parameters. 4.1.1 Reference Model Standard box models have long been the default model type for different building performance simulations. Research centers like Lawrence Berkeley National Laboratory (LBL) and École 42 Polytechnique Fédérale de Lausanne have their own definition of a reference model. One standard model definition introduced by Reinhart have been modeled by Rhino 3D. The reference office is meant to represent a south facing sidelit office, which is occupied daily from 8AM to 6PM. The office is not obstructed by neighboring buildings. Its interior room dimensions are 3.6 m (~140”) x 8.2 m (~323”) x 2.8 m (~110”) (Figure 21). Ratio of room depth to height in this reference model is about 3.5. This ratio was chosen so that the effect of daylighting remains visible for all variants (Reinhart et al, 2013). In this study the double skin face façade is considered fully glazed. 4.1.2 Model Component The interior materials are fixed for all the simulations. Optical properties of building components are listed in Table 3. Figure 21: Reference model 43 Table 3: Reference model materials (Reinhart et al, 2013) 4.2 Defining Variables Table 4 shows different variables and the range of possible values that are potentially important for DSF daylight design and affect the daylight performance and visual comfort in different cities. The approach of this research is examining cavity depth, different envelope materials, walkway and shading devices design and their effect on daylight and visual comfort in a south faced, double skin façade office in three different locations in the United States. Table 4: Variables and range of possible values Variables Per Facade Range of Possible Values Envelope Design Depth of Cavity 6” to 6’ Envelope Material Transparent Material Clear Glass-Visual Transmittance Change Coated and Tinted Glass- Vt and Reflection Change Frit Glass Surface Material Ceiling Lambertian diffuser with 80% reflectance Floor Lambertian diffuser with 20% reflectance External ground Lambertian diffuser with 20% reflectance Interior wall Lambertian diffuser with 50% reflectance 44 Translucent Material Clear Glass-Translucent Material Walkway Design Position of Walkway Finish Floor Level 3’ Above Finish Floor Level 3’ Below Ceiling Walkway Material Metal 10% Reflection Metal 40% Reflection Metal 70% Reflection Walkway Perforation 25% Perforation 50% Perforation 75% Perforation Shading Device Design Shading Device Position Inside the Cavity 3” from the Outer Layer Middle of DSF Cavity 3” from the Inner Layer Shading Device Size (Width) and Shape 4” to 16” Shading Device Material 10% Reflection 40% Reflection 70% Reflection The three cities that have been chosen are Los Angeles (CA), New York (NY), and Houston (TX). There are three reasons for choosing these cities. They are located in three different latitudes (Los Angeles: 34.05, New York: 40.67 and Houston: 29.76). New York, Los Angeles 45 and Houston are among the five most populated city lists in US. Therefore there are more potential for having office buildings in these cities. These locations are in three different climate zones. 4.3 Simulation Approach DIVA is chosen for daylight and visual comfort simulations in this research. DIVA has Radiance engine, and give the user the ability to do dynamic and annual simulations. For modeling and parametric design purposes, Rhinoceros and Grasshopper are used. 4.3.1 Simulation Setting The first step to set the simulation environment is defining the analysis nodes and working plane. There have been 24 sensors placed 3’ above the finish floor for daylight analysis (Figure 23). Figure 22: Grasshopper parametric design and DIVA plugin 46 In order to simulate daylight and glare accurately, the Radiance parameter settings have been changed (Figure 24). Figure 24: Radiance parameters setting for simulation model Figure 23: Working plane and sensors 47 Table 5: Radiance parameter definitions and ranges (http://radsite.lbl.gov) Parameter Definition Parameter Range Min Fast Accur Max ab N Set the number of ambient bounces to N. This is the maximum number of diffuse bounces computed by the indirect calculation. A value of zero implies no indirect calculation. 0 0 2 8 ad N Set the number of ambient divisions to N. The error in the Monte Carlo calculation of indirect illuminance will be inversely proportional to the square root of this number. A value of zero implies no indirect calculation. 0 32 512 4096 as N Set the number of ambient super-samples to N. Super-samples are applied only to the ambient divisions which show a significant change. 0 32 256 1024 ar res Set the ambient resolution to res. This number will determine the maximum density of ambient values used in interpolation. Error will start to increase on surfaces spaced closer than the scene size divided by the ambient resolution. The maximum ambient value density is the scene size times the ambient accuracy (see the −aa option below) divided by the ambient resolution. 8 32 128 0 aa acc Set the ambient accuracy to acc. This value will approximately equal the error from indirect illuminance interpolation. A value of zero implies no interpolation. 0.5 0.2 0.15 0 48 The table above gives a definition for the radiance parameters and their ranges. Having the "min" value in the simulation setting, gives the fastest rendering. The "fast" value gives a fast reliable rendering result. Setting the simulation by the "accur" value gives accurate rendering results. The "max" value is the setting needed to get the maximum accuracy (http://radsite.lbl.gov). One of the most important parameters for simulating a double-skin façade and taking to account the internal reflection between the layers of the glass is ambient bounces number or ab. This parameter defines maximum number of diffuse bounces, which can happen between two layers of double-skin façade. Figure 25: The effect of parameters on the way simulation works (Redrawn based on Compagnon, 1997) 49 Based on the tests and background studies, the parameters are set as shown on table 6. In this table the default values in DIVA has been compared with this research setting. Table 6: Parameter setting number for simulation Parameter Default DIVA Setting Setting number ab 2 8 ad 1000 1000 aa 0.1 0.1 as 20 64 ar 300 128 4.3.2 Custom Material for Simulations DIVA uses the Radiance script and definitions for materials. Every material has its own definition and optic properties. The types of materials that have been used and changed for simulations are: Glass (BRTDfunc and BSDF), translucent material, and plastic material. Glass: A clear glass is defined in Radiance by three optical properties. These properties defined the transmissivity at normal incidence. With this equation, one can calculate the transmissivity from transmittance (http://radsite.lbl.gov/). tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn “modifier glass id 0 0 0 3 redTransmission greenTransmission blueTransmission” Red, green and blue are transmittance value. 50 BRTDfunc (Bidirectional Reflectance Distribution Function): “The material BRTDfunc gives the maximum flexibility over surface reflectance and transmittance, providing for spectrally- dependent specular rays and reflectance and transmittance distribution functions” (http://radsite.lbl.gov/). mod BRTDfunc id 10+ rrefl grefl brefl rtrns gtrns btrns rbrtd gbrtd bbrtd funcfile transform 0 9+ rfdif gfdif bfdif rbdif gbdif bbdif rtdif gtdif btdif A10 ..  rrefl, grefl and brefl specify color coefficients for the reflection of the surface.  rtrns, gtrns and btrns specify the color coefficients for the transmission of surface.  rbrtd, gbrtd and bbrtd specify the color coefficients for the directional diffuse part of reflection and transmission. To define complex glass, Optic 6 and Optic 5 has been used. This software which is developed by Lawrence Berkeley National Laboratory (LBL) has a library of glass optical properties. Radiance script of BRTDFunc can be exported for each glass by using this software (Figure 26). Figure 26: Glass optical properties, Radiance script can be exported from Optic 6 51 Below is an example of exported material from optic6. void glass Low Iron glass 0 0 3 0.962 0.987 0.975 void BRTDfunc Low Iron front 10 0.076 0.079 0.081 0.883 0.906 0.896 0 0 0 0 9 0 0 0 0 0 0 0 0 0 void BRTDfunc Low Iron back 10 0.086 0.092 0.094 0.883 0.906 0.896 0 0 0 0 9 0 0 0 0 0 0 0 0 0 Glass transmittance:0.90 Front reflection: 0.078 Back reflection: 0.091 Basically, Optic 6 gives three scripts for each glass from the library. The difference between the three materials is reflection; the transmission is largely the same. Using the Front BRTDfunc gives more accurate reflectance on the front of the glass. The back transmission gives more accurate reflectance on the back of the glass. These glass scripts has been copied to DIVA material library and used for simulations. BSDF: This material type “loads an XML (eXtensible Markup Language) file describing a bidirectional scattering distribution function” (http://radsite.lbl.gov/).Windows 7 software form LBL can be used for modeling cellular shades, vacuum glazing, deflected glass, vertical venetian blinds and perforated screens. 52 Figure 27: Making multi-layer glazing system with Window 7 By using Window 7, multi layer glazing systems and frit glass are defined and used for daylight simulation. Frit Glass: To write the most accurate frit glass script, the suggestion from LBL was to use Radiance’s glaze script by Jack DeValpine. The first step is to choose the layer of glass from Optic 6 or 5, and export them as the radiance script. The next step would be using Optics2glazedb which process radiance output from Optics 5 to format suitable for glaze script. Then the user should define the glass pane numbers for each layer of glass and add the glass and frit data manually in the right spot as shown on Figure 28 (de Valpine , 2009). 53 vir-ve82m v-175 v-933 Enter the number of panes: 2 Window normal faces interior | | | | | | | | | | | | | | | |-> | | | | | | | | | | | | s1 s2 s3 s4 Supported surface types are: 1 - ppg-clear-6 2 - vir-ve12m 3 - vir-ve22m 4 - vir-ve32m 5 - vir-ve42m 6 - vir-ve52m 7 - vir-ve62m 8 - vir-ve72m 9 - vir-ve82m 10 – v-175 11 – v-933 # Material surface normal points to interior #Number of panes in system: 2 #Exterior surface s1 type ppg-clear-6 #Inner surface s2 type: vir-ve12m #Inner surface s3 type: ppg-clear-6 #Exterior surface s4 type: ppg-clear-6 #Exterior normal hemispherical reflectance: 0.113415413 #Interior normal hemispherical reflectance: 0.121470215 #Normal hemispherical transmittance: 0.699637633 # Void BRTDfunc glaze2-unnamed 10 If(Rdot,cr(fr(0.081), ft(0.86), fr(0.042)),cr(fr(0.065),ft(0.756),fr(0.081))) If(Rdot,cr(fr(0.086), ft(0.896), fr(0.049)),cr(fr(0.058),ft(0.808),fr(0.086))) If(Rdot,cr(fr(0.088), ft(0.882), fr(0.043)),cr(fr(0.067),ft(0.744),fr(0.089))) ft(0.896)*ft(0.808) ft(0.882)*ft(0.744) 0 0 0 glaze2.cal 0 9 0 0 0 0 0 0 0 0 0 Figure 28: OptictoGlazedb, input for writing a frit glass script (de Valpine , 2009). By using the Radiance glaze script, the definitions for the frit glass have been generated. 4.3.3 Simulation of Shading Device Simulation by DIVA enables the user to do both static and dynamic shading device analysis. In real building design, shading devices are not always open or closed. In all DIVA simulations, the user would be able to choose if the occupant can adapt the control of shading device or they will be controlled automatically. In this case the shading device will be controlled based on the glare at occupant view point (Figure 29). In addition to this the user can divide the shading device into several independent groups. In this setting each shading device group acts separately and controls glare (Figure 30). 