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Design of double skin (envelope) as a solar chimney: adapting natural ventilation in double envelope for mild or warm climates

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Design of double skin (envelope) as a solar chimney: adapting natural ventilation in double envelope for mild or warm climates

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Content DESIGN OF DOUBLE SKIN (ENVELOPE) AS A SOLAR CHIMNEY: ADAPTING NATURAL VENTILATION IN DOUBLE ENVELOPE FOR MILD OR WARM CLIMATES by Lutao Wang A Thesis Presented to the FACULTY OF THE SCHOOL OF ARCHITECTURE UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF BUILDING SCIENCE December 2010 Copyright 2010 Lutao Wang ii Acknowledgements Thanks to Prof. Douglas Noble who is my committee chair, for his guidance during the whole research process. Thanks to Prof. Greg Otto who is my committee member, for bringing me into this topic, his sincerely help during every step of my thesis research, and especially for teaching me the research philosophy which will keep having positive impact on my future work. Thanks to Jeffrey Vaglio who is my committee member, for his guidance on double-skin facades studies and generous help with my language on writing. Thanks to Prof. Marc Schiler who is the director of MBS program, for his help and support during last two years Finally, thanks to all my classmates at MBS 2008. iii Table of Contents Acknowledgements ............................................................................................................. ii List of Tables ...................................................................................................................... vi List of Figures .................................................................................................................. viii List of Functions ............................................................................................................... xii Abstract ............................................................................................................................ xiii Chapter 1: Introduction ....................................................................................................... 1 1.1 Environment pollution .......................................................................................... 1 1.2 Climate change .......................................................................................................... 1 1.3 Energy Conservation ................................................................................................. 2 1.4 Natural Ventilation in Building ................................................................................. 3 Chapter 2: Research Background ........................................................................................ 5 2.1 Natural Ventilation ..................................................................................................... 5 2.1.1 Benefits of Natural Ventilation ........................................................................... 6 2.1.1.1 Energy use and environmental effect ........................................................... 6 2.1.1.2 Indoor environmental quality and occupant satisfaction .............................. 6 2.1.2 Drawbacks and design constraints of Natural ventilation .................................. 7 2.1.2.1Air humidity .................................................................................................. 7 2.1.2.2 Uncertainly in performance .......................................................................... 8 2.1.3 Three Basic Natural Ventilation Types .............................................................. 8 2.1.3.1 Single-sided ventilation ................................................................................ 8 2.1.3.2 Crossing ventilation ...................................................................................... 9 2.1.3.3 Stack-effect ventilation ............................................................................... 10 2.2 Double-skin Facades Building ................................................................................ 11 2.2.1 Definition of Double-skin Facades ................................................................... 11 2.2.2 Classification of double-skin facades ............................................................... 12 2.2.2.1 Box Window Type ...................................................................................... 12 2.2.2.2 Shaft-box type Façade ................................................................................ 12 2.2.2.3 Corridor Facade .......................................................................................... 13 2.2.2.4 Multistory Facades .................................................................................... 14 2.2.3 Advantages and Disadvantages of Double-skin Facades ................................. 15 2.2.3.1 Advantage ................................................................................................... 15 iv 2.2.3.2 Disadvantage .............................................................................................. 17 2.3 Solar Chimney ......................................................................................................... 18 2.4 Thermal Comfort Zone ............................................................................................ 19 Chapter 3: Research Scope, Objectives and Methodology ............................................... 23 3.1 Research Scope ........................................................................................................ 23 3.2 Research Objectives ................................................................................................ 26 3.3.1 Case setting ....................................................................................................... 27 3.3.2 Baseline Building ............................................................................................. 30 3.3.3 CFD Simulation .................................................................................................... 32 3.3.3.1 Software Verification .................................................................................. 33 3.3.3.2 Building Model ........................................................................................... 39 3.3.3.3 Generating meshes ..................................................................................... 41 3.3.3.4 Calculating process ..................................................................................... 42 3.3.4 Examining results ............................................................................................. 43 3.4 Energy simulation .................................................................................................... 44 3.4.1 Instruction of IES-VE ....................................................................................... 45 3.4.2 Procedure of Energy Simulation ....................................................................... 45 3.4.2.1 Building Model ........................................................................................... 45 3.4.2.2 Apache Thermal Simulation ....................................................................... 46 3.4.2.2.1 Simulation period and time step .......................................................... 46 3.4.2.2.2 Model Link ........................................................................................... 47 3.4.2.2.3 Apache HV AC Link ............................................................................. 47 3.4.2.2.4 Construction Database ......................................................................... 48 3.4.2.3 Thermal Analysis Output Analysis ............................................................. 48 3.4.2.3.1 ASHRAE/CIBSE Loads ....................................................................... 48 3.4.2.3.2 Building Energy and Carbon Analysis ................................................. 49 Chapter 4: Computational Fluid Dynamic Analysis ......................................................... 50 4.1 Research Objective .................................................................................................. 50 4.2.1 Cavity Depth ..................................................................................................... 51 4.2.1.1 Simulation Result ....................................................................................... 51 4.2.2 Double-skin Height .......................................................................................... 58 4.3 Available range of Weather Condition ..................................................................... 59 4.3.1 Wind Speed ....................................................................................................... 60 4.3.1.1 Indoor Temperature .................................................................................... 60 4.3.1.2 Indoor Air Speed Analysis .......................................................................... 65 4.3.1.3 Equivalent Temperature Reduction Effect ................................................. 70 4.3.1.4 PMV ........................................................................................................... 73 4.3.2 Available Outdoor Temperature ....................................................................... 75 4.3.2.1 Upper range ................................................................................................ 75 v 4.3.2.2 Bottom Range of Available Temperature ................................................... 79 4.4 Problems of Natural Ventilation .............................................................................. 85 4.4.1 Temperature Stratification ................................................................................ 86 4.4.1.1 Reason of temperature stratification ........................................................... 86 4.4.1.2 Solutions to temperature stratification ....................................................... 87 4.4.2 Horizontal Uneven Temperature Distribution .................................................. 88 4.5 Improvement ........................................................................................................... 88 4.5.1 Increase ceiling height ...................................................................................... 89 Chapter 5: Energy Simulation ........................................................................................... 92 5.1 Climate Zone ........................................................................................................... 92 5.2 Building Model ........................................................................................................ 94 5.3 Thermal setting ........................................................................................................ 95 5.3.1 Construction ...................................................................................................... 96 5.3.2 Macroflo Opening Types .................................................................................. 98 5.3.3 HVAC Profile ................................................................................................. 102 5.4 Apache Energy Simulation ................................................................................ 105 5.4.1 Annual energy consumption ........................................................................... 105 5.4.2 Cooling Energy ............................................................................................... 107 5.4.3 Typical day energy consumption analysis ...................................................... 108 Chapter 6: Conclusion and Further Work ........................................................................ 111 6.1 The available climate range for natural ventilation ................................................ 111 6.2 Cavity Depth .......................................................................................................... 112 6.3 Stack Height .......................................................................................................... 113 6.4 Ceiling Height ....................................................................................................... 114 6.5 Energy Consumption ............................................................................................. 114 6.6 Further Work .......................................................................................................... 115 6.6.1 Case study ....................................................................................................... 115 6.6.2 Extended Climate Zone .................................................................................. 116 6.6.3 Other factor related to thermal comfort .......................................................... 116 Bibliography ................................................................................................................... 117 vi List of Tables Table 3-1: Full Table of Wind Factors…………..………...…………………………......28 Table 3-2: Input Variables……………………………….………...…………………….29 Table 3-3: Glass material setting…………………..……………………..………………30 Table 3-4: Construction material setting…………………………………....…………....31 Table 4-1: Basic climate condition setting………………………………..……..….........50 Table 4-2: Temperature difference, pressure difference and air flow in different stack heights……………....……………………………………………………………………59 Table 4-3: Indoor air temperature in different outdoor wind speed…………....………...63 Table 4-4: Indoor air temperature in different outdoor wind speed……………...………69 Table 4-5: Relationship between air velocity and equivalent temperature reduction....…72 Table 4-6: Indoor temperature comparison between T=80℉ and T=85℉.......................78 Table 4-7: Indoor temperature comparison between T=65℉ and T=70℉………….…..80 Table 4-8: Indoor air speed comparison between T=60 ℉, T=65℉ and T=70℉……..…83 Table 4-9: Indoor equivalent temperature reduction when T=60℉, T=65℉ and T=70 ℉…………...……………………………………………………………………...84 Table 4-10: Indoor equivalent air temperature when T=60℉, T=65℉ and T=70 ℉………………………………………………………………………………......84 Table 5-1: Building envelope requirement for Climate Zone5…………...………….......97 Table 5-2: Building opening schedule………………………………………….......……99 Table 5-3: HV AC system schedule……………………………………………......…....102 vii Table 5-4: Energy consumption comparison…………………….………………..……105 Table 5-5: Monthly cooling energy comparison ………………………………...……..107 viii List of Figures Figure 1-1: Annual energy consumption break down………………………...………….3 Figure 2-1: Single-sided ventilation………...……………..………………………..…….9 Figure 2-2: Cross Ventilation………………...…………………………...……………...10 Figure 2-3: Stack-effect Ventilation…………………………………..…………………10 Figure 2-4: Different types of double-skin illustration………………...………………...15 Figure 2-5: Solar Chimney Model…………………...…………………………………..18 Figure 2-6: ASHRAE STD 55 Thermal Comfort Zone……………...…………………..20 Figure 2-7: Proposed Adaptive Comfort Standard for ASHRAE STD 55, Applicable for Naturally Ventilated Buildings…………………………………………………………...22 Figure 3-1: Double-skins & Solar Chimney building illustration………...……………..24 Figure 3-2: Wall and roof section from Designbuilder………………...…………...…... 31 Figure 3-3: Section of Airpak model………………………...…………………………..31 Figure 3-4: Isometric of Airpak model………...………………………………………...32 Figure 3-5: Program structure of Airpak……………………………………………..….33 Figure 3-6: Box Building………………………………………………………………...34 Figure 3-7: Temperature Contour……………………………………………….……….34 Figure 3-8: Velocity Contour……………………………………………………….……35 Figure 3-9: Shaft Building……………………………………………………….………35 Figure 3-10: Temperature Contour…………………………………………….………...36 ix Figure 3-11: Velocity Contour…………………………………………………..……….37 Figure 3-12: Simple Double-skin………………………………………………………...38 Figure 3-13: Temperature Contour…………………………………….………………...38 Figure 3-14: Velocity Contour…………………………………………………………...39 Figure 3-15: Interface of Airpak…………………………………………………………41 Figure 3-16: Advanced solver setup-Screen shot from Airpak 2.0…………………..….43 Figure 3- 17: Interface of ApacheSim………………………………………………..….46 Figure 4-1: Temperature difference curve……………………………………….………53 Figure 4-2: Pressure difference curve……………………………………………………54 Figure 4-3: Air flow volume curve………………………………………………….…...55 Figure 4-4: Speed contour section in different cavity depths………………….………...57 Figure 4-5: Speed contour section in different wind speed……………………….……..60 Figure4-6: Test zone distribution……………………………………………….………..63 Figure 4-7: Indoor air temperature curve……………………………………….….