A Comparative Analysis On The Effect Of Double- Skin Façade Typologies On Overall Building Energy Consumption Performance In A Temperate Climate

Transcription

1 A Comparative Analysis On The Effect Of Double- Skin Façade Typologies On Overall Building Energy Consumption Performance In A Temperate Climate DT175a Module: ARCH4258 Final Year Dissertation Aaron Regazzoli C Supervisor: Rory Greenan 10/05/2013

2 Abstract Abstract One of the most important factors affecting the energy performance within a building is a carefully and efficiently designed façade. The primary aim of this research was to present a critical examination of the effect on the energy consumption of an office building located within a temperate climate utilising Double-Skin Façade construction as opposed to a conventional single-skin curtain wall system. A comparative analysis of the effect on the overall energy consumption within an office building was investigated in which a combination of various Double-Skin Façade configurations, systems and cavity depths were utilised. The use of computer aided dynamic thermal modelling was incorporated in order to ensure the calculation of accurate and efficient simulations of the various Double- Skin Façade systems due to the complex nature of the various functions within the façade cavity. Through the use of the dynamic thermal modelling simulations, a detailed analysis of the efficiency of each respective combination of Double-Skin Façade construction simulated was comprised. As such the optimum façade combination for use within an office building located in a temperate climate was identified. Bsc Architectural Technology i

3 Acknowledgements Acknowledgements I would like to express my sincere thanks and appreciation to all staff of Dublin Institute of Technology throughout my time within the college. In particular to my current year head Sima Rouholamin for always finding the time when I was in need of any assistance or guidance. My assistant year head David Palmer, this dissertation wouldn t have been possible without his continuous guidance and direction. I truly appreciate his interest and association with this research. My research supervisor Rory Greenan, who provided me with valuable knowledge and input throughout the course of the dissertation. In particular for getting me started with the complex simulations and patiently replying to any queries which I had. Finally, I am indebted to my family, girlfriend and friends for encouraging me to pursue this degree and research, without their support and encouragement throughout my time within the course this would not have been possible. Aaron Regazzoli, May Bsc Architectural Technology ii

4 Declaration Declaration I hereby declare that the work described within this dissertation is, except where otherwise stated, entirely my own work and has not been submitted as an exercise for a degree at this or any other university. Aaron Regazzoli, 10/05/2013. Bsc Architectural Technology iii

5 Contents Table of Contents Abstract... i Acknowledgements... ii Declaration... iii 1.0 Introduction Double-Skin Façade Concept Research Objectives Double Skin Façade Configuration Double-Skin Façade Construction Double-Skin Façade Configuration Box Façade Corridor Façade Shaft-Box Façade Multi-Storey Façade Double-Skin Façade System Naturally Ventilated Cavity Sealed Cavity Regulating Cavity (Mixed-Mode Ventilation) The Role of Double-Skin Façades Energy Consumption Energy Performance - Double-Skin Façade Thermal Buoyancy (Stack Effect) Dynamic Thermal Modelling - Methodology Research Context Establishing Base Model Parameters Hawkins House Redevelopment Drum Office Area Conventional Single-Skin Façade Base Model Analysis Double-Skin Façade Configurations Bsc Architectural Technology iv

6 Contents 4.3 Analysis / Simulations SunCast Vista Results Analysis MacroFlo Dynamic Thermal Modelling Simulations Analysis of Simulation Results Annual Energy Consumption (mwh) Annual Heating and Cooling Loads (kwh) Annual Energy Consumption (kwh/m²) Conclusions and Recommendations Comparison of Façade Configuration Energy Consumption Recommendations Optimum Cavity Depth Areas for Further Research References Appendix 1: The History of Double-Skin Façades... 1 Appendix 2: IES Virtual Environment User Interface... 1 Appendix 3: Double-Skin Façade Energy Consumption and Cost Analysis... 1 Bsc Architectural Technology v

7 Table of Figures Table of Figures Chapter 1 Figure 1.1: Impact of the building façade on energy consumption (King, 2010) Figure 1.2: Typical Double-Skin Façade Configuration (ArchiExpo, 2003)... 3 Chapter 2 Figure 2. 1: Typical Double-Skin Façade Composition (Caine, 2013) Figure 2. 2: Corridor Façade Google SketchUp Model... 7 Figure 2. 3: Box Façade Google SketchUp Model... 7 Figure 2. 4: Multi-Storey Façade Google SketchUp Model... 7 Figure 2. 5: Shaft-Box Façade Google SketchUp Model... 7 Figure 2. 6: Box Façade Elevation... 8 Figure 2. 7: Box Façade Section... 8 Figure 2. 8: Box Façade Plan... 8 Figure 2. 9: Site Assembley of Prefabricated Box Façade Elements (Oesterle, et al., 2001) Figure 2. 10: Corridor Façade Section... 9 Figure 2. 11: Corridor Façade Elevation... 9 Figure 2. 12: Corridor Façade Plan... 9 Figure 2. 13: Corridor Façade (Oesterle, Lieb, Lutz, & Heusler, 2001) Figure 2. 14: Shaft-Box Façade Elevation Figure 2. 15: Shaft-Box Façade Section Figure 2. 16: Shaft-Box Façade Plan Figure 2. 17: ARAG 2000 Building Shaft-Box Façade (Oesterle, et al., 2001) Figure 2. 18: Multi-Storey Façade Plan Figure 2. 19: Multi-Storey Façade Elevation Figure 2. 20: Multi-Storey Façade Section Figure 2. 21: Multi-Storey Façade (Gonchar, 2013) Figure 2. 22: Classification of Double-Skin Façades and Ventilation Methods Figure 2. 23: Sketch Indicating airflow induced due to the stack effect Figure 2. 24: Motorised Façade Ventilation Opening (BBRI, 2004) Bsc Architectural Technology vi

8 Table of Figures Chapter 3 Figure 3. 1: Schematic diagram heat transfer through a Double-Skin Façade Figure 3. 2: Double-Skin Façade Winter and Summer Operations (Gonchar, 2013) Chapter 4 Figure 4. 1: Proposed Redevelopment of Hawkins House South-Façade Figure 4. 2: Hawkins House Redevelopment which highlights the proposed office area Figure 4. 3: IES Applications User Interface Figure 4. 4: IES Room Function Interface. The office area (in green) and additional Hawkins House redevelopment (pink) is highlighted above Figure 4. 5: IES Room Template Interface Figure 4. 6: Hawkins House Redevelopment 3D IES Virtual Environment Model Figure 4. 7: Hawkins House Redevelopment IES 3D Base Model Figure 4. 8: Corridor Façade Figure 4. 9: Multi-Storey Façade Figure 4. 10: Shaft-Box Façade Figure 4. 11: Box Façade Figure 4. 12: IES SunCast Solar Shading Calculations Figure 4. 13: ApacheSim Parameters User Interface Figure 4. 14: Vista Results Analysis Interface Figure 4. 15: MacroFlo Openings Database Manager Interface Chapter 5 Figure 5. 1: Annual Energy Consumption Dynamic Thermal Modelling Simulations Figure 5. 2: Annual Heating and Cooling Loads - 200mm Cavity Depth Figure 5. 3: Annual Heating and Cooling Loads - 600mm Cavity Depth Figure 5. 4: Annual Heating and Cooling Loads mm Cavity Depth Figure 5. 5: Box Façade Annual Energy Consumption (kwh/m²) Figure 5. 6: Corridor Façade Annual Energy Consumption (kwh/m²) Figure 5. 7: Shaft-Box Façade Annual Energy Consumption (kwh/m²) Figure 5. 8: Multi-Storey Façade Annual Energy Consumption (kwh/m²) Figure 5. 9: Shaft-Box Façade Configuration Airflow Concept Bsc Architectural Technology vii

9 Table of Figures Chapter 6 Figure 6. 1: Annual Energy Consumption Facade Efficiency Comparison Figure 6. 2: Multi-Storey Façade Regulating Cavity Determination of Optimal Cavity Depth Figure 6. 3: Annual Energy Consumption Cost Optimal Cavity Depth Figure 6. 4: Horizontal Pivoting Transparent Slats (Teuxido, 2013) Appendix 1 Appendix 1. 1: Steiff Factory Giengen, Germany. Circa 1904 (Solla, 2013) Appendix 1. 2: Famhouse Box-Type Windows in Mürren, Switzerland (Oesterle, et al., 2001) Appendix 1. 3: Narkomfin Housing Building, Moscow, Russia. Circa 1928 (Wolfe, 2013) Appendix 1. 4: Corbusier Sketch Illustrating Ideas (Tascón & Hernandez., 2008) Appendix 2 Appendix 2. 1: Office Room Conditions Appendix 2. 2: Double-Skin Façade Room Conditions Appendix 2. 3: Double-Skin Façade MacroFlo Opening Template Sealed Cavity... 2 Appendix 2. 4: Double-Skin Façade MacroFlo Opening Template Naturally ventilated Cavity Appendix 2. 5: Double-Skin Façade MacroFlo Opening Template Regulating Cavity Appendix 3 Appendix 3. 1: Annual Energy Consumption Overview (mwh) Bsc Architectural Technology viii