54 Figure 29: Dynamic shading device with DIVA-automated control based on glare Figure 30: Annual automatic shading diagram in comparison to annual glare chart The shading slats angle change, based on the glare simulation to prevent visual discomfort. 55 4.3.4 Simulation Limitations and Considerations There are some considerations and limitations for using DIVA simulation software and Grasshopper plug-ins for testing the variables. 4.3.4.1 Simulation Limits with Correlations to Modeling Software There are two plug-ins for DIVA simulation. One of them works directly in the Rhino environment, and the other is the plug-in for Grasshopper. There are some differences between these two plug-in, and exploring these issues helps with choosing the right simulation approach. There are two major differences: 1. It is not possible to do annual glare simulation with the DIVA-Grasshopper plug-in. 2. The DIVA-Grasshopper plug-in cannot read the BRTDFunc and BSDF material script. Communicating with software developers replied that this issue will be solved in next version of DIVA (Version 2.2). 4.3.4.2 DIVA Simulation and Target Setting Considerations Testing the annual simulation “daylight autonomy” and changing the glass reflectance and transmittance shows that this target is less sensitive about the glass reflectance comparing to the transmittance. Further communication with LBL proved the fact that for annual simulations, glass transmission has a much greater effect than reflectance. In result, when testing the glass reflectance effect, point in time and static simulation will show the effect more accurately. 56 4.4 Testing Simulation and Model Setting In order to make certain that DIVA is capable of calculating the effects of the variables involved, two tests have been done: Testing if the software takes to account internal reflection and if the software consider to layers of glass. 4.4.1 Testing the Internal Reflection Internal reflection between two layers of façade skins is one of the most important issues that should be considered in the simulation. When one ray of light hits the outer layer of glass, a percentage of it will pass through and hit the inner layer of glass. In this case, depending on the reflectance of that material, a percentage of the light will be reflected and hit again to the outer layer of glass and this happen multiple times. It was initially unclear if the software took into account internal reflections so it has been tested. A shoe-box model was created (Figure 31). The envelope of the outer box is an opaque material and light passes through the inner box from the opening in the top. For the first setting, the inner box envelope’s material has been set opaque with 50% reflection. For the second setting, the material has been changed to transparent with 50% reflection. Figure 31: Model to Test the Internal Reflection Inner Box Envelope Outer Box Envelope 57 Table 7: The result for opaque and transparent material by 50% reflection (fc) In order to test the material setting and check if they are working as transparent and opaque, this time the sensors were placed adjacent to the interior box ( Figure 32). The point in time illuminance simulations were run and the results are shown in the table below. The material setting is actually working for both the transparent and opaque materials. Table 8: The results for opaque and transparent material with 50% reflection-working plane outside the interior box 21 Dec 9a.m 21 Dec 12p.m 21 Dec 3p.m 21 Jun 9a.m 21 Jun 12p.m 21 Jun 3p.m 21 Sep 9a.m 21 Sep 12p.m 21 Sep 3p.m Opaque 50% Reflection 85.56 133.58 73.54 190.7 241.24 183.49 155.28 204.56 136.87 Transparent 50% Reflection 85.99 133.54 73.78 191.51 240.47 183.92 154.84 204.33 137.10 21 Sep 9a.m 21 Sep 12p.m 21 Sep 3p.m Opaque 50% Reflection 0 0 0 Transparent 50% Reflection 12 15 11 Working plane adjacent to the interior box Figure 32: Testing the material setting 58 The next set of simulation has been done with opaque material and different reflection to compare the results with 50% reflectance. The results show almost the same illuminance on the working plane with the opaque and transparent material (50%) reflection (Figure 36). The other sets of the results show that material definitions were correct and by changing the material reflection, the result will change as well. From these sets of simulations, it can be concluded that the software does take to account the internal reflection. Figure 33: Point in time illuminance (fc) for different reflection 4.4.2 Testing Two Layers Façade The software also has been tested to find out if it takes to account two layers of glass. The reference model with 36” depth of cavity and two layers of glass with 65% Vt has been simulated (Figure 34), and the results were compared without the outer layer of glass. 0 100 200 300 400 500 600 35 50 65 80 Point in time illuminance (fc) Material reflection properties 21 Dec 9a.m 21 Dec 12p.m2 21 Dec 15p.m 21 Jun9a.m 21 Jun12p.m 21 Jun 15p.m 21 Sept 9a.m 21 Sept 12p.m 21 Sept 15p.m 59 Comparing the results of average daylight autonomy and average working plane illuminance for two different models show that having the outer layer of glass have reduced the quantity of light in the space (Table 9: Single and double-skin facade comparison). It can be concluded that the simulation setting takes to account two layers of glass. Table 9: Single and double-skin facade comparison 4.5 Solution Analyzing Using Evolutionary Algorithms A genetic algorithm has been used in many studies to analyze the different solutions for the problem (See Chapter 2, section 3.6). These algorithms try to find the best fitness for the problem. Grasshopper has one component (Galapagos) and one plug-in (Octopus) for this purpose. DA 21 Dec 9a.m 21 Dec 12p.m 21 Dec 3p.m 21 Jun 9a.m 21 Jun 12p.m 21 Jun 3p.m 21 Sep 9a.m 21 Sep 12p.m 21 Sep 3p.m Single Skin Facade 77.72% 16.06 25.17 13.84 35.96 45.16 34.42 29.14 38.25 25.84 Double Skin Facade 60.84% 10.47 16.24 8.94 23.25 29.18 22.32 19.01 24.73 16.68 Figure 34: Single and Double Skin Model 60 Galapagos (Grasshopper component): Variables are called genes in the evolutionary algorithms; genomes are the specific value for each gene or variable (the sliders in grasshopper). The Galapagos component lets the user choose as many genes as they want. The user is able to set the genomes value range. By changing the value of each gene, the simulation result will change and it can become better or worse. Combination of genes will also have another effect on the results, which can be different from each gene effect (Figure 35). 61 Figure 35: Different genes, and genomes in Galapagos component Fitness in Galapagos is the goal that the user wants to reach by changing the variables, for example, more daylight and less glare (Figure 36). Figure 36: Galapagos connected to the average DA, the threshold number set in Galapagos editor After setting the genomes, fitness and threshold the simulation will be run constantly and when the numbers get closer to the fitness threshold, it will explore more in that region to find better solutions (Figure 37). 62 Figure 37: Galapagos finding the best fitness to maximize daylight autonomy by changing the shading device size and position Octopus (Grasshopper plug-in): With this plug-in, the user can do a multi-objective analysis and show the trade-off between different targets and how the parametric variable design can affect each objective. Results are shown in two to six dimensional Pareto Frontier charts that compare the analysis results. 4.6 Multi-Objective Analysis Objective’s Target Spatial daylight autonomy 300/50% (sDA 300/50%) is considered as the preferred metric for analysis of daylight availably based on the IESNA, 2012 recommendation. “sDA 300/50% is reported as the percent of analysis points across the analysis area that meet or exceed this 300 lux value for at least 50% of the analysis period” (IESNA, 2012). The working plane is placed 3’ above the floor, and 24 sensors are defined to measuring daylight autonomy. For comparing the results, average daylight autonomy have been considered. DIVA simulation shows each sensor value and will color code them based on the result (Figure 38). 63 The metric selected for glare objective study is daylight glare probability. Numbers greater than 40 indicate disturbing glare and visual discomfort for the tenants. The occupant viewport that is selected for comparing the glare is shown on Figure 39. Annual glare has been analyzed for all the variables. Figure 38: Daylight autonomy result sample, showing the sensors position Intolerable Glare DGP: 82 percent Figure 39: The occupant viewport looking at the monitor for glare analysis 64 Figure 40 is showing a sample of annual glare result, as it is shown on the image the hours that the occupant experience disturbing and intolerable glare (DGP>40) is shown red. Figure 40: Annual glare result In addition to the annual glare graphic result, the software provides a table that shows the DGP result for each day and hour of the year. By using this document, the percentage of working hours that occupant experience disturbing and intolerance glare can be calculated and used to compare the results (Figure 41). Month Day Hour DGP 1 1 1.00 0.0033 1 1 2.00 0.0033 1 1 3.00 0.0033 1 1 4.00 0.0033 1 1 5.00 0.0033 1 1 6.00 0.0033 1 1 7.00 0.0033 1 1 8.00 0.1043 1 1 9.00 0.2596 1 1 10.00 1.0000 1 1 11.00 1.0000 1 1 12.00 1.0000 1 1 13.00 0.9929 1 1 14.00 0.2509 1 1 15.00 0.2332 1 1 16.00 0.1864 Figure 41: Annual glare result- Showing month, day, hour and DGP Month of the year 65 4.7 Multi-Objective Trade off Chart In order to present the trade-off between the daylight autonomy and visual comfort, a plot has been created for each location. Daylight quantity gets credit based on the daylight autonomy percentage result. For the visual comfort, the percentage of occupied hour that the DGP is higher than 40 has been calculated and shown on the chart. Each variable has been color coded to help the designers to investigate each design parameter effect on daylight quantity and visual comfort. Figure 42: Sample of trade-off chart-(The trade-off between daylight and visual comfort) 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Anuual Glare % Daylight Autonomy % 66 The research methodology can be summarized as follow (Figure 43). Figure 43: Research methodology summary Constant Parameters Variables Simulations Results Reference Model Model Dimensions Model Interior Material Occupancy Schedule Simulation Setting Depth of Cavity Envelope Material Walkway Design Shading Device Location: Los Angles New York Houston Research Objective Daylight Autonomy- Target: 300 lux Visual Comfort Target: Daylight Glare Probability<40 Trade-off Chart Daylight Autonomy vs. Annual Glare for Different Locations Simulation Process Modeling by Rhinoceros Variables by Grasshopper Simulation by Diva 67 Chapter 5: Results Effect of all defined variables (chapter 4, section 4.2) on daylight autonomy and annual glare has been investigated. The simulation settings have been validated in two ways. Simulation Setting Validation For testing the reference box model setting and making sure that the setting is accurate, two steps have been considered. Comparing the reference model results with previous research (Reinhart, 2013) and comparing the results with two software programs (DIVA and IES VE) is plotted. In the first step, the model was made exactly like the reference model that has been described in chapter 4, section 4.1.1. (Reinhart, 2013). Comparing daylight autonomy (44%) and glare analysis (0% ) show the same results. DIVA-for-Rhino Simulation Daylight Autonomy (300lux) Mean Daylight Autonomy= 44.48% of time occupied Annual Glare: 0% Figure 44: Comparing the result from the previous research with same model and setting 68 The next step was comparing the results with two different software (DIVA and IES VE). A reference double-skin façade box office with a 36” cavity depth has been modeled, and the result of illuminance and glare has been compared with DIVA and IES VE. Both software tools use the Radiance engine. Since IES VE only measures static metrics, working plane illuminance has been simulated for the model for three days of the year and three different hours. The results for point in time illuminance, show less than 10% difference, which shows that the simulation setting is accurate (Figure 45). Using a point-in-time glare simulation in DIVA and IES VE the visual comfort of a person at the camera viewpoint has been simulated. Point in time glare has been analyzed from the occupant view point for the office space with both software. DIVA and IES VE are using different metrics to analysis glare. For June and December both show the same results. The difference is that for Figure 45: Point in time illuminance results-Right: IES VE, Left: Diva 69 the 9 a.m and 12 p.m September, IES VE (One of the IES VE glare analysis which indicate glare when luminance is 7 times higher than the average.) show glare and DIVA’s DGP calculation is showing a value of 27, which is not above the glare threshold (Figure 46). 