…….64 Figure 4-8: Indoor Air Speed Contour Section…………………………………………..65 Figure 4-9: Air Velocity Vector Section When Wind Velocity is 2.0 m/s (400f/m)…….67 Figure 4-10: Air Velocity Vector Section When Wind Velocity is 1.0m/s (200f/m)……68 Figure 4-11: Air Velocity Vector Section When Wind Velocity is 0.5m/s (100f/m)……69 Figure 4-12: Indoor air speed curve……………………………………………………...70 Figure 4-13: Equivalent air temperature reduction curve………………………………..71 x Figure 4-14: Indoor equivalent air temperature curve…………………………………...72 Figure 4-15: Indoor Air Speed Contour Section…………………………………….…...74 Figure 4-16: T=80℉ Section Temperature Contour……………………………….……76 Figure 4-17: T=85 ℉ Section Temperature Contour………………………………..…..77 Figure 4-18: T=80 ℉ Work Plane Temperature Contour………………………………..77 Figure 4-19: T=85 ℉ Work Plane Temperature Contour………………………………..78 Figure 4-20: Indoor equivalent air temperature curve when T=80℉ and T=85℉……...79 Figure 4-21: Indoor air temperature curve when T=60℉, 65℉ and T=70℉…………...80 Figure 4-22: Indoor air speed curve when T=65 ℉ and T=70℉…………………….…..83 Figure 4-23: Indoor equivalent air temperature curve when T=60℉, T=65 ℉ and T=70 ℉…………………………………………...………………….…………………...85 Figure 4-24: Trace of air movement……………………………………………………..87 Figure 4-25: Indoor air temperature cut plane…………………………………………...88 Figure 4-26: Indoor temperature contour section-increased ceiling height…….……..…90 Figure 4-27: Indoor PMV contour section-increased ceiling height……………………91 Figure 5-1: Weather data of Chicago………………………………………………..…..94 Figure 5-2: Building model in IES-VE…………………………………………………..95 Figure 5-3: Interface of Building Template Manager in IES-VE…………………….….96 Figure 5-4: Opening Annual Profile……………………………………………………100 Figure 5-5: Opening Weekly Profile……………………………………………………100 xi Figure 5-6: Opening Daily Profile……………………………………………………...101 Figure 5-7: Opening types setting………………………………………………………101 Figure 5-8: Apache system HVAC setting……………………………………………..103 Figure 5-9: HVAC cooling daily profile………………………………………………..103 Figure 5-10: HVAC heating condition setting………………………………………….104 Figure 5-11: HVAC heating daily profile………………………………………………104 Figure 5-12: Energy consumption chart………………………………………………..106 Figure 5-13: Monthly cooling energy comparison chart……………………………….108 Figure 5-14: Energy consumption curve on Jul 28 th ……………………….……….......109 xii List of Functions Function 2-1: Optimum Thermal Comfort Temperature in Natural Ventilation………....21 Function 4-1: Estimated Natural Ventilation Flow Rate…………………………………52 xiii Abstract In United States, space heating, space cooling and ventilation of buildings consume 33% of the annual building energy consumption and 15% of the total annual energy consumption, leading to a number of energy and environment problems. Natural ventilation for heating, cooling and ventilation is a good solution and double-skin & solar chimney facades are a good architectural form for natural ventilation. The main work of this research is to study appropriate size of architectural forms (cavity depth and height of stack space) and available weather conditions (outdoor temperature and wind velocity) for natural ventilation at double-skin & solar chimney building, and potential energy saving by applying natural ventilation in double-skins facade building. This research can provide guideline to help designers to determine cavity depth and height of stack space for double-skin & solar chimney building at available climate zone. 1 Chapter 1: Introduction Human-being are becoming more and more dependent on usage of fossil fuel because of the rapid development of industry. Tons of fossil fuel are being used in different areas including: automobile, building, manufactory and so on. Overwhelming usage of fossil fuel leads to three serious problems: environment pollution, climate change and energy shortage. 1.1 Environment pollution 75% of energy is converted from fossil fuel by combustion nowadays. (Data from VIRTUAL CHEMBOOK Elmhurst College Charles E Ophardt, 2003) The process of combustion causes a lot of pollution, so fossil fuels cannot be regarded as renewable or sustainable energy. The negative side-effect on the process of converting fossil fuels to available energy include: air pollution, water pollution, solid waste and land degradation. All of those seriously threaten the health and normal life of human-being. 1.2 Climate change According to “Fossil fuel and its impact on the environment”, eSSORTMENT, (http://www.essortment.com/all/fossilfuelimpa_rhxu.htm), usage of fossil fuel is 2 considered as the largest contributing factor to global warming by releasing greenhouse gases into atmosphere. Carbon dioxide produced by combustion of fossil fuel is considered as the prominent contributor to increasing temperature. In accordance with “The information of Greenhouse Gases List”, Buzzle.Com(http://www.buzzle.com/articles/greenhouse-gases-list.html), Carbon dioxide is the second major greenhouse gases after water vapor, taking around 25% of the greenhouse gases. Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) between the beginning and the end of last century because of global warming. (Data from Energy Business Daily, September 29th, 2009 by EBR_EBdaily). Increasing surface temperatures will cause the melt of glacier, increase sea level, reduction in feasible land. 1.3 Energy Conservation According to “The Building Sector, Architecture 2030”, buildings consume 48% of the annual energy in US and 31% of the building energy is consumed by ventilation, space cooling and space cooling. That means every year HVAC system consumes 15% of total energy in United States, which also contributes a lot to global warming problem. 3 Figure 1-1: Annual energy consumption break down (The Building Sector, Architecture 2030 http://www.architecture2030.org/current_situation/building_sector.html) 1.4 Natural Ventilation in Building It is necessary to introduce renewable and passive energy to building mechanical system. Natural ventilation for cooling and ventilation is a good solution. Also double-skins facade is a good architectural form for natural ventilation. For natural ventilation in double-skin & solar chimney building, the building height, height: height-to-depth ratio, cavity depth and opening size are those most important elements in determining overall performance. It is very hard for the designer to know how to define parameters of a building, because there is no easy way to predict the performance of natural ventilation. This investigation examines how the size of the cavity depth and height of shaft space of affects the performance of natural ventilation. A theoretical building which is a 3-story 4 office building is established as a base case, and then buildings with different parameters are compared in mild seasons weather conditions. The performance of natural ventilation in mild seasons is examined using the Computational Fluid Dynamic (CFD) software AIRPAK. And energy consumption of theoretical building is simulated by Integrated Environmental Solution-Virtual Environment (IES-VE) software. Using the CFD simulation, data will be obtained including the indoor temperature, air velocity, humidity, Predicted Mean Vote (PMV), Percentage of Persons Dissatisfied (PPD) and air flow path of the different cases. The CFD simulation results will help determine appropriate cavity depth and shaft space height in climate zone with long mild seasons. Finally, the energy simulation done by IES-VE can provide data of the amount of energy saving by introducing natural ventilation in double-skin facades in the theoretical office building in Chicago. Chicago was selected because of the wide range of temperature which is from extreme cold to mild temperature, and then to extreme hot weather and double-skin & solar chimney building is the type of configuration which can fit for different seasons according to controllable openings. This research provides guidelines to help designers determine the building height, cavity depth and shaft space height when designing double-skin & solar chimney office buildings. 5 Chapter 2: Research Background 2.1 Natural Ventilation Definition of Natural Ventilation Natural ventilation in building completely depends on natural source as the driving force for ventilation (Hazim B. Awbi, 2008). The natural ventilation is driven by pressure difference between inlet and outlet on the building envelope, generated by natural force: wind pressure difference or thermal pressure difference (Hazim B. Awbi, 2008). Natural Ventilation relies on climate conditions, because it completely depends on natural force. Natural ventilation can provide fresh air for occupants inside and cool down the indoor temperature if climate condition allows. Whether natural ventilation works is determined by the prevailing outdoor conditions: temperature, wind speed, humidity and surrounding topography (Hazim B. Awbi, 2008). Generally, there are three types of natural ventilation configurations for buildings: single-side ventilation, cross-ventilation and stack-effect ventilation (Hazim B. Awbi, 2008). 6 2.1.1 Benefits of Natural Ventilation 2.1.1.1 Energy use and environmental effect Usage of natural ventilation can help buildings conserve the energy consumed by HVAC system (Hazim B. Awbi, 2008). According to the statistic of DOE report, HVAC system consumes almost 15% of annual energy in US every year, so applying natural ventilation strategy in building can save a great amount of energy annually. It will help to release the pressure for energy. The research result conducted by IEA ECBCS-Annex 35 (Heiselberg, 2002) reveals that because of the reduction in energy consumption for fans and cooling, energy can be conserved by natural ventilation in case study buildings. Meanwhile applying natural ventilation can also be beneficial to the environment. By reducing the use of fans and cooling equipment, Carbon Dioxide (CO 2) emission and other pollutant emission produced by HVAC system is greatly reduced (Hazim B. Awbi, 2008). That can help reduce building’s impact on global warming and environment pollution. 2.1.1.2 Indoor environmental quality and occupant satisfaction Natural ventilation brings in fresh outside air to cool down the indoor air temperature to satisfy occupant’s thermal comfort (Hazim B. Awbi, 2008). According to a comparative 7 study by Hummelgaard et al. (2005) in naturally ventilated building and mechanically ventilated building, occupants in naturally ventilated building report higher satisfaction than in mechanically ventilated building even though indoor air temperature and the concentration of CO 2 were higher in naturally ventilated building. And less Sick-Building Syndrome (SBS) symptoms are reported among occupants in naturally ventilated building than in mechanically ventilated building (Hazim B. Awbi, 2008). 2.1.2 Drawbacks and design constraints of Natural ventilation 2.1.2.1 Air humidity Natural ventilation cannot be applied in humid climate zones because there is no dehumidification function in natural ventilation (Hazim B. Awbi, 2008). High humidity will make occupants feel very uncomfortable even though air temperature inside is within a comfortable range (Hazim B. Awbi, 2008). So in region with high level of humidity in summer such as Florida, conventional air conditioning is necessary to work to remove the water vapor from indoor rather than merely depending on natural ventilation to get rid of the indoor heat (Hazim B. Awbi, 2008). 8 2.1.2.2 Uncertainly in performance Natural ventilation completely relies on natural driving force-wind or air temperature difference, so natural ventilation can only work under certain outdoor climate condition (Hazim B. Awbi, 2008). The perquisite for natural ventilation is that the outdoor temperature ranges between the maximum and minimum acceptable indoor comfort temperature (Hazim B. Awbi, 2008). For cross-ventilation, certain levels of wind speed should be achieved to drive the ventilation (Hazim B. Awbi, 2008). For stack-effect ventilation, there should be enough temperature difference between the top and low opening to provide enough stack effect for ventilation (Hazim B. Awbi, 2008). So unless outdoor air temperature and wind speed meet certain requirement, natural ventilation cannot work to achieve the goal. 2.1.3 Three Basic Natural Ventilation Types 2.1.3.1 Single-sided ventilation For single-sided ventilation, opening is only located on one side of the wall. The only opening is both the outlet and inlet for ventilation (Hazim B. Awbi, 2008). The driving force for ventilation is thermal buoyancy in winter and wind turbulence in summer. This is the simplest type of ventilation, which fits for small office space (Hazim B. Awbi, 2008). But compared to other types of ventilation, limited air flow rate can be generated 9 by single-sided ventilation and it cannot be applied in space with large room depth because ventilated air cannot penetrate far enough into the space (Hazim B. Awbi, 2008). Figure 2-1: Single-sided ventilation 2.1.3.2 Crossing ventilation For cross ventilation, there are two or more openings on different sides of the walls (Hazim B. Awbi, 2008). Normally, the main driving force for cross ventilation is wind pressure difference between openings on different walls (Hazim B. Awbi, 2008). Ventilation air comes in from the windward openings, passes through the occupant’s space and then comes out from the leeward openings (Hazim B. Awbi, 2008). The advantage of cross ventilation is that high air flow rate can be achieved when outside wind speed is within the recommended range for natural ventilation (Hazim B. Awbi, 2008). But cross ventilation is very unstable and unpredictable because it relies heavily on outdoor wind condition (Hazim B. Awbi, 2008). So cross ventilation fits for regions where wind speed is comparative sTable in cooling or mild seasons. 10 Figure 2-2: Cross Ventilation 2.1.3.3 Stack-effect ventilation Openings are at both low and high levels in stack-effect ventilation (Hazim B. Awbi, 2008). The main driving force is thermal buoyancy (Hazim B. Awbi, 2008). When there is temperature difference on the vertical direction, warmer air with lower density and more buoyant therefore will rise above the colder air and create upward air stream (Hazim B. Awbi, 2008). So warmer inside air will rise and escape from the upper opening on the wall and the colder outside air will come in from the lower opening (Hazim B. Awbi, 2008). The greater outside-inside temperature difference and longer distance between higher and lower opening is, the better ventilation performance will be achieved. Figure 2-3: Stack-effect Ventilation 11 2.2 Double-skin Facades Building 2.2.1 Definition of Double-skin Facades According to the Belgian Building Research Institute [BBRI], (2002): An active façade is a façade covering one or several stories constructed with multiple glazed skins. The skins can be air tighten or not. In this kind of façade, the air cavity situated between the skins is naturally or mechanically ventilated. The air cavity ventilation strategy may vary with the time. Devices and systems are generally integrated in order to improve the indoor climate with active or passive techniques. Most of the time such systems are managed in semi automatic way via control systems. In addition, according to Uuttu, (2001) describes the Double Skin facade: A pair of glass skins separated by an air corridor (also called cavity or intermediate space) ranging in width from 20 cm to several meters. The glass skins may stretch over an entire structure or a portion of it. The main layer of glass, usually insulating, serves as part of a conventional structural wall or a curtain wall, while the additional layer, usually single glazing, is placed either in front of or behind the main glazing. The layers make the air space between them work to the building’s advantage primarily as insulation against temperature extremes and sound. Harrison and Boake, (2003) in the Tectonics of the Environmental Skin: Described the Double Skin Facade system as essentially a pair of glass “skins” separated by an air corridor. The main layer of glass is usually insulating. The air space between the layers of glass acts as insulation against temperature extremes, winds, and sound. Sun-shading devices are often located between the two skins. All elements can be arranged differently into numbers of permutations and combinations of both solid and diaphanous membranes. 12 2.2.2 Classification of double-skin facades There are four types of double-skin facades: box-window type, shaft-box type facade, corridor facade and multistory facade (Harris Poirazis, 2006). 2.2.2.1 Box Window Type Box window type is the oldest type of double-skin façades. The whole cavity is divided into grid (Eberhard Oesterle, 2001). On the horizontal, the cavity is separated by the constructional axes, or by the boundary of room-for-room basis (Eberhard Oesterle, 2001). On the vertical, it is divided by the story-for-story basis, or just individual room elements (Eberhard Oesterle, 2001). There are both intake and exhaust openings on the external façade, serving to ventilate both cavity space and internal space (Eberhard Oesterle, 2001). Box window type has good sound insulation and is widely used for building located in noisy environment (Eberhard Oesterle, 2001). 