10 Table of Tables Table of Tables Chapter 1 Table 1.1: Reasearch Objectives Mapped to Methods...5 Appendix 3 Appendix Table 3.1: Base Model Experimental Parameters...1 Appendix Table 3.2: Base Model Examination...1 Appendix Table 3.3: IES Test Results...2 Appendix Table 3.4: IES Test Results...2 Appendix Table 3.5: IES Test Results...2 Appendix Table 3.6: IES Test Results...3 Appendix Table 3.7: IES Test Results...3 Appendix Table 3.8: IES Test Results...3 Appendix Table 3.9: IES Test Results...4 Appendix Table 3.10: IES Test Results...4 Appendix Table 3.11: IES Test Results...4 Appendix Table 3.12: IES Test Results...5 Appendix Table 3.13: IES Test Results...5 Appendix Table 3.14: IES Test Results...5 Bsc Architectural Technology ix

11 Chapter 1 Introduction 1.0 Introduction The primary aim of this research is to present a critical examination of the energy performance associated with the use of various Double-Skin Façade typologies and systems in an office building located within a temperate climate. The concept of Double-Skin Façade construction is not a recent methodology and dates back to the middle of the 19th century. However, rapid development of the concept began during the 1970 s as a result of the oil crisis of 1973 and 1979 (Dickson, 2003). A growing concern regarding energy consumption during this period resulted in an acceleration in improvements within the glass industry, and in turn Double-Skin Façade technology also seen significant advancements (Bayram, 2003). A detailed account of the history of Double-Skin Façades can be seen in Appendix 1. Currently within the construction industry, buildings are not merely a simple combination of stone and glass. In fact according to (Bayram, 2003) they are becoming increasingly more energy efficient and as a result are achieving high performance standards due to constant technological advancements and ever increasing performance requirements. The building façade acts as a filter between the internal and external environments. As a result It provides protection to the building interior from undesirable impacts such as excessive heat gain, cold, radiation and wind generated from the external environment (Consultants, 2013). As a result the façade is the primary moderator between the external and internal environments, which underlines the importance of the façade as a key aspect of reducing overall energy consumption (Palmer, 2011). According to (King, 2010) 8% of energy consumption within office buildings is as an direct result of heat loss through the façade walls and windows; however the façade can have an indirect effect on a further 56% of energy consumed through related functions such as infiltration, HVAC heating, cooling and air-conditioning and lighting (Palmer, 2011), see figure 1.1 below for a diagrammatic representation of the effects in which the building façade impacts on overall energy consumption. BSc Architectural Technology 1

12 Chapter 1 Introduction Figure 1. 1: Impact of the building façade on energy consumption (King, 2010). The possibility of Double-Skin Façade construction providing a reduction in energy consumption related to heating and cooling loads in an office building is studied to determine whether it is an energy efficient method of façade construction. In addition a brief cost analysis will be outlined to evaluate if reduced energy consumption justifies the initial construction costs in a long-term assessment. Previous cost analysis show that the initial cost of Double-Skin Façade construction can range from 200%-300% of conventional single-skin façade construction, depending on the façade composition (Bayram, 2003). 1.2 Double-Skin Façade Concept The term Double-Skin Façade can be defined as a combination of a traditional single-skin façade which is doubled on the outside by a second layer, essentially an additional glazed façade. Each of these layers are commonly referred to as a skin, hence the origin of the widely used term Double-Skin Façade. In addition, a naturally ventilated, sealed or self-regulating cavity is located between each skin having a width which can range from several centimetres at the narrowest to several metres for the widest accessible cavities (BBRI, 2004). BSc Architectural Technology 2

13 Chapter 1 Introduction The glazing may stretch over an entire structure or over just a portion of it. The internal layer of glass, typically insulating, serves as part of a conventional structural wall or a curtain wall, while the additional layer, usually single glazed, is placed in front of the main glazing and as a result creates the air space (Uuttu, 2001). An example of typical Double-Skin Facade configuration is shown below in figure 1.2: Internal Layer External Layer Grated Walkway Ventilation Grille Spandrel Panel Figure 1. 2: Typical Double-Skin Façade Configuration (ArchiExpo, 2003). According to (Arons, 2000) the main objectives of the Double-Skin Façade concept can be briefly defined under the following headings: 1. Reduced Energy Consumption and Ecological Responsibility 2. Natural Ventilation 3. Cost Reduction 4. Acoustic Insulation 5. Occupant Comfort 6. Increased Occupant Productivity 7. Additional Building Security BSc Architectural Technology 3

14 Chapter 1 Introduction 1.3 Research Objectives The Aim of this research is to provide a critical evaluation as to whether Double-Skin Façade construction plays an important role in reducing energy consumption within office buildings in a temperate climate. The objectives of this research are as follows: 1. To characterise the various methods of Double-Skin Façade configuration and construction used within the construction industry. 2. To research and establish the advantages and disadvantages associated with the respective systems of Double-Skin Façade construction. 3. To determine the role and effect of Double-Skin Façade construction on energy consumption and performance of buildings. 4. To carry out a comparative analysis of the effect on energy consumption on buildings through various Double-Skin Façade configurations and systems as opposed to conventional curtain wall construction. 5. To determine the performance efficiency against conventional curtain wall construction and the associated payback durations of each respective system in relation to the information obtained through research. 6. To establish the optimal combination of Double-Skin Facade configuration, system and cavity depth in relation to overall building energy consumption for use within an office building located in a temperate climate. Objectives mapped to Research Methods: Objectives Characterise the various methods of Double-Skin Façade configurations. To research and establish the advantages and disadvantages associated with the respective systems of Double-Skin Façade construction. To determine the role and effect of Double-Skin Façade construction on energy consumption and performance of buildings. Research Methods Review current literature on methods of classification of Double-Skin Façade typologies. Review current literature on the advantages and disadvantages that are associated which each respective system of Double-Skin Façade configuration with the construction industry. Review available data and literature on the role and effect that Double-Skin Façade construction plays on the consumption of energy within buildings. BSc Architectural Technology 4

15 Chapter 1 To carry out a comparative analysis of the effect on energy consumption on buildings through various Double-Skin Façade configurations and systems as opposed to conventional single-skin curtain wall construction. To determine the performance efficiency against conventional curtain wall construction and the associated payback durations of each respective system in relation to the information obtained through research. To establish the optimal combination of Double-Skin Façade configuration, system and cavity depth in relation to overall building energy consumption for use within an office building located in a temperate climate. Introduction To perform computer aided dynamic thermal modelling on various scenarios to determine the respective energy consumption of various Double-Skin Façade configurations. Prepare a comparison of results from thermal dynamic modelling to determine respective system efficiency. Review of current data on estimated Double-Skin Façade construction costs and provide detailed outputs of payback periods of each respective system tested. Through the comparison and analysis of the results obtained through the use of the dynamic thermal modelling simulations, to identify and determine the most efficient combination of the various double-skin façade parameters evaluated. Table 1.1: Reasearch Objectives Mapped to Methods. In Conclusion, through a detailed investigation into the various methods of Double- Skin Façade construction and configuration, the knowledge required in order to effectively and efficiently determine the parameters of the dynamic thermal modelling simulations are to be identified. BSc Architectural Technology 5

16 Chapter 2 Double-Skin Façade Configuration 2.0 Double Skin Façade Configuration In this chapter the typical composition of a Double-Skin Façade is examined in further detail, together with an explanation of the various methods of classification used within the construction industry to define the Double-Skin Façade configuration. 2.1 Double-Skin Façade Construction There are a wide range of definitions from a large range of authors as to what components actually constitute a Double-Skin Façade. However, the layers of a Double-Skin Façade are generally comprised of the following elements: External Glazing: The exterior layer usually comprises of heat strengthened safety or laminated safety glass. It may be airtight or open with air inlet and outlet openings controlled by either manual or automated opening vents. This layer may be completely glazed and is used as a rain screen to provide protection to the interior layer from the external climatic conditions (Lee, Selkowitz, Bazjanac, Inkarojrit, & Kohler, 2002). Internal Glazing: The interior layer is usually comprised of a fixed or operable thermal insulating double or triple pane glazed unit. Clear, low emmitance coating, solar diffusion glazing, etc. can be used on the internal glazing in order to reduce the radiative heat gains to the interior. This layer is generally comprised of some built or opaque elements and may contain fixed or operable casement or hopper windows, depending on the ventilation strategy used (Lee, et al., 2002). Figure 2. 1: Typical Double-Skin Façade Composition (Caine, 2013). BSc Architectural Technology 6