5.1 Depth of Cavity Effect on Daylight and Visual Comfort In all simulations for depth of cavity, these items have been considered fixed:  Building interior material (see chapter 4, section 4.2.1)  Inner and outer layer of double-skin façade: clear glass with 65% Vt  Office working schedule: 8 a.m to 6 p.m  South oriented façade  Daylight Autonomy target: 300 lux (30 fc) In this section the depth of cavity effect on daylight and glare is investigated. The chart below shows the effect of cavity depth on daylight autonomy and annual glare in the reference office model for different locations (Figure 47). Figure 46: Diva and IES VE point in time glare simulation 70 0 10 20 30 40 50 60 70 80 90 100 6 12 18 24 30 36 42 48 54 60 66 72 Daylight Autonomy (%) Depth of Cavity (Inch) Los Angeles New York Houston Increasing the depth of the cavity and changing walkway width from 6” to 72” shows about 25% decrease on daylight autonomy (Figure 48). Figure 47: First test modeling approach X: Constant Y: Variable Figure 48: Effect of cavity depth on daylight autonomy 71 Figure 49: Los Angeles - Daylight autonomy distribution (different depth of cavity) 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy (%) Distance from the double-skin glazed facade (feet) 12" 24" 36" 48" 60" 72" Figure 50: New York - Daylight autonomy distribution (different depth of cavity) 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy (%) Distance from the double-skin glazed facade (feet) 12" 24" 36" 48" 60" 72" Figure 51: Houston - Daylight autonomy distribution (different depth of cavity) 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy (%) Distance from the double-skin glazed facade (feet) 12" 24" 36" 48" 60" 72" 72 By changing the depth of cavity, annual glare has decreased by about 35% for Los Angeles and NewYork. The results show about 25% decrease on annual glare for Houston (Figure 52). It is suspected that these changes are the effect of the walkway width changing. In the next simulation approach, walkway width remains at 72” and the outer layer glass position changed inside the cavity (Figure 53). Figure 53: Depth of cavity -Second test modeling approach 0 10 20 30 40 50 60 70 80 90 100 6 12 18 24 30 36 42 48 54 60 66 72 Annual glare (%) Depth of cavity (Inch) Los Angeles New York Houston Figure 52: Effect of depth of cavity on visual comfort X: Constant Y: Variable 73 Figure 54: Effect of cavity depth on daylight autonomy (Second modeling approach) 0 10 20 30 40 50 60 70 80 90 100 6 12 18 24 30 36 42 48 54 60 66 72 Daylight autonomy (%) Depth of cavity (Inch) Los Angeles New York Houston Depth of cavity with fixed walkway width has almost no effect on daylight autonomy, based on the second modeling approach (Figure 54). The glare study based on the second modeling approach shows less than a 2 percent change in annual glare (Figure 55). Figure 55: Effect of cavity depth on annual glare (Second modeling approach) 0 10 20 30 40 50 60 70 80 90 100 6 12 18 24 30 36 42 48 54 60 72 Annual glare Outer layer glass position in cavity with fixed walkway Los Angeles New York Houston 74 Figure 56: Multi-story closed cavity modeling-Without walkway The last approach for investigating the effect of cavity depth on daylight is simulating a multi- story closed cavity type of double-skin façade without a maintenance walkway. The middle floor has been chosen for the study (Figure 56). Changing the depth of the cavity has almost no effect on daylight autonomy in multi-story closed double skin façades, although comparing these results with the first modeling approach shows that the walkway design can be an important element in daylighting performance of double-skin facades (Figure 57). Figure 57: Depth of cavity effect on daylight autonomy-Multi-story closed cavity DSF 0 10 20 30 40 50 60 70 80 90 100 6 12 18 24 30 36 42 48 54 60 66 72 Daylight Autonomy(%) Depth of Cavity(Inch) Los Angeles New York Houston 75 The effect of changing the cavity in a multi-story DSF with a closed cavity on glare show about 10% change in all the cities (Figure 58). Figure 58: Effect of cavity depth on annual glare for multi-story DSF 5.2 Envelope Material Effects on Daylight and Visual Comfort In order to investigate the effect of envelope material on daylight autonomy and visual comfort, two major categories have been considered: the sequence of layers and frit-clear glass combinations. 5.2.1 Testing the Visual Transmittance and Sequence of Layers Effect on Daylight and Visual Comfort-Clear Glass The first set of simulations uses clear glass with 65% Vt for the outer layer glass. The inner layer is also clear glass, but the visual transmittance of the glass changes from 35% to 85%.The reference model with a 36” cavity has been used for all the simulations in this section. The results show more than a 30% decrease in daylight autonomy for all three locations (Figure 59). 0 10 20 30 40 50 60 70 80 90 100 6 12 18 24 30 36 42 48 54 60 66 72 Annual glare (%) Depth of cavity (Inch) Los Angeles New York Houston 76 The second set of simulations considers clear glass with 65% Vt for the inner layer glass. The outer layer is also clear glass but the visual transmittance of the glass change from 35% to 85%. The results are almost the same as the first simulation (Figure 60). Based on the simulation results it can be concluded that the sequence of layers for clear glass with different Vt do not have effect on daylight autonomy. Figure 59: Effect of changing Vt of inner layer glass on daylight autonomy 0 10 20 30 40 50 60 70 80 90 100 35 45 55 65 75 85 Daylight autonomy (%) Visual transmittance (%) Los Angeles New York Hosuton 0 10 20 30 40 50 60 70 80 90 100 35 45 55 65 75 85 Daylight autonomy (%) Visual transmittance (%) Los Angeles New York Houston Figure 60: Effect of changing Vt of outer layer glass on DA 77 The second step is to find out the effect of Vt changing and the sequence of glass layers on visual comfort. The results show that annual glare decrease about 20% in New York and Los Angeles and about 7% in Houston (Figure 61). The results of changing the visual transmittance of the outer layer also show the same results on visual comfort. It can be concluded that the sequence of layers with clear glass has almost no effect on visual comfort and daylight autonomy. 5.2.2 Testing the Effect of Coated and Clear Glass Combinations on Daylight and Visual Comfort The effect of coated glass and clear glass combination on daylight have been analyzed. In the first set of simulations, the outer layer has been considered clear glass with 65% Vt and outer layer changed to different coated glass. The results on daylight autonomy and visual comfort are summarized (Table 10). Annual glare on the table indicates the percentage of occupied hours (8a.m-6p.m) that DGP (daylight glare probability) is higher than 40%. 0 10 20 30 40 50 60 70 80 90 100 35 45 55 65 75 85 Annual glare(%) Visual transmittance (%) Los Angeles New York Hosuton Figure 61: Effect of changing Vt of inner layer glass on annual glare 78 Table 10: Effect of coated glass on outer layer of DSF (Inner layer: clear 65%Vt) Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Low iron glass Vt: 90%-Reflection:8% 73.94% 25% 68.41% 29% 69.97% 14% Reflective tinted glass Vt: 25%-Reflection:55% 39.75% 1% 36.41% 9% 35.97% 0% Reflective tinted glass Vt: 25%-Reflection:35% 36.53% 1% 36.5% 8% 35.94% 0% For the second set of the simulations the outer layer is considered clear with 65% Vt and the inner layer changes to the coated glass. The results for daylight autonomy and annual glare are shown on Table 11. Table 11: Effect of coated glass on inner layer of DSF (Outer layer: clear 65%Vt) Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Low iron glass Vt: 90%-Reflection:8% 73.12% 24% 68.02% 29% 69.41% 14% Reflective tinted glass Vt: 25%-Reflection:55% 41.69% 1% 38.72% 9% 38.09% 0% 79 Reflective tinted glass Vt: 25%-Reflection:35% 36.31% 1% 36.47% 8% 35.78% 0% Changing the sequence of clear and coated glass shows almost no effect on daylight autonomy and visual comfort results. 5.2.3 Testing the Effect of Coated Glass Combinations on Daylight and Visual Comfort This set of simulations investigates the effect of two layers of coated glass and their sequence on DSF daylight performance. For each set, the definition of glass, working plane average daylight autonomy, daylight autonomy distribution, and annual glare results are shown. 5.2.3.1 Coated Glass Effect on Daylight and Visual Comfort-Set 1 The definitions of the two layers of glass are as follows (From Optic6 software, see chapter 4.3.2) Low Iron Float Glass Transmittance= 0.907 Front Reflectance= 0.081 Back Reflectance= 0.081 void glass Low_Iron 0 0 3 0.980 0.991 0.986 void BRTDfunc Low_Iron 10 0.080 0.082 0.083 0.900 0.910 0.905 0 0 0 . 0 9 0 0 0 0 0 0 0 0 0 void BRTDfunc Low_Iron 10 0.080 0.082 0.083 0.900 0.910 0.905 0 0 0 . 0 Reflective Glass-6mm Transmittance= 0.680 Front Reflectance= 0.265 Back Reflectance= 0.262 void glass reflective_glass_26 0 0 3 0.759 0.741 0.672 void BRTDfunc reflective_glass_26 10 0.203 0.244 0.240 0.697 0.680 0.616 0 0 0 . 0 9 0 0 0 0 0 0 0 0 0 void BRTDfunc reflective_glass_26 10 0.203 0.244 0.240 0.697 0.680 0.616 0 0 0 . 0 80 9 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 Changing the sequence of layer with the defined material shows almost no effect on annual glare and daylight autonomy (Table 12). Table 12: Daylight autonomy and annual glare results- First setting Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Inner layer: Reflective glass/ Outer layer: Low iron glass 78% 32% 72.16% 36% 74.38% 21% Inner layer: Low iron glass/Outer layer: Reflective glass 77.66% 32% 71.72% 35% 73.94% 21% 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy Distance from the double-skin glazed facade (feet) Los Angeles New York Houston Figure 62: Daylight autonomy distribution on working plane- First set 81 5.2.3.2 Coated Glass Effect on Daylight and Visual Comfort-Set 2 The definition of the second set of simulation glass is as follows: Transmittance= 0.849 Front Reflectance= 0.110 Back Reflectance= 0.107 void glass 10pct_ReflectiveGlass 0 0 3 0.902 0.936 0.900 void BRTDfunc 10pct_ReflectiveGlass 10 0.095 0.110 0.125 0.828 0.860 0.826 0 0 0 . 0 9 0 0 0 0 0 0 0 0 0 void BRTDfunc 10pct_ReflectiveGlass 10 0.095 0.110 0.125 0.828 0.860 0.826 0 0 0 . 0 9 0 0 0 0 0 0 0 0 0 Transmittance= 0.363 Front Reflectance= 0.347 Back Reflectance= 0.344 void glass 34pct_ReflectiveGlass 0 0 3 0.294 0.432 0.438 void BRTDfunc 34pct_ReflectiveGlass 10 0.256 0.331 0.298 0.270 0.396 0.402 0 0 0 . 