2.2.2.2 Shaft-box type Façade Shaft-box Façade is a special form of Box-type façade. It has shaft on the vertical direction to create stack effect to ventilate the cavity (Eberhard Oesterle, 2001). Actually it is a box-type façade which get rid of the separation between floors (Eberhard Oesterle, 2001). On very story, the vertical shafts are linked with adjoining box-window by means 13 of bypass opening (Eberhard Oesterle, 2001). Because warmer air with lower density and more buoyant will raise up above the cold air to the top of the shaft, the opening at the bottom of external will absorb cold fresh air from outside and opening at the top of building will extract the warm (Eberhard Oesterle, 2001). In shaft-box façade, it does need as many opening as box-type façade, since it can create stronger uplift within the shaft (Eberhard Oesterle, 2001). Due to less opening, it can provide better sound insulation at the same time (Eberhard Oesterle, 2001). However, the height of shaft is limited for stack ventilation in shaft-box façade (Harris Poirazis, 2006). Beyond certain height stack effect will be not strong enough to draw natural ventilation (Harris Poirazis, 2006). So normally, shaft-type façade fits for low- rising building if it wants to apply natural ventilation (Harris Poirazis, 2006). 2.2.2.3 Corridor Facade There is no separation on the horizontal direction and separated on story-for-story basis in Corridor Façade (Eberhard Oesterle, 2001). Divisions are foreseen along the horizontal length of the corridor only where this is necessary for acoustic, fire-protection or ventilation reasons (Eberhard Oesterle, 2001). In the context of ventilation, this will usually be necessary at the corners of buildings where great differences in air pressure 14 occur, and where opening s in the inner façade layer would result in uncomfortable drafts from cross-current (Eberhard Oesterle, 2001). This problem can generally be avoided by closing off the corner spaces at the sides (Eberhard Oesterle, 2001). In the rest of the corridor, there are likely to be only relatively small differences of air pressure, and these can be used to support the natural ventilation (Eberhard Oesterle, 2001). 2.2.2.4 Multistory Facades The whole double-skin space can extend in both horizontal and vertical direction in the multistory facades building (Eberhard Oesterle, 2001). The double-skins space is adjoined together by a number of rooms (Eberhard Oesterle, 2001). There are very few divisions in the intermediate space between inner and outer facades, and in some extreme condition, double-skins space can even extend the entire building envelope (Eberhard Oesterle, 2001). And multistory facades building is the type of double-skins being studied in this thesis work. Opening can be located on either upper or lower part of facades, to provide outlet and inlet for natural ventilation. 15 1. Facade 2. Shaft 3. Corridor 4a. Window 4b. Box Figure 2-4: Different types of double-skin illustration (Double Skin Façade-A Literature Review Harris Poirazis) 2.2.3 Advantages and Disadvantages of Double-skin Facades 2.2.3.1 Advantage Acoustic insulation: it is considered as the most important reason for building using double-skin facades (Eberhard Oesterle, 2001). For some office buildings, it has strict standard for indoor noisy level, but they are close to heavy traffic or crowded downtown area. Double-skin space can help reduce the sound transmission from room to room or outside resource to internal office space, greatly keeping privacy and quiet environment for office space (Eberhard Oesterle, 2001). In winter: double-skin space can perform as air buffer to reduce the heat transfer between outside and inside to achieve the goal of saving the energy consumption on HVAC system (Eberhard Oesterle, 2001). In winter, openings on both internal and external 16 facades are closed to form air-tight space. Sun radiation can heat air in cavity space to high temperature (Eberhard Oesterle, 2001). And there is no direct air mass transfer between cavity space and outside. So the reduced air flow speed and increased air temperature at cavity space will lead to dramatic reduction of heat loss caused by heat transfer (Eberhard Oesterle, 2001). So a lot of double skin facades buildings are located at frigid cold regions where it can fully take advantage of the thermal insulation. In summer: heat in cavity space can be extracted by natural or mechanical ventilation if the openings can be properly located on the facades. As Lee et al. (2002) describe: As radiation from absorbed radiation is emitted into the intermediate cavity, a natural stack effect results, which causes the air to rise, taking with it additional heat. Energy Saving: According to Oesterle et al., (2001): Significant energy savings can be achieved only where Double Skin Facades make window ventilation possible or where they considerably extend the period in which natural ventilation can be exploited. By obviating a mechanical air supply, electricity costs for air supply can be reduced. This will greatly exceed the savings mentioned before. Energy saving can be achieved by using natural ventilation or hybrid ventilation and introducing day-lighting into office space. 17 Architectural atheistic: all glass facades can greatly improve the aesthetics of building. The transparency is what a lot of designers pursue for the aesthetic of the building. And double-skin facades can provide highest level of transparency for building (Harris Poirazis, 2006). Emergency escape: in some emergency situation such as fire, double-skin space can be even used as temporary fire escape (Harris Poirazis, 2006). 2.2.3.2 Disadvantage High construction cost and maintenance: double-skin facades cost higher than conventional facades (Harris Poirazis, 2006). In addition, it also adds the budget on construction, cleaning, operating, inspection, servicing, and maintenance because of the additional cost on cavity space (Harris Poirazis, 2006). Without considering the benefits of energy savings through the buildings life cycle, double-skin facade will increase the investment on first cost (Harris Poirazis, 2006). Over-heating problem: if the shaft space cannot be well designed to ensure adequate air circulation, over-heating risk exists in hot weather (Harris Poirazis, 2006). In extreme hot weather, due to strong solar heat flux, the air temperature in the cavity space will be much higher than outside air temperature (Harris Poirazis, 2006). If ventilation is 18 insufficient in the cavity space, hot air will get trapped in certain areas and make certain internal façade nearby areas extremely hot (Harris Poirazis, 2006). 2.3 Solar Chimney According to Heating, Cooling and HVAC Jan 2008-Solar Chimney, the definition of solar chimney is referred to as: A thermal chimney-is a way of improving the natural ventilation of building by using convection of air heated by passive solar energy. A simple description of a solar chimney is that of a vertical shaft utilizing solar energy to enhance the natural stack ventilation through a building. Figure 2-5: Solar Chimney Model (Heating, Cooling and HVAC, Solar Chimney, Viewed 10 February 2010, <http://coolexcooling.com/2008/01/25/solar-chimney/>) 19 Normally, the height of solar chimney will be higher than that of main body of building. During the day time, the black-painted thermal storage wall absorbs the heat from sun radiation, to make the temperature in the chimney much higher than in other normal cavity space. The heat can strengthen the stack-effect and create an updraft of air in chimney. The updraft of air escapes from the upper chimney aperture and creates negative pressure in the shaft. That will help bottom aperture suck in outside cold air to keep convection in the chimney. 2.4 Thermal Comfort Zone The traditional Thermal Comfort Zone is defined by ASHRAE STD 55. The principle of ASHRAE STD 55 is the heat balance model of human being, which is determined by four environmental factors (temperature, thermal radiation, humidity and air speed) , and two personal factors (activity and clothing). According to the ASHRAE STD 55, the upper range of acceptable indoor temperature is 82.5℉. 20 Figure 2-6: ASHRAE STD 55 Thermal Comfort Zone But it is very difficult to meet the standard’s relatively narrow range of interior thermal comfort without the support of mechanical system, even in mild climatic zone (Richard J. de Deara, 2002). So the old version of ASHRAE STD 55 has its limitation when applied to energy saving issue (Richard J. de Deara, 2002). According to Richard J. de Deara,*, Gail S. Brager, Revisions to ASHRAE Standard 55, July 2002: The steeper gradient of observed responses in NV buildings compared to HVAC buildings suggests that occupants of HV AC buildings become more finely adapted to the narrow, constant conditions typically provided by mechanical conditioning, while occupants of NV buildings prefer a wider range of conditions that more closely reflect outdoor climate patterns. 21 Occupants will become very critical about thermal condition if they live at year-around air-spaced environment (Richard J. de Deara, 2002). For occupants live at Natural Ventilated buildings, they can get more used to thermal diversity and seasonal variability (Richard J. de Deara, 2002). And then they will have tolerance to wider range of temperature than in HVAC buildings as existing ASHRAE STD 55 (Richard J. de Deara, 2002). According to the same paper mentioned on last paragraph, comfort zone is shown as Figure. Indoor optimum comfort temperature T comf is related to mean outdoor bulb temperature T a , out , and their relationship is: T comf= 0.31 T a , out + 17.8±5 Function 2-1: Optimum Thermal Comfort Temperature in Natural Ventilation (Richard J. de Dear, , Gail S. Brager, Revisions to ASHRAE Standard 55, July 2002) And the comfort zone widths for NV buildings is with comfort zone band of 5℃ for 90% acceptability and 7 ℃ for 80% acceptability, both centered on optimum comfort temperature T comf . 22 Figure 2-7: Proposed Adaptive Comfort Standard for ASHRAE STD 55, Applicable for Naturally Ventilated Buildings (Richard J. de Deara, Gail S. Brager, Revisions to ASHRAE Standard 55, July 2002) So for example, if outdoor temperature is 80 ℉ (26.7 ℃), the optimum comfort temperature is 78.9℉(26.1℃), 87.9 ℉(31.1℃) for 90% acceptability as upper limit and 91.6 ℉ (33.1 ℃) for 80% acceptability as upper limit; 69.9 ℉ (21.1 ℃ ) for 90% acceptability as lower limit and 66.2℉(19.1℃) for 80% acceptability as lower limit. And it the flowing research analysis, 90% acceptability will be chosen as the standard to judge the availability of Natural Ventilation in buildings. 23 Chapter 3: Research Scope, Objectives and Methodology 3.1 Research Scope According to the description of the double-skin façade characteristics and solar chimney in Chapter 2, we can summarize the thermal performance of double-skin facades building at climate zone with long frigid cold winter and mild season. Winter: Intermediate cavity (space) is closed to form air buffer, air in cavity is heated by solar radiation. Heating load can be reduced by double-skin. Mild seasons: Openings are closed on double-skin facades, and HVAC system works for ventilation. Summer: Openings on external façade are open but controllable openings on internal façade are closed. Stack effect ventilation is working to reduce the risk of overheating. Although mechanical cooling is needed for cooling, double-skin space can still help reduce cooling load. So for the aspect of thermal performance, traditional double-skin facades buildings only take advantage of double-skin in winter. During mild seasons and summer, double-skin 24 facades buildings do not have obvious advantage on thermal performance over other conventional buildings. However, the weather condition of mild seasons is proper for natural ventilation. According to the shaft space characteristics in double-skin facades, double-skin facades buildings have great potential to introduce natural ventilation in mild seasons when outdoor temperature is around occupant’s thermal comfort temperature. In addition, natural ventilation can be further strengthened because of the special configuration which is solar chimney added to double-skins. Figure 3-1: Double-skins & Solar Chimney building illustration 25 The approach of this research is to combine concepts of double-skin and solar chimney together to extend the available days for natural ventilation. The thermal performance of Double-skin + Solar Chimney building will be: Winter: openings on double-skin are closed to create a thermal buffer. The performance is the same as a normal double-skin in winter. Mild season: operable windows are open on the internal façade, top and bottom of the shaft space. Stack-effect ventilation is strengthened by solar chimney. Fresh air will come into indoor space through openings on the facade opposite to double-skin side and escape from internal operable windows on double-skin side as stagnant air, relying on the negative pressure caused by stack effect. If wind speed and direction are favorable, cross ventilation can be achieved to improve the natural ventilation for indoor space. In conditions without favorable wind, thermal buoyancy is the only driving force for ventilation. Merely natural ventilation works at most of mild season. The ventilation air flow path is shown as Figure 3-1. Summer: in extremely hot weather, only natural ventilation cannot provide enough cooling. In this situation, operable windows on the internal facades are closed to prevent 26 hot air in cavity space coming into the indoor occupancy’s space. Openings on the top and bottom of the shaft-space are open to allow stack-effect ventilation to get rid of the heat in cavity space. Mechanical and natural ventilation are working together to provide cooling and ventilation. 3.2 Research Objectives Applying natural ventilation can help save energy consumption and reduce emission of carbon dioxide, in order to release the environmental pressure on earth. The research objective is to study if double-skin & solar chimney is a good architectural configuration for natural ventilation and energy conservation solution. And how these architectural features of double-skin building (cavity depth, building height, room height: room depth ratio, operable opening size) affect the performance of natural ventilation. To realize the objective, Computational Fluid Dynamic (CFD) software, Airpak 2.0, was selected as the tool to simulate the process of natural ventilation. Inputs of building features in simulation include: orientation, building height, depth: height ratio, cavity depth and operable window size; climate inputs include: temperature, wind speed and wind direction. Outputs from CFD tools include: indoor air temperature, pressure, air flow velocity, PMV and PPD (those parameters judge natural ventilation performance in 27 double-skin & solar chimney building). Depending on these inputs and outputs data, a database regarding to natural ventilation in double-skin & solar chimney building can be built up. The database can be a guideline for designers who want to introduce natural ventilation into buildings. 3.3 Research Methods and Procure There are five main steps in my research: 1. Case setting 2. Build up baseline building 3. CFD simulation 4. Energy simulation 5. Result analysis 3.3.1 Case setting There are a lot of parameters possible to affect the result of natural ventilation. They include: outdoor temperature, wind velocity, wind speed and direction, solar radiation, pressure, building height, cavity depth, height: depth ratio, operable window size, building orientation, type of shading, material of double-skin facades and so on. There 28 can be more than thirty possible variables and each of them has several possible conditions. For example: to fully cover all the possibilities of wind condition, both orientation and speed of wind should be considered. And wind condition should be tested as below Table showing: South North East West 0.5m/s 1.0m/s 1.5m/s 2/0m/s Table 3-1: Full Table of Wind Factors But the concern is that if wind speed input is like that, the orientation of openings on the building should be also further divided to south, north, east and west. In that situation, there will be too many combinations of input merely under the subject of wind speed, and that will make the conclusion very difficult to be drawn. 