17 Chapter 2 Double-Skin Façade Configuration Intermediate Cavity: The intermediate cavity between the external and internal layers can be naturally, regulating (mixed-mode ventilation) or completely sealed. The width of the cavity can vary as a function of the applied concept and can range from 200mm to over 2m. The width of the intermediate cavity determines the physical properties of the façade and the way in which it is maintained (Streicher et al., 2007). Any adjustable sun shading or day lighting equipment enhancement devices are generally installed within the intermediate cavity to protect the internal rooms from external elements and as a less expensive method than the use of externally mounted systems. The airflow throughout the intermediate space is determined by solar induced thermal buoyancy and through the effects of the wind (Oesterle, et al., 2001). 2.2 Double-Skin Façade Configuration There are many methods of configuration and classification of Double-Skin Façades. Each one is dependent on design principles such as the origin and direction of air flow within the cavity, the façade configuration and also according to the form in which the intermediate space is divided. However, the principle factor which determines the Double-Skin Façades classification is according to the desired ventilation function (Oesterle, et al., 2001). There are four main categories of configuration of Double-Skin Façades, as mentioned below: 1. Box Façade: (Figure 2.2) 2. Corridor Façade (Figure 2.3) 3. Shaft-Box Façade (Figure 2.4) 4. Multi-Storey Façade (Figure 2.5) Figure 2. 2: Box Façade Google SketchUp Model Figure 2. 3: Corridor Façade Google SketchUp Model Figure 2. 4: Shaft-Box Façade Google SketchUp Model Figure 2. 5: Multi-Storey Façade Google SketchUp Model BSc Architectural Technology 7

18 Chapter 2 Double-Skin Façade Configuration Box Façade According to (Oesterle, et al., 2001) the Box Façade is one of the oldest forms of Double-Skin Façade configuration. It is comprised of modular single storey Double-Skin Façade box units which are divided by structural bay widths or on a room-by-room basis (Lee, et al., 2002). The exterior single glazed skin contains openings in order to allow the ingress of fresh air and the egress of stale air. Resulting in the ability of both the intermediate space and internal rooms to be naturally ventilated (Oesterle, et al., 2001). Figure 2. 2: Box Façade Elevation Figure 2. 3: Box Façade Section Figure 2. 4: Box Façade Plan Box Façade configuration is most commonly used in situations where consideration is given due to high external noise levels and when there are special requirements regarding the transmittance of sound between adjoining rooms (Oesterle, et al., 2001). According to (Uuttu, 2001) the main advantages of a Box Façade configuration are: 1. Improvement of sound insulation both horizontally and vertically across the façade cavity. 2. Division into fire protection levels is achievable throughout the façade cavity. 3. Occupant Controlled natural window ventilation can be achieved. Figure 2. 5: Site Assembley of Prefabricated Box Façade Elements (Oesterle, et al., 2001). BSc Architectural Technology 8

19 Chapter 2 Double-Skin Façade Configuration Corridor Façade A Corridor Façade is a single-storey façade which is separated horizontally at each intermediate floor area (Uuttu, 2001). It does not contain any vertical divisions except those that are required at the corner of the building or elsewhere due to structural, acoustic or fire protection reasons (Lee, et al., 2002). The exterior single glazed skin contains openings that are usually positioned in a staggered format from bay to bay in order to prevent stale air extracted on one floor entering the cavity space of the floor immediately above (Oesterle, et al., 2001). Figure 2. 7: Corridor Façade Elevation Figure 2. 6: Corridor Façade Section Figure 2. 8: Corridor Façade Plan A Corridor Façade configuration is typically used in the situation of high-rise buildings (Oesterle, et al., 2001). According to (Uuttu, 2001) the main advantages of a Corridor Façade configuration are: 1. Improvement of sound insulation both horizontally and vertically across the façade cavity. 2. Division into fire protection levels is achievable throughout the façade cavity. 3. Occupant Controlled natural window ventilation can be achieved. Figure 2. 9: Corridor Façade (Oesterle, Lieb, Lutz, & Heusler, 2001). BSc Architectural Technology 9

20 Chapter 2 Double-Skin Façade Configuration Shaft-Box Façade The Shaft-Box Façade is a unique variation of a Box Façade configuration with a combination of both a Double-Skin Façade with a Multi-Storey Cavity and one with a single-storey cavity (Uuttu, 2001). It is comprised of an alternating layout of box façade units and vertical shaft elements that are linked through airflow openings (Oesterle, et al., 2001). As a result the vertical height of the shaft creates strong uplift forces due to the increased stack effect and draws the air from the box façade elements up to the top of the shaft where it is exhausted (Lee, et al., 2002). Figure 2. 10: Shaft-Box Façade Elevation Figure 2. 11: Shaft-Box Façade Section Figure 2. 12: Shaft-Box Façade Plan Shaft-Box Façade configuration is typically used in low-rise buildings (Oesterle, et al., 2001). According to (Uuttu, 2001) the main advantages of a Shaft-Box Façade configuration are: 1. Improvement of sound insulation both horizontally and vertically across the façade cavity. 2. Occupant Controlled natural window ventilation can be achieved. 3. Provides additional building security. Shaft Element Figure 2. 13: ARAG 2000 Building Shaft-Box Façade (Oesterle, et al., 2001). BSc Architectural Technology 10

21 Chapter 2 Double-Skin Façade Configuration Multi-Storey Façade In a Multi-Storey Façade the cavity is not separated horizontally or vertically by divisions, it extends over the whole extent of the building envelope (Oesterle, et al., 2001). The principle behind a Multi-Storey Façade is dependent on air that accumulates at the top of the cavity will heat up on a warm day and as a result will be exhausted from the openings in the roof or external skin and in turn will result in cooler air being drawn in from the base of the façade and replacing the exhausted air (Uuttu, 2001). Figure 2. 15: Multi-Storey Façade Elevation Figure 2. 16: Multi-Storey Façade Section Figure 2. 14: Multi-Storey Façade Plan A Multi-Storey Façade configuration is most suited where external noise levels are high and acoustic insulation is a key design requirement (Oesterle, et al., 2001). According to (Uuttu, 2001) the main advantages of a Multi-Storey Façade configuration are as follows: 1. Improvement of sound insulation both horizontally and vertically across the façade cavity. 2. Occupant Controlled natural window ventilation can be achieved. 3. Provides additional building security. 4. Shading devices placed within the cavity are protected from the climatic elements as opposed to externally mounted systems Figure 2. 17: Multi-Storey Façade (Gonchar, 2013). BSc Architectural Technology 11

22 Chapter 2 Double-Skin Façade Configuration 2.3 Double-Skin Façade System In addition there are numerous combinations and design possibilities by varying the partition configuration, ventilation system and airflow method (Aksamija). Sealed Regulating Figure 2. 18: Classification of Double-Skin Façades and Ventilation Methods Naturally Ventilated Cavity The British Standard BS EN (12792., 2003) defines the process of natural ventilation as dependent on pressure differentiation without the aid of air movement components. The two driving forces that determine the effectiveness of natural ventilation in Double-Skin Façades are the differences in pressure within the cavity generated by thermal buoyancy, or the stack effect, and also by the effect of wind velocity (BBRI, 2004). The principle of the stack effect is dependent on the theory that the warm air inside the cavity is less dense than the cooler external air, and as a result will be drawn out from openings located at the top of the building envelope; as a result cooler denser air will enter openings lower down. The process will continue if the air entering the building is continuously heated, typically by casual or solar gains (Baker, 2013). The principle of the stack effect is shown in figure 2.23 to the right. Cavity Airflow Solar Radiation Figure 2. 19: Sketch Indicating airflow induced due to the stack effect Sealed Cavity According to (Permasteelisa, 2013) a sealed cavity, or closed cavity façade, refers to the method in a Double-Skin Façade construction whereby the cavities between the internal and external layers are completely sealed. The concept of a Closed Cavity Façade is simple and provides a number of benefits according to (Permasteelisa, 2013) such as: BSc Architectural Technology 12