0 9 0 0 0 0 0 0 0 0 0 void BRTDfunc 34pct_ReflectiveGlass 10 0.256 0.331 0.298 0.270 0.396 0.402 0 0 0 . 0 9 0 0 0 0 0 0 0 0 0 Similar to the first setting, the sequence of layer show almost no effect on daylight autonomy and visual comfort (Table 13). Table 13: Daylight autonomy and annual glare results- Second setting Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Inner layer: 35pct Reflective glass/Outer layer: 10pct Reflective glass 43.31% 3% 40.34% 10% 39.67% 0% Inner layer: 10pct Reflective glass/Outer layer: 35pct Reflective glass 42.88% 0% 39.41% 10% 38.88% 0% 82 Figure 63: Daylight autonomy distribution on working plane- Second set 5.2.3.3 Coated Glass Effect on Daylight and Visual Comfort-Set 3 The definition of the third set of simulation glass is as follows: Transmittance= 0.264 Front Reflectance= 0.554 Back Reflectance= 0.541 void glass 55pct_ReflectiveGlass 0 0 3 0.339 0.281 0.150 Void BRTDfunc 55pct_ReflectiveGlass 10 0.492 0.548 0.562 0.311 0.257 0.137 0 0 0 . 0 9 0 0 0 0 0 0 0 0 0 void BRTDfunc 55pct_ReflectiveGlass 10 0.457 0.576 0.532 0.311 0.257 0.137 0 0 0 . 0 Transmittance= 0.267 Front Reflectance= 0.335 Back Reflectance= 0.357 void glass 33pct_ReflectiveGlass 0 0 3 0.358 0.272 0.214 void BRTDfunc 33pct_ReflectiveGlass 10 0.333 0.339 0.298 0.329 0.249 0.196 0 0 0 . 0 9 0 0 0 0 0 0 0 0 0 void BRTDfunc 33pct_ReflectiveGlass 10 0.272 0.353 0.231 0.329 0.249 0.196 0 0 0 . 0 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy Distance from the double-skin glazed facade (feet) Los Angeles New York Houston 83 9 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 Third set of simulation with higher reflection material, the sequence of layers show about 3% change on daylight autonomy and no effect on visual comfort (Table 14). Table 14: Daylight autonomy and annual glare results- Third setting Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Inner layer: 55pct Reflective glass/Outer layer: 33pct Reflective glass 23.84% 1% 21.56% 8% 20.78% 0 Inner layer: 33pct Reflective glass/Outer layer: 55pct Reflective glass 20.53% 1% 18.47% 8% 17.41% 0 84 Figure 64: Daylight autonomy distribution on working plane- Third set 5.2.3.4 Coated Glass Effect on Daylight and Visual Comfort-Set 4 The definition of the fourth set of simulation glass is as follows: Transmittance= 0.228 Front Reflectance= 0.693 Back Reflectance= 0.711 void glass 70pct_ReflectiveGlass 0 0 3 0.229 0.259 0.228 void BRTDfunc 70pct_ReflectiveGlass 10 0.707 0.685 0.721 0.210 0.237 0.209 0 0 0 0 9 0 0 0 0 0 0 0 0 0 void BRTDfunc 70pct_ReflectiveGlass 0.707 0.702 0.721 0.210 0.237 0.209 0 0 0 .0 9 0 0 0 0 0 0 0 0 0 Transmittance= 0.680 Front Reflectance= 0.233 Back Reflectance= 0.262 void glass 25pct_ReflectiveGlass 0 0 3 0.759 0.741 0.672 void BRTDfunc 25pct_ReflectiveGlass 10 0.203 0.244 0.240 0.697 0.680 0.616 0 0 0 0 9 0 0 0 0 0 0 0 0 0 void BRTDfunc 25pct_ReflectiveGlass 10 0.203 0.244 0.240 0.697 0.680 0.616 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy Distance from the double-skin glazed facade (feet) Los Angeles New York Houston 85 For the fourth set of simulations, higher reflective glass have been chosen. The sequence of layer show about 5% change on daylight autonomy and no effect on annual glare (Table 15). Table 15: Daylight autonomy and annual glare results- Fourth setting Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Inner layer: 70pct Reflective glass/ Outer layer: 25pct Reflective glass 39.25% 1% 35.43% 7% 35.05% 0 Inner layer: 25pct Reflective glass/ Outer layer: 70pct Reflective glass 34.06% 1% 30.19% 7% 29.94% 0 Figure 65: Daylight autonomy distribution on working plane- Fourth set 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy Distance from the double-skin glazed facade (feet) Los Angeles New York Houston 86 The results of these four sets of simulations show, that the higher the reflectance of the glass the more important is the sequence of the glass layers. Placing the higher reflective glass on the inner layer of the DSF will result in higher daylight autonomy and it does not show a significant effect on visual comfort. 5.2.4 Testing the Effect of Translucent Panel and Glass Combination on Daylight and Visual Comfort In this set of test one layer of the double-skin façade was considered clear glass with 65% Vt and the other layer a translucent panel with 20% transmittance and 40% reflection. The results are show that the sequences of glass and translucent material have an effect on daylight autonomy. Placing the higher reflective translucent panel on the inner layer causes to higher daylight autonomy (Table 16). Table 16: Effect of translucent and glass material on Daylight autonomy and annual glare Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Inner layer: Translucent Panel Outer layer: Clear Glass 37.41% 0% 34.31% 0% 32.47% 0% Inner layer: Clear Glass Outer layer: Translucent Panel 31.34% 0% 27.38% 0% 25.47% 0% Further investigation on the effect of translucent and glass material sequence on daylight autonomy, shows that the difference is not the same for all cavity depths (Figure 66). 87 Figure 66: Cavity depth effect on daylight autonomy difference by changing the sequence of layers 5.2.5 Testing the Effect of Frit Glass on Daylight and Visual Comfort In this section, the effects of four sets of frit and clear glass combinations have been analyzed on daylight autonomy and glare. For all these simulations, the walkway was assumed to have 50% perforation in order to be able to investigate the effect of frit glass patterns on annual glare. For an accurate definition of the frit glass as it was described on chapter 4, the de Valpine (2009) script was used. The glass has been assumed as a double clear glass (65% Vt) with inner frit coating (50% coverage, 40% Vt and 25% reflection). 5.2.5.1 Frit and Clear Glass Effect on Daylight and Visual Comfort- First Set of Pattern The pattern for the first set of simulations is shown on Figure 67. 0 5 10 15 20 25 30 35 40 45 50 12 24 36 48 60 72 Daylight autonomy (%) Depth of Cavity (Inch) Inner Layer: Translucent-LA Outer Layer: Translucent-LA Inner Layer: Translucent-NY Outer Layer: Translucent-NY Inner Layer: Translucent-HOU Outer Layer: Translucent-HOU 88 Figure 67: Frit and clear glass combination-First set of pattern Table 17: Effect of frit and clear glass on daylight autonomy and visual comfort-First set Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Optioon1: All Frit Glass Inner Layer/ Clear Glass Outer Layer 60.97% 8% 56.59% 9% 56.97% 3% Optioon2: All Frit Glass Outer Layer/ Clear Glass Inner Layer 63.82% 8% 59.76% 9% 59.96% 3% Optioon3: Frit Glass and Clear for Both Layer/ Parallel Pattern 64.88% 9% 60.16% 10% 60.72% 3% Optioon4: Frit Glass and Clear for Both Layer/ Diagonal Pattern 62.22% 9% 57.56% 10% 57.78% 3% Optioon5: Frit Glass and Clear for Both Layer/ Overlapped Pattern 62% 9% 57.23% 10% 57.45 3% 89 5.2.5.2 Frit and Clear Glass Effect on Daylight and Visual Comfort- Second Set of Pattern The second set of simulation pattern is shown on Figure 68. Figure 68: Frit and clear glass combination -Second set of pattern Table 18: Effect of frit and clear glass on daylight autonomy and visual comfort-Second set Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Optioon1: All Frit Glass Inner Layer/ Clear Glass Outer Layer 45.68% 2% 41.23% 6% 40.56% 0% Optioon2: All Frit Glass Outer Layer/ Clear Glass Inner Layer 48.76% 3% 43.53% 7% 42.89% 0% Optioon3: Frit Glass and Clear for Both Layer/ Parallel Pattern 49.34% 4% 44.88% 7% 44.38% 1% Optioon4: Frit Glass and Clear for Both Layer/ Diagonal Pattern 50.11% 4% 45.06% 7% 44.97% 1% Optioon5: Frit Glass and Clear for Both Layer/ Overlapped Pattern 49.23% 4% 44.47% 7% 44.02% 1% 5.2.5.3 Frit and Clear Glass Effect on Daylight and Visual Comfort- Third Set of Pattern The third set of frit and clear glass pattern model is shown below. The results for this set of pattern are shown on Table 19. 90 Figure 69: Frit and clear glass combination -Third set of pattern Table 19: Effect of frit and clear glass on daylight autonomy and visual comfort-Third set Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Optioon1: All Frit Glass Inner Layer/ Clear Glass Outer Layer 53.65% 6% 49.69% 8% 49.21% 1% Optioon2: All Frit Glass Outer Layer/ Clear Glass Inner Layer 57.38% 6% 53.41% 8% 53.03% 2% Optioon3: Frit Glass and Clear for Both Layer/ Parallel Pattern 57.45% 6% 52.62% 9% 52.13% 2% Optioon4: Frit Glass and Clear for Both Layer/ Diagonal Pattern 57.7% 6% 53% 9% 52.84% 2% Optioon5: Frit Glass and Clear for Both Layer/ Overlapped Pattern 57.93% 6% 53.38% 9% 53.11% 2% 5.2.5.4 Frit and Clear Glass Effect on Daylight and Visual Comfort- Fourth Set of Pattern In this set of simulations, it has been decided to have the same area and proportion of frit to clear glass as it was designed on third set. The only difference is that in this set of simulation the pattern has been designed perpendicular. The difference between third set and fourth set is shown on Figure 70. 91 Figure 70: Difference of modeling from third set to fourth set of simulation Table 20: Effect of frit and clear glass on daylight autonomy and visual comfort-Fourth set Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Optioon1: All Frit Glass Inner Layer/ Clear Glass Outer Layer 53.19% 5% 49.38% 7% 48.12% 1% Optioon2: All Frit Glass Outer Layer/ Clear Glass Inner Layer 56.62% 6% 52.85% 9% 52.12% 2% Optioon3: Frit Glass and Clear for Both Layer/ Parallel Pattern 56.93% 6% 53.21% 9% 51.66% 2% Optioon4: Frit Glass and Clear for Both Layer/ Diagonal Pattern 57.14% 6% 53.37% 9% 52.31% 2% Optioon5: Frit Glass and Clear for Both Layer/ Overlapped Pattern 57.48% 6% 53.78% 9% 53.02% 3% Based on all the frit and clear glass combination and pattern settings, the results show that having the frit glass on both layers of double skin façade will increase daylight autonomy, compared to having them only on the inner layer. The results do not show significant effect on daylight autonomy and visual comfort between the different pattern settings. 92 5.3 Walkway Parametric Design Effect on Daylight and Visual Comfort Depending on the purpose of walkway, their designs are very different. In this part three characteristic of walkways have been analyzed: the walkway position in the cavity, different materials for walkway, and the walkway percent perforation. 5.3.1 Walkway Position inside the Cavity Effect on Daylight and Visual Comfort Two different positions (3 feet above finished floor and 3feet below the ceiling) of the walkway have been analyzed and the result is shown in comparison to the floor level walkway position (Figure 71). Changing the position of walkway from the floor level to the working plane level increase daylight autonomy by about 10% and decrease visual comfort by 5% for all three locations (Table 21). Figure 71: Modeling to test the effect of walkway position on daylight autonomy and glare Walkway 3’ above the floor Walkway 3’ below the ceiling 93 Table 21: Effect of walkway position on daylight autonomy and glare Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare 3’ Above finish floor 71.61% 16% 65.78% 21% 66.99% 9% 3’ Below ceiling 66.94% 13% 56.59% 19% 61.14% 7% Finish floor level 60.84% 11% 56.59% 14% 56.76% 4% 5.3.2 Walkway Material Effect on Daylight and Visual Comfort The reflectance of the walkway material has been changed from 10% to 70%. By changing the walkway reflectance, daylight autonomy has increased by 20%. Annual glare results show about 10% increase in Los Angeles and New York, although for Houston this variable only show 2% increase on annual glare (Table 22). 