29 So there will be endless possible combinations if too many possibilities has been taken consideration. Obviously, it is impossible to simulate all the possible conditions. It is necessary to only choose those essential parameters as input variables. The items marked as red are variables which will be tested in the further research. Input Variables Input A B C D E Temperature 60℉ 65℉ 80℉ 85℉ 90℉ Wind Velocity 0 m/s 0.5m/s (100f/m) 1.0m/s (200f/m) 2.0m/s (400f/m) Height 2 floors 3 floors 4 floors 6 floors 8floors Height : Depth of building 1:1 1:2 1:3 1:4 1:5 Cavity 1’ 2’ 3’ 4’ 5’ Operable Window Size 15% 20% 25% 30% Stack Height 111.1% building height 133.3% building height 155.5% building height 177.7% building height Table 3-2: Input Variables Output : Temperature, Air velocity , Pressure , PMV , PPD To better analyze each parameter, only one parameter is changed each time in each set of test, meanwhile keeping other parameters constant. 30 3.3.2 Baseline Building A baseline building is built up as the fundamental of test. Values of parameters given to baseline building are set as default value for each variable. Each default value will keep constant when testing other parameters. Default Values: Height: 2 Storey; Wind Velocity 6 ft/s; Height: Depth=1:3; Window Area: 15%; Solar Radiation on double-skin: 700W/m2; Heat Source: Lamp, PC and Occupant; Solar Radiation on other walls: N/A; Temperature: 80° F. Materials: Insulated Glass Window gas type and thickness Innermost pane SHG-C Exterior glass(Laminated) Low-E 0.710 Interior glass Air Space 20mm Low-E 0.636 Direct solar transmission Light transmission U-value W/m2-K Exterior glass(Laminated) 0.680 0.811 4.233 Interior glass 0.509 0.761 2.060 Table 3-3: Glass material setting 31 Construction Material Structure U-value W/m2-K Wall 102mm Brick+50.00 Air layer+100.00PUR+100.00 Concrete+13.00 Plaster 0.225 Roof 19.00mm Asphalt+13.00 Fibreboard+114.00mm XPS Extruded Polystyrene+100.00 Cast Concrete 0.250 Floor 100.00 mm Cast Concrete 4.730 Table 3-4: Construction material setting Wall Section Roof Section Figure 3-2: Wall and roof section from Designbuilder Building model in Airpak Figure 3-3: Section of Airpak model 32 Figure 3-4: Isometric of Airpak model 3.3.3 CFD Simulation The simulation of natural ventilation in double-skin & solar chimney is conducted by CFD tools. Airpak 2.0 is a powerful and easily to be used CAE software based on FLUENT computational fluid dynamic (CFD) solver engine for thermal and fluid-flow calculation. The software is developed for ventilation system to deal with problems related to airflow, heat transfer contaminant transport, thermal comfort, indoor air quality and building external air flow. Airpak provides a friendly interface that is easily learned by users without professional fluid dynamic knowledge to build up models and meshes for CFD calculation. The Fluent solver can provide robust and quick calculation. 33 Figure 3-5: Program structure of Airpak 3.3.3.1 Software Verification Before cases simulation, capability of Airpak in simulating natural ventilation and stack effect need to be tested. To verify the software, I did three simple sets of tests: cross- ventilation in simple box, stack-effect ventilation in simple shaft and cross & stack-effect ventilation in simple box & shaft. The simulation results show that main characteristics of test cases match the basic principle of natural ventilation and prove that Airpak is capable to simulate the performance of natural ventilation in double-skin & solar chimney building. Build Model Create Mesh Calculate Solution Examine Result Fluent Airpak 34 Case 1 Simple Box Figure 3-6: Box Building Figure 3-7: Temperature Contour 35 Figure 3-8: Velocity Contour Case 2 Simple Shaft Figure 3-9: Shaft Building 36 Figure 3-10: Temperature Contour 37 Figure 3-11: Velocity Contour 38 Case 3 Simple Double-skin Building Figure 3-12: Simple Double-skin Figure 3-13: Temperature Contour 39 Figure 3-14: Velocity Contour 3.3.3.2 Building Model In order to simulate building with complex shape and indoor details, Airpak provides different types of models for designers. The basic model can be divided into four main types: object-based model building with predefined objects, macros, 2D object shapes and 3D object shapes. 40 Object-based model building with predefined objects contain: rooms, blocks, fan (with hubs), person, openings, vents, partitions, walls, sources, resistances, hoods and wires. Macros: atmospheric boundary layer, closed box, diffusers, ducts and solar flux. 2D object shapes: rectangular, circular, inclined and polygon. Complex 3d object shapes: prisms, cylinders, ellipsoids, elliptical and concentric cylinders and prism of polygonal and varying cross-section. The interface of Airpak2.0 is shown below. The main menu bar on the top provides five basic functions of Airpak: File, Model, Solution, Post and Report. When any of the functions is selected, different function-specific selectors will be shown under the main menu bar for further selections. The option menu is located on the top right of the main window where users can get online help and general control for visual displaying. 41 1.File 2. Model 3.Solution 4.Post 5.Report Figure 3-15: Interface of Airpak 3.3.3.3 Generating meshes Airpak needs to generate a computational mesh which is the basis for the calculation procedure. Generating a proper mesh is highly dependent on the accuracy and time consumption of the CFD calculation (Lei Xu, 2003). If the mesh is too coarse, the calculation result will be inaccurate. If the mesh is too fine, the calculation process will be extremely time costly. If mesh is fine in some areas but coarse in somewhere else, calculation will be very hard to converge (Lei Xu, 2003). There are two types of mesh in Airpak: hexahedral and tetrahedral. The hexahedral mesher is the default mesher in 42 Airpak and used for normal shapes in most cases (Lei Xu, 2003). The tetrahedral mesher has better performance in dealing with complicated mesh shapes (Lei Xu, 2003). 3.3.3.4 Calculating process The calculation process of Airpak based on FLUENT CFD’s finite-volume solver can solve steady-state or transient problems of fluid flow. There are four different equations offered for the calculation in different conditions, including: Indoor zero equation, zero equation, two equation and RNG k-e equation. Depending on the certain equation, the calculation can solve the problems on the aspect of pressure, momentum, temperature viscosity, body forces, turbulent kinetic energy and turbulent dissipation rate according to setting different under-relaxation factors (Lei Xu, 2003). In my study of natural ventilation problem, I used Indoor zero equation. Because according to Airpak 2.1 Tutorial Guide, 18.2.1 Indoor Zero-Equation Turbulence Model: The indoor zero-equation turbulence model was developed specially for indoor airflow simulations. It addresses the need of HVAC engineers for a simple but reliable turbulence model that can be used with modest desktop computing resources. 43 Figure 3-16: Advanced solver setup-screen shot from Airpak 2.0 3.3.4 Examining results The results of the Airpak simulation provides plenty of information for designers to do analysis of air flow. The display attributes of the result include: contours, vectors, particles and mesh. The parameters of simulation results include: speed, temperature, pressure, viscosity ratio, vorticity, mean age of air, PMV, PPD and angular deviation (Lei Xu, 2003). Four different attributes of display provide different visions for designers the do the analysis of the results. 44 Contour: it provides clear graphic for distribution of certain parameters in certain level and plane slices. Vector: it helps the designer understand the result over a point grid. The vector arrow shows the direction of each parameter and the length of the arrow represents the magnitude of the parameter value. Particle: from the particle, the designer can know the position of the fluid at certain moments in time that the designer wants to trace, such as CO 2 , outside air, pollutant particles and so on. 3.4 Energy simulation In order to the estimate the approximate energy conservation by using natural ventilation in double-skin & solar chimney building, energy simulation tools need to be used. There are several energy simulation tools available, including: EnergyPro, eQuest, Design Builder and Integrated Environmental Solution-Virtual Environment (IES-VE). IES-VE was selected as the simulation tool for this research. 45 3.4.1 Instruction of IES-VE The <Virtual Environment> is an integrated suite of applications linked by a Common User Interface (CUI) and a single Integrated Data Model (IDM). This means that all the applications have a consistent “look and feel” and that data input for one application can be used by the others. Modules such as “ApacheSim” for thermal simulation, “Radiance” for lighting simulation, and “SunCast” for solar shading analysis. “ModelIT” is the application used for input of 3D geometry used to describe the model. (From <VE> User Guide <Virtual Environment> 5.9) 3.4.2 Procedure of Energy Simulation 3.4.2.1 Building Model There are two ways to have building model in IES-VE. One is to directly create the 3D model by the components within the <Virtual Environment> ModelIT, the other way is to import the existing model from other software, such as Revit. The model in this research is a theoretical box building without many complex components. So the building model is created directly in ModelIT in this thesis research. 46 3.4.2.2 Apache Thermal Simulation Thermal simulation will be done by Thermal-ApcheSim. According to <VE> User Guide <Virtual Environment> 5.9: ApacheSim is a dynamic thermal simulation program based on first-principles mathematical modeling of heat transfer processes occurring within and around building. Figure 3- 17: Interface of ApacheSim 3.4.2.2.1 Simulation period and time step IES-VE can choose any period during a year as simulated period by selecting a starting and ending date of that period. Normally 10 minutes will be set as the simulation time step for most of the regular building. For simulations which need to capture the detail of 47 the operation or energy conservation, a shorter time step may be set to meet the more frequent requirement. 3.4.2.2.2 Model Link MacroFlo Link: this option can adjust the exposure type, crack flow coefficient, crack length, openable area, opening threshold temperature and opening degree to specify the details of natural ventilation. 3.4.2.2.3 Apache HVAC Link ApacheHVAC defines the performance of heating, ventilation and air conditioning systems. It is highly related to ApacheSim, and optionally to MacroFlo. It allows users to define varieties of items in HVAC, including: control operation and its impact on comfort performance, energy use, fresh air loads, free cooling, heat recovery, component sizing, sizing of mechanical air flows, system psychrometrics, distribution efficiency, boiler and chiller performance, fan and pump energy and mixed-mode operation. In this thesis research, the research subject is natural ventilation but not the details of HVAC. Not all the optional items will be defined in ApacheHVAC. The more important issue here is the relationship between the operation of HVAC and climate conditions such 48 as ambient temperature and wind speed that are essential in studying energy usage by using natural ventilation. 3.4.2.2.4 Construction Database Construction Database can view and edit the thermal properties of building construction such as wall, roof, window and door. Those parameters are used in thermal applications: ApacheCalc, ApacheLoads and ApacheSim. 3.4.2.3 Thermal Analysis Output Analysis IES-VE can provide plenty of output data for the user to analyze building performance. Those outputs include: heating and cooling load, energy usage, carbon emission, fuel break down, daylighting report and standard compliance. Data can be shown as an annual value, monthly value, daily value or even hourly value. 3.4.2.3.1 ASHRAE/CIBSE Loads ASHRAE Loads can calculate heating and cooling load according to ASHRAE Heat Balance Method. (From IES-VE Manual 5.9) 49 CIBSE Loads conduct the heat loss and heat gain calculation in accordance with procedure laid down in CIBSE Guide A. (From IES-VE Manual 5.9) 3.4.2.3.2 Building Energy and Carbon Analysis The simulation results from Apache System present Building System Energy and Carbon Dioxide summaries, Peak Hourly Room Loads and Room Environmental Conditions. Beside presenting data of energy consumption and Carbon Dioxide emission in different, IES-VE can also automatically compare data with certain standard, such as 2030 Challenge and LEED credit. Below is the brief introduction of function related to 2030 Challenge and LEED credit: Architecture 2030 Challenge Compliance IES-VE can calculate the estimated annual building energy consumption and then compare it with the target of each five years in 2030 challenge. LEED Day-lighting Credit 8.1 Report. Day-lighting illuminance level in each room of the model can be calculated by FlucsDL analysis in IES-VE. 50 Chapter 4: Computational Fluid Dynamic Analysis 4.1 Research Objective In order to study if it is appropriate to apply natural ventilation to a Double-skin & Solar Chimney office building, two fundamental issues need to be known from Airpak Computational Fluid Dynamic (CFD) simulation. 1. How architectural features (cavity depth, building height, operable window size and room height to depth ratio) affect natural ventilation. 2. What climate condition (temperature and wind speed) is available for natural ventilation in Double-skin & solar chimney building? Below Table 4-1 is the basic climate condition setting for the Airpak CFD simulation, all the other cases are based on the basic one. Outdoor Bulb Temperature Wind Speed Solar Flux South North Case 1 80℉ (26.71F 2.0 m/s 700 W/m 2 400 W/m 2 Case 2 1.0 m/s Case3 0.5 m/s Case 4 0 m/s Table 4-1: Basic climate condition setting 51 4.2 Architectural feature In the first step of Computational Fluid Dynamic (CFD) simulation, the two most important architectural features of double-skin will be discussed. They are cavity depth and solar chimney height. These important elements will dramatically affect the ventilation rate. 4.2.1 Cavity Depth Cavity depth is the most important double-skin facades characteristic for ventilation. That is because the depth of cavity can greatly affect the efficiency of natural ventilation by deciding the turbulence and air movement in the double skin space. The research will focus on analyzing temperature, pressure and air flow rate in the double-skin space with different cavity depths. Those are the most important parameters that can represent capability of ventilation. 4.2.1.1 Simulation Result First research objective is the temperature difference (T) between average temperature of the inlet and outlet of double skin space (T I ) and outdoor temperature (T O ). According to the equation of natural ventilation, the larger T I is, the more stack vent airflow rate can be 52 generated. On the other hand according to the principle of stack effect ventilation, the fundamental driven force for stack effect is the temperature difference between indoor and outdoor. So when the outdoor temperature is constant, the larger the temperature difference is the stronger driven force can be generated. Here, ventilation efficiency is proportional to T or T I . Function 4-1: Estimated Natural Ventilation Flow Rate (Andy Walker, The Fundamentals of Natural Ventilation, Buildings, October1 2008) where: Q S = Stack vent airflow rate, ft³/s A = cross-sectional area of opening, ft² (assumes equal area for inlet and outlet) C d = Discharge coefficient for opening g = gravitational acceleration, around 32.2 ft/s² on Earth H d = Height from midpoint of lower opening to neutral pressure level (NPL), ft NPL = location/s in the building envelope with no pressure difference between inside and outside (ASHRAE 2001, p.26.11) T I = Average indoor temperature between the inlet and outlet, °F T O = Outdoor temperature, °F Temperature Difference: When cavity depth is 3’, the temperature difference (T) achieves the max value which is 63°F. The highest T happens when cavity depth is 3’, and it decreases when cavity depth either gets higher or lower than 3’. The decreasing gradient is sharper when cavity is 53 lower than 3’. The smallest temperature difference (T) appears when cavity depth is 1’, which is only 27°F. Figure 4-1: Temperature difference curve Pressure Difference: The second research objective is pressure difference (P) which is the direct driven force for ventilation and should be proportional to temperature difference theoretically. Theoretically, larger pressure difference provides stronger driven force for stack-effect ventilation. 