23 Chapter 2 Double-Skin Façade Configuration A sealed Double-Skin Façade improves glazing transparency. Greater energy and cost efficiency compared to naturally ventilated methods. A sealed façade cavity is an energy saving method of façade construction Regulating Cavity (Mixed-Mode Ventilation) As opposed to either solely naturally ventilated or sealed cavities, it is possible for several ventilation methods to be utilised simultaneously within a Double-Skin Façade configuration. In certain cases, the ventilation method can be regulated and determined by motorised ventilation openings which react with environmental parameters, such as cavity air temperature, etc. (BBRI, 2004). Motorised ventilation openings, as presented in figure 2.24, enable the possibility to vary from one method of ventilation to another as a function of their position (BBRI, 2004). According to CIBSE Guide A (2005) guidelines such as when the cavity air temperature exceeds a mean temperature of 28 the motorised ventilation openings will be activated in order to allow the dissipation of heat from the façade cavity and as a result prevent overheating within the façade cavity. Figure 2. 20: Motorised Façade Ventilation Opening (BBRI, 2004). In conclusion, the various Double-Skin Façade configurations and systems mentioned above, in addition with the variation of the cavity depth, are to be examined to determine the overall effect on building energy consumption. The role in which Double-Skin Façade construction affects building energy consumption is explored within the next chapter in order to determine the main energy saving principles associated with the use of the Double-Skin Façade concept. BSc Architectural Technology 13

24 Chapter 3 The Role of Double-Skin Façades - Energy Consumption 3.0 The Role of Double-Skin Façades Energy Consumption In this chapter the effect on façade performance in the context of Double-Skin Façade construction is presented, together with an explanation of the various performative concepts associated. As briefly mentioned in Chapter 1, the use of Double-Skin Façade construction provides various performance enhancing benefits to the building envelope. According to (Arons, 2000) these benefits can be defined under the following headings: 1. Reduced Energy Consumption and Ecological Responsibility: Reduced energy consumption is achieved by minimising solar gain through the façade and reducing cooling loads. 2. Cost Reduction: Double-Skin Façades are significantly more expensive to construct than a conventional single-skin façade, however according to (Saelens, 2002) their use reduces long-term costs due to reduced energy consumption. 3. Natural Ventilation: Due to the protection of the external skin, natural ventilation through the cavity can be achieved whilst not compromising occupant comfort during harsh climatic conditions such as wind, rain and snow. 4. Acoustic Insulation: Due to the addition of an external skin, it is possible to achieve the same degree of acoustic insulation with the windows open as you can with the windows closed in conventional single-skin façade construction. 5. Occupant Comfort/Productivity: As occupants are able to control light penetration with louvers or shading devices and to regulate air movement and temperature with operable windows the overall building comfort levels are increased. In turn due to increased environmental control and comfort levels, work productivity is increased. 6. Additional Security: Double-Skin Façades provide a relatively unobtrusive method of achieving building security due to a continuous glazing layer with small ventilation grilles as opposed to project openings with bars or vents. BSc Architectural Technology 14

25 Chapter 3 The Role of Double-Skin Façades - Energy Consumption 3.1 Energy Performance - Double-Skin Façade Energy consumption in relation to Double-Skin Façades for heating and cooling loads is directly related with the total glazing area as the majority of the heat gains and losses occur through the glass surfaces (Bayram, 2003). Various standard values defining thermal transmission are used in building physics. The coefficient of thermal transmission (U-Value) is the standard that is used to describe the transfer of heat through a construction element in terms of the ambient temperature differential on both sides of the construction element. The unit of measurement of the U-Value is W / m² K (Oesterle, et al., 2001). Although due to the nature of Double-Skin Façade construction the calculation of heat transfer is a complex process as there are a wide range of methods of heat transfer occurring simultaneously. These methods of heat transfer include laminar and turbulent flows, temperature differentiation, density stratifications and varying air-velocities (Tascón & Hernandez., 2008). As a result the use of standard U-Value calculations for determining the thermal performance of Double-Skin Façade construction is not a particularly suitable method as in reality steady state calculations are not truly representative of the complex scenarios which occur within a Double-Skin Façade cavity. See figure 3.1 below for a schematic diagram of heat transfer through a Double-Skin Façade. Figure 3. 1: Schematic diagram heat transfer through a Double-Skin Façade. BSc Architectural Technology 15

26 Chapter 3 The Role of Double-Skin Façades - Energy Consumption However, according to (Bayram, 2003) the factor which has the greatest influence on energy consumption in the context Double-Skin Façade is the stack effect, or thermal buoyancy. 3.2 Thermal Buoyancy (Stack Effect) Thermal Buoyancy is defined as the process which occurs when the density of the air between the exterior and interior layers of a Double-Skin Façade is increased due to the heat generated from the greenhouse effect. As the density of the air increases inside the intermediate space pressure and temperature differences develop along the height of the façade (Tascón & Hernandez., 2008). As a result of these pressure differences will be drawn out from openings located at the top of the building envelope; as a result cooler denser air will enter openings lower down. The process will continue if the air entering the building is continuously heated, typically by casual or solar gains (Baker, 2013). According to (Arons, 2000) there are two main operations which take place in Double-Skin Façades, summer and winter operations. Each system is advantageously utilised to reduce energy consumption during the respective hot and cold seasons. 1. Summer Operations: The air in the cavity removes excess heat by means of the stack effect in order to prevent excessive heat accumulation in the cavity. If an accumulation of heat is formed in the cavity unwanted heat passes into the internal spaces. Therefore, the temperature of the inner skin is kept lower and conduction, convection and radiation from the internal skin to the occupied space is reduced. Accordingly less heat is transferred from the outside to the inside, and less energy is required to cool the space. 2. Winter Operations: In winter the Double-Skin Façade utilises a sealed cavity, with no air circulation. As the cavity heats up it increases the temperature of the internal skin, and as a result reduces the conductive, convective and radiant losses. Accordingly less heat is transferred from the inside to the outside, and less energy is required to heat the space. See figure 3.2 below for a diagramatic explanation of the variations in Double-Skin Façade summer and winter operations. BSc Architectural Technology 16

27 Chapter 3 The Role of Double-Skin Façades - Energy Consumption Figure 3. 2: Double-Skin Façade Winter and Summer Operations (Gonchar, 2013). The configuration of the system used is directly related with the climate in which the building is located. Some studies show that the heating demand of the Double-Skin Façades is higher than single-skin conventional façades. On the other hand, its concept as a thermal buffer utilising the stack effect to remove excessive heat in summer decreases the cooling loads significantly. Furthermore previous studies show that as compared to the conventional single-skin façade systems Double-Skin Façades are credited with a 30% reduction in energy consumption (Bayram, 2003). In the remaining chapters the author intends to provide a critical examination of energy consumption associated with each respective Double-Skin Façade system. Each system will be examined through a number of varying parameters to determine the effectiveness, or inefficiency, of the specific system in question. BSc Architectural Technology 17

28 Chapter 4 Dynamic Thermal Modelling - Methodology 4.0 Dynamic Thermal Modelling - Methodology In this chapter the methodology used to perform a parametric analysis on Double- Skin Façade energy performance is presented, together with a brief overview of the parameters chosen as a basis for the computer aided dynamic thermal modelling simulations. 4.1 Research Context As the primary aim of this research is to present a critical examination of energy performance of Double-Skin Façades in office buildings in a temperate climate, the building selected to be used as a base model for the dynamic thermal modelling calculations was the proposed design of the Redevelopment of The Hawkins House Offices on Hawkins Street, Dublin 2. The area of the building selected for detailed analysis is the proposed Drum located on the south façade, as shown in Figure 4.1 below: Proposed Drum Figure 4. 1: Proposed Redevelopment of Hawkins House South-Façade. Due to the nature of Double-Skin Façade construction, computer modelling has been extensively used to predict energy consumption. For the purpose of the computer aided dynamic thermal modelling, IES Virtual Environment (VE) software is used for the building simulation analysis on the various façade configurations, systems and depths examined on the proposed Drum of Hawkins House. BSc Architectural Technology 18

29 Chapter 4 Dynamic Thermal Modelling - Methodology 4.2 Establishing Base Model Parameters In order to provide an accurate and extensive critical analysis of Double-Skin Façade energy consumption, a wide range of variations and permutations are to be examined. As a result the effectiveness and efficiency of each respective system will be clearly identifiable and comparable under numerous conditions. In addition to the comparison of each Double-Skin façade system, an initial analysis using a conventional single-skin façade will be carried out in order to provide a comparable base energy consumption value. In order to achieve maximum comparability and relevance the conventional single-skin façade will be of the same wall construction as each respective Double-Skin Façade systems internal skin. A brief diagram of the variations of Double-Skin Façade for examination within the software is shown below: Box Façade Corridor Façade Shaft-Box Façade Multi-Storey Façade Naturally Ventilated Cavity Sealed Cavity Regulating Cavity 200mm 600mm 1000mm Hawkins House Redevelopment Drum Office Area As highlighted in figure 4.2 to the right, the proposed office area located on the south façade of the Hawkins House Redevelopment will provide the basis for the computer aided dynamic thermal analysis on the energy performance on Double-Skin Facades. The proposed office area is comprised of a total of five floors, with a total combined floor area of m². Figure 4. 2: Hawkins House Redevelopment which highlights the proposed office area. Due to the complexity of the IES Virtual Environment software one limitation of the research resulted in the computer aided thermal model using a rectangular floor plan BSc Architectural Technology 19

30 Chapter 4 Dynamic Thermal Modelling - Methodology in the proposed office area as opposed to the elliptical drum shape as shown above. In order to achieve a representative as possible model, the rectangular office floor plan is comprised of the key dimensions of the major and minor axis of the elliptical drum shape (14.8m & 11.2m respectively). IES Virtual Environment is divided into a number of applications which each have specific performative or informative functions in a wide range of areas relating to thermal performance, design, solar shading etc. For the purpose of a dynamic thermal modelling analysis of the Hawkins House Redevelopment the Virtual Environment Applications which must be utilised are as follows: Model IT SunCast Apache Thermal Vista Results Macroflo Microflo CFD The first step involved in the utilisation of the IES Virtual Environment software is to create a 3D model of the desired building area, ie. The Drum. This 3D model provides the basic information required for the additional IES applications to run simulations and calculations. Figure 4. 3: IES Applications User Interface. The IES application in which you create and edit buildings and components is Model IT. Even though the thermal analysis is specifically focused on the Drum office area, in order to create an accurate model it is necessary that the entire Hawkins House Redevelopment is digitally modelled. This is to ensure the integrity of the dynamic thermal calculations as the effects the surrounding building has on the office area will be considered and evaluated, i.e. shading from the sun and the effect of the wind. In order to the Hawkins House redevelopment in its entirety, two main modelling functions must be used, Room and Adjacent Building. These functions define which areas of the 3D model will be examined for detailed dynamic thermal BSc Architectural Technology 20

31 Chapter 4 Dynamic Thermal Modelling - Methodology modelling and which will not be included the output of direct results respectively. As shown in figure 4.4 below the user interface enables the selection of the room function upon Modelling of the room. Figure 4. 4: IES Room Function Interface. The office area (in green) and additional Hawkins House redevelopment (pink) is highlighted above. The next step in defining the room parameters is the assignment of room templates. The room templates define a number of user defined pre-set values as shown below: Room Attributes Constructions MacroFlo Opening Types Thermal Conditions Figure 4. 5: IES Room Template Interface. A detailed account of the room templates for both the area and double skin façade cavity used within the dynamic thermal modelling analysis can be a seen in Appendix 2 (Figure ). The IES 3D Hawkins House Redevelopment model can be seen in figure 4.6 below, highlighting the room function defined office area and adjacent building defined redevelopment. BSc Architectural Technology 21

32 Chapter 4 Dynamic Thermal Modelling - Methodology The Drum Office Area Room Function Redevelopment Adjacent Building Function Figure 4. 6: Hawkins House Redevelopment 3D IES Virtual Environment Model Conventional Single-Skin Façade Base Model Analysis In order to achieve a high level of result integrity an initial analysis using a conventional single-skin façade will be carried out on the Office Area. This step is necessary to provide a comparable base energy consumption value and as a result to calcite the efficiency, or inefficiency of each respective Double- Skin Façade system to be examined. In order to achieve maximum comparability the conventional single-skin façade will Figure 4. 7: Hawkins House Redevelopment IES 3D Base Model. be of the same wall construction as each respective Double-Skin Façade systems internal skin. The single-skin base model is shown above in figure 4.7. BSc Architectural Technology 22

33 Chapter 4 Dynamic Thermal Modelling - Methodology Double-Skin Façade Configurations In order to provide an accurate and extensive critical analysis of Double-Skin Façade energy consumption, a wide range of variations and permutations are to be examined. The variations which are to examined can be defined under the following three headings: 1. Double-Skin Façade Type. 2. Double Skin Façade System. 3. Depth of the Double Skin Façade Cavity. As previously described in Chapter 2, the four main methods of classification of Double-Skin Façade are as follows: Box Façade Corridor Façade Shaft-Box Façade Multi-Storey Façade Figure 4. 11: Box Façade Figure 4. 8: Corridor Façade Figure 4. 10: Shaft-Box Façade Figure 4. 9: Multi-Storey Façade Each type of Double-Skin Façade will be assessed by varying the configuration of the cavity within the IES 3D model. Google SketchUp models of the various configurations to be examined are shown above in figures In addition to each Double-Skin Façade configuration, there are a number of cavity system variations to be examined. As previously described in Chapter 3, the three main system variations are as follows: A Naturally Ventilated Cavity. A Sealed Cavity. A Regulating (mixed-mode ventilation) Cavity. BSc Architectural Technology 23

34 Chapter 4 Dynamic Thermal Modelling - Methodology Accordingly each respective system was created within the IES MacroFlo Openings Database Manager. This allows for a detailed composition of ventilation openings and window systems as required. A detailed account of the MacroFlo Opening Profiles for the various Double-Skin Façade cavity systems used within the dynamic thermal modelling analysis can be a seen in Appendix 2 (figure ). In addition to the variations in Double-Skin Façade configuration and system to be assessed, the effect of the depth of the cavity on energy consumption within the office area will also be examined. The dimensions of the cavity to be assessed are as follows: 200mm. 600mm. 1000mm. A broad range of depths (400mm variation in each) is to be examined in order to achieve a large spectrum of results and to determine the effect of varying the cavity depth. 4.3 Analysis / Simulations Upon completion of the 3D model in the Model IT interface, the next step is to run the various additional IES components in order to generate detailed experimental result outputs SunCast The purpose of SunCast is to analyse the way in which solar gains impact the building. These impacts are also quantified in terms of heat gains and energy consumption within the building for later integration with ApacheSim. The use of SunCast as a method of calculating annual solar shading calculations is shown in figure 4.12: Calculation Parameters Interface Solar Shading Calculations Output Figure 4. 12: IES SunCast Solar Shading Calculations. BSc Architectural Technology 24

35 Chapter 4 Dynamic Thermal Modelling - Methodology ApacheSim The purpose of ApacheSim is to model dynamic interactions between the building, the external climate, the internal loads and processes and the building mechanical systems. It integrates information generated from additional IES applications and performs detailed performance simulations. It is within this application that detailed analysis in relation to energy consumption will be calculated on the Drum office area. The user interface for setting the parameters of using the ApacheSim application is shown below in figure Figure 4. 13: ApacheSim Parameters User Interface Vista Results Analysis Vista Results Analysis is located under the thermal group of applications within the IES Virtual Environment suite. Its primary function is to act as a tool which is efficient and easy to analyse the results from one or more simulations carried out using the dynamic thermal modelling tools within IES. In figure 4.14, the user interface for the comparison of dynamic thermal modelling is shown. Vista Results Analysis Calculations Output Results Parameter Interface Figure 4. 14: Vista Results Analysis Interface. BSc Architectural Technology 25

36 Chapter 4 Dynamic Thermal Modelling - Methodology MacroFlo The primary function of the MacroFlo application is for analysing infiltration and natural ventilation in buildings. It utilises a zonal airflow model to calculate air movement in and through the building, driven by wind and buoyancy induced pressures. For the purpose of comparing various Double-Skin Façade cavity airflow systems, MacroFlo enables the input of data such as air flow characteristics, opening profile, etc. which is necessary for an effective comparison of the various cavity airflow systems. As previously mentioned in the type of Double Skin Façade systems to be examined comprise of naturally ventilated, sealed and regulating (mixed-mode) cavities. The user interface of the MacroFlo Openings Database Manager is shown below in Figure 4. 15: MacroFlo Openings Database Manager Interface. In conclusion, through the use of each IES application as mentioned above the aim of performing dynamic thermal calculations is to determine if Double-Skin Façade construction provides a viable solution to reduce overall energy consumption as opposed to a conventional single-skin façade. BSc Architectural Technology 26

37 Base Model 200mm 600mm 1000mm Chapter 5 Dynamic Thermal Modelling Simulations 5.0 Dynamic Thermal Modelling Simulations Annual Energy Consumption (mwh) As described in the previous chapter the aim of performing dynamic thermal modelling calculations is to carry out a comparative analysis of the effect on energy consumption within the Drum office area and to identify the most energy efficient configuration in terms of the set parameters. In this chapter the results obtained through the parametric analysis on Double-Skin Façade energy performance are presented. 5.1 Analysis of Simulation Results The overall energy consumption within the office area is evaluated under the effect on heating and cooling loads in relation to the use of various combinations of Double-Skin Façade configurations, systems and depths. In order to provide an accurate comparison of results, the energy consumption related to heating and cooling loads for a conventional single-skin façade is also evaluated (as previously described in Chapter ) Annual Energy Consumption (mwh) The annual energy consumption of each respective Double- Skin Façade configuration, system and varying cavity depth examined is shown to the right in Figure 5.1. Regulating Cavity Sealed Cavity Naturally Ventilated Cavity Regulating Cavity Sealed Cavity Naturally Ventilated Cavity Regulating Cavity Sealed Cavity Naturally Ventilated Cavity For the purpose of clarity each method of Double-Skin Façade configuration, system and depth examined are presented as a group in order to quickly determine the efficiency of each system and to highlight any potentially inefficient variations in terms of annual energy consumption. Please refer to Appendix 3 (figure 3.1) for an additional detailed analysis and account of the office annual energy consumption for each of the respective simulations performed Base Model 200mm 600mm 1000mm Naturally Naturally Naturally Regulating Regulating Ventilated Sealed Cavity Ventilated Sealed Cavity Ventilated Sealed Cavity Cavity Cavity Cavity Cavity Cavity Regulating Cavity Multi-Storey Façade Shaft-Box Façade Corridor Façade Box Façade Base Model Figure 5. 1: Annual Energy Consumption Dynamic Thermal Modelling Simulations. BSc Architectural Technology 27

38 Chapter 5 Dynamic Thermal Modelling Simulations As previously discussed, detailed dynamic thermal simulations were carried out on each method of Double-Skin Façade configuration, system and depth as mentioned below: Double-Skin Façade Configuration. Double-Skin Façade Cavity Airflow System. Double Skin Façade Cavity Depth. In order to determine the most efficient combination of the Double-Skin Façade variations examined, a detailed analysis of each configuration, system and cavity depth are presented below Annual Heating and Cooling Loads (kwh) A detailed examination of the annual heating and cooling loads (kwh) of the office area of each respective Double-Skin Façade configuration and system are presented below. Each are defined under the various cavity depths used within the dynamic thermal modelling simulations mm Cavity Depth Annual Heating Load (kwh) Annual Cooling Load (kwh) Base Model Annual Heating Load (kwh) Annual Cooling Load (kwh) 200mm Naturally Ventilated Cavity Annual Heating Load (kwh) Annual Cooling Load (kwh) 200mm Sealed Cavity Annual Heating Load (kwh) Annual Cooling Load (kwh) 200mm Regulating Cavity Base Model Box Façade Corridor Façade Shaft-Box Façade Multi-Storey Façade Figure 5. 2: Annual Heating and Cooling Loads - 200mm Cavity Depth. BSc Architectural Technology 28

39 Chapter 5 Dynamic Thermal Modelling Simulations mm Cavity Depth Annual Heating Load (kwh) Annual Cooling Load (kwh) Base Model Annual Heating Load (kwh) Annual Cooling Load (kwh) 600mm Naturally Ventilated Cavity Annual Heating Load (kwh) Annual Cooling Load (kwh) 600mm Sealed Cavity Annual Heating Load (kwh) Annual Cooling Load (kwh) 600mm Regulating Cavity Base Model Box Façade Corridor Façade Shaft-Box Façade Multi-Storey Façade Figure 5. 3: Annual Heating and Cooling Loads - 600mm Cavity Depth mm Cavity Depth Annual Heating Load (kwh) Annual Cooling Load (kwh) Base Model Annual Heating Load (kwh) Annual Cooling Load (kwh) 1000mm Naturally Ventilated Cavity Annual Heating Load (kwh) Annual Cooling Load (kwh) 1000mm Sealed Cavity Annual Heating Load (kwh) Annual Cooling Load (kwh) 1000mm Regulating Cavity Base Model Box Façade Corridor Façade Shaft-Box Façade Multi-Storey Façade Figure 5. 4: Annual Heating and Cooling Loads mm Cavity Depth. BSc Architectural Technology 29

40 Chapter 5 Dynamic Thermal Modelling Simulations Upon initial review of the annual heating and cooling loads (kwh) within the office area of the Hawkins House Redevelopment, it is clear that the conventional singleskin façade base model has a greater demand on annual cooling loads than that of heating loads. However, in each of the various Double-Skin Façade simulations carried out it is clear that the annual heating load demand is substationally greater than that of the cooling load. This would suggest that although the heating demand associated with a Double-Skin Façade is increased compared to a conventional single-skin façade, the concept of a thermal buffer utilising the stack effect to remove excessive heat within the cavity reduces the cooling loads significantly. Due to this fact, overall annual energy consumption in relation to Double-Skin Façade construction may be greater than that of a conventional single-skin façade due to the increased heating loads. However, According to The European Energy (Portal., 2013), as of November 2012 in Ireland, Industry prices per kwh for natural gas (heating demands) and electricity (cooling demands) are and respectively. This is an important economical aspect to consider as the costs associated with the heating and cooling of a building has a ratio of approximately 3:1. As a result, due the increased cooling load demand of a conventional single-skin façade construction, the use of a Double-Skin Façade in reality still provides a more cost effective method of façade construction in terms of consumption of energy. A detailed account of the annual cost, and loads in relation to energy consumption of each scenario can be seen in Appendix 3 (table ) Annual Energy Consumption (kwh/m²) The annual energy consumption within the office area of the Hawkins House redevelopment is presented below under the various Double-Skin Façade configurations evaluated (A Box Façade, Corrdidor Façade and a Multi-Storey Façade configuration). The results are presented as per square metre of floor area (total floor area m²) This is necessary in order to determine and easily compare the overall performance of each Double-Skin Façade configuration in greater detail. BSc Architectural Technology 30

41 Annual Energy Consumption (Kwh/m²) Annual Energy Consumption (Kwh/m²) Chapter 5 Dynamic Thermal Modelling Simulations Box Façade Base Model 200mm 600mm 1000mm Base Model Naturally Ventilated Sealed Cavity Regulating Cavity Figure 5. 5: Box Façade Annual Energy Consumption (kwh/m²). Corridor Façade Base Model 200mm 600mm 1000mm Base Model Naturally Ventilated Sealed Cavity Regulating Cavity Figure 5. 6: Corridor Façade Annual Energy Consumption (kwh/m²). BSc Architectural Technology 31

42 Annual Energy Consumption (Kwh/m²) Annual Energy Consumption (Kwh/m²) Chapter 5 Dynamic Thermal Modelling Simulations Shaft-Box Façade Base Model 200mm 600mm 1000mm Base Model Naturally Ventilated Sealed Cavity Regulating Cavity Figure 5. 7: Shaft-Box Façade Annual Energy Consumption (kwh/m²). Multi-Storey Façade Base Model 200mm 600mm 1000mm Base Model Naturally Ventilated Sealed Cavity Regulating Cavity Figure 5. 8: Multi-Storey Façade Annual Energy Consumption (kwh/m²). BSc Architectural Technology 32

43 Chapter 5 Dynamic Thermal Modelling Simulations Upon review of the annual energy consumption of each Double-Skin Facade configuration examined within the office area of the Hawkins House Redevelopment, it is clear that the configuration which is performing the least efficiently in terms of annual energy consumption is the Shaft-Box Façade configuration. As such, the least efficient variation of the Shaft-Box Façade configuration examined is the 1000mm naturally ventilated cavity. The annual energy consumption has a value of kwh/m², approximately 62% less efficient than the conventional single-skin base model ( kwh/m²). As highlighted in Appendix 3 (table 3.5) the detailed cost analysis highlights that this elevated value is attributed to by high annual heat loading demands (54,757.8 kwh) and as a result, is the only configuration which is more expensive per annum than the base model of the conventional single-skin façade. Due to the nature of the Shaft-Box Façade, ie. dependent on various shafts to induce the stack effect and cause air flow from the box elements in order to remove excessive heat from the cavity (see figure 5.9). The high heating load may be as a result of excessive airflow through the cavity due to a combination of the elevated exposed façade of the office are (wind effects) and due to the large depth (1000mm) of the naturally ventilated cavity. In conclusion, the various dynamic thermal modelling simulations carried out on each respective Double-Skin Façade configuration, cavity airflow system and depth are presented above. Through the results obtained from the simulations, the optimal combination of Double-Skin Façade construction is to be identified in order to provide a quantified conclusion on the most efficient method of construction for use within a temperate climate. Figure 5. 9: Shaft-Box Façade Configuration Airflow Concept. BSc Architectural Technology 33

44 Annual Energy Consumption (kwh/m²) 6.0 Conclusions and Recommendations 6.0 Conclusions and Recommendations Through the results obtained within the dynamic thermal modelling simulations, as discussed in the previous chapter, this chapter aims to provide a recommendation as to which is the most energy efficient combination of Double-Skin Façade configuration, system and depth of cavity to be utilised in an office building in a temperate climate. 6.1 Comparison of Façade Configuration Energy Consumption As highlighted within the various results in the previous chapter, the annual energy consumption (kwh/m²) within the office area of the Hawkins House redevelopment was presented under each of the four Double-Skin Façade configurations evaluated within the dynamic thermal modelling simulations (see figures ). In order to determine which Double-Skin Façade configuration and cavity airflow system is achieving the highest degree of efficiency in relation to energy consumption, each of the best case scenarios from the four figures of results in relation to façade configuration are shown together below in Table 6.1: Façade Efficiency Box Façade Corridor Façade Regulating Cavity 200mm Shaft-Box Façade Multi-Storey Façade Regulating Cavity 1000mm Figure 6. 1: Annual Energy Consumption Facade Efficiency Comparison. BSc Architectural Technology 34

45 Annual Energy Consumption (kwh/m²) 6.0 Conclusions and Recommendations As indicated above, each of the best case scenarios of the Double-Skin Façade configurations and systems evaluated are utilising a regulating cavity, underlining its efficiency as opposed to the utilisation of a naturally ventilated or sealed cavity. However, the 1000mm Multi-Storey Double-Skin Façade with a regulating cavity is the most efficient façade construction combination evaluated. This combination achieved an annual energy consumption value of kwh/m², an increase in efficiency of approximately 16% as opposed to the base model utilising a conventional single-skin façade ( kwh/m²). In order to determine the most efficient combination of the Multi-Storey Double-Skin Façade with a regulating cavity in terms of energy consumption a number of additional dynamic thermal modelling simulations were undertaken at increased cavity depths of 1200mm, 1400mm and finally 1800mm. These calculations were performed to identify and establish the optimal depth of the cavity in terms of energy consumption. A comparison of the energy consumption in relation to the cavity depths is shown below in table 6.2: Multi-Storey Façade - Optimal Cavity Depth mm 600mm 1000mm 1200mm 1400mm 1800mm Multi-Storey Façade Figure 6. 2: Multi-Storey Façade Regulating Cavity Determination of Optimal Cavity Depth. BSc Architectural Technology 35

46 6.0 Conclusions and Recommendations As indicated above in figure 6.2, the optimal cavity depth of the Multi-Storey Double- Skin Façade with a regulating cavity is located at a depth of approximately 1100mm. Initially, the graph indicates a steady increase in energy efficiency of the Double-Skin Façade between the respective depths of 200mm and 600mm. The energy efficiency then gradually begins to stabilise between the respective depths of 600mm and 1200mm, before reducing in efficiency at an approximate depth of 1200mm. A steady decrease in efficiency between the respective depths of 1200mm and 1400mm becomes considerably more substantial beyond a depth of 1400mm to 1800mm. This trend indicates that beyond a certain depth of cavity (1200mm) the efficiency of the Double-Skin Façade begins to decrease, becoming less efficient the greater the depth, thus highlighting the importance of the need for careful consideration when designing the dimensional parameters of a Double-Skin Façade construction. However, even though the optimal cavity depth of the Multi-Storey Double-Skin Façade with a regulating cavity is approximately 1100mm, there is only a relatively small difference in terms of annual energy consumption between a cavity of 1000mm and 1200mm (25 kwh/m²). As such, further exploration in relation to the annual cost () of the office area in relation to energy consumption of each depth is shown below in figure 6.3: Multi-Storey Façade - Optimal Cavity Depth Base Model 1200mm 1000mm mm 1200mm Base Model Base Model Multi-Storey Cavity Annual Energy Consumption Cost () Figure 6. 3: Annual Energy Consumption Cost Optimal Cavity Depth. BSc Architectural Technology 36

47 6.0 Conclusions and Recommendations As highlighted above in figure 6.3, the difference in cost of the annual energy consumption between the 1000mm and 1200mm Multi-Storey regulating cavity is a relatively unimpressive However, a substantial difference in the cost of annual energy consumption of the office area of 1, exists between the 1000mm cavity depth and the conventional single-skin façade base model. This indicates a substantial improvement of 31% in annual energy efficiency between the conventional single-skin façade base model and the Multi-Storey Double-Skin Façade with a 1000mm regulating cavity system. 6.2 Recommendations Optimum Cavity Depth The primary aim of this research was to determine and evaluate the effect in which various configurations, systems and cavity depths of Double-Skin Façade construction plays in relation to overall the energy consumption of an office building within a temperate climate. Additionally, to establish and determine the optimal combination of Double-Skin Façade configuration, cavity airflow system and cavity depth in relation to overall building energy consumption for use within the façade of the office area of the Hawkins House redevelopment. Through the careful analysis of the results of the simulations of the dynamic thermal modelling of the variations and combinations of Double-Skin Façade construction, it is clear that the most efficient method of Double-Skin Façade construction for use within the office area of the Redevelopment of Hawkins Hawkins House is comprised of the following main parameters: A Multi-Storey Double Skin Façade Configuration. A Regulating (mixed mode) cavity ventilation system. A 1000mm cavity depth. In conclusion, this combination of Double-Skin Façade construction provides increased annual percentage efficiency in terms of energy consumption of 31%, and a substantial cost saving of 1, as opposed to the use of a conventional single-skin façade. BSc Architectural Technology 37

48 6.0 Conclusions and Recommendations 6.3 Areas for Further Research Double-Skin Façade construction has excellent potential for a further decrease in overall building energy consumption in a wide range of research areas. Some of the main areas for further thought and research arising from this dissertation are: The potential harnessing of heat generated within the Double-Skin Façade cavity for reintegration within the building. As the temperature within the cavity can reach extremely high temperatures, the ability to collect such heat is a viable option as opposed to releasing the heat generated back into the environment. This can be achieved through various methods in which the overall energy consumption of the building can be decreased further, such as: The use of phase-change materials. The use of mechanical heat recovery systems. Another viable method of potentially reducing overall building energy consumption is the use and integration of photovoltaic panels within the external skin of the Double- Skin Façade. This is an interesting area of further research as the high levels solar of exposure in which double-skin facades receive provides an ideal situation for the collection of solar energy and generation of electricity while also providing often much needed solar shading to the building interior. Another area of further research in which the possibility of building energy consumption can be decreased is through the use of an external skin comprised of horizontal slats of transparent and translucent glass (see figure 6.4). The orientation of this method of external skin configuration is regulated by the use of a building management system and as such construction protects the interior of building from large amounts of solar Figure 6. 4: Horizontal Pivoting Transparent Slats (Teuxido, 2013). radiation and thus regulates the interior temperature reducing overall cooling loads. BSc Architectural Technology 38

49 References References , B. E. (2003). Ventilation for buildings, Symbols, terminology and graphical symbols. Aksamija, A. Context Based Design of Double Skin Facades: Perkins + Will Research Journal. ArchiExpo. (2003). from Arons, D. (2000). Properties and Applications of Double-Skin Building Facades. Massachusetts Institute of Technology. Baker, N. (2013). Natural ventilation - stack ventilation. from Naturalventilation-stackventilation.aspx Bayram, A. (2003). Energy Performance of Double Skin Facades In Intelligent Office Buildings: A Case Study in Germany., The Middle East Technical University. BBRI, B. B. R. I. (2004). Ventilated Double Facades - Classification and Illustration of Facade Concepts: Department of Building Physics, Indoor Climate and Building Services. Caine, T. (2013). Green Buildings: The Cambridge Public Library. Consultants, B. (2013). Building Envelope. from Crespo, A. M. L. (2002). History of the Double-Skin Facade: Harvard School of Design. Dickson, A. (2003). Modelling Double-Skin Facades. University of Strathclyde, Glasgow, Scotland. Gonchar, J. (2013). More Than Skin Deep From Architectural Record Originally published in the July 2010 issue of Architectural Record Architectural Record's Continuing Education Center. from Heimrath, R., Hengsberger, H., Mach, T., Streicher, W., & Waldner, R. (2005). Best Practice for Double-Skin Facades: Institute of Thermal Engineering, Graz University of Technology. King, D. (2010). Engineering a Low Carbon Built Environment. London: The Royal Academy of Engineering. Lee, E., Selkowitz, S., Bazjanac, V., Inkarojrit, V., & Kohler, C. (2002). High- Performance Commercial facades: Ernest Orlando lawerence Berkeley National Laboratory. Oesterle, E., Lieb, R.-D., Lutz, M., & Heusler, W. (2001). Double-Skin Facades - Integrated Planning: Prestel. Palmer, D. (2011). A Decision Making tool, Guidance and Considerations to Optimise Energy Consumption and Occupant Comfort when Replacing Facades on Exisiting Buildings. The University of Bath., Bath. Permasteelisa, G. (2013). Closed Cavity Facades. from Poizaris, H. (2006). Double-Skin Facades - A literature Review: Lund University, Lund Institute of Technology. Portal., E. E. (2013). Renewable energy in final energy consumption. from BSc Architectural Technology 39

50 References Saelens, D. (2002). Energy Performance Assessment of Single Story Multiple-Skin Facades. Solla, I. F. (2013). Façades Confidential: 11/01/ /01/2011. from Streicher, W., Heimrath, R., Hengsberger, H., Mach, T., Waidner, R., Flamant, G., et al. (2007). On the Typology, Costs, Energy Performance, Environmental Quality and Operational Characteristics of Double Skin Facades in European Buildings. [Article]. Advances in Building Energy Research, 1, Tascón, & Hernandez., M. (2008). Experimental And Computational Evaluation Of Thermal Performance And Overheating In Double Skin Facades: University of Nottingham. Teuxido, C. (2013). Double skin façade of Agbar Tower in Barcelona, by Jean Nouvel [226]. Uuttu, S. (2001). Study of Current Structures in Double-Skin Facades. Helsinki University of Technology, Helsinki. Wolfe, R. (2013). The Sociohistoric Mission of Modernist Architecture:. BSc Architectural Technology 40

51 Appendix 1 Appendix 1: The History of Double-Skin Façades Although the concept of Double-Skin Façades is not new, there is a growing tendency within the construction industry for architects and engineers to incorporate them into projects. Information on the history of Double-Skin Façades can be obtained through a wide range of articles, books, reports, etc. However according to (Saelens, 2002) in 1849, Jean-Baptiste Jobard, the director of The Industrial Museum in Brussels, was the first person to describe the idea of a mechanically ventilated multiple-skin façade. He mentioned his theory of how in winter hot air should be circulated between two glazing, while in summer it should be cold air. His theory however is not mentioned for another 65 years. In 1914, Paul Scheerbaert mentions a similar idea in his book Glasarchitectur. It is apparent that as early as the 19 th century consideration was given to the performance of buildings, especially in terms of thermal performance. One can still find an example of this in old farmhouses with box-type windows in Mürren, Switzerland. It is possible to open the box windows but also remove the outer casements completely. They are constructed in such a manner that in summer, the inner-casements can be opened and the outer layer of glazing removed. This allows an adaptation of the building envelope to the climatic conditions (Oesterle, et al., 2001). The first example of a Double-Skin wall construction can be found from the year 1903 in the Steiff Factory in Giengen, Germany. The aim of the project was to maximise day lighting but to also to provide protection from the harsh climate Appendix 1. 2: Famhouse Box-Type Windows in Mürren, Switzerland (Oesterle, et al., 2001). Appendix 1. 1: Steiff Factory Giengen, Germany. Circa 1904 (Solla, 2013). BSc Architectural Technology 1

52 Appendix 1 of the region. In order to achieve these goals a three storey structure was erected. It comprised of a ground floor acting as storage space with two upper floors as work areas. The building was regarded as a complete success and thus two extensions were built in 1904 and They were constructed using the same double-skin façade construction method but timber was used as the main structural material due to budgetary reasons. All buildings are still in use today (Heimrath, Hengsberger, Mach, Streicher, & Waldner, 2005). Also in the year 1903, the Post Office Savings Bank in Vienna, Austria, held a competition for the design of its main building. Otto Wagner won the competition and the bank was built in two construction phases from 1904 to It contained a double-skin aluminium skylight supported by steel columns in the main hall (Poizaris, 2006). By the end of the 1920 s, double-skin façades began to advance with other considerations in mind. There are two main examples which can be used to highlight this (Uuttu, 2001). Appendix 1. 3: Narkomfin Housing Building, Moscow, Russia. Circa 1928 (Wolfe, 2013). In 1928 in Russia, Moisei Ginzburg investigated the possible use of doubleskin sections in the communal service blocks of the Narkomfin housing building, in Moscow. Ginzburg was very interested in the technical aspects of windows and how to achieve greater performance standards (Uuttu, 2001). Also at the same time in Moscow, Le Corbusier was in the process of designing the Centrosoyus. The following year in Paris he would then undertake the design of La Cité de Refuge and the Immeuble Clarte. Each of the initial projects were designed with Le Corbusier concept of mûr neutralisant. His theory predicted that the transmission losses and gains would disappear by the circulation of air at room temperature through the building cavity. However his Appendix 1. 4: Corbusier Sketch Illustrating Ideas (Tascón & Hernandez., 2008). BSc Architectural Technology 2

53 Appendix 1 system was deemed as too expensive and inefficient to build and thus the idea was abandoned (Saelens, 2002). However, there was then little or no progress made in double-skin façade construction up until the late 70 s and early 80 s of the century (Poizaris, 2006). The oil crisis of 1973 and 1979 had a positive effect and resulted in a boost on the development rate of insulating glazing as greater awareness on energy consumption became evident. Many innovative improvements to the technology were made with the introduction of low-emissivity coating and inert gas filled cavities. In the same period an awareness grew on the effects of external shading, thermal mass and the role of ventilation in relation to building performance standards (Dickson, 2003). During the 80 s double-skin façades finally began to gain momentum within the construction industry. Most of the façades constructed during this era were designed with consideration to environmental factors, such as the offices of Leslie and Godwin, or with the aesthetic effect of multiple layers of glass (Poizaris, 2006). During the 90 s there were two main factors which began to have a large influence of the proliferation of double-skin façades. The increase of environmental concerns began to influence architectural design not only from a technical standpoint but also due to political influences that make green buildings a good image for corporate architecture. In addition the rapid development of software and hardware allowed designers to carry out highly complex calculations in order to effectively design façades (Heimrath, et al., 2005). As a result these factors make double-skin façades an ideal option for use in high rise buildings. Typically they are provided with a large budget and the aim of achieving an environmentally friendly image. Another aspect which makes them particularly effective with high-rise buildings is the fact that a double-skin façade allows windows to be opened despite strong wind conditions incurred on certain floors due to their height within the building. Examples of such can be found in RWE AG Headquarters by Ingenhoven, Overdiek Kahlen und Partner, the Commerzbank Headquarters by Foster and Partners, both of which were completed in Germany in The work of Renzo Piano in the Debis Tower in 1998 is a less extreme example of this tendency. The firm carried out a BSc Architectural Technology 3

54 Appendix 1 thorough environmental analysis of the façades in the building. As a result the idea of creating an environmentally friendly skyscraper was progressed by the concept of allowing the skin to adapt to the individual requirements (Crespo, 2002). BSc Architectural Technology 4

55 Appendix 2 Appendix 2: IES Virtual Environment User Interface Appendix 2. 1: Office Room Conditions. Appendix 2. 2: Double-Skin Façade Room Conditions. BSc Architectural Technology 1

56 Appendix 2 Appendix 2. 4: Double-Skin Façade MacroFlo Opening Template Naturally ventilated Cavity. Appendix 2. 3: Double-Skin Façade MacroFlo Opening Template Sealed Cavity. BSc Architectural Technology 2

57 Appendix 2 Appendix 2. 5: Double-Skin Façade MacroFlo Opening Template Regulating Cavity. BSc Architectural Technology 3

58 Appendix 3 Appendix 3: Double-Skin Façade Energy Consumption and Cost Analysis A detailed analysis of the various results obtained within the thermal dynamic simulations is highlighted within the current 70 appendix, in addition to a number of detailed cost analysis calculations. The results obtained include: 60 Natural Gas Consumption (kwh). Electricity Consumption (kwh). 50 Annual Energy Consumption (mwh). Annual Energy Consumption (kwh/m²). 40 Annual Energy Consumption Cost (). Percentage Efficiency (Opposed to Base Model). 30 An overview of the annual energy consumption (mwh) of each 20 respective Double-Skin Façade combinations is available to the right in Appendix 3 Figure Dublin Experimental Parameters Building Area (m²) Natural Gas Price () Electricity Price () Project Baseline (kwh/m²) 110, 210 Appendix Table 3.1: Base Model Experimental Parameters Dublin (Curtain Wall Construction) Cost () Natural Gas Consumption (kwh) Electricity Consumption (kwh) , Annual Energy Consumption (mwh) , Energy Consumption ( kwh/m²) Appendix Table 3.2: Base Model Examination. 0 Base Model Base Model Box Façade Corridor Façade Shaft-Box Façade Naturally Ventilated Cavity Multi-Storey Façade Sealed Cavity 200mm Regulating Cavity Appendix 3. 1: Annual Energy Consumption Overview (mwh). Naturally Ventilated Cavity Sealed Cavity 600mm Regulating Cavity Naturally Ventilated Cavity Sealed Cavity 1000mm Regulating Cavity Multi-Storey Façade Shaft-Box Façade Corridor Façade Box Façade Base Model BSc Architectural Technology 1