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy Distance from the double-skin glazed facade (feet) Los Angeles-3' Above finish floor New York-3' Above finish floor Houston-3' Above finish floor Los Angeles-3' Below ceiling New York-3' Below ceiling Houston-3' Below ceiling Figure 72: Effect of walkway position on daylight autonomy distribution 94 Table 22: Effect of walkway material on daylight autonomy and visual comfort Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Metallic 10% Refl 54.63% 13% 51.14% 14% 51.60 7% Metallic 40% Refl 64.75% 15% 60.89% 16% 61.02 7% Metallic 70% Refl 74.33% 23% 70.38% 25% 71.17 9% The daylight autonomy distribution shows that this difference is less in the front of the room and more in the back of the room (Figure 73). The results show that the reflectance of walkway material has a significant effect on daylight. 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy Distance from the double-skin glazed facade (feet) Los Angeles-10% Refl New York- 10% Refl Houston-10% Refl Los Angeles-70% Refl New York-70% Refl Houston-70% Refl Figure 73: Effect of walkway material on daylight autonomy distribution 95 5.3.3 Walkway Perforation Effect on Daylight and Visual Comfort In this part, the walkway was designed with 25%, 50% and 75% perforation and the effects of this design have been analyzed on daylight autonomy and glare (Figure 74). Changing the perforation of the walkway from solid to 75% perforated, shows about 12% increase on daylight autonomy and 7% decrease on visual comfort (Table 23). Table 23: Effect of walkway perforation on daylight autonomy and visual comfort Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Solid Walkway 60.84% 11% 56.59% 14% 56.76% 4% 25% Perforation 63.73% 16% 60.58% 19% 68.69% 9% 50% Perforation 68.23% 17% 64.90% 21% 64.24% 9% 75% Perforation 71.22% 19% 69.05% 22% 60.84% 10% Figure 74: Walkway perforation models for the simulations 96 The results of the walkway design parameters show that all of the variables have direct significant effect on daylight and visual comfort in the cell test office space. 5.4 Shading Device Parametric Design Effect on Daylight and Visual Comfort In this part, the effects of different shading device design have been investigated on daylight and visual comfort in double-skin facade. The variables are the position of shading device inside the cavity, different material, size and shape of shading device. All the simulations for shading device design were tested based on a closed 36” walkway and another set by 50% perforated, 36” walkway. 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy Distance from the double-skin glazed facade (feet) Los Angeles-25% Perforation New York- 25% Perforation Houston-25% Perforation Los Angeles-50% Perforation New York-50% Perforation Houston-50% Perforation Figure 75: Effect of walkway perforation on daylight autonomy distribution 97 5.4.1 Position of Shading Device inside the Cavity Three shading device positions were considered to explore their effect on daylight autonomy and visual comfort. As shown on Figure 76, the positions are: 3” from the outer layer and 3” from the inner layer, and middle of the cavity. For investigating the position effect all the louver slat were assumed with 4” width with 50% reflection. Figure 76: Position of shading device for DA and glare simulation 5.4.1.1 Position of Shading Device inside the Cavity-Solid Walkway Changing the position of shading device in a double-skin façade cavity with solid walkway shows no effect on daylight autonomy. The glare study shows that only in Los Angeles there is 5% reduction on annual glare (Table 24). Table 24: The effect of shading device position inside a double skin facade cavity-Solid walkway Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare 3” From the outer layer 55.91% 9% 51.88% 10% 51.34% 2% 98 Middle of cavity 55.67% 6% 51.52% 9% 51.30% 1% 3” From the inner layer 55.28% 4% 51.22% 9% 51.22% 1% 5.4.1.2 Position of Shading Device inside the Cavity-50% Perforated Walkway Same set of simulation have been done for a 50% perforated walkway. The results show that placing the shading device closer to the outer layer increased daylight autonomy by 6%, and annual glare increased by less than 3% (Table 25). Table 25: The effect of shading device position inside a double skin facade cavity-50% perforated walkway Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare 3” From the outer layer 65.28% 14% 59.94% 16% 60.59% 4% Middle of the Cavity 62.62 13% 58.19 14% 57.32% 4% 3” From the inner layer 59.47% 10% 53.38% 13% 53.81% 4% 99 5.4.2 Shading Device Material In this part the effect of shading device material on daylight autonomy and glare have been investigated. Same as the previous set of simulation, in this part the effect of variable was tested on a 36” solid walkway and on a 50% perforated one. The position of the shading device was considered 3” from the outer layer of glass, and the shading device width is 4”. 5.4.2.1 Shading Device Material- Solid Walkway Metallic materials have been considered for the shading device and the reflection have been changed from 20% to 80%. Increasing the reflection of shading device’s material, increase daylight autonomy by 10%, and annual glare by less than 6% for all locations (Table 26). 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy Distance from the double-skin glazed facade (feet) Los Angeles-3" From outer layer New York-3" From outer layer Houston-3" From outer layer Los Angeles-3" From inner layer New York-3" From inner layer Houston-3" From inner layer Figure 77: Effect of shading device position on daylight autonomy distribution- 50% perforated walkway 100 Table 26: The effect of shading device material on daylight and visual comfort-Solid walkway Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Metallic 20% Refl 51.06% 7% 47.97% 8% 46.97% 0% Metallic 50% Refl 55.91% 9% 51.88% 10% 51.34% 2% Metallic 80% Refl 61.99% 12% 58.09% 14% 57.88% 5% 5.4.2.2 Shading Device Material- 50% Perforated Walkway The reflectance of material has been also investigated with a 50% perforated walkway. The overall results are the same as the solid walkway test (Table 27). Table 27: The effect of shading device material on daylight and visual comfort-50% perforated walkway Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare Metallic 20% Refl 60.38% 11% 56.53% 13% 56.78% 6% Metallic 50% Refl 65.28% 14% 59.94% 16% 60.59% 4% Metallic 80% Refl 70.97% 19% 65.34% 21% 65.83% 10% 101 By investigating the daylight autonomy distribution it can be concluded that changing the shading device material reflectance has almost no effect on daylight autonomy of the front sensors, although it shows more than 10% difference in the back of the room sensors. 5.4.3 Shading Device Size and Spacing The effects of the shading device’s size on daylight autonomy and visual comfort have been investigated in this part. The width of shading device changed from 4” to 16”. For all these simulations the shading device is positioned near the outer layer and it is 50% reflective (Figure 79). Figure 78: The effect of shading device material reflection on daylight autonomy distribution 0 10 20 30 40 50 60 70 80 90 100 3 6 9 12 15 18 21 24 Daylight autonomy Distance from the double-skin glazed facade (feet) Los Angeles-Metallic 20% Refl New York-3" Metallic 20% Refl Houston-Metallic 20% Reflr Los Angeles-Metallic 50% Refl New York-Metallic 50% Refl Houston-Metallic 50% Refl Los Angeles-Metallic 80% Refl2 New York-Metallic 80% Refl3 Houston-Metallic 80% Refl4 102 Figure 79: Shading device size and spacing change modeling for DA and glare simulation 5.4.3.1 Shading Device Size Effect- Solid Walkway By changing the shading device size from 4” to 16”, daylight autonomy decrease about 7% for all locations (Table 28). Table 28: The effect of shading device width on DSF daylight autonomy and visual comfort- Solid walkway Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare 4” Width-3” Spacing 55.91% 8% 51.88% 10% 51.34% 2% 8” Width-6” Spacing 50.62% 0% 46.72% 0% 46.12% 2% 12” Width-9” Spacing 48.32% 0% 45.03% 0% 44.86% 0% 16” Width-12” Spacing 47.33% 0% 44.85% 0% 43.35% 0% 5.4.3.2 Shading Device Size Effect- 50%Perforated Walkway Changing the shading device size with perforated walkway show about 8% decrease on daylight autonomy and less than 5% increase on visual comfort for all the cities (Table 29). 103 Table 29: The effect of shading device width on DSF daylight autonomy and visual comfort-50% perforated walkway Los Angeles New York Houston DA Annual Glare DA Annual Glare DA Annual Glare 4” Width-3” Spacing 65.28% 14% 59.94% 16% 60.59% 3% 8” Width-6” Spacing 61.44% 11% 56.09% 12% 56.31% 1% 12” Width-9” Spacing 59.03% 9% 54.38% 11% 54.62% 0% 16” Width-12” Spacing 56.91% 7% 52.62% 9% 52.38% 0% As the results show, by increasing the width of the louver slats, the daylight autonomy and glare decrease. The effect is less noticeable when the shading device gets wider. It was expected that the results to be the same for different sizing options as the proportion of shading device width and spacing are the same. Further study in this area and checking the results with different software can be suggested. 5.4.4 Dynamic Shading Device Simulation The user is able to model a dynamic shading device in DIVA. The dynamic shading device is controlled by glare analysis. As a result, louver slats will rotate in a way to prevent the glare for a certain chosen view port. The dynamic shading for this set of simulation is separated in two groups; the first step is rotating the slats by 30 degree and next step by 60 degree to control the glare. For all of these simulations, the walkway is considered to have a 50% perforation, and shading device width is 4”. 104 As the results show by using dynamic shading, the occupant will not experience any glare, although comparing the results of daylight autonomy with the static shading situation shows about 20% difference for Los Angeles and New York. This difference is less for Houston, as it needs less control for glare, based on the annual glare results with static shading design. This probably comes from the higher sun angles on the lower latitude places (Figure 80). Annual glare with static shading device Annual glare with dynamic shading device Shading device opening- closing pattern LA 14% annual glare Average DA 40.31% NY 16% annual glare Average DA 35.06% HOU 3%annual glare Average DA 44.67% 105 Figure 80: Automatic shading device effect on daylight and visual comfort 5.4.5 Multi Variable Analysis Shading Device (Size, curvature, position and rotation) The Galapagos component has been used to explore the effect of changing the size, curvature, and position of the shading device inside the double-skin façade cavity on daylight autonomy and glare. The daylight autonomy threshold has been set at 40 percent, and three variables were defined: the position of shading device, size of shading device and changing the curvature of the device. The setting is based on minimum 4” shading width and at least 2” space between the glass layers and shading device. For all of the simulations, the walkway is 50% perforated. The first 5 shading devices with the highest daylight autonomy have been analyzed for the visual comfort as well. The results show one factor in common for all the Galapagos solutions. The best position for the shading device without considering the size and shape is in the range of 1 inch to 9 inch form the outer layer for the 36 inch depth of cavity (Table 30). Table 30: Multi-variable shading device design- Effect on daylight autonomy and annual glare Los Angeles Position inside cavity (Inch for the outer layer) Shading device width (Inch) Shading device curvature DA Annual Glare 1 6 Inch 5 Inch Flat Slat 64.38 13% 2 3 Inch 6 Inch 62.76 14% 3 7 Inch 8Inch Flat Slat 61.65 11% 106 4 2 Inch 8 Inch 61.23 9% 5 3Inch 7 Inch 60.09 7% New York Position inside cavity (Inch for the outer layer) Shading device width (Inch) Shading device curvature DA Annual Glare 1 5 Inch 5 Inch Flat Slat 58.50 14% 2 3 Inch 8Inch Flat Slat 57.24 13% 3 8 Inch 6 Inch 55.33 14% 4 7 Inch 7 Inch 54.82 8% 5 2 Inch 10 Inch Flat Slat 53.27 10% 107 Houston Position inside cavity (Inch for the outer layer) Shading device width (Inch) Shading device curvature DA Annual Glare 1 4Inch 6Inch Flat Slat 58.93 4% 2 2Inch 8Inch Flat Slat 56.63 1% 3 8 Inch 6 Inch 55.34 0 4 7Inch 7 Inch 52.79 0 5 2 Inch 7 Inch 51.06 0 108 Chapter 6: Analysis and Discussion The effect of each variable on daylight autonomy and annual glare were described for three different locations (see chapter 5). In this chapter, the results are analyzed, and the effects of each study are summarized. All of the results have been plotted on a trade-off chart (trade-off between daylight autonomy and annual glare), for each city. These charts can help the designers to find out the best ways to make the balance between electrical energy saving and visual comfort. The daylight autonomy objective can tell the designers about the electric lighting energy savings. Basically the percentage of the working hour that daylight autonomy goal is met (300lux~30 fc in this study), daylight is enough for the space, and there is no need for electrical lighting. Annual glare will inform the designer about the percentage of the working hour times during which the occupant can feel visual discomfort. 