0 10 20 30 40 50 60 70 1' 2' 3' 4' 5' Temp Difference between top and bottom( ℉) Temp Difference between top and bottom( ℉) 54 When cavity depth is 4’, pressure difference between top and bottom opening arrives at the highest value which is 12.3 N/m 2 . Pressure difference value decreases when cavity depth either increases or decreases. The minimum pressure difference also appears when cavity depth is 1’. The minimum pressure difference is 7.4 N/m 2 . Figure 4-2: Pressure difference curve Air Flow Rate The third research objective is air flow rate. Air flow rate can directly represent the efficiency of natural ventilation. The distribution curve of air flow rate from top opening is very similar to that of temperature difference between top and bottom openings. Peak 0 2 4 6 8 10 12 14 1' 2' 3' 4' 5' Pressure Difference between top and bottom(N/m2) Pressure Difference between top and bottomN/m2 55 value occurs when cavity depth is 3’ and minimum occurs when cavity depth is 1’, they are 0.85m 3 /s and 0.03m 3 /s. Figure 4-3: Air flow volume curve If cavity depth goes down to 1’, the narrow cavity will generate a strong turbulence effect which will disturb the normal convection in the double-skin space so that effective natural ventilation cannot be formed in the double-skin space. In addition, it is not realistic to have a cavity depth lower than 1’ because of the maintenance and cleaning issue. It is necessary to keep operable part in the cavity space for maintenance and cleaning, so the depth of cavity should be at least large enough to allow building cleaning staff to assess. For the upper limit of cavity depth, if the cavity space is too wide to 5’, 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1' 2' 3' 4' 5' Air Flow Volume from Upper Opening (m3/s) Air Flow Volume from Upper Opening m3/s 56 not enough convection can be generated to support the air movement. The conclusion that natural ventilation efficiency will get worse when cavity depth exceeds 5’ can be deduced from the fact that natural ventilation performance is worse when cavity depth is 5’ than that when cavity depth is 3’ and 4’. This is because the relationship between cavity depth and natural ventilation efficiency generally follows the Quadratic equation curve (from Jin, Z. 2001, Building Environmental Science) and performance achieves best when cavity depth is around 3’ to 4’. According to the test results of three parameters (Table 4-1 to Table 4-2) and the analysis above, between the range of 1’ and 5’, best ventilation can be achieved when cavity depth is around 3’ to 4’. And when cavity depth is too wide or too narrow, natural ventilation will not have good performance. 57 Cavity=1’ Cavity=3’ Cavity=5’ Figure 4-4: Speed contour section in different cavity depths From the speed contour, in the cavity space, when cavity depth is 1’, air is with relatively high speed at the lower part of the cavity space but with low speed at the upper part of the cavity. That means intense air movement mainly happens at the lower part of double-skin space and air cannot exhaust efficiently from top opening. When the cavity depth is 5’, an unobvious upstream air is formed according to Figure 4-4. When cavity depth is 3’, 58 obvious upstream which is represented by green is formed. That means main upstream speeds at around 1.5 m/s, which is a good speed for natural ventilation So speed contour section further proves that best natural ventilation performance can be achieved when cavity depth is around 3’. 4.2.2 Double-skin Height The height of double-skin space is the other important characteristic which has great potential impact on natural ventilation. To study the height of the double-skin space, each case is set with different stack height over the top of room. The difference between the height of double-skin space and top of main building are 3’, 9’, 15’ and 21’ separately. Temperature difference, pressure difference and air flow rate are also three parameters used to analyze the performance of stack-effect ventilation. From the data of Table 4-3, there is no obvious improvement when stack height increases. Best performance can be achieved when stack height is 21’ higher than the original roof of building. When stack height is 21’ higher than roof, temperature difference is 68 degree F, pressure difference is 12.5 N/m 2 and air flow rate is 0.98m 3 /s, all of these parameters are the best among all the tested conditions. But if considering the cost of 59 increasing the height of stack, it is not valuable to chase minor improvement on ventilation in the expense of high construction cost. Difference between stack height and main building height 3’ (11.1% H building ) 9’ (33.3% H building ) 15’ (55.5% H building ) 21’ (77.7% H building ) Temp Difference between stack space and outdoor ( °F) 54 63 65 68 Pressure Difference between top and bottom N/m2 9.6 11.7 11.3 12.5 Air Flow from Upper Opening m3/s 0.67 0.85 0.87 0.98 Table 4-2: Temperature difference, pressure difference and air flow in different stack heights 4.3 Available range of Weather Condition It is important to know the range of weather conditions available for natural ventilation. Defining the range of weather conditions can help the designer make a preliminary prediction if the double-skin system is available for natural ventilation in a certain climate zone according to the climate data. Comparing available temperature range with local climate data can help the designer roughly count the number of available days for natural ventilation in a year. 60 4.3.1 Wind Speed In this section, the available range of wind speed will be discussed. In order to study the acceptable range for wind speed, building parameters follow baseline building and outdoor temperature is set at 80 ℉. 4.3.1.1 Indoor Temperature Below Figure 4-5 shows temperature contour sections when wind speed is 0.5 m/s (100f/m), 1.0 m/s (200f/m) and 2.0 m/s (400f/m) from. V=0.5m/s(100f/m) V=1.0m/s(200f/m) V=2.0m/s(400f/m) Figure 4-5: Speed contour section in different wind speed 61 Outdoor wind speed V=2.0m/s (400f/m) Temperature contour sections show the general indoor temperature condition when applying natural ventilation. When wind velocity equals to 2.0m/s(400f/m), indoor temperature keeps in good condition because most of the indoor area is marked with blue and green color. The temperature is between 81 ℉and 87℉ at indoor space. In general, the average temperature is 85 ℉, temperature stratification is generated close to the north wall because of direct solar radiation on the wall. At the occupant’s most thermal sensitive area where is 1.3m (43in) above the floor, air temperature is all below 85℉. Although it is almost reaches the upper limit of thermal comfort zone (see the definition of thermal comfort zone on 2.4 Thermal Comfort Zone), indoor air speed has the same effect as temperature reduction. That will be discussed in next section. Outdoor wind speed V=1.0m/s(200f/m) When outdoor wind velocity is 1.0m/s (200f/m) from north direction, the condition of indoor air temperature is not as good as when wind velocity is 2.0m/s(400f/m), but is still acceptable for indoor thermal comfort. The average temperature is 86 ℉. Temperature stratification is more serious compared to that when wind velocity is 1.0m/s (200f/m). Overheat problem exists at the space close to north wall, especially at the upper part of 62 north side. Temperature is above 95℉ (35℃) there and thermal uncomfortable will be caused at these areas. The overheat problem is caused by the direct solar flux on the north wall. It can be eliminated by adding shading or thermal mass on the north envelope. But even though overheating exists, it only happens at the upper area of each floor where is above occupant’s sensitive zone. At occupant’s thermal sensitive zone where is floor level to 6’ height, air temperature still maintains at thermal comfort acceptable temperature. So overheating will not affect occupant’s thermal comfort too much. Outdoor wind speed V=0.5m/s (100f/m) When outdoor wind speed falls to only 0.5 m/s (100f/m), green occupies more area compared to that when wind velocity is 1.0m/s(200f/m). Occupant’s most sensitive thermal comfort zone where height is 43 in above floor is almost marked by green and blue. So the temperature exceeds acceptable thermal comfort temperature when wind velocity is 0.5 m/s (100f/m). Natural ventilation cannot work alone to satisfy thermal comfort under this condition. 63 The data of temperature is recorded on Table 4-4. A test point is set at the height of 1.1m (43in) where it is most sensitive to occupant’s thermal comfort. Horizontal test zone is divided into North Zone, Inner Zone and South Zone, and the average temperature of North Zone, Inner Zone and South Zone is represented by A, B and C separately. The Number represents the floor level. For example, 1A represents for north zone on the first floor. Figure4-6 Test zone distribution 1A 1B 1C 2A 2B 2C 3A 3B 3C V=0.5 84.74 84.92 85.64 85.46 84.92 84.38 85.82 85.28 85.1 V=1 84.56 83.84 83.12 84.92 84.2 83.48 85.64 84.02 83.66 V=2 84.56 83.12 82.04 84.74 83.48 82.22 84.92 83.48 82.22 Table 4-3 Indoor air temperature in different outdoor wind speed 64 From Table 4-3, when outdoor temperature is 80 ℉ and wind speed is between 0.5 m/s (100f/m), 1.0 m/s (200f/m) and 2.0 m/s (400f/m), average indoor air temperature at tested zone is ranged from 82 ℉ to 86 ℉. From Figure 4-7, there is temperature gradient from north to south. Temperature at north side is higher than that at south side. According to the definition of thermal comfort zone described on Chapter2.4,when outdoor temperature is 80 ℉, thermal comfort zone is from 69.9℉ to 87.9℉ for 90% acceptability. So indoor temperature is within 90% acceptable thermal comfort zone, but very close to the upper limit at some areas. However, thermal comfort is not only related to temperature but also air speed. Different air speed can make occupant with different thermal feelings at the same temperature. This discussion will be extended on next section. Figure 4-7: Indoor air temperature curve (A represents North, C represents South) 80 81 82 83 84 85 86 87 1A 1B 1C 2A 2B 2C 3A 3B 3C V=0.5 V=1 V=2 65 4.3.1.2 Indoor Air Speed Analysis V=0.5m/s(100f/m) V=1.0m/s(200f/m) V=2.0m/s(400f/m) Figure 4-8: Indoor Air Speed Contour Section From Figure 4-8 Indoor Air Speed Contour Section, air speed distribution on the vertical direction can be shown. 66 Outdoor wind speed V=2.0m/s (400f/m) When outdoor air speed is 2.0m/s(400f/m), the fastest air appears at the air inlet on the north wall, with a velocity of 1.76 m/s. The most speedy area is the lower part near north side, where is marked by red color. The air speed there is around 1.7 m/s. According to Table 4-5, the air speed at 2.0m/s (400f/m) is adequate air speed for ventilation in hot and humid area. Although the air speed at red area is 2.0 m/s which is beyond the most comfortable range of air speed, it won’t bring a lot of discomfort to occupants. Because that area is beyond sensitive area, speedy air will not have much influence on occupant’s thermal comfort there. Meanwhile the speed of 2.0 m/s (400f/m) has the same effect as reducing 3.9 ℉ related to thermal comfortable. Occupant’s most thermally-sensitive area, between 1.2m (47in) and 1.8m (71in) above floor area, is covered by blue. That means air speed there is around 0.5 m/s (100f/m). According to Table 4-5, this air speed is noticeable and acceptable air speed for thermal comfort. It has the same effect as reducing 1.9 degree to occupant’s thermal comfort. So when outdoor wind speed is 2.0 m/s (400f/m), indoor air speed is acceptable to thermal comfort and can help reduce equivalent indoor air temperature. 67 Figure 4-9 Air Velocity Vector Section When Wind Velocity is 2.0 m/s (400f/m) Outdoor wind speed V=1.0m/s (200f/m) When outdoor air speed is 1.0m/s (200f/m), the maximum air speed for the whole building is 2.5 m/s at the outlet of the building. The lower layer of the indoor space is marked by green which means that air speed there is around 1.26 m/s. According to Table 4-5, the speed of 1.3 m/s is upper boundary of air-conditioned spaces and good air velocity for natural ventilation in dry and humid climates. Meanwhile, it can have the same effect as around 3.3 degree temperature reduction. At the middle and upper part of indoor space, it is marked as blue vector arrow which means air speed is below 0.45 m/s. The speed of 0.45m/s is noticeable and accepTable for occupants’ thermal comfort and can offset 1.9 degree for air temperature. 68 Figure 4-10 Air Velocity Vector Section When Wind Velocity is 1.0m/s (200f/m) Outdoor wind speed V=0.5m/s (100f/m) When outdoor air speed is 0.5 m/s (100f/m), the velocity vector is colored by blue at most of the occupied space and the vector line is less dense than that when outdoor velocity is 1.0m/s(200f/m) or 2.0m/s(400f/m). The average air speed at the area between 1.2m (42in) and 1.8m(71in) where is most sensitive to occupant’s thermal comfort is around 0.25 m/s which is barely noticeable but comfortable speed for occupants and has the same effect as 1.1 degree temperature reduction. 69 Figure 4-11: Air Velocity Vector Section When Wind Velocity is 0.5m/s (100f/m) V(m/s) 1A 1B 1C 2A 2B 2C 3A 3B 3C 0.5 0.17 0.19 0.14 0.13 0.12 0.11 0.11 0.1 0.1 1.0 0.15 0.15 0.16 0.12 0.13 0.13 0.16 0.13 0.13 2.0 0.23 0.24 0.32 0.31 0.29 0.29 0.32 0.3 0.28 Table 4-4: Indoor air temperature in different outdoor wind speed 70 Figure 4-12: Indoor air speed curve In general, using the same testing methodology as that for temperature, the average air speed at each tested zone is ranged from 0.2.0m/s(400f/m) to 0.32.0m/s(400f/m). According to ASHRAE Standard 55, the comfortable range air speed is 0.1.0m/s(200f/m) to 0.3 m/s. When air speed is ranged from 0.3 m/s to 1.0 m/s (200f/m), air motion is noticeable but still acceptable to most of occupants depending on activities being performed. When air motion is over 1.0 m/s (200f/m), it is a little unpleasant and disruptive. 4.3.1.3 Equivalent Temperature Reduction Effect Air speed not only can directly affect occupant’s thermal comfort by air movement but can also indirectly affect thermal comfort according to equivalent temperature reduction. The increased air speed has the same effect as temperature reduction. The relationship between air velocity and equivalent temperature reduction is shown below on Table4-6. 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 1A 1B 1C 2A 2B 2C 3A 3B 3C V=0.5 V=1 V=2 71 According to the relationship between air speed and air temperature reduction, when outdoor wind speed is 2.0m/s (400f/m), equivalent temperature reduction is from 2.3 degree to 3.2 degree; when outdoor wind speed is 1.0 m/s (200f/m), the equivalent temperature reduction is from 1.0 to 1.5 degree; when outdoor temperature is 0.5 m/s (100f/m), the equivalent temperature reduction is from 1.0 to 2.0 degree. So if considering the factor of air speed, the equivalent indoor thermal temperature is from 79 ℉ to 84.5 ℉. That range of indoor temperature is acceptable to occupants. That means when outdoor temperature is 80 ℉, outdoor wind speed is between 0.5 m/s (100f/m) and 2.0m/s (400f/m), double-skin & solar chimney building can only use natural ventilation to provide cooling and ventilation for occupants. Figure 4-13: Equivalent air temperature reduction curve 0 0.5 1 1.5 2 2.5 3 3.5 1A 1B 1C 2A 2B 2C 3A 3B 3C V=0.5 V=1 V=2 72 Figure 4-14: Indoor equivalent air temperature curve Air Velocity Equivalent Temperatu re reduction I-P SI Fp m M ph m/s kp h ℉ ℃ Effect on comfort 10 0.1 0.05 0.2 0 0 Straight air, slight uncomforTable 40 0.5 0.2 0.8 2 1.1 Barely noticeable but comforTable 50 0.6 0.25 1.0 2.4 1.3 Design velocity for air outlets that near occupants 80 1 0.4 1.6 3.5 1.9 Noticeable and comforTable 160 2 0.8 3.2 5 2.8 Very noticeable but accepTable in certain high- activity areas if air is warm Table 4-5: Relationship between air velocity and equivalent temperature reduction (FromP281 Heating Cooling and lighting) 76 77 78 79 80 81 82 83 84 85 86 1A 1B 1C 2A 2B 2C 3A 3B 3C V=0.5 V=1 V=2 73 Table 4-5 (Continued) 200 2.3 1.0 3.7 6 3.3 Upper limit for air-conditioned spaces Good air velocity for natural ventilation in dry and humid climates 400 4.5 2.0 7.2 7 3.9 Good air velocity for ventilation in hot and humid climates 900 10 4.5 16 9 5.0 Considered a gentle breeze when felt outdoors 4.3.1.4 PMV PMV can represent the indoor thermal comfort condition more directly than temperature and air speed. PMV stands for “Predicted Mean Vote” of a large amount of population exposed to a certain environment toward thermal comfort. The PMV value is ranged from -3 to 3. PMV value between -0.5 and 0.5 means the thermal environment is neutral and comfortable for occupants. According to ASHRAE STD 55: The ASHRAE thermal sensation scale, which was developed for use in quantifying people's thermal sensation, is defined as follows: +3 hot +2 warm +1 slightly warm 0 neutral –1 slightly cool 74 –2 cool –3 cold V=0.5m/s(100f/m) V=1.0m/s(200f/m) V=2.0m/s(400f/m) Figure 4-15: Indoor Air Speed Contour Section In Figure 4-15, blue and navy blue bands represent PMV value between -0.37 and 0.47 which is in thermal comfort range. When wind velocity is 1.0m/s(200f/m), most of the area is occupied by blue and navy blue, that means natural ventilation can satisfy occupants’ thermal comfort requirement. When wind velocity is 0.5 m/s (100f/m), blue still occupies most of the area, but navy blue and green are on more area than when outdoor wind speed is 1.0m/s (200f/m). 75 4.3.2 Available Outdoor Temperature In this section, the available temperature range for natural ventilation will be discussed. 4.3.2.1 Upper range In this section, the acceptable outdoor temperature range will be discussed. In above section, 80 ℉ has been proved to be an acceptable outdoor temperature for applying natural ventilation in double-skin & solar chimney building. So for the purpose of natural cooling, natural ventilation can work when outdoor temperature equals to or below 80 ℉. In this section, the upper limit of available temperature for natural ventilation will be tested. In order to test upper range of available temperature, other parameters beside outdoor temperature keep constant. In test cases, architectural features keep the same as the baseline building, wind speed is set as 1.0m/s(200f/m). For each case, outdoor temperature increases 5 degree compared to the previous available case until natural ventilation cannot satisfy thermal comfort in that case. And the temperature of last case will be seen as the upper range of acceptable temperature for natural ventilation. And the bottom range of outdoor temperature will be tested by the same methodology. To test the upper range of outdoor temperature, 85 ℉ is tested after 80℉. 76 From Figure 4-16 to Figure 4-19, compare the CFD simulation results between when outdoor temperature is 80℉ and outdoor temperature is 85℉, indoor thermal comfort condition is worse when outdoor temperature is 85℉. And from the Table 4-4 the range of average temperature at each tested zone is from 87.74 ℉ to 91.52 ℉ when outdoor temperature is 85 ℉.. Even considering the air speed effect on thermal comfort, the equivalent temperature at most of the occupant’s space is beyond the thermal comfort zone (See 2.4 Thermal Comfort Zone). So 85℉ is not an acceptable outdoor temperature for natural ventilation in double-skin & solar chimney building. The maximum available outdoor temperature for natural ventilation is 80℉ . Figure 4-16: T=80 ℉ Section Temperature Contour 77 Figure 4-17: T=85 ℉ Section Temperature Contour Figure 4-18: T=80 ℉ Work Plane Temperature Contour 78 Figure 4-19: T=85 ℉ Work Plane Temperature Contour 1A 1B 1C 2A 2B 2C 3A 3B 3C T=80 ℉ 84.56 83.84 83.12 84.92 84.2 83.48 85.64 84.02 83.66 T=85 ℉ 89.18 89.54 87.74 91.52 89 87.92 90.98 89.18 88.1 Table 4-6: Indoor temperature comparison between T=80 ℉ and T=85℉ 79 Figure 4-20: Indoor equivalent air temperature curve when T=80℉ and T=85℉ 4.3.2.2 Bottom Range of Available Temperature At mild season, outdoor temperature is around or slightly lower than the bottom line of thermal comfort range temperature. At this situation, natural ventilation only serves the function of ventilation to provide enough fresh air for occupants, because no cooling demand is needed from natural ventilation. To test the bottom range of available outdoor temperature for natural ventilation, situations of outdoor temperature is70℉, 65℉ and 60℉ are tested. The outdoor wind speed is set as 1.0m/s(200f/m). CFD simulation results show that when outdoor temperature is 60 ℉, average temperature at tested zones is from 63.84℉ to 69.24℉; 78 80 82 84 86 88 90 92 94 1 2 3 4 5 6 7 8 9 T=80 T=85 80 when outdoor temperature is 65℉, average temperature at tested zones is ranged from 71.2℉ to 76.8℉; when outdoor temperature is 70℉,average temperature at tested zones is ranged from 74.6℉ to 79.5℉. Temperature distribution when outdoor temperature is 60℉ , 65℉ and 70℉ ( ℉) 1A 1B 1C 2A 2B 2C 3A 3B 3C T=60 ℉ 68.42 69.22 63.84 67.96 69.24 63.94 67.24 68.78 64.22 T=65 ℉ 73.4 76.8 71.2 74.6 76.2 71.4 73.9 74.8 71.2 T=70 ℉ 78.8 79.5 74.6 77.7 78.6 75.2 78.2 79.8 74.8 Table 4-7: Indoor temperature comparison between T=65℉ and T=70℉ Figure 4-21: Indoor air temperature curve when T=60℉, 65℉ and T=70℉ 0 10 20 30 40 50 60 70 80 90 1A 1B 1C 2A 2B 2C 3A 3B 3C T=60 T=65 T=70 81 The indoor air speed is ranged from 0.13 m/s to 0.2.0m/s(400f/m) when outdoor temperature is 60h; ranged from 0.13m/s to 0.19m/s at each test zone when outdoor temperature is 65 ℉; and ranged from 0.14m/s to 0.18m/s when outdoor temperature is 70 ℉. According to Table 4-5 Relationship between air velocity and equivalent temperature reduction, when air speed is below 2.0m/s(400f/m), it is barely noticeable but comfortable air speed. In addition, according to Table 4-5, the equivalent reduction at that range is from 1.1℉ to 2.1℉. The following Table 4-7 shows the specific temperature reduction at each different tested zone. At this situation, because outdoor temperature is close to the bottom range of thermal comfort temperature, indoor air speed will have negative effect on thermal comfort, that is different compare to when outdoor temperature is close to upper range of thermal comfort zone. If considering the temperature reduction effect by air movement, the equivalent room temperature will be reduced by several degrees. The equivalent room temperature is shown as below Table 4-10 and Figure 4-19. When outdoor temperature is over 65℉, average equivalent temperature at most of the tested zones is within the thermal comfort range. Temperature at most of the tested zones besides south zones exceeds 70 z and temperature at south zones are 69.24ne at each floor is a litately. So when outdoor temperature is 65℉, natural ventilation can provide fresh air for indoor 82 occupants and meanwhile keep indoor temperature within the acceptable comfortable range. So 65 ℉ can be regarded as a secure temperature for natural ventilation. When temperature is above 65 ℉, occupant will not have any cold feeling because of natural ventilation. When outdoor temperature falls to 60 ℉, the average temperature of the whole tested zone is 67℉. And according to 2.4 Thermal Comfort Zone: T comf= 0.31 T a , out + 17.8±5 Bottom range of thermal comfort zone when outdoor temperature is 60 ℉ is 63.7 ℉. In these tested zones, the south zone is relatively cooler than other zones. In general, even though temperature in certain zones will be a little lower than acceptable comfortable temperature, occupants can feel thermal comfortable at most of the zones even considering the negative effect caused by indoor air movement. So when outdoor temperature is 60 ℉, it is still possible to use natural ventilation in double-skin & solar chimney building. But indoor configuration should be arranged appropriately. For example, it is better to put equipments in cooler areas. 83 Indoor air speed distribution when outdoor temperature is 60 ℉,65℉ and 70℉ (m/s) 1A 1B 1C 2A 2B 2C 3A 3B 3C T=60℉ 0.14 0.15 0.2 0.15 0.13 0.19 0.15 0.14 0.18 T=65 ℉ 0.13 0.13 0.2 0.14 0.13 0.19 0.15 0.15 0.19 T=70 ℉ 0.15 0.15 0.21 0.18 0.14 0.15 0.14 0.14 0.18 Table 4-8: Indoor air speed comparison between T=60 ℉, T=65℉ and T=70℉ Figure 4-22: Indoor air speed curve when T=65 ℉ and T=70℉ 0 0.05 0.1 0.15 0.2 0.25 1A 1B 1C 2A 2B 2C 3A 3B 3C T=60 T=65 T=70 84 Equivalent temperature reduction( ℉) 1A 1B 1C 2A 2B 2C 3A 3B 3C T=60 ℉ 1.2 1.3 2 1.3 1.1 1.9 1.3 1.2 1.8 T=65 ℉ 1.1 1.1 2 1.2 1.1 1.9 1.3 1.3 1.9 T=70 ℉ 1.3 1.3 2.1 1.8 1.2 1.3 1.2 1.2 1.8 Table 4-9: Indoor equivalent temperature reduction when T=60℉, T=65℉ and T=70℉ Equivalent indoor air temperature( ℉) 1A 1B 1C 2A 2B 2C 3A 3B 3C T=66 ℉ 68.42 69.22 63.84 67.96 69.24 63.94 67.24 68.78 64.22 T=65 ℉ 72.3 75.72 69.24 73.46 75.18 69.52 72.64 73.54 69.34 1A 1B 1C 2A 2B 2C 3A 3B 3C T=70 ℉ 77.5 78.22 72.56 75.92 77.42 73.9 77.06 78.68 73.04 Table 4-10: Indoor equivalent air temperature when T=60℉, T=65℉ and T=70℉ 85 Figure 4-23: Indoor equivalent air temperature curve when T=60℉,T=65℉ and T=70℉ 4.4 Problems of Natural Ventilation The most important advantage of natural ventilation is energy conservation. But comparing to mechanical ventilation, natural ventilation is less controllable and will cause some problems on thermal comfort issue. Without considering the humidity issue, the thermal comfort issue in this thesis is mainly related to temperature. Without Air Conditioning to provide temperature control at indoor space, the temperature cannot be evenly distributed indoor by natural ventilation. So that will cause uneven temperature problem that is although the indoor average temperature is within the thermal comfort zone, temperature is either too high or too low in certain position of the room. 0 10 20 30 40 50 60 70 80 90 1A 1B 1C 2A 2B 2C 3A 3B 3C T=60 T=65 T=70 86 4.4.1 Temperature Stratification In general, from the Figure 4-5 section of temperature contour, there is temperature stratification in the room. The stratification is getting seriously when wind speed decreases. When outdoor wind speed is 2.0m/s (400f/m), temperature stratification only happens at the north side of room; when wind speed is 0.5 m/s (100f/m), temperature stratification spreads to the whole area of room. 4.4.1.1 Reason of temperature stratification The reason of temperature stratification is the dead zone of air movement in the room. That is because indoor air stream comes in through lower opening at the windward side and exhausts through the upper opening on the south leeward side. Figure-20 Trace of Air Movement displays the path of air stream. As it shows, there is a dead zone at upper north corner of the room where no main air stream passes through. So heat cannot be brought away by ventilation and will get accumulated at the dead zone area, that causing temperature there higher than other area of the room. On the vertical direction, temperature difference can achieve 9 degree at most. Occupant will feel thermal uncomfortable due to vertical temperature difference. 87 Figure 4-24 Trace of air movement 4.4.1.2 Solutions to temperature stratification The most simple and effective solution is to increase the height of ceiling. Although higher ceiling will strengthen vertical temperature stratification, it can increase the range of each band of the stratification. When ceiling is high enough, only the bottom stratification can influence occupant, so occupant won’t feel the relative high temperature at the upper parts of room. The details about the effect of increasing ceiling will be discussed on 4.5.1. 88 4.4.2 Horizontal Uneven Temperature Distribution Temperature is also uneven horizontally, because north side is warmer than south side. From Table 4-4 and Figure 4-25, average temperature on the north zone will be 3 degree higher than that on south zone. That will cause occupants to feel different level of thermal comfort in different position of the room. V=0.5m/s (100f/m) V=1.0m/s(200f/m) V=2.0 m/s (400f/m) Figure 4-25: Indoor air temperature cut plane 4.5 Improvement To reduce the influence of those problems on thermal comfort to least, it is necessary make some changes on building’s architectural feature to improve the indoor thermal comfortable level. 89 4.5.1 Increase ceiling height To prevent the influence of temperature stratification on thermal comfort, increasing ceiling height is one optional solution. To study the effect of increasing ceiling height, the tested case keeps the height of first two floors the same as basic case and increases the ceiling height of third floor to 13.5 feet. It can help to have a clear comparison about thermal conditions between different ceiling heights. The section temperature contour shows the improvement on thermal comfort by increasing the ceiling height. From Figure 4-26, although temperature stratification becomes more serious on third floor when ceiling height is increased, the range of each temperature band becomes wider according to the increase of ceiling height. On the first two floors, occupant activity’s space is covered by both green and blue band. That means temperature range occupants can experience is from 80.6℉ to 89℉. On the third floor, occupant activity’s space is only covered by blue. That means occupants will not feel the temperature stratification at the upper part of room. From PMV section contour, on the third floor, occupants totally stay at blue area where PMV is between 0 and 0.2 which represents thermal comfort. On the first floors where ceiling height is 9 feet, the top part of occupant is covered by green. That means part of 90 occupant is on the relatively warm area and will not feel as much thermal comfortable as on third floor. In conclusion, from the comparison between third floor and first two floors, increasing ceiling height is a effective way to weaken the influence of thermal stratification on occupant’s thermal comfort. Figure 4-26: Indoor temperature contour section-increased ceiling height 91 Figure 4-27: Indoor PMV contour section-increased ceiling height 92 Chapter 5: Energy Simulation In this chapter, energy performance of Double-skin & Solar Chimney building will be discussed. The primary goal of introducing the concept of Double-skin & Solar Chimney into office building is energy conservation. The thermal comfort performance has been discussed in Chapter 4, the CFD simulation proves that proper design of Double-skin & Solar Chimney in certain climate condition can promise acceptable thermal comfort for occupants. Basing on the results of Chapter 4, energy saving is calculated in this chapter. Annual building energy performance of Double-skin & Solar Chimney is simulated by IES-VE. 5.1 Climate Zone The assumed location of climate zone is Chicago. The reason to choose Chicago is that Chicago is in cold climate zone where most of the existing double skin buildings are located. And during Mar to Jun, monthly mean maximum temperature is below 80℉, mean minimum temperature is higher than 32 ℉ and temperature does not exceed 80 ℉ on most of days. Those climate conditions meet the perquisite of natural ventilation. So Chicago is a potential location to apply natural ventilation and can take advantage of double-skin & solar chimney building. 93 But the current situation is that most double-skin buildings in Chicago only take the advantage of thermal insulation from double-skin in winter. Normally they still use A.C rather than natural ventilation for ventilation and space cooling during the mild and warm seasons. According to the CFD simulation and analysis in Chapter 4, natural ventilation can be applied when ambient temperature is between 60 ℉ and 80 ℉, wind speed is between 0.5 and 1.5 m/s (300f/m). That range of weather condition can be realized in Chicago from Mar to Jun at most of time. 94 Figure 5-1: Weather data of Chicago 5.2 Building Model In the Model Builder-ModelIT-Building modeler, building geometric model can be built up. The model has three stories, each floor is 9 feet high. The floor plan is 27’ wide and 95 54’ long. Double-skin space is with 3’ wide cavity space and 33’ high, 9’ higher than the top of main building. Figure 5-2: Building model in IES-VE 5.3 Thermal setting Since the building is a theoretical building, the setting of building parameters is based on ASHRAE Standard 90.1-2004. Those parameters include construction materials, mechanical system and internal loads. The operation of operable openings and mechanical system will follow the basic requirement of natural ventilation. After geometric model of building has been built up, properties of building are defined at “Thermal-VE Compliance”. The controllable template types include: Room Attributes, 96 Constructions, Macroflo Opening Types, Electric Lighting and Radiation Surface Properties. Figure 5-3: Interface of Building Template Manager in IES-VE 5.3.1 Construction In the theoretical building, construction materials are assigned according to ASHRAE Standard 90.1-2004. According to ASHRAE standard 90.1-2004 Table B-1 US Climate Zones, Chicago is located in Zone 5A. From ASHRAE 90.1-2004 Table5.5-5 Building Envelope Requirements For Climate Zone 5(A,B,C), building construction materials can 97 be properly chosen. The circled items on Table 5-1 are chosen values for according parameters. Table 5-1: Building envelope requirement for Climate Zone5 ( ASHRAE STD 90.1-2004) 98 5.3.2 Macroflo Opening Types As IES-VE 5.9 Manual describes: In the Virtual Environment, an opening is a window, door or hole created in ModelIT. These objects may also be used to represent other types of penetratio in the building fabric such as louvers and grilles. Opening Types provide a means for specifying the air flow characteristics of windows and doors for the purpose of analyzing natural ventilation and infiltratio in MacroFlo. Holes represent a special category of opening with constant and unmodifiable air flow characteristics, and are not associated with Opening Types. The air flow characteristics of an opening include its crackage, openable area and exposure to the outside environment, as well as parameters indicating how its area varies with time and (optionally) with room temperature. MacroFlo Opening Types are attached to openings in the model using facilities provided in the MacroFlo Application View. Because double-skin space plays different roles during winter, mild seasons and summer separately. The operable openings on the double-skin should be in different modes during these seasons. During winter mode, all the controllable windows on the building are closed to form thermal buffer in double-skin cavity to increase heat resistance and decrease heating load. On mild season mode, all controllable windows are open for natural ventilation. On summer mode, only openings on external façade of double-skin are open to introduce stack-effect ventilation into double-skin space to help reduce 99 cooling load in summer ；but the windows on internal façade of double-skin and the opposite wall of double-skin are closed mechanical cooling. According to the CFD simulation on Chapter 4, the available temperature for natural ventilation is between 60℉ and 80℉. So basing on the general requirements of natural ventilation, operable windows’ schedule is as below. Winter Mild Season(60<Tem<80) Summer Opening on external skin Closed Open Open Openings on internal skin and north wall Closed Open Closed Table 5-2: Building opening schedule Opening profile is set in IES-VE to realize the control of opening as shown in Table 5-2. For openings on external skin, during winter (Oct-Mar) the opening is set as off (closed); during Apr to Sep which includes summer, setting of annual profile depends on weekly and daily profile. For daily profile, condition is set as when outdoor temperature is between 60 ℉ and 80 ℉, and wind speed is between 0.5m/s (100f/m) and 2.0 m/s (400f/m), opening is on (open); otherwise opening is off. 100 For openings on internal skin and north wall, the only difference is that when temperature is above 80 ℉, the opening on daily profile will be set as off (closed) again. Figure 5-4: Opening Annual Profile Figure 5-5: Opening Weekly Profile 101 Figure 5-6: Opening Daily Profile Figure 5-7: Opening types setting 102 5.3.3 HV AC Profile According to the analysis on Chapter 4, when outdoor temperature is between 60 ℉ and 80℉, wind speed is between 0.5 m/s (100 f/m) and 1.5 m/s (300f/m), natural ventilation is available for building. If conditions go beyond that range, building has to depend on HVAC system to provide either heating or cooling. Below is the Heating and Cooling profile for HV AC system. For cooling, A.C starts working only when Outdoor temperature above 80℉and Outdoor Air Speed < 0.5 m/s (100f/m)or Outdoor Air Speed > 1.5 m/s (300f/m). Winter Mild Season(60<Tem<80) Summer Mechanical Heating On Off Off Mechanical Cooling Off Off On Table 5-3: HV AC system schedule 103 Figure 5-8: Apache system HV AC setting Figure 5-9: HV AC cooling daily profile 104 Figure 5-10: HV AC heating condition setting Figure 5-11: HV AC heating daily profile 105 5.4 Apache Energy Simulation After setting the thermal properties of building, it goes to Apache Simulation. Software simulates energy performance of doubles-skin building with natural ventilation and without natural ventilation separately. By comparing results, energy saving by natural ventilation on double-skin building can be predicted. In addition, it will be also compared with average building energy consumption and Target on 2030 Challenge. 5.4.1 Annual energy consumption Following Table 5-5 shows the simulation results of annual building energy consumption. Annual Energy Consumption(KBtu/Sqft) Normal Double skin DS with Natural Ventilation Average Building 2010 Target in 2030 Challenge Energy Consumption(KBtu/Sqft) 59 38 90 46 Table 5-4: Energy consumption comparison 106 Figure 5-12: Energy consumption chart According to the energy simulation by IES-VE, using natural ventilation in mild seasons and summer can help building to save up to 37% annual energy compared to double-skin building without natural ventilation; and 21% more energy efficiency than current 2010 Target in 2030 Challenge. Those data proves that using natural ventilation can achieve a great amount of energy saving for office building. And it can create great economical and environment benefit. 0 20 40 60 80 100 Annual Energy Consumption(KBtu/Sqft) Normal Double-Skin Double-Skin with NV Average Building 2010 Target in 2030 Challenge 107 5.4.2 Cooling Energy The energy saved by natural ventilation is mainly from cooling energy saving during mild season. of the cooling energy is consumed by HVAC for space cooling and ventilation in traditional building. The comparison between monthly cooling energy of traditional double-skin building without using natural ventilation and double-skin & solar chimney building with natural ventilation can quantitatively illustrate energy saving capacity of natural ventilation. From Table 5-6, using natural ventilation can save a great amount of energy from May to Sep. That is because temperature is within the available range for natural ventilation from May to Sep in Chicago. If using a set of more sophisticated control system to control operable window and HVAC strictly according to outdoor temperature, more cooling energy can be saved. Monthly cooling energy comparison With Natural Ventilation Without Natural Ventilation Jan 0 0 Feb 0 0 Mar 0 0 Apr 0 0 May 0.45 9.4 Jun 1.86 20.7 Jul 2.7 28.5 Table 5-5: Monthly cooling energy comparison 108 Table 5-5 (Continued) Aug 2.2 19.9 Sep 0.11 18 Oct 0 0 Nov 0 0 Dec 0 0 With Natural Ventilation Without Natural Ventilation Summed Total 7.32 96.5 Figure 5-13: Monthly cooling energy comparison chart 5.4.3 Typical day energy consumption analysis A typical day in summer is picked up to compare the daily energy consumption between traditional building without natural ventilation and double-skin & solar chimney building with natural ventilation. 0 5 10 15 20 25 30 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec With Natural Ventilation Without Natural Ventilation 109 Jul 28 is chosen. For building without natural ventilation, HVAC starts working as early as 6:00 am when HV AC outdoor set-point temperature is 72 ℉. But for building with natural ventilation, HVAC will not start working until outdoor temperature reaches 80 ℉. From Figure 5-14, the 8 degree difference makes HV AC starting time around 6 hours later in double-skin & solar chimney building. With Natural Ventilation Figure 5-14: Energy consumption curve on Jul 28 t 110 Figure 5-14 (Continued) Without Natural Ventilation 111 Chapter 6: Conclusion and Further Work According to CFD simulation and energy simulation, the research tests both thermal and energy performance of natural ventilation in double-skin & solar chimney building. The research tests the available outdoor climate range for natural ventilation in double-skin & solar chimney office building; the influence of double-skin’s architectural features on the performance of natural ventilation; indoor thermal comfort condition by using natural ventilation and the potential of energy conservation by applying natural ventilation in double-skin & solar chimney building. 6.1 The available climate range for natural ventilation The CFD simulation result shows that when outdoor temperature is between 60℉ and 80 ℉, and equivalent wind speed is between 0.5 m/s (100f/m) and 1.5 m/s (300f/m), it is good for natural ventilation in double-skin & solar chimney building. When ambient temperature is between 60 ℉ and 80℉, and equivalent wind speed is between 0.5 m/s (100f/m) and 1.5 m/s (300f/m) real indoor average temperature in occupant’s most sensitive space is between 71 ℉ and 86 ℉ . If consider the equivalent temperature reduction of wind speed, the equivalent indoor thermal temperature range is reduced to between 69 ℉ and 83℉. I was not able to understand this sentence. (Because air speed 112 has the same effect as thermal temperature reduction which has been discussed on 4.3.1.3 Equivalent Temperature Reduction Effect) The range of temperature is acceptable for thermal comfort for occupants. If the air temperature exceeds 80 ℉, even though considering the effect of air movement on temperature reduction, indoor air temperature is still too high to make occupants thermal comfortable when air speed is below 1.0 m/s. PMV also reveals that indoor environment is too warm for thermal comfort when outdoor temperature exceeds 80 ℉. On the other side, when outdoor temperature is lower than 60 ℉, the indoor temperature is too cold for occupants’ thermal comfort without mechanical heating. 6.2 Cavity Depth When cavity depth is between 3 feet and 4 feet, good natural ventilation performance can be achieved. If the cavity depth is narrower than 3feet, temperature difference and pressure difference between inlet and outlet opening will decrease and then air flow rate will decrease accordingly. When cavity depth is smaller than 3 feet, the smaller the cavity depth is, the worse natural ventilation is performed. That is because strong turbulence will be generated in narrow cavity to disturb the air circulation movement in the cavity space. If the cavity depth goes wider than 4 feet, temperature difference and pressure 113 difference between inlet and outlet opening decrease, and air flow rate decreases as well. This is because air circulation movement cannot be well formed when cavity depth is too wide. But the decreasing gradient is not as sharp as that when cavity depth is less than 3 feet. 6.3 Stack Height When stack space height (h) is less than double of main building height(H)(H<h<2H), the higher stack space is, the better natural ventilation performance is. When stack height is from 27’ to 33’, ( that is from 0% to 33% higher than height of main building, H<h<1.33H) natural ventilation performance improves with stack height increases. And the increasing gradient is sharp. When the stack height is from 33’ to 54’, (that is from 33% to 100% higher than main building height, 1.33H<h<2H) natural ventilation performance also improves with the increase of stack height. But the increasing gradient is much flatter. So it will be less valuable to increase the height of stack space for the purpose of improving natural ventilation efficiency when stack height over 33’ for the three story building (h>1.33H). Because in this situation, the minor energy saving by increasing the height of stack space cannot compensate the higher cost due to increasing the height of stack space. 114 6.4 Ceiling Height It is better to set the ceiling height of each floor high enough to weaken thermal stratification’s influence on occupant. There is thermal stratification appearing indoor because there is some dead zone where naturally ventilated air stream cannot pass through. According to the CFD simulation on Chapter 4, when ceiling height is 9 feet, temperature of lower part of occupant’s activity space is sustained in thermal comfort zone, but temperature of upper part of the occupant’s activity space is too warm to stay within comfort zone. So occupants will feel thermal uncomfortable at upper part of activity space. If the ceiling height increases to 13.5 feet, temperature of the whole activity zone is sustained in thermal comfort zone, even though the thermal stratification becomes more serious. 6.5 Energy Consumption Theoretical building is assumed to be located at climate zone 3A, such as Chicago. The energy simulation was conducted in double-skin & solar chimney building under the condition that outdoor temperature is between 60 ℉ and 80 ℉ and wind speed is between 0.5 m/s and 1.5 m/s (300f/m). The efficiency of the natural ventilation in that condition has been proved by CFD simulation. Result reveals that introducing natural ventilation into double-skin & solar chimney building can make building 37% more energy 115 efficiency than normal double-skin building without natural ventilation and 21% more energy efficiency than 2010 target building according to 2030 challenge. 6.6 Further Work 6.6.1 Case study In this thesis study, research is only about the theoretical building, but without case study of existing building. Because simplifying the details of the building can help to focus on the fundamental principle of the natural ventilation and save time on simulation. Although theoretical study can help to summarize the principle of natural ventilation, there are differences between existing building and theoretical building when it apply natural ventilation So on the next step, a double-skin building will be chosen from climate zone 3A for case study. HOBO device will be installed in typical area. HOBO tested results will be used to compare with CFD simulation result to verify the accuracy of CFD simulation. Real information of building construction, internal load and mechanical system will be used in CFD and energy simulation. 116 6.6.2 Extended Climate Zone The existing research on energy consumption is limited to climate zone 3A. In the further research, more climate zones will be taken into consideration. Energy saving in different climate zones will be calculated to get a complete database about the energy saving because of using natural ventilation in double-skin & solar chimney buildings. 6.6.3 Other factor related to thermal comfort In this research, parameters used to analyze the thermal comfort are temperature and air motion, without considering humidity issue here. But humidity is also an important issue related to thermal comfort. In further research, humidity issue will be also studied. 117 Bibliography American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc 2007, ANSI/ASHRAE Standard 62.1-2007-Ventilation for Acceptable Indoor Air Quality, ISSN 1041-2336, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc 2004, ANSI/ASHRAE/IESNA Standard 90.1-2004-Enregy Standard for Building Except Low- Rise Residential Buildings, American Society of Heating, Refrigerating and Air- Conditioning Engineers, Atlanta American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc 2004, ANSI/ASHRAE Standard 55-2004-Thermal Environmental Conditions for Human Occupancy, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta Architecture 2030, The Building Sector, Viewed 10 July 2010, <http://www.architecture2030.org/current_situation/building_sector.html> Asfour, OS & Gadi, MB 2007, ‘A comparison between CFD and Network models for predicting wind-driven ventilation in buildings’, Building and Environment, vol.42, no.12, pp.4079-4085 Awbi, Hazim.B 2008, ‘Ventilation System Design and Performance’, Taylor & Francis, London; New York Brager, GS & de Dear, RJ 2002, ‘Thermal comfort in naturally ventilated buildings: revisions to ASHRAE Standard 55’, Energy and Buildings, vol.34, no.6, pp.549-561 Chen, Q & Xu, W. 1998, ‘A zero-equation turbulence model for indoor airflow simulation’, Energy and Buildings, vol.28, no.2, pp.109-111 Department of Architecture and Built Environment 2006, ‘Double Skin Facades-A literature review’, report prepared by H Poirazis, Department of Architecture and Built Environment , Lund University, Lund Institute of Technology, Sweden Ding, W & Hasemi, Y & Yamada, T 2005, ‘Natural ventilation performance of a double- skin façade with a solar chimney’, Energy and Buildings, vol.37, no.7, pp.411-418 118 Energy Business Daily, Japan Takes the Lead to Stop Climate Change, Viewed 3 March 2010, <http://energybusinessdaily.com/global-warming/japan-takes-the-lead-to-stop- climate-change/ > Fluent Inc. 2001, Airpak User’ s Guide Heating, Cooling and HVAC, Solar Chimney, Viewed 10 February 2010, <http://coolexcooling.com/2008/01/25/solar-chimney/> Integrated Environmental Solutions Limited 2008, <VE> User Guide <Virtual Environment> 5.9 Jin, Z. 2001, ‘Building Environmental Science’ ( 建筑环境学), China Architecture & Building Press, Beijing Jiru, T.E, Haghihat,F 2008, ‘ Modeling ventilated double skin facade-A zonal approach’, Energy and Buildings, V ol.40, no. 8, pp.1567-1576 Lechner, Norbert 2009, ‘Heating, cooling, lighting: sustainable design methods for architects’, John Wiley & Sons, Hoboken, N.J. Li, Q 2009, ‘CFD study of the thermal environment in an air-conditioned train station buildingte of Techn and Environment’, vol.44, no.7, pp.1452-1465 Mehta, Mohit, 2005, ‘NATURAL VENTILATION ANALYSES OF AN OFFICE BUILDING WITH OPEN ATRIUM’, paper presented to Ninth International IBPSA Conference, Montreal, 15-18 Aug Mei, L 2008, ‘Nodal network and CFD simulation of airflow and heat transfer in double skin facades with blinds’, Building services engineering research & technology, vol.29, no.1, pp.45-59 Oesterle, E. 2001, ‘Double-skin facades: integrated planning’, Prestel, Munich Santamouris, M. 1998, ‘Natural ventilation in buildings: a design handbook’, James and James (Science Publishers) Ltd., London 119 Walker, A. 2008, ‘The Fundamentals of Natural Ventilation’, Buildings, V ol. 102, no.10; pp. 34 Wikipedia 2010, Natural Ventilation, Wikipedia, Viewed 3 August 2010, < http://en.wikipedia.org/wiki/Natural_ventilation> Wikipedia 2010, Solar Chimney, Wikipedia, Viewed 5 August 2010, < http://en.wikipedia.org/wiki/Solar_chimney> Xu, L 2003, ‘Effectiveness of Hybrid Air Conditioning System in a Residential House’, PHD Dissertation, Waseda University, Tokyo

Abstract (if available)

Abstract In United States, space heating, space cooling and ventilation of buildings consume 33% of the annual building energy consumption and 15% of the total annual energy consumption, leading to a number of energy and environment problems. Natural ventilation for heating, cooling and ventilation is a good solution and double-skin & solar chimney facades are a good architectural form for natural ventilation. The main work of this research is to study appropriate size of architectural forms (cavity depth and height of stack space) and available weather conditions (outdoor temperature and wind velocity) for natural ventilation at double-skin & solar chimney building, and potential energy saving by applying natural ventilation in double-skins facade building. This research can provide guideline to help designers to determine cavity depth and height of stack space for double-skin & solar chimney building at available climate zone.

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Asset Metadata

Creator Wang, Lutao (author)

Core Title Design of double skin (envelope) as a solar chimney: adapting natural ventilation in double envelope for mild or warm climates

School School of Architecture

Degree Master of Building Science

Degree Program Building Science

Publication Date 12/10/2010

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

Tag CFD,double-skin facades,energy conservation,natural ventilation,OAI-PMH Harvest

Place Name USA (countries)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Noble, Douglas (committee chair), Otto, Greg (committee member), Vaglio, Jeffrey (committee member)

Creator Email lutaowan@usc.edu,wanglutao0203@hotmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m3596

Unique identifier UC155634

Identifier etd-Wang-4131 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-428521 (legacy record id),usctheses-m3596 (legacy record id)

Legacy Identifier etd-Wang-4131.pdf

Dmrecord 428521

Document Type Thesis

Rights Wang, Lutao

Type texts

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

Repository Name Libraries, University of Southern California

Repository Location Los Angeles, California

Repository Email cisadmin@lib.usc.edu