6.1 Variables Effect Summary The effect of different variables (depth of cavity, envelope material, and walkway and shading device design) on daylight autonomy and visual comfort can be summarized as follow:  Depth of cavity: The simulations data shows that the only important factor in depth of cavity that affects daylight and visual comfort is walkway width. As expected, the distance between the layers of glass does not show any significant difference in daylight autonomy and visual comfort. By changing the depth of cavity and walkway width from 6 inches to 72 inches, daylight autonomy decrease about 24% in all three chosen cities. Annual glare results show about 109 35% decrease for New York and Los Angeles and about 25% for Houston. Based on the data, all of these changes are the effect of the walkway overhang.  Envelope material: The results show that for clear glass and glass with low reflectance properties, the sequence of layers is very minimal, and it can effectively be ignored. Although, when a high reflectance material is being used in DSF, the sequence of layers shows about 5% difference in daylight autonomy. This factor does not show significant effect on annual glare. The internal reflection between layers of façade causes higher daylight autonomy while the high reflective façade layer is placed inside. The thermal effects were not tested. Testing combination of frit and clear glass and changing the frit glass pattern shows that by having all the frit coated glass on inner layer, daylight autonomy and annual glare have decreased. Changing the patterns shows that daylight autonomy and glare only have changed by the frit glass to clear glass area proportion and pattern does not play an important role in this case.  Walkway design: All of the variables (position, material reflection and perforation) in walkway design have significant effect on daylight autonomy and visual comfort. Changing the walkway position form the finish floor level to 3feet above the floor, daylight autonomy have increased by about 10% for all cities. The results show that the annual glare increase about 5% in Los Angeles and Houston and about 7% for New York. Changing the walkway material reflectance shows a significant effect on daylight level and visual comfort. By changing the reflectance of the material from 10% to 70%, daylight autonomy for all three locations shows about 20% increase. Visual comfort 110 decrease by about 10% for Los Angeles and New York; it shows a very minimal effect on Houston annual glare. Based on the daylight autonomy distribution data, the most increase in daylight autonomy has happened on the sensors at the back of the room. Changing the walkway perforation, from solid to 75% perforated design shows more than 10% increase in daylight quantity. By changing this variable, visual comfort has been decreased about 6% for all the cities.  Shading device design: Designing a shading device for a double-skin façade is similar to single skin façade. While working with high reflective layers of glass and shading device, internal reflection should be considered, and this is the difference of DSF shading device design from the conventional façade design. The effect of each variable in shading device design is explained below. The position of the shading device inside the cavity has been tested with a solid 36” and 50% perforated 36” walkway. In the first case, the position of shading device did not show any effect on daylight autonomy and visual comfort. By the perforated walkway, placing the shading device closer to the outer layer shows about 6% increase in daylight autonomy. This position of shading device shows 4% decrease in visual comfort for Los Angeles and New York, although the annual glare did not show any change in Houston. It can be concluded that by placing the shading device near the outer layer and having a perforated walkway, the high angle sun can penetrate in to the space. Increasing the reflection of shading device, in both simulation assumptions (solid and perforated walkway) shows 10% increase in daylight autonomy. Annual glare 111 simulations show that the effect of shading device material on visual comfort is less than 8% for Los Angeles and New York and it is about 5% for Houston. 6.2 Trade-Off Charts It is important for designers to be able to strike an appropriate balance between daylight quantity and visual comfort. In order to make this process easier, trade-off charts have been plotted for each city. The single-skin façade data on the chart is representing a one layer reference office with 36” solid overhang (same as the DSF walkway); the envelope is fully glazed with 45% Vt glass material (The double-skin façade reference model have been considered with 65% Vt glass therefore the single-skin façade has chosen by 45% Vt glass). The trade-off charts show how much each parameter affect the daylight autonomy and glare. By plotting the results on these charts, the user can find out about the balance between these two objectives. The line on the chart represents the variables that have the highest daylight autonomy and the lowest annual glare. None of the other variables can dominate these settings. As it is shown on the charts, different kinds of variables with almost the same daylight autonomy show different results for annual glare. The trade-off charts will help designers to choose the solutions with the highest daylight autonomy and lowest annual glare. The highest daylight autonomy and glare value is for the closed cavity multi-story double skin façade (without walkway). One example that can be interpreted from this charts for Los Angeles show that it is better to have a wider walkway and higher visual transmittance glass, comparing to have a small walkway and lower visual transmittance (Figure 81). 112 0 5 10 15 20 25 30 35 40 45 50 0 10 20 30 40 50 60 70 80 90 100 Anuual Glare % Daylight Autonomy % Shading Device Design-Solid Walkway Shading Device Design-50% Walkway Depth of Cavity Depth of Cavity-Multi Story Closed DSF Clear Glass Changing Vt Clear and Complex Glass Combination Complex Glass Combination Frit Glass Pattern Walkway Design Single-skin facade Figure 81: Trade-off chart- Los Angeles The variables those are closer to the line, show better design solutions (More daylight autonomy with less glare). 113 It can be extracted from the trade-off chart for New York that in most cases frit and clear glass combinations show better results (more daylight autonomy and less glare) than the shading device design options (Figure 82). This will still depend on the individual arrangements. 0 5 10 15 20 25 30 35 40 45 50 0 10 20 30 40 50 60 70 80 90 100 Annual Glare % Daylight Autonomy % Shading Device Design-50% Perforated Walkway Shading Device Design-Solid Walkway Depth of Cavity Depth of Cavity-Multi Story Closed DSF Clear Glass Changing Vt Clear and Complex Glass Combination Complex Glass Combination Walkway Design Frit Glass Pattern Single-skin façade Figure 82: Trade-off chart- New York 114 An example of sample data from the Houston trade-off chart shows that having a highly reflective walkway would be a good design solution. This variable shows more daylight autonomy and almost the same annual glare results as the low reflective walkway (Figure 83). 0 5 10 15 20 25 30 35 40 45 50 0 10 20 30 40 50 60 70 80 90 100 Annual Glare % Daylight Autonomy % Shading Device Design-Solid Walkway Shading Device Design-50% Perforated Walkway Depth of Cavity Depth of Cavity-Multi Story Closed DSF Clear Glass Changing Vt Clear and Reflective Glass Combination Reflective Glass Combination Frit Glass Pattern Walkway Design Single-Skin Facade Figure 83: Trade-off chart- Houston 115 Los Angeles and Houston charts show less diversity compared to the New York chart. The largest difference is coming from the annual glare objective results. The charts show that for all the variables, Houston and New York show the least and highest amount of annual glare. The 36” walkway that was fixed in most of the simulations, reduce the glare problem in Houston and Los Angeles. As the New York has the highest latitude and due to the low angle of incidence of the sun's rays the walkway overhang has less effect on glare objective for this city. In almost all of the tests, Los Angeles shows higher daylight autonomy, based on the same variable. The variables have been categorized in four major areas: depth of cavity, envelope material, walkway design, and shading device design. The reference office has been modeled and edited using Rhino and Grasshopper. All the variables have been studied using DIVA software to show their effects on objectives of the research (daylight autonomy and glare). The final results have been plotted on the trade-off chart to show the designers how to strike an appropriate balance between daylight quantity and visual comfort. 116 Chapter 7: Conclusions and Future Work Following section provide summary of the work and presents the conclusions based on the hypothesis statement. Limitations of the study and possible future work are also included. 7.1 Conclusion The hypothesis described as: The different parameters of the double-skin façade have significant direct effects on daylight level and visual comfort inside the space. The results show that not all of the DSF design variables have significant effect on daylight and visual comfort. The results show the only parameter that is important for the depth of cavity is the walkway width. The sequence of glass layers did not show a significant effect on daylight and visual comfort, when a clear glass or glass with low reflectance properties is being used. Although placing a highly reflective glass on the inner layer shows about a 5% increase on daylight autonomy and no effect on annual glare (due to the internal reflection between façade layers). The pattern of frit glass and clear glass combination did not show a significant effect. For all the variables of walkway and shading device design, the results show significant effect on daylight autonomy and annual glare results. From most to least, the impact significance of these parameters is: walkway design options (width, material reflectance, position and perforation), shading device design options (material and position), and sequence of façade layer. By using the simulation results and trade-off charts, designers will be able to find an appropriate balance between visual comfort and daylight availability while designing a double-skin façade. 117 7.2 Limitations of Study DIVA, plug-in for Grasshopper has some limitation in daylight autonomy and glare simulation. The plug-in cannot read BSDF material properties, and cannot simulate glare. For this study, all of the models have been tested in Rhino environment which can simulate annual glare. Due to these issues batch simulation was not possible and each variable should have been tested manually. In order to make a pattern on envelope with different materials, the user should model the pattern manually and assign the right material to each part. Radiance material cannot define the patterns of envelope. The present study was designed to determine the effect of double-skin façade parameters on visual comfort and daylight autonomy. Defined variables may have effects on energy, thermal performance and natural ventilation of the double-skin façade building, as well. Due to the limitation of the time and defined scope of the work, these effects have not been investigated. 7.3 Future work Four major areas can be considered for future work: different objectives, new variables, validation, and creating new tool for glare analysis. 7.3.1 Objective Studies The effect of each set of variables on thermal performance and natural ventilation can be analyzed. DIVA, uses the EnergyPlus engine to provide thermal analysis. The next step of the study, can be taking the models and variables and testing the effect of them on energy performance of the DSF building. In this case, an energy performance and daylight quantity 118 trade-off chart can be presented. It is expected that this would be particularly useful with thermal simulations of overhangs and/or walkways. 7.3.2 Variable Studies Other variables can be studied: different orientations, complex glass and shading devices, changing the skin geometry, and validation. The next step of the study can be adding more variables to this research, for example building orientation other than south. More complex glass coating and shading device material and feature (like prismatic glazing, holographic coating, electrochromic) can be studied in future research. Analyzing more complex geometries like double-skin faceted facades and Retroflex louver is suggested for future study. Varying geometry parameters can be modeled by using Grasshopper and DIVA. 7.3.3 Validation Validation of the research results is another possible future study area. Although in this study the basic DSF model was analyzed by two different software (IES VE and DIVA) and the results were compared, the next step would be comparing the results with scale model and real building data. A scale model of a double skin façade can be made, and the results can be compared with the DIVA simulation’s acquired data. 7.3.4 Glare Simulation Plug-in for Grasshopper The DIVA simulation for Grasshopper does not have glare analysis simulation. For this research all of the models were exported and the Glare simulation was done on the Rhino environment which can simulate annual glare. In order to make it easier for designers and researchers a glare simulation can be added to the DIVA for Grasshopper component. 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Center for the Built Environment (CBE). 125 Appendix A Nomenclature aa Ambient Accuracy ab Ambient Bounces ad Ambient Divisions ar Ambient Resolution BGI British Glare index BRTD Bidirectional Reflectance and Texture Data CGI CIE Glare Index DA Daylight Autonomy DGI Daylight Glare Index DGP Daylight Glare Probability DSF Double-Skin Facade DSP Daylight Saturation Percentage fc Foot-canlde Refl Reflectance of Materials SHGC Solar Heat Gain Coefficient Spec Specular Reflection SPT Single Point in Time Working Plane Illuminance SSF Single Skin Façade tn Transmissivity Tn Transmittance 126 UDI Useful Daylight Illuminance UGR CIE Unified Glare Rating VCP Visual Comfort Probability Vt Visual Transmittance 127 Appendix B Effect of depth of cavity on annual glare-Different walkway projection Los Angeles-12” Cavity Los Angeles-24” Cavity Los Angeles-36” Cavity Los Angeles-48” Cavity Los Angeles-60” Cavity Los Angeles-72” Cavity New York-12” Cavity New York -24” Cavity 128 New York -36” Cavity New York -48” Cavity New York -60” Cavity New York -72” Cavity Houston-12” Cavity Houston -24” Cavity Houston -36” Cavity Houston -48” Cavity Houston -60” Cavity Houston -72” Cavity 129 Effect of depth of cavity on annual glare-Fixed 72” walkway Los Angeles -6” Cavity Los Angeles -72” Cavity New York -6” Cavity New York -72” Cavity Houston -6” Cavity Houston -72” Cavity Effect of depth of cavity on annual glare-Multi-story closed cavity Los Angeles -12” Cavity Los Angeles -24” Cavity Los Angeles -36” Cavity Los Angeles -48” Cavity 130 Los Angeles -60” Cavity Los Angeles -72” Cavity New York -12” Cavity New York -24” Cavity New York -36” Cavity New York -48” Cavity New York -60” Cavity New York -72” Cavity Houston -12” Cavity Houston -24” Cavity 131 Houston -36” Cavity Houston -48” Cavity Houston -60” Cavity Houston -72” Cavity Appendix C Effect of envelope material on annual glare-Clear glass Los Angeles-Outer layer 65% Vt Inner layer: 35% Vt Los Angeles-Outer layer 65% Vt Inner layer: 45% Vt Los Angeles-Outer layer 65% Vt Inner layer: 55% Vt Los Angeles-Outer layer 65% Vt Inner layer: 65% Vt Los Angeles-Outer layer 65% Vt Inner layer: 75% Vt Los Angeles-Outer layer 65% Vt Inner layer: 85% Vt New York-Outer layer 65% Vt New York -Outer layer 65% Vt 132 Inner layer: 35% Vt Inner layer: 45% Vt New York -Outer layer 65% Vt Inner layer: 55% Vt New York -Outer layer 65% Vt Inner layer: 65% Vt New York -Outer layer 65% Vt Inner layer: 75% Vt New York -Outer layer 65% Vt Inner layer: 85% Vt Houston-Outer layer 65% Vt Inner layer: 35% Vt Houston -Outer layer 65% Vt Inner layer: 45% Vt Houston -Outer layer 65% Vt Inner layer: 55% Vt Houston -Outer layer 65% Vt Inner layer: 65% Vt Houston -Outer layer 65% Vt Inner layer: 75% Vt Houston -Outer layer 65% Vt Inner layer: 85% Vt Effect of envelope material on annual glare-Coated glass 133 Los Angeles- First set Inner layer: 8% Refl- 90% Vt Outer layer: 0.26% Refl-68% Vt Los Angeles- First set Inner layer: 0.26% Refl-68% Vt Outer layer: 8% Refl- 90% Vt New York- First set Inner layer: 8% Refl- 90% Vt Outer layer: 0.26% Refl-68% Vt New York- First set Inner layer: 0.26% Refl-68% Vt Outer layer: 8% Refl- 90% Vt Houston- First set Inner layer: 8% Refl- 90% Vt Outer layer: 0.26% Refl-68% Vt Houston- First set Inner layer: 0.26% Refl-68% Vt Outer layer: 8% Refl- 90% Vt Los Angeles- Second set Inner layer: 30% Refl- 35% Vt Outer layer: 10% Refl-85% Vt Los Angeles- Second set Inner layer: 10% Refl-85% Vt Outer layer: 30% Refl- 35% Vt New York- Second set Inner layer: 30% Refl- 35% Vt Outer layer: 10% Refl-85% Vt New York- Second set Inner layer: 10% Refl-85% Vt Outer layer: 30% Refl- 35% Vt 134 Houston- Second set Inner layer: 30% Refl- 35% Vt Outer layer: 10% Refl-85% Vt Houston- Second set Inner layer: 10% Refl-85% Vt Outer layer: 30% Refl- 35% Vt Los Angeles- Third set Inner layer: 55% Refl- 25% Vt Outer layer: 33% Refl-25% Vt Los Angeles- Third set Inner layer: 33% Refl-25% Vt Outer layer: 55% Refl- 25% Vt New York- Third set Inner layer: 55% Refl- 25% Vt Outer layer: 33% Refl-25% Vt New York- Third set Inner layer: 33% Refl-25% Vt Outer layer: 55% Refl- 25% Vt Houston- Third set Inner layer: 55% Refl- 25% Vt Outer layer: 33% Refl-25% Vt Houston- Third set Inner layer: 33% Refl-25% Vt Outer layer: 55% Refl- 25% Vt Los Angeles- Fourth set Los Angeles- Fourth set 135 Inner layer: 70% Refl- 22% Vt Outer layer: 25% Refl-68% Vt Inner layer: 25% Refl-68% Vt Outer layer: 70% Refl- 22% Vt New York- Fourth set Inner layer: 70% Refl- 22% Vt Outer layer: 25% Refl-68% Vt New York- Fourth set Inner layer: 25% Refl-68% Vt Outer layer: 70% Refl- 22% Vt Houston- Fourth set Inner layer: 70% Refl- 22% Vt Outer layer: 25% Refl-68% Vt Houston- Fourth set Inner layer: 25% Refl-68% Vt Outer layer: 70% Refl- 22% Vt Effect of envelope material on annual glare-Frit and clear glass Los Angeles-First set All frit inner layer Los Angeles-First set Option3 Los Angeles-First set Option4 Los Angeles-First set Option5 New York-First set New York -First set 136 All frit inner layer Option3 New York -First set Option4 New York -First set Option5 Houston -First set All frit inner layer Houston -First set Option3 Houston -First set Option4 Houston -First set Option5 Los Angeles-Second set All frit inner layer Los Angeles- Second set Option3 Los Angeles- Second set Option4 Los Angeles- Second set Option5 137 New York- Second set All frit inner layer New York - Second set Option3 New York- Second set Option4 New York - Second set Option5 Houston - Second set All frit inner layer Houston - Second set Option3 Houston - Second set Option4 Houston - Second set Option5 Los Angeles-Third set All frit inner layer Los Angeles- Third set Option3 138 Los Angeles- Third set Option4 Los Angeles- Third set Option5 New York- Third set All frit inner layer New York - Third set Option3 New York- Third set Option4 New York - Third set Option5 Houston - Third set All frit inner layer Houston - Third set Option3 Houston - Third set Option4 Houston - Third set Option5 Effect of envelope material on annual glare-Translucent and clear glass Los Angeles Outer Layer: Translucent material 25% Refl Inner Layer: 65% clear glass Los Angeles Outer Layer: 65% clear glass Inner Layer: Translucent material 25% Refl 139 New York Outer Layer: Translucent material 25% Refl Inner Layer: 65% clear glass New York Outer Layer: 65% clear glass Inner Layer: Translucent material 25% Refl Houston Outer Layer: Translucent material 25% Refl Inner Layer: 65% clear glass Houston Outer Layer: 65% clear glass Inner Layer: Translucent material 25% Refl Appendix D Effect of walkway design on annual glare-Walkway position Los Angeles-3’ Below ceiling Los Angeles-3’ Above finish floor New York-3’ Below ceiling New York-3’ Above finish floor Houston-3’ Below ceiling Houston-Above finish floor 140 Effect of walkway design on annual glare-Walkway material Los Angeles-Metallic 10% Reflection Los Angeles- Metallic 70% Reflection New York- Metallic 10% Reflection New York- Metallic 70% Reflection Houston- Metallic 10% Reflection Houston- Metallic 70% Reflection Effect of walkway design on annual glare-Walkway perforation Los Angeles-Solid walkway Los Angeles- 25% Perforation walkway Los Angeles- 50% Perforation walkway Los Angeles- 75% Perforation walkway 141 New York-Solid walkway New York- 25% Perforation walkway New York-50% Perforation walkway New York- 75% Perforation walkway Houston-Solid walkway Houston- 25% Perforation walkway Houston-50% Perforation walkway Houston- 75% Perforation walkway Appendix E Effect of shading device design on annual glare-Shading device position Los Angeles- 3” from outer layer Los Angeles- 3” from inner layer 142 New York- 3” from outer layer New York- 3” from inner layer Houston- 3” from outer layer Houston- 3” from inner layer Effect of shading device design on annual glare- Shading device material Los Angeles- Metallic 20% Ref Los Angeles- Metallic 50% Ref Los Angeles- Metallic 80% Ref New York- Metallic 20% Ref New York- Metallic 50% Ref New York- Metallic 80% Ref 143 Houston- Metallic 20% Ref Houston- Metallic 50% Ref Houston- Metallic 80% Ref Effect of shading device design on annual glare- Shading device size Los Angeles-4” inch shading device Los Angeles-8” inch shading device Los Angeles-12” inch shading device Los Angeles-16” inch shading device New York-4” inch shading device New York -8” inch shading device New York -12” inch shading device New York -16” inch shading device 144 Houston-4” inch shading device Houston -8” inch shading device Houston -12” inch shading device Houston -16” inch shading device

Abstract (if available)

Abstract The demand for fully glazed, highly transparent façades has increased in recent decades as architects and clients embrace the style, and modern construction methods and materials have made them economically viable. Double‐skin façades are also becoming more common as a system that can be highly transparent and if designed appropriately more energy efficient than conventional systems. As a relatively new system, there is still limited data about energy performance and occupant comfort of the different variants of double skin façades. ❧ Designing the façade elements of the building to make a well daylit space is a challenging issue for designers. A well daylit office space will reduce the energy consumption of the building and will make a comfortable, healthier, and productive work environment for users. Too much daylight can introduce glare, heat gain, and other negative impacts. ❧ As a multi‐objective analysis, the trade‐offs between daylight quantity and visual comfort in the office spaces are complex, but it is possible for a designer to find an appropriate balance. Daylight autonomy (DA) metric of 300 lux (~30 fc) has been chosen as a target for measuring daylight quantity based on IESNA 2012 recommendation and daylight glare probability (DGP) as the metric for measuring visual comfort. ❧ Using a virtual office test cell of 27 by 12 by 9 feet, five façade parameter effects have been studied: depth of cavity

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Asset Metadata

Creator Motevalian, Elham (author)

Core Title Double skin façades performance: effects on daylight and visual comfort in office spaces

School School of Architecture

Degree Master of Building Science

Degree Program Building Science

Publication Date 07/15/2014

Defense Date 06/27/2014

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag daylight,DIVA daylight simulation,double‐skin façade,OAI-PMH Harvest,trade‐off chart,visual comfort

Format application/pdf (imt)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Noble, Douglas (committee chair), Kensek, Karen M. (committee member), Schiler, Marc (committee member)

Creator Email elham.motevalian@gmail.com,motevali@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c3-441582

Unique identifier UC11287193

Identifier etd-Motevalian-2689.pdf (filename),usctheses-c3-441582 (legacy record id)

Legacy Identifier etd-Motevalian-2689.pdf

Dmrecord 441582

Document Type Thesis

Format application/pdf (imt)

Rights Motevalian, Elham

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA