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Natural Ventilation in Buildings and the Tools for Analysis

Permanent Link: http://ufdc.ufl.edu/UFE0024277/00001

Material Information

Title: Natural Ventilation in Buildings and the Tools for Analysis
Physical Description: 1 online resource (103 p.)
Language: english
Creator: Mozaffarian, Romina
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: Building Construction -- Dissertations, Academic -- UF
Genre: Building Construction thesis, M.S.B.C.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Master of Science in Building Construction NATURAL VENTILATION IN BUILDINGS AND THE TOOLS FOR ANALYSIS By Romina Mozaffarian August 2009 Chair: Robert J. Ries Cochairman: Svetlana Olbina Major: Building Construction Natural ventilation is using natural air to condition the interior of a building with minimal mechanical equipment. In other words, it is ventilating the building with natural air. Natural ventilation offers the means to control air quality in buildings, to directly condition indoor air with cooler outdoor air, to indirectly condition indoor air by night cooling of building thermal mass, and to provide refreshing airflow past occupants when desired. Implementing natural ventilation for conditioning can reduce electrical consumption, can recover the valuable building space typically used by all-air mechanical systems, can potentially provide health, comfort, and productivity advantages, in buildings and increases the efficiency of energy and material resources which are the purposes of a sustainable building, or green building. The objective of this study is to improve the environmental performance of ventilation and temperature control systems in buildings by using natural ventilation instead of mechanical systems. The main focus of this study is natural ventilation through wind. By using a technique for natural ventilation, the outdoor air can be introduced into the building to circulate air. Another primary focus is the selection of software for modeling a building with a natural ventilation system.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Romina Mozaffarian.
Thesis: Thesis (M.S.B.C.)--University of Florida, 2009.
Local: Adviser: Ries, Robert J.
Local: Co-adviser: Olbina, Svetlana.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024277:00001

Permanent Link: http://ufdc.ufl.edu/UFE0024277/00001

Material Information

Title: Natural Ventilation in Buildings and the Tools for Analysis
Physical Description: 1 online resource (103 p.)
Language: english
Creator: Mozaffarian, Romina
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: Building Construction -- Dissertations, Academic -- UF
Genre: Building Construction thesis, M.S.B.C.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Master of Science in Building Construction NATURAL VENTILATION IN BUILDINGS AND THE TOOLS FOR ANALYSIS By Romina Mozaffarian August 2009 Chair: Robert J. Ries Cochairman: Svetlana Olbina Major: Building Construction Natural ventilation is using natural air to condition the interior of a building with minimal mechanical equipment. In other words, it is ventilating the building with natural air. Natural ventilation offers the means to control air quality in buildings, to directly condition indoor air with cooler outdoor air, to indirectly condition indoor air by night cooling of building thermal mass, and to provide refreshing airflow past occupants when desired. Implementing natural ventilation for conditioning can reduce electrical consumption, can recover the valuable building space typically used by all-air mechanical systems, can potentially provide health, comfort, and productivity advantages, in buildings and increases the efficiency of energy and material resources which are the purposes of a sustainable building, or green building. The objective of this study is to improve the environmental performance of ventilation and temperature control systems in buildings by using natural ventilation instead of mechanical systems. The main focus of this study is natural ventilation through wind. By using a technique for natural ventilation, the outdoor air can be introduced into the building to circulate air. Another primary focus is the selection of software for modeling a building with a natural ventilation system.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Romina Mozaffarian.
Thesis: Thesis (M.S.B.C.)--University of Florida, 2009.
Local: Adviser: Ries, Robert J.
Local: Co-adviser: Olbina, Svetlana.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024277:00001


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1 NATURAL VENTILATION IN BUILDI NGS AND THE TOOLS FOR ANALYSIS By ROMINA MOZAFFARIAN A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN BUILDING CONSTRUCTION UNIVERSITY OF FLORIDA 2009

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2 2009 Romina Mozaffarian

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3 To my great parents, Dr. Moha mmad Ali Mozaffarian and Zahra Zahedi, my lovely brother and sisters, Ramin, Rozita and Roya Mozaffarian This venture would not be possible without their love and support.

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4 ACKNOWLEDGMENTS I would like to take this oppor tunity to thank everyone who helped m e to complete my thesis. First, I would like to thank my committee chairman, Dr. Robert J. Ries for his great support throughout my course of study and his time and guidance. I would also like to thank my cochair, Dr. Svetlana Olbina for her great support and encouragement and my committee member, Dr. Charles J. Kibert for guiding me to choose this interesting t opic and for his support. I would like to thank my parents, Dr. Moha mmad Ali Mozaffarian and Zahra Zahedi, and my lovely brother and sisters, Ramin, Rozita and Roya Mozaffarian, fo r their encouragement, time, and support, both in this accomplishmen t and throughout my education overall. They minimized the burden of my study with their sup port and love. I especially owe appreciation to my dad who has always been a great role model es pecially in education. I also want to thank my lovely mom for being there for me whenever I ne eded her most. Her positive attitude and love made the environment a friendly one. I thank my sisters, Rozita and Roya, whose help and support enabled me to accomplish this task. I also want to thank my friend Dr. Ayyoub Mehdizade Momen for his time, help, and suppor t throughout my thesis especially with FLUENT packages. I also wanted to thank my other friend, Maya Joanni des for her help, time and support with writing of my thesis.

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5 TABLE OF CONTENTS Page ACKNOWLEDGMENTS ............................................................................................................... 4LIST OF TABLES ...........................................................................................................................8LIST OF FIGURES .........................................................................................................................9ABSTRACT ...................................................................................................................... .............12 CHAP TER 1 INTRODUCTION .................................................................................................................. 13Introduction .................................................................................................................. ...........13Problem Statement ............................................................................................................. .....13Research Objectives ........................................................................................................... .....13Significance of the Study ........................................................................................................14Limitations of the Study ...................................................................................................... ...142 LITERATURE REVIEW .......................................................................................................16Introduction .................................................................................................................. ...........16Definitions of Natural Ventilation .......................................................................................... 17Different Kinds of Ventilation ................................................................................................17Wind-Driven Cross Ventilation .......................................................................................17Buoyancy-Driven Stack Ventilation ................................................................................ 18Single-Sided Ventilation ................................................................................................. 18Stack Ventilation with Sub-Slab Distribution .................................................................18Hybrid Ventilation Systems ............................................................................................ 18Wind-Stack Driven Ventilation ....................................................................................... 19Wind Catcher or Badgir ...................................................................................................19Technologies for Natural Ventilation ..................................................................................... 28Solar Chimney ................................................................................................................. 28Building Characteristics and Openings ........................................................................... 30Advantages of Natural Ventilation Systems ........................................................................... 33Comparisons between Natural and Mechanical Ventilation .................................................. 34Cooling Energy Savings and Li mits of Applicability ..................................................... 34Occupant Health, Comfort and Productivity ................................................................... 34Duct Cleanliness and Filtration ....................................................................................... 34Fan Power ........................................................................................................................34HVAC Equipment Cost and Space Requirements .......................................................... 35Ambient Air Quality ........................................................................................................ 35Disadvantages of Natural Ventilation Systems ......................................................................36Desiccants .................................................................................................................... ...........36Montmorillon ite Clay ...................................................................................................... 36

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6 Silica Gel (SiO2 H2O) ...................................................................................................37Molecular Sieve (Synthetic Zeolite Na12Al03SiO212XH2O) .........................................37Calcium Oxide (CaO) ......................................................................................................37Calcium Sulfate (CaSO4) ................................................................................................. 37Calculations for Amount of Desiccants ........................................................................... 37Desiccant in Commercial Buildings ................................................................................ 38How to Use Desiccants ....................................................................................................38Advantages of Desiccants ................................................................................................ 39Disadvantages of Desiccants ...........................................................................................39Design Suggestion for Hot and Humid Climate ..................................................................... 39Double-skin Facade Configuration .................................................................................. 39Benefits of Double Skin Facade ......................................................................................40Natural Ventilation Analysis and Design Tools .....................................................................40LoopDA Natural Ventilation De sign and Analysis Software ......................................40AIOLOS Software ...........................................................................................................42Autodesk Ecotect .............................................................................................................43Ventilation and airflow in Autodesk Ecotect ........................................................... 43Prevailing winds .......................................................................................................44Disadvantage of Ecotect fo r natural ventilation .......................................................44Green Building Studio .....................................................................................................44Input of green building studio .................................................................................. 44Output of green building studio ............................................................................... 44Advantages of using Green Building Studio ............................................................ 45Simplified Calculations of Air Change ........................................................................... 45Computational Fluid Dynamics-CFD .............................................................................. 47Summary ....................................................................................................................... ..........483 RESEARCH METHODOLOGY ...........................................................................................62Introduction .................................................................................................................. ...........62Wind Tower or Badgir as a Specific Kind of Ventilation Design ..........................................62Analytical Tools for the Examination of Natural Ventilation with a Badgir ......................... 63Autodesk Ecotect Process ...................................................................................................... .63Inputs Required for Autodesk Ecotect are as following. ........................................................ 63Simplified Calculations Based On Psychrometric Chart ........................................................ 63Input of Psychrometric Chart .................................................................................................. 64Average Temperature ......................................................................................................64Relative Humidity ........................................................................................................... 64Dew Point ........................................................................................................................64Air Change Calculation ...................................................................................................65FLUENT Package ................................................................................................................ ...65Input of FLUENT Package ..............................................................................................66Badgir Model Information in FLUENT Package ............................................................ 68

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7 4 RESULTS AND ANALYSIS................................................................................................. 82Introduction .................................................................................................................. ...........82Similarities between Wind Towers/Badgirs of Buildings in United States and Middle East with New Techniques .............................................................................. 82Benefits of Badgirs in Green Building/Sustainable Building ..........................................82Autodesk Ecotect, Simplified Calculation and FLUENT package ................................. 83Autodesk Ecotect ....................................................................................................................83Simplified Calculations of Air Change ................................................................................... 84FLUENT Package ................................................................................................................ ...84Results of Building with Badgir ...................................................................................... 84Results of Building without Badgir .................................................................................865 CONCLUSIONS ................................................................................................................... .96LIST OF REFERENCES ...............................................................................................................99BIOGRAPHICAL SKETCH .......................................................................................................103

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8 LIST OF TABLES Table page 2-1 Temperature and wind speed of outside air and badgir air ................................................ 59 3-1 Maximum and Minimum Temperature in Gainesville, Florida ......................................... 73 3-2 Average Relative humidity (%) .........................................................................................73 3-3 Wind Speed (m/s) .......................................................................................................... ....77 4-1 Requirements for typical badgirs in different climate regions ........................................... 88

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9 LIST OF FIGURES Figure page 2-1 Schematic of wind-driv en cross ventilation. ...................................................................... 49 2-2 Buoyancy-driven stack ventilation ....................................................................................49 2-3 Schematic of single-sided ventilation ................................................................................50 2-4 Schematic of stack ventilati on with sub-slab distribution ................................................. 50 2-5 Different parts of badgir.................................................................................................. ...51 2-6 Comparison between inside temperature (C) and height of badgir (m ) of Yazd University in Yazd, Iran, year 2003 at 3:00 pm for 10 days period ..................................51 2-7 Space under badgir which has water reservoi r (ab -anbar) located under holed slab. ........ 52 2-8 Plan of badgirs with six a nd eight interior wall dividers ................................................... 52 2-9 Badgir with four in terior wall dividers .............................................................................. 52 2-10 Badgir with eight in terior wall dividers .............................................................................53 2-11 Badgir in Dolat-abad in Yazd, Iran .................................................................................... 53 2-12 Plan views of different wind towers ..................................................................................54 2-13 Typical plan of four directional wind towers ..................................................................... 54 2-14 Flat badgir roof in Yazd, Iran ............................................................................................54 2-15 Badgir with shed roof in Yazd, Iran ................................................................................... 55 2-16 Circulation of air dur ing the day and night ........................................................................ 55 2-17 Stairs under badgir columns to water reservoir (ab-anbar) ................................................56 2-18 Modern badgir or Kolah Farangy Badgirin Tabas, Iran. ................................................56 2-19 Circulation of air thr ough a building with badgir .............................................................. 57 2-20 Section of badgir with dampers and small pool underneath .............................................. 57 2-21 Cross section of a building in Zion National Park visitor center .......................................58

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10 2-22 (a)Comparisons between percentage of relative hum i dity and water capacity in different desiccants, (b) Comparison betw een time in hours and water capacity of different desiccants ............................................................................................................58 2-23 Evaporative cooler ....................................................................................................... ......60 2-24 CFD model ................................................................................................................ .........60 2-25 CFD model ................................................................................................................ .........60 2-26 Plots of prevailing winds from weathe r data, showing annual wind frequency and speed (left) and summ er wind temperatures (right). .......................................................... 61 2-27 Solar chimney ............................................................................................................ ........61 2-28 Window openings .......................................................................................................... ....61 3-1 Three dimensional view of a simplif i ed Rinker Hall in Ecotect Software ........................ 71 3-2 Locational Data and Prevailing winds ............................................................................... 71 3-3 Hourly temperatures ....................................................................................................... ....72 3-4 Psychrometric chart ....................................................................................................... ....74 3-5 Wind directions state ..........................................................................................................75 3-6 Wind direction local ...................................................................................................... .....76 3-7 15 year average MSLP (mean sea level pr essure), JJA (June, July, and August) and DJF (December, January and February) months. .............................................................. 78 3-8 Rinker Hall model in meter in FLUENT package ............................................................. 79 3-9 Computational domain (Rinker Hall) and the elem ents that were used in this study ........ 79 3-10 Badgir. ................................................................................................................................80 3-11 Rinker Hall first floor plan ............................................................................................. ....80 3-12 Rinker Hall main entrance ................................................................................................ .81 4-1 Monthly diurnal averages ..................................................................................................89 4-2 Weekly summary ............................................................................................................ ...89 4-3 Monthly rainfalls ................................................................................................................90 4-4 Prevailing winds .......................................................................................................... .......90

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11 4-5 Prevailing winds .......................................................................................................... .......91 4-6 Hourly operational profile ..................................................................................................91 4-7 Weekly data ............................................................................................................... ........92 4-8 Monthly diurnal averages ..................................................................................................92 4-9 Thermal comfort ........................................................................................................... .....93 4-10 Velocity contours of the building with Badgir .................................................................. 93 4-11 Static Pressure contours of the building with badgir .........................................................94 4-12 The temperature contours in the building and the volum e average of the temperature in the building with badgir .................................................................................................94 4-13 The pressure contours in the building ................................................................................ 95 4-14 The temperature contours in the building .......................................................................... 95

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12 Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Master of Science in Building Construction NATURAL VENTILATION IN BUILDI NGS AND THE TOOLS FOR ANALYSIS By Romina Mozaffarian August 2009 Chair: Robert J. Ries Cochair: Svetlana Olbina Major: Building Construction Natural ventilation is using natural air to cond ition the interior of a building with minimal mechanical equipment. In other words, it is ve ntilating the building with natural air. Natural ventilation offers the means to control air qual ity in buildings, to dir ectly condition indoor air with cooler outdoor air, to i ndirectly condition indoor air by ni ght cooling of building thermal mass, and to provide refreshing airflow past occupants when desired. Implementing natural ventilation for conditioning can reduce electrical consumption, can recover the valuable building space typically used by all-air mech anical systems, can potentially provide health, comfort, and productivity advantages, in buildings and incr eases the efficiency of energy and material resources which are the purposes of a sustaina ble building, or green building. The objective of this study is to improve the environmental perf ormance of ventilation and temperature control systems in buildings by using na tural ventilation instead of mechanical systems. The main focus of this study is natural ventilation through wind. By using a technique for natural ventilation, the outdoor air can be introduced into the building to circ ulate air. Another primary focus is the selection of software for modeling a build ing with a natural ventilation system.

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13 CHAPTER 1 INTRODUCTION Introduction Studies have shown that it is difficult to vent ilate buildings in diffe rent clim ates without using mechanical and/or elec trical equipment (McEneaney 2005). While historically all buildings employed natural ventilation, this pr actice has been disregarded due to developing electrical cooling and heating devices (McEneaney 2005). When the flow of kinetic energy or the buoyancy driven force of the ai r (convection) is used for ventilation purposes, then this type of ventilation is typically called natural ventilation. This research describes different techniques and designs for natural ventilati on in buildings. Some advantages of having natural ventilation include reducing energy and opera tion costs, better indoor air quality, a healthier and more productive environment (Emmerich et al. 2001).This study focuses on natural ventilation caused by the wind. Review of literature reveals that a traditional wind tower or badgir can be a useful technique for natural ventilation. Problem Statement The use of a wind tower (badgir) on a building without m echanical equipment has not been commonly studied as a solution for natural vent ilation. Also, choosing software for natural ventilation in buildings was studied. The case study uses the hot and humid conditions in July in Gainesville, Florida. Humidity inside the case study building was not modeled or estimated for simplicity. The case study indicates that humidity is very likely to be high and outside of comfort parameters (ASHRAE 55). Research Objectives The objectiv e of this study is to improve the environmental performance of ventilation and temperature control systems in buildings by us ing natural ventilation instead of mechanical

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14 systems. Natural ventilation can reduce the elect rical consumption of buildings by using natural resources such as wind and solar energy. The main focus of this study is natural ventilation through wind. By using a technique for natural vent ilation, the outdoor air can be introduced into the building to circulate air. Mo reover, if the air pa sses over a water reservoir it can reduce the inside temperature of the build ing, though it is also likely to in crease relative humidity. Another primary focus is the selection of software fo r modeling a building with a natural ventilation system. A case study building, Rinker Hall, School of Building Constructi on at University of Florida has been modeled with three tools, Autodesk Ecotect, simplified calculations of air change and Computational Fluid Dynamics software. At the end, the result of each tool has been compared, evaluated and a recommendation made. Significance of the Study A sustainable building, or green building is an outcom e of a design which focuses on increasing the efficiency of resource use energy, water, and materials while reducing building impacts on hum an health and the environment during the building's lifecycle, through bette r design, construction, operation and maintenan ces (Frej 2005). Im plementing natural ventilation for conditioning can reduce electrical consumption in buildings and increases the efficiency of energy and material resources. Also by designing a badgir for natural ventilation in buildings, human health and healthy environm ent are enhanced. The result of this study determines the potential for natural ventilation and cooling air inside bu ildings with a minimum usage of electrical air conditioning equipment. Limitations of the Study One of the lim itations of this study is choosi ng user-friendly and precise software for the modeling. In over viewing available programs (Loop DA, AIOLOS, Autodesk Ecotect, Green Building Studio and Computational Fluid Dynami cs-CFD) the research b ecomes challenging. In

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15 addition, information and resources on natural vent ilation especially about wind tower or badgir as a kind of ventilation are often limited to sp ecific countries like Iran in which it is commonly used.

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16 CHAPTER 2 LITERATURE REVIEW Introduction Natural ventilation is ventilation provided by therm al, wind, or diffusion effects through doors, windows, or other intentional ope nings in the building (ASHARE 62.1 2007). Historically many buildings in the past us ed natural ventilation. It is economical and energy efficient to cool the building without using any mechanical equipment. Natural ventilation supplies outdoor air to the interior of the building for ventilation and cooling. Natural ventilation can be substituted for part of a mechanical system th rough proper design and appropriate building location and use which he lps to reduce construc tion, energy and operating costs. Some benefits of having a naturally ventilated building are to provide indoor air quality and comfort, which leads to healthier and more productive building occupants (McEneaney 2005). Natural ventilation brings natural elements such as wind, humidity, and warm or cold air through design of building form to let fresh outd oor air in and indoor air out. Some ways of doing this include operable window s, exhaust vents located high in the building, intake vents located low in the building, atria, internal stairwells, ventilation chimneys and small fans (solar powered) and open building plans to facilitate air movement (McEneaney 2005). By reducing the size of mechanical systems, construction cost savings and energy savings due to natural ventilation will occur. Some of the benefits beside energy and cost savings are improving occupant health, quality of life, and productivity. Some st udies show that by creating a productive and healthy environment in buildings patients could make progress more quickly, students can receive a bette r grade, and residences sell or re nt more quickly (McEneaney 2005).

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17 Definitions of Natural Ventilation There are different definiti ons of natural ventilation. Ventilation provided by therm al, wind, or di ffusion effects through doors, windows, or other intentional openings in the building (ASHARE 62.1). The process of supplying and removing air through an indoor space by natural means (Roulet 2002). Passively supplying outdoor air to a building interior for vent ilation and cooling (Busby). Pressure differences between the inside and the outside of th e building (UFC 2004). Using local wind and temperature differences between the inside and outside of the building to move air through th e structure (Chastain 2000). W ind and thermal buoyancy as driving forces to create the desired thermal environment and transport away undesired contaminants (Kleiven 2003). Providing the fresh outdoor air in to a building and circ ulate it in the building or a room to dilute or remove pollutants (Li 2003). Based on different definitions of natural ventilation, specific de finition of natural ventilation has been used in this study. Wh en the Kinetic energy or the buoyancy driven force of the air is used for ve ntilation purposes, the type of ve ntilation is typically called natural ventilation. Different Kinds of Ventilation There are three kinds of natu ral ventilation system s: wi nd-driven cross ventilation, buoyancy-driven stack ventilation, single-sided ventilation, stack vent ilation with sub-slab distribution, hybrid ventilation and wind-stack driven ventila tion (Emmerich et al. 2001). Wind-Driven Cross Ventilation Having ventilation openings on opposite sides of a closed space is wind-driven cross ventilation. Figure 2-1 s hows a schematic of cro ss ventilation in multi-room building which is also called global cross ventilation. In order to have a sufficient ventilati on flow, there should be a significant difference in wind pressure between the inlet and outlet openings (Emmerich et al. 2001).

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18 Buoyancy-Driven Stack Ventilation Buoyancy-driven stack ventilation will happen based on density differences of cool and warm air. Figure 2-2 shows a schematic of stac k ventilation for a multi -room building. By a chimney or atrium, sufficient buoyancy forces will happen. Good design is the way to combine both wind effects and buoyancy effects in stack ventilation schemes (Emmerich et al. 2001). Single-Sided Ventilation In single-sided ventilation, singl e room s are ventilated. Figure 2-3 indicates a schematic of single-sided ventilation in a build ing. Driving forces for singlesided ventilation are relatively small and are highly variable. Th e least attractive natural vent ilation solution happens by singlesided ventilation. This ventilation provides ventilated air for indi vidual offices compared to other kind of ventilation (E mmerich et al. 2001). Stack Ventilation with Sub-Slab Distribution By using in-slab or acces s-floor distribution of fresh air, greater control of air distribution across the building section is observed. Figure 2-4 shows a schematic of stack ventilation with a sub-slab distribution system (Emmerich et al. 2001). Hybrid Ventilation Systems Hybrid ventilation system s attempt to combine the benefits of both natural and mechanical ventilation in an optimal way. The primary purpose of ventilation is to provide acceptable indoor air quality and indoor temperatur es. In natural ventilation, the forces of wind and air density differences are used to m ove air through the build ing (Heiselberg 1999, Heiselberg 2000). Hybrid ventilation takes advantage of natural ventilation forces, using mechanical forces only when natural forces ar e not sufficient. The combination of natural ventilation and modern design techniques, materi als and control strategies has great potential (Szikra 2000). This modernized technique for designing new buildings a nd retrofitting requires

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19 more integrated design and construction of buildings, more thermal insulation, reducing noncontrolled in filtration and using mechanical ventilation systems with heat recovery. Today higher indoor air quality is required, so mechanical ventila tion systems consume considerable amounts of electric energy for fans and heat through the heating co ils. It is possible to apply traditional natural ventilation systems. Although it does not provide the acceptable comfort level for the occupants and consumes large amounts of en ergy to heat the fresh ai r. So, the solution is a hybrid ventilation system that combines natural and mechanical driving forces. A hybrid ventilation system can be described as a system with a comfortable internal environment using different features of both natura l ventilation and mechanical systems at different times of the day or seasons of the year. It is a ventilation system where mechanical and natural forces are combined in a two-mode system. Hybrid ventilati on is a two-mode system which is controlled to minimize energy consumption while maintaining acceptable indoor air quality and thermal comfort. The two modes refer to natural and mechanical driving forces. The purpose of its control system is to establish the desired air change rate but lowest possible energy consumption (Heiselberg 1999, Heiselberg 2000). Wind-Stack Driven Ventilation This m ethod has been used in ancient times in hot climates. Two methods have been used in ancient buildings in Iran: curved-roof air vent systems and wind tower systems. Wind tower systems are as old as 4000 BC. Malkaf or wi nd-catch was used by ancient Egyptians in the houses of Tal Al-Amarna as well (Allard 1998). Wind Catcher or Badgir Central Iran has a very large da y-to-night tem perature differen ce, ranging from very cool to extremely hot. The air tends to be very dry all day long. Most buildin gs are constructed of very thick ceramics with extremely high insulati on values and thermal mass. Furthermore, towns

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20 centered in the desert tend to be packed closel y together with high walls and ceilings compared to Western architecture. Maximi zing shade at ground level helps lower the temperature in these areas. The heat of direct sun light is minimized with small windows that do not face the sun. Southern Iran has a very similar climate to Flor idas weather. These southern cities are near the Persian Gulf, which has a hot and humid climate. Because of the heat, humidity, and wind in central and southern Iran in summer seasons, wind towers or badgirs have been used and are one of the masterpieces of Iranian engineering. Badgirs have been us ed to cool the buildings with natural ventilation for centuries since 4th millennium B.C. (Bahadori 2008). Different components of badgir: Badgirs have different part s in different heights. Different parts of the badgir are as follows (Bahadori 2008): The roof of the badgir, which is located at th e top of badgir in different shapes and sizes. The body of the badgir, which is located on the top part of the badgir and has openings in order to capture winds. The column of the badgir, which is located on the bottom part of the badgir and conducts wind into the building or water re servoir (Ab-Anbar) (Bahadori 2008). Figure 2-5, shows different part s and heights of badgir as it has been explained (Bahadori 2008). Some cities of Iran such as Yazd, Kashan and Esfahan have daily winds. Badgirs are typically built toward the direction of the winds. Interior walls of badgirs are divided to one, two, four, six and eight divisions. The top part of the badgir (roof of the badgir) is toward the sky and is closed. The bottom part of the badgir is toward the column and the building. Sometimes badgirs conduct the wind toward an Ab-anbar (water reservoir) in the bu ilding in order to have better cooling. The bottom part of badgirs, or the column of badgi rs, has thicker walls than the rest of the badgir (Bahadori 2008).

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21 Main objective of badgir installation: The main task of badgir is conducting the outdoor wind into the building and either circulating the air or cooling the building (or both) in order to provide a comfort zone for liv ing or working (Bahadori 2008). Badgir and architecture: South and central regions of Iran have different climates. Each of these climates has its own specific archite cture. Building a badgir was one of the most important parts of design in the old architecture of Iran. Many badgirs have been used in different designs and sizes in the buildings to have a better conditi on inside the building. Badgirs could either be part of the build ing, sit on top of the roof, or be attached to the building. Badgirs may have been used for beauty and decoration of the home as they were for cooling buildings by natural ventilation (Bahadori 2008). Material and color of badgirs: The materials forming the wind-catcher structure are important. Due to the high fluctuation of temper ature between day and ni ght in the hot and dry climate, the badgir usually constructed with mu d-brick, becomes cool at night by radiation and convection. During the day, sun-dried brick walls prevent th e heat of the outside air from entering the building. During the cooler night, th is kind of material allows the ab sorbed heat to be released to the inside of the building. The sun-dried brick wo rks as insulation and also as the heating source for buildings (Bahadori 2008). In hot and dry clim ates like Yazd in Iran, mud-brick or brick together with plaster of cob (clay and straw) are the main materi als of the badgir. Mud brick has high thermal mass. The wind-catcher faade in this climate is plastered with cob. Its bright color helps to reflect the suns radiation from the wi nd catcher surface and its non-absorption by that surface. At the same time, the presence of straws inside the mud increase s coarseness of faade texture, which hinders the absorption of sun radiation. In hot and humid climates like Bandar

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22 Lenghe in Iran, plasters and lime plasters which ha ve white color are being used. These materials prevent humidity penetration into walls of wind catcher. Their white colo r hinders sun radiation absorption and increases its reflection (A'zami 2005). Light colors painted on external surfaces of buildings decrease the daily temperature increase caused by the suns radiation. Therefore, it increases thermal stability. Gatch plastering is one of the most common plastering used in Ir anian architecture. This plastering absorbs solar energy and it has been used on ex terior surfaces (Bahadori 2008). Height of badgirs: Heights of badgirs are different based on different climates. Usually, badgir is shorter in hot and dry weather. The height of the badgi r affects the temperature of air inside the buildings. In figure 26 shows how the temperature of air inside the building depends on height of the badgir. When the height of a ba dgir is larger, the temperature is higher mainly due to the heat absorption of th e column of the badgir in the sun. The taller the badgir is, the better its ability to dir ect the wind. Typically, the height of badgirs is 5 meter (Bahadori 2008). Opening of badgir: The length of each opening is a minimum of about 20cm. The thickness of the wall between the openings is 8 to 10 cm. Based on these calculations, the builders could have known how many openings were needed. Usually there are more openings to direction of the wind. Also, the la st two openings of badgirs are us ually closed to increase the effectiveness of the winds circulation. There are thin wood en pieces protruding from the openings of the badgir. These w ooden pieces are in about every di stance of 2-1/4 meters. These wood pieces are not only for strengthening the struct ure but also to balance the weight (Bahadori 2008). Figure 2-20 shows where the wooden pi eces are located in badgir columns. Badgir column: If the badgir is tall, wooden cradling or gatch /plaster cradling, framework for supporting a coved or vaulted ceiling, is used every 2 meters. This system starts from the

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23 bottom of badgir. Without this system, the wind would enter and leave through the opening in the badgir directly across from its entrance. Usua lly interior divider walls are diagonal (Bahadori 2008). Bottom of badgir: There are some badgirs which have a small pool or the ab-anbar on the bottom which is connected to the building where the badgir is located. On top of these small pools or ab-anbar, there is a squa re opening of 1m to 1.5m dia gonal and height of 1.5m. Figure 2-7 shows the opening on top of the ab-anbar of a build ing with a badgir located in Yazd-Iran (Bahadori 2008). Roof of badgir: Badgirs with ab-anbar unde rneath have usually six to eight interior walls or dividers in order to conduct air to the ab-anbar (Figure 2-8). Th ese kinds of badgirs are usually located in hot and dry climates like Yazd in Iran because in th ese climates direction of winds changes a lot. Figure 2-9 shows a badgir with four interior wall divisions in a residential building in Yazd, Iran. These kinds of badgirs are usually located in hot and humid climates because in these climates the direction of winds doesnt ch ange a lot. Figure 2-10 shows a badgir with six interior wall divisions. These kinds of badgirs are usually located in hot and humid climates because in these climates the direction of winds changes a lot. The roof of the badgir is usually wooden. The roof is sometimes bowl-shaped to hol d water which evaporates to cool the surface. Now, with new technologies, pipes are used in order to expel water outside the building. The tallest badgir of this kind is located in Dolata bad garden in Yazd (Fi gure 2-11) (Bahadori 2008). The four directional towers, chahar-tarafe are the most popular wind towers. They have four main vertical shafts divided by partitions. Most of the wind towers in hot and dry regions use this kind of configuration. This kind of th e tower is very common an d locally is called the Yazdi Tower in Yazd (Azami 2005).Figures 2-12 shows di fferent structures that wind towers or

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24 badgirs can have. Figure 2-13 show s typical plans of four directional wind tower or badgir. (Azami 2005). Orientation of badgirs: Badgirs openings are located in the direction of the wind. Because wind is the principal driving force for natural ventilation in badg ir systems, architects must know the direction of the wind in the specific region in wh ich the building is located in order to design a badgir (Bahadori 2008). Sizes of badgir in different climates: The sizes of badgir roofs depend on varying climates. Flat badgir roofs with a size of 1meter x 1meter and badgir heights of 3-5meters are typical for hot and humid climates (See Figure 2-14) (Bahadori 2008). Shed badgir roofs with size of 0.5 meter x 0.5meter or 1.2meter x 0.6meter and a height of 1.8 2.1meters are typical for hot and dry climates (see Figure 2-15) (Bahadori 2008). Detailed structure of wood and plast er in badgir without new technology: Because plaster did not adhere well to wood, early badgirs in Iran used a thick rope called Sazoo. Sazoo was wrapped around the end of wood, which helped the wood adhere to the plaster (Bahadori 2008). Badgirs performance during the day: During the day, hot weat her outside meets the body of the badgir which had been cooled from the night before. The outside hot air transfers its heat to the column and walls inside the badgir. In this process, the hot air is cooled in the column of the badgir. The density of the air increases and thus air it fl ows inside the building and cools the building. Finally, the air leaves the building through th e windows, doors and openings. Figure 2-16 shows the circulation of air in badgir dur ing the day (Bahadori 2008). Badgirs performance during the night: During the night, colder outside air comes inside the building through windows and doors. Because c ooler air has higher density, it stays on the

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25 bottom and the hot air rises. This pressure differe nce circulates the air causing to cold air come inside the building and cool it. Th e stored heat from the column of the badgir that is hotter than the ambient air is transferred to the air. Since the hot air has le ss density, it rises in the column and leaves the building from the openings in the badgir. The cold ambient air replaces this air through the windows and doors of th e building. Figure 2-8 also shows the circulation of air in badgir during the night (Bahadori 2008). Badgirs in windy condition: When there is a windy conditi on, the wind passes through the openings of the badgir, through doors, and through windows. This causes a pressure difference, which helps with the circulation of air inside the bu ilding. This pressure difference allows the outside air from various openings to come inside the bu ilding and exit through the windows, doors, and other openings of the badgirs which are against the direction of the wind (Bahadori 2008). Badgirs with ab-anbar: Badgirs with Ab-anbar (water reservoir) system usually are located in places with hot and dry climates, such as in the city of Bam, Iran (Bahadori 2008). Outside air passes through a channel and evapor ates water in the Ab-anbar (a small pool underground). Evaporation decreases air temperatur e and increases the relative humidity of air. Therefore the outside air becomes cooler and circulates throughout th e building, cooling the building. Finally, the air leaves the building through the windows and doors. Figure 2-17 shows the stairs and the conducting channel to an ab-anb ar underneath a badgir in Yazd, Iran. Figure 27 as it has been explained before shows the sp ace underneath a badgir. This badgir located in Yazd, Iran has ab-anbar underneath a holed slab (Bahadori 2008). There are other badgirs which are called Kolah Fara ngy. These badgirs have dome shapes which have different layers or steps (See Figure 2-18). They have openings covered with

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26 nets. These badgirs share the same functions an d processes in cooling the building as other badgirs (Bahadori 2008). The process of air circulation throughout the building: Figure 2-19 shows the processes of the circulation of air th roughout a building (Bahadori 2008): The air enters to the building at the point 1. Some of the wind exits at the poi nt 2: Usually it happens for ba dgirs with only one interior wall divider which is not common. Some of the wind passes points 3 to 4 and 5. If the point 4, where a control doo r is located, is closed, all of the outside air passes through points 3 to 4. If the point 4 is open, where a control door is located, all of the outsi de air passes through points 3 to 5 and cools the building. In this process, outside air will confront with the air which pa sses through underground water which is humid. The outside air starts the evaporation process and loses its heat, become cold air and cools the building. The n, air exits the buildi ng through windows or doors which are shown in fi gure 2-10 (Bahadori 2008). As a result, the building will have natural ve ntilation without any electrical equipment. Often, underneath the badgir, the temperature can become uncomfortably. So, a room exists underneath the badgir with control doors than can be used to redirect the flow of air (Bahadori 2008). Badgirs with new techniques/dampers: There are places in Iran which the speed of wind is very low. In these places, there are badgirs with wet surf aces called dampers (Figure 2-20). These surfaces have small holes which are wet. There is a pump which directs water from a small pool or ab-anbar to the t op of the building with badgir. A fountain is located on top of a clay surface in the top pa rt of the badgir. The water is used to keep the dampers wet. When the wind passes through the small pool or ab-anbar, water evaporates and the air is cooled. Colder air

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27 has higher density than the outside air and this ca uses the circulation of air inside the building (Bahadori 2008). Wind tower in Zion National Park visitor center, United States: Zion National Park Visitor Center applied a wind tower for natural ventilation in United St ates (See Figure 2-21). The weather condition in this area in summer is hot and dry, in wint er is cold and icy. In this building, downdraft cooling towers are the prim ary cooling system. Cool towers work like a chimney in reverse. Water is pumped onto a honey comb media at the top of the tower. Ambient air passes through this system evaporating water. Then cooled air, which is denser than the ambient air, falls through the tower under its own weight. Fina lly, it enters the building. When this natural ventilation system works, no fans are required to cool the building. Windows are strategically placed in the building to relieve hot air. Then, cool air moves through the space. The cool towers enhance energy performance. Also th ey give the building a unique aesthetic style. These wind towers are inspired by the evaporativ e cooling effects of the Virgin River slot canyon, which makes Zion famous (Torcellini et al. 2002). Mechanical input to the cooling system in Zion National Park visitor center: The only mechanical input to the cooling system is a pum p which circulates water through the evaporative media. This system is useful especially in hi gh ventilation rates in the summer when there are a lot of visitors in the building. Al so, when there is a low ventilati on rate in the winter and there are fewer visitors. Natural infiltration also pr ovides adequate ventil ation during the winter (Torcellini et al. 2002). The cool towers provide cooling to the main area of the visitor center. Visitors find the towers fascinating as a beautiful architectural element and give them special attention. The interaction of the visitors with the cooling system provides an attractive place that normally

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28 would not be achieved with a traditional cool ing system. Wind towers operate whenever a traditional single-stage evaporative cooler would operate. When the capacity of the cool towers cannot meet the building cooling loads, the building temperature drifts to the high 70Fs in summer. To minimize the number of days with high temperatures, the interior mass of the building is cooled by nighttime natura l ventilation (Torcellini et al. 2002). Results of temperature based on different time and wind speed: Table 2-1 shows the result of tests from the badgir with dampers in Yazd University in Iran on September, 11, 2003. This result shows that temperature of outside ai r drops after going thr ough the badgir process. Also, the wind speed drops after the badgir process at a different time of the day. The temperature of the air going to the building is almost constant. This is due to the high heat capacity of the water in the ab-a nbar which behaves like a heat sink since it has easy heat transfer with the ambient soil. The soil te mperature (ground temperature) is almost constant and does not change significantly day by day or season by season. This fact is used later in CFD modeling. The average of difference temperature is 13.26C (Bahadori 2008). Technologies for Natural Ventilation Solar Chimney A solar chimney is one of the ways of i mproving natural ventilation in the building. Solar chim neys in buildings help to reduce energy usage, CO2, and pollution in general. The solar chimney has been used for centuries in different places, especially in the Middle East and by the Romans. A solar chimney is a vertical shaft utilizing sola r en ergy to help the natural stack ventilation through a building (Bansal et al. 1993). The solar chim ney consists of a black-painted chimney that ab sorbs the heat during the day to ventilate the building. There is a suction created at the chimney s base which can be used to ventilate and cool the building. In hot, windless days, a sola r chimney provides ventilation.

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29 Badgir is a name which has been used to descri be solar chimneys in the Middle East and has been explained in the research (Bansal et al. 1993). Solar Chimney consists of various parts. The Solar Collector Area: On the top part of the chimney or in the entire shaft, there is an area which is called the solar coll ector area. In order to utiliz e and retain solar gains, the type of glazing, orientation, insulation, and thermal properties are important. The Main Ventilation Shaft: The height, loca tion, cross section, and the thermal properties of the structure have important effect on ventilation shaft. The Inlet and Outlet Air Openi ng: The sizes and locations of where the openings are found have significant outcome (Bansal et al. 1993). Based on Figure 2-27, this solar chimney provide s passive home cooling by allowing air to enter in from the bottom and rise out at the top (Bansal et al. 1993). To have a better result using a solar chimney, its location needs to be higher than the roof level and oriented to the direction of the sun. Using a glazed surface on opposite side of the chim ney will cause more heat gain. Openings in the vents in the chimney can be located away from the direction of the wind. By allowing incom ing air to pass through underground ducts before entering the building, the cooling effect is m aximi zed (Bansal et al. 1993). The use of a solar chimney benefits natural ve ntilation and passive co oling strategies of buildings and reduces energy use, CO2 and pollution. Other benefits of using solar chimneys for improving natural ventilation are to have a be tter ventilation on hot days in the building, reducing dependence on wind and wind-driven vent ilation, improving control of air flow through a building, and helping to have a better choice of air intake, improving ai r quality, reducing noise levels in urban areas, increasing night time vent ilation rates and also minimizing the use of fossil fuel energy ( Bansal et al. 1999).

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30 Building Characteristics and Openings The ventilation rate in a natura lly-ventilated building depends on some characteristics such as wind speed, temperature difference between th e interior and exteri or, the size of the ventilation openings, and the distance betw een openings. The wind speed and temperature differences cannot be controlled and cha nge based on the location. So, the design and management of a natural ventilation system con centrates more on the placement and sizing of the openings. The following are different openings used in naturally-ventilated buildings. The size of the openings, the climate of the lo cation and the specific season of the year can control the ventilati on rate (Chastain 2000). Sizing of Ridge and Eave Openings for Winter Ventilation: Adjustable eaves and stationary ridge vents had been one kind of ventil ation used in cold and temperate regions. They provide ventilation for moisture control a nd temperature modification (Chastain 2000). Ridge Opening: A continuous stationary open ridge th at runs through the entire building is one of the best ways of ventilation. It prov ides a minimum ridge opening of 6 inches for all dairy buildings up to 30 ft wide and 2 inches of open ridge for every 10 feet of building width for wider buildings (MWPS-7 1995). The spaces between the trusses can be used for eave vents. There should be enough spaces to at least of the ridge vent size (1 in per 10 ft of building width) to let the vent to be open for better airflow during mild winter weather (Chastain 2000). Roof Slope: The roof slope is one of the importa nt factors in designing a naturally ventilated building. It needs a r oof with a 4/12 pitch for enough separation distance between the eave and the ridge opening (Chastain 2000). Windows: There are different kinds of window wh ich let natural ve ntilation pass through. The area of openings can control the amount of airflow which flows. Figure 2-28 shows different window openings. Horizontal pivot windows provide the highest ve ntilation capacity as shown

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31 on the right side of Figure 2-28. Horizontal pivot windows have mo re ventilation capacity than center vertical pivot wi ndows. Casement windows and pivot windows have the same advantages and the difference is casement windows are open to strong blast of the wind. With bay windows, pressure differences can be localized (Iannone 1999). Passive Cooling Systems: Applying passive cooling techni ques is one of the most important parts in designing a building. Saving energy and reducing pollution are some of the environmental and economical benefits (Ia nnone 1999). Some of these passive cooling techniques are as follows: Architectural methods: the domed roof, vaulte d roof, ventilated roof, high roof and double roof. Ventilated roofs include the naturally-ventilated, advanced naturally-ventilated, micro -and artificially-ventilate d roof (Iannone 1999). Domed and Vaulted Roof: This kind of roof has been used usually in hot and dry regions. There is a small opening at the t op of these roofs. The material of these roofs are made from locally-available material such as stone or bric k masonry and covered with a plaster finish. The opening of the roof is an escape path for hot air and for ventilation. Curved roofs reflect more radiation than flat roofs. Since thermal stratification causes hot ai r to gather within the building in space under the roof, a significantly comfortabl e feeling will be created at the floor level (Sanjay 2008). Curved Roofs: Curved roofs absorb more diffuse ra diation than the flat roofs but the amount of beam radiation is as same as flat one s. Curved roofs with an opening on top are more energy efficient in hot arid climatic conditions for natural ven tilation (Sanjay 2008). Ventilated Roofs: There are naturally ventilated, ar tificially ventilated and microventilated roofs. Ventilated buildings are stru ctures that have hollow walls and roofs through

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32 which a certain amount of air-flow is maintained The air-flow is regulated in a way that minimum heat is transferred to or from the building interior and ex terior (Sanjay 2008). Naturally Ventilated Roofs: Wind pressure can ventilate the buildings naturally. Then, an air flow will drive to cool the building. Mechan ical energy will not be used. During daytime, the air gap performs as an extra insu lating layer in the vent ilated building. The in sulation layer of air has lower temperature in ventilat ed building than a typical buildi ng surface. Even though, the air flow velocity in the gap is lower than the am bient wind speed. Part of the daytime heat gain transfers to the air in the ga p. Because of natural convection, the air flowing through the gap renews this air. Therefore, inside wall/roof surface wont warm up. This technique has been traditionally used in buildings centuries ago (Sanjay 2008). Artificially Ventilated Roofs: The air flow in artificially ven tilated roofs is due to forced convection. Mechanical methods for example blower, induced draught fans are some of forced convections. In the process of flowing air throug h air gaps, the temperature of room air reduces. So, the room air will become more comfortable and better (Sanjay 2008). Advanced Naturally Ventilated Roofs: Internal sources of heat can warm the air and drives the air flow. So, when ther e is internal source of warmth in cluding at night, airflow can be assured at all times (Sanjay 2008). Micro-Ventilated Roofs: Roofs with small sized thickne ss ducts are micro-ventilated roofs. There are two layers of terracotta tiles with small thickness in between. Terracotta tiles are made from clay and molded in the form of tile s. Ducts have been created by the two layers obtained by continuous opening along the eaves course (inlet) and along the ridge course (outlet) or even by insertion of special ve ntilation tiles. The air flows into these duct. The thickness of air

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33 duct can be 4 to 6 centimeter. When the air duc t thickness increases, the energy saving increases (Sanjay 2008). High Roof: Historical buildings have been marked by high roofs. In buildings with high roofs, warm air collects at the top and cool air re mains at the floor level. Therefore, at the floor level, the air temperature is in a comfortable zone (Sanjay 2008). Double Roof: In this kind of roofs, there are two r oofs or ceilings with an air gap between. There are usually two concrete cei lings one above the other with an air gap in between. The air gap performs as a thermal resistance between the fi rst roof, exposed to the heat of direct sun, and the second slab below (Sanjay 2008). Advantages of Natural Ventilation Systems Advantages of natural ve ntilation are as f ollows. Removal of mechanical air handling systems. Reducing cooling energy consumption. Eliminating the use of fan power required. Providing quantitative health, comf ort, and productivity advantages. Providing qualitative advantages of fresh air in the minds of most occupants. Having better control of thei r environments and less rest rictive comfort criteria. Reducing significant fraction costs of conven tional mechanical ventilation systems in commercial buildings. Eliminating the large sp atial requirements that conventional mechanical systems demand. Avoiding the duct cleanliness dilemma, and its a ttendant costs (Emmerich and Stuart Dols 2001).

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34 Comparisons between Natural and Mechanical Ventila tion There are more benefits to have natural vent ilation than mechanical ventilation. Some of these benefits are cooling energy savings, better comfort, productivity and occupant health. The following are some comparisons between using mech anical and natural ventilation in buildings. Cooling Energy Savings and Limits of Applicability Natural ventilation can pay costs of coo ling, the associated energy costs and carbon dioxide em issions. Based on where the building is located, this cost can change because of different buildings thermal performan ce (Emmerich and Stuart Dols 2001). Occupant Health, Comfort and Productivity Based on research in both European and No rth Am erican countries, there are lower symptoms in the naturally ventilated buildings compared to mechanical ly ventilated and airconditioned buildings (Mendell et al. 1996). Natural ventilati on systems can provide more healthful, comfortable, and productive environmen ts than mechanical systems. Architects have accepted natural ventilation as one of several objectives of high quality sustainable design (Emmerich and Stuart Dols 2001). Duct Cleanliness and Filtration Duct clean liness and building air quality ar e intimately linked (Limb 2000). Natural ventilation systems can solve this problem by replacing ductwork with ha bitable spaces that serve to direct naturally-driven airf lows (Emmerich and Stuart Dols 2001). Fan Power Natural v entilation can be accomplished by either natural means or mechanical means. In Cooling the building mechanically, fans become one of the mechanical means which use a significant amount of the energy (BRECSU 2000). By comparing to different mechanical cooling systems, naturally ventilated buildings in the United Kingdom offset from 20 kWh/m2 to

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35 60 kWh/m2 of fan energy consumption annually fo r cooling purposes, approximately $1.70/m2 ($0.16/ft2) to $5.20/m2 ($0.48/ft2) annually in energy costs. As a result, these savings account for approximately 15 % of total energy consumpti on in U.K. office buildings (Heikkinen and Heimonen 2000). HVAC Equipment Cost and Space Requirements HVAC equipm ent cost and space requirements mechanical heating, ventilating, and air conditioning equipment often are one of the large cost of constr uction of new buildings and the renovation of existing buildings. These costs may be expected to range from 35 % to 45 % of construction costs in larger o ffice and institutional buildings (Emmerich and Stuart Dols 2001). Consequently, by replacing or at least reducing mechanical syst ems for ventilation and cooling one of the potentially quite la rge cost savings can be saved (Emmerich and Stuart Dols 2001). Mechanical air handling equipment including fans, filters, heating and cooling coils, vertical distribution shafts a nd ducts, horizontal distribution du ct networks, dampers, supply diffusers and return grilles consume vast amount s of space. Therefore, mechanical equipments consume about 20 % to 40 % of the total volume of the building. Natura l ventilation systems recover much of this volume as occupied space for the spatial interior of the building. This recovered space (volume) may be used for formal architectural objectives or for daylight distribution (Emmerich and Stuart Dols 2001). Ambient Air Quality Another im portant issue in natu ral ventilation systems is th e impact of ambient air quality. Typical natural ventilation systems do not use filtr ation. The filtration in mechanical ventilation systems does not remove all contaminants from th e outdoor air. It generally includes some form of particle filtration. Natural ventilation help s improve indoor air qual ity. Also, it can control indoor humidity and airborne contaminants which are health hazards. So, the acceptability of

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36 having a better ambient air quality in natural ventilation systems must be considered (Emmerich and Stuart Dols 2001). Disadvantages of Natural Ventilation Systems Lack of heat recovery capabiliti es (E mmerich and Stuart Dols 2001). Difficult to control when natural driving fo rces are small (Emmerich and Stuart Dols 2001). Lack of filtration capabilities particularly urban, with high outdoor particle and gaseous contaminant concentrations (Emmerich and Stuart Dols 2001). Unable to control humidity especially in hot and humid climates (Bahadori 2008). Desiccants Controlling moisture has always been challengi ng for engineers. Controlling m oisture in hot humid climates is even more challenging. Desiccants are one of the materials which can be used to control moisture. To achieve optimum use of this material, temperature and humidity play an important role. The dew point is the mo st useful combined measure of temperature and humidity. Dew point is the temp erature at which the water vapor content of the air is at saturation. The dew point varies with the amount of water in the air. A desiccant will absorb the water vapor in the air and lower the humidity. Figure 2-22 illustra tes the absorption rate and the absorption capacity of different desiccants. Figu re 2-22 also shows how much each desiccant has a tendency to absorb water also effectiveness of each desiccant at different temperatures and extreme water vapor concentrations. There are diffe rent desiccants such as montmorillonite clay, silica gel, molecular sieve, calcium ox ide and calcium sulfate (Lavan 1982). Montmorillonite Clay Montm orillonite clay is a naturally occurring ab sorbent. This material has been created by drying magnesium aluminum silicate. This clay will successfully regenerate for repeated use at

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37 very low temperatures without significant corro sion or swelling. This clay is inexpensive and also its effectiveness within normal temp erature and humidity is high (Lavan 1982). Silica Gel (SiO2 H2O) This is the most commonly used desiccant whic h has been made from sodium silicate and sulfuric acid. Its pores have an enormous area which will absorb and hold water. Silica gel is very proficient at temperatur es below 77F (25C). It lose s its absorption capacity when temperatures begin to rise. One of the best bene fits of silica gel is its noncorrosive and non-toxic nature (Lavan 1982). Molecular Sieve (Synthetic Zeolite Na12Al03SiO212XH2O) Molecular sieve has an intern al absorptive surfac e area of 700 to 800 sq m per g. Because of its unique structure, molecular sieve does not abso rb moisture as much as silica gel or clay as temperatures rises. Molecular sieve is high in cost per unit (Lavan 1982). Calcium Oxide (CaO) Calcium oxide has a moisture absorptive cap acity of not less than 28.5% by weight. The unique feature of this material is that it will absorb a much greater amount of water vapor compared to other materials. It is most effective where there is a high concentration of water vapor (Lavan 1982). Calcium Sulfate (CaSO4) Calcium sulfate is an inexpensive material which is created by the controlled dehydration of gypsum. It is chemically stable, non-decomposed, non-toxic and non-corrosive (Lavan 1982). Calculations for Amount of Desiccants To determ ine the amount of desiccant to be used in the building, the calculations below is required (Lavan 1982).

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38 Amounts of desiccant required = K x V K = 0.161 (in gal.) or 0.0007 (in cu. in.) or 1.2 (in cu. ft.) V = the volume (in gal., cu. in. or cu. ft.). For calculating how much desiccant is needed, follow the steps below: (1) Calculate the volume of the building in cu. ft. (2) Determine the unit of desiccant required by using the formula above. (3) Select the type of desiccant that meets your needs according to Table 2-3. Desiccant in Commercial Buildings Desiccan t systems have been used over the la st 15 years as a component of HVAC systems in commercial buildings. There has been an improvement and benefits in buildings with desiccant component. More recently, active desiccant systems are used for ventilating systems. Desiccants which are solid are more common to use for commercial buildings (ASHRAE 1999). Places like supermarkets and refrigerated wareho uses, which all contain refrigeration systems, air become cool more effectively when most of the buildings moisture load is removed by an active (heat-reactivated) desiccant system. Active desiccants remove water from process air by adsorption which can apply by using wheels like Fi gure 2-23. These wheels dry the air with heat from natural gas. Dehumidification by adsorpti on provides enormous capacity compared to cooling-based dehumidification. A desiccant wheel only needs to dry the incoming fresh air, rather than drying all the air ci rculating through the restaurant. Th is keeps installed costs to a minimum which is very benefici al for commercial buildings. How to Use Desiccants One of the most common ways of using desicc ants in an air stream is to embed the material into a lightweight honeycomb shaped ma trix formed into a wheel. Supply air passes through one section where water va por is absorbed by the desic cant. Then the wheel rotates

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39 slowly into a second air stream which is known as the reactivation air. The air dries the desiccant and carries the moisture out of the buildi ng (ASHRAE 1999).Figure 2-23 illustrates how the system works. Advantages of Desiccants Active desiccant wheels dry deeply and achieve good control of hum idity. The quantities of moisture which can be removed by activ e desiccant wheels depend on (ASHRAE 1999): Air temperature and moisture of entering air The type and quantity of desiccant The depth of the wheel The surface area of the honey comb The velocity of air moving through the wheel The speed of wheel rotation Commercial desiccant wheels are usually set between 180F and 225F (82C and 107C). When the moisture from the supply air has be en removed, the temperature of the supply air is higher. By transferring from latent heat to se nsible heat, the temperatur e of the supply air rises 80% to 90%. The amount of energy or heat which ha s been released by a material or object is latent heat. Potential energy in the form of th ermal energy or heat is sensible heat (ASHRAE 1999). Disadvantages of Desiccants Active whee ls require heat input in order to dry the desiccant which adds to operating cost. Desiccant systems add to in itial cost (ASHRAE 1999). Design Suggestion for Hot and Hu mid Climate Double-skin Facade Configuration Other desig n suggestion for hot and humid climates is the double-skin faade configuration. Double-skin facades have differe nt layers or skins: construction, external, intermediate and inner skin. The external and internal skins can be made of single or double glazed glass panes of float glass or safety glass. At the intermediate space, there is an adjustable

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40 sun shading device for thermal control. There are different double skin constructions such as Box Window facade, Shaft-box facade, Corridor facade and Multi-story faade (Wong et al. 2006).The performance of the double-skin facade depends on the ventilation means. The modes of ventilation could be either natural or buoyanc y driven, forced or mechanically driven and mixed which is both natural and forced driven. This technique can be used in different climates like Florida as well (Wong et al. 2006). Benefits of Double Skin Facade There is a significant energy saving when natu ral ventilation is appl ied through the use of the double skin faade (Wong et al 2006). Computational Fluid Dyna m ic models have been used in order to find a new type of double-skin facad e configuration which pr ovides a better indoor thermal comfort in the hot and humid climate (Wong et al. 2006). Natural Ventilation Analysis and Design Tools This section presents a summary of the currently available tools for designing and analyzing natural ventilation syst em s in buildings. Outputs of some of these tools will be compared. Tools with easy access and better deta iled result will be chosen for research methodology. LoopDA Natural Ventilation De sign and Analysis Software The Loop Equation Design Method has been proposed for sizing ventilation airflow com ponents of natural and hybrid ventilati on systems. While the approach has been demonstrated on a limited basis, the method has been automated in order to better evaluate its reliability under a more controlled, less erro r-prone, environment. A computer program developed by National Institute of Standards and Tec hnology that im plements the Loop Equation Design Method of sizing which are the openings of na turally ventilated buildings. The tool, referred to as LoopDA for Loop Design and Analysis, is included with an existing multi-zone

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41 analysis tool. LoopDA provides th e designer of natural ventilati on systems with an environment in which to perform and document the process of designing the opening sizes of natural ventilation systems and analyzing the system behavior under a variety of operating conditions. The LoopDA program provides an example of its application to the design of a naturally ventilated building and describes needs for future enhancements to the tool to increase its usefulness within the design comm unity (Dols and Emmerich 2003). The Loop Equation Design Method consists of the following eight steps (Dols and Emmerich 2003): Lay out the global geometry and multi-zone topo logy of the natural ventilation flow loops for each zone of the building. Identify an ambient pressure node and additiona l pressure nodes at entries and exits of each flow component along the loops. Establish design conditions: wind pressure coefficients for envelope flow components, ambient temperature, wind speed and direction, and interior temperatur es; evaluate ambient and interior air densities. Establish first-order design criteria and appl y continuity to determine the objective design airflow rates required for each natu ral ventilation flow component. Form the forward loop equations for each loop established in step 1 above by systematically accounting for all pressure changes while traversing the loop. Determine the minimum feasible sizes for each of the flow components by evaluating asymptotic limits of the loop equation for the design conditions. Develop and apply a sufficient number of technical or non-technical design rules or constraints to transform the under-determ ined design problem defined by each loop equation into a determined problem. Develop an appropriate operati onal strategy to accommodate th e regulation of the natural ventilation system for varia tions in design conditions.

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42 AIOLOS Software It is sof tware which calculates the airflow rate, energy consumption and number of hours of overheating in natural ventilation configurations. This tool can be used for design purposes or simply for a deeper insight into mechanisms involved in natural ve ntilation (Allard 1998). The following possibilities are offere d by AIOLOS Software (Allard 1998): Calculation of the global airf low rates in simulated zone. Calculation of airflow rate th rough openings in the building Sensitivity analysis for examination of the impact of specific parameters on natural ventilation Find the best process of appr opriate opening sizes for rece iving best airflow rates. A thermal model for evaluating the impact of different natural vent ilation strategies on thermal behavior of the building. These calculations can be done for a short time period (a number of days) or an extended time period (up to a year). This to ol helps the user the possibility of fast evaluation of the climate in the region, which the building is located. Results are in tabular or graphical form. Statistical treatment is possible for a better under standing of the results (Allard 1998). This AIOLOS software has been used for hot and humid climate conditions like Florida (Andrade 2000). The following information can be establishe d from a model made by AIOLOS software (Andrade 2000): Climatic conditions for a given model. The use of natural ventila tion for cooling buildings. The air circulation through the building. Based on results, critical paths for air ci rculation through the building and the most suitable characteristics for the architectura l components are determined (Andrade 2000).

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43 The application of the simplified model will produce recommendations, in each step of an iterative process, leading, for example, to the redesign and relocation of ventilation ducts, inlet and outlet grilles, doors, windows, ventilated roofs or to the replacement of materials or constructional systems not compatible with ther mal comfort optimization, by natural means. The solutions defined by the simplified decision mode l will be, at the end, validated by comparing them to the solutions defined by the direct si mulation with a building physics tool (Andrade 2000). AIOLOS software will be used mainly to calculate airflows, energy consumption and number of hours of overheating. Vortex software will be used to characterize patterns of air circulation through the internal spaces of the building and also in the immediate external environment (Andrade 2000). Autodesk Ecotect Autodesk Ecotect is an industr y leading building an alysis program which allows designers to work in 3D and apply the tools necessary for an energy efficient and sustainable future. Ecotect is a complete building design and enviro nmental analysis tool that covers the broad range of simulation and analysis functions re quired to truly understand how a building design will operate and perform (ecotect.com website). Ventilation and airflow in Autodesk Ecotect Ecotect allows generating bot h the geom etry and analysis grids for export directly to computational fluid dynamics (CFD) tools such as NIST-FDS, FLUENT and WinAir4. After the calculations in these tools are complete, it is then possible to import result s back into Ecotect for display within the context of the original mode l. Figure 2-24 and 2-25 show the building with CFD analysis and results (ecotect.com website).

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44 Prevailing winds By using data in the hourly weather file, Ecotect can overlay wi nd speed and direction directly on top of the current m odel, making it es pecially relevant to na tural ventilation and wind shelter strategies. Then, this plot can also show temperature, humi dity and rainfall, over any date and time range (ecotect.com webs ite) as shown in figure 2-26. Disadvantage of Ecotect for natural ventilation The analysis routines in Ecot ect do not show detailed air-flow and ventilation inform ation. Green Building Studio Autodesk Green Building Studio enables architec ts to quickly calculate the operational and energy implications of early design decisions. The Autodesk Green Building Studio web service automatically generates geometrically accurate, de tailed input files for major energy simulation programs. Green Building Studio uses the DOE -2.2 simulation engine to calculate energy performance and also creates geometrically accura te input files for Energy Plus. Green Building Studio web service users are able to eliminate redundant data entry and dramatically reduce the time and expense traditionally associated with whole-building energy simulation analysis (energy.gov website). Input of green building studio Minim um manual inputs required from end users are 'building type' and 'zip code'. Users may specify additional input parameters to the ex tent they have been enabled in the BIM/CAD program's Graphical user interface. All other simulation variables supplied by the Autodesk Green Building Studio web service may be view ed and edited in other DOE-2.2 or gbXML compatible applications (energy.gov website). Output of green building studio Outputs for each des ign scenario modeled include:

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45 Estimated Energy and Cost Su mmary (annual, lifecycle) Annual carbon footprint specific to region and utility mix Renewable energy potential ( photovoltaic and wind) Weather data summary and user defined graphics Building and site specific natural ventilation potential US EPA Energy St ar comparison Water and day lighting preliminary analysis for LEED Energy End-Use Charts Building Summary of construction ar eas, equipment capacities, etc. gbXML file for import to Trane TRACE 700 or other gbXML-compliant tools DOE-2.2 file for import to eQUEST Energy Plus IDF file for editi ng and running in Energy Plus VRML file Advantages of using Green Building Studio Autodesk Green Building Studio reduces tim e and cost of building design and lifecycle management processes. Major bene fits include (energy.gov website): Enables hourly whole building energy, carbon and water analys es much earlier in the design process. Reduces design and analysis costs, allowing more design options to be explored within budget. Compression of early design time, speed ing project time to completion. Accelerates analysis for LEED compliance. Simplified Calculations of Air Change Data can be established f rom a psychrometri c chart in order to do calculations for air change. A psychrometric chart is a graph of the p hysical properties of mo ist air at a constant pressure which often equated to an elevation relative to sea level. The chart graphically expresses how various properties relate to each other (see Figure 3-26). The thermo physical properties found on most psychrometric charts are (Wikipedia 2009): Dry-bulb temperature (DBT) is the temperature of air measured by a thermometer freely exposed to the air which is shielded f rom radiation and moisture. In construction, it is an im portant consideration when designing a building for a certain climate (Nall 2004). It is

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46 typically the x-axis, the horizontal axis, of the graph. The unit for tem perature in psychrometric chart is Fahrenheit. The therm odynamic wet-bulb temperature (WBT) is a thermodynamic property of a m ixture of air and water vapor. When a volume of air is cooled adiabatically to saturation by evaporation of water into it, all latent he at will be supplied by the volume of air. The temperature of an air sample that has passe d over a large surface of liquid water in an insulated channel is the thermodynamic wetbulb temperature. This thermodynamic wet bulb temperature will become saturated (100 pe rcent relative humidity) by passing through a constant-pressure, ideal, adiabatic saturation chamber. Meteorologist and others may use the term "isobaric wet-bulb temperature" to refer to the "thermodynamic wet-bulb temperature". It is also called the "adiabat ic saturation temperature". The thermodynamic wet-bulb temperatur e is plotted on a psychrometric chart. The va lue indicated by a simple wet-bulb therm ometer often provides an ad equate approximation of the thermodynamic wet-bulb temperature. For an accurate wet-bulb thermometer, the wet-bulb temperature and the adiabatic saturation temperature are approxima tely equal for air-water vapor mixtures at atmospheric temperature and pressure ( VanWylen and Sonntag 1973). The dew point is that temperat ure at which a m oist air sample at the same pressure would reach water vapor saturation. The dew point is also called a saturation point. The dew point is assoc iated with relative humidity. A high relative humidity indicates that the dew point is closer to th e current air temperature. Relativ e humidity of 100% indicates that the dew point is equal to the current temperature and the air is maximally saturated with water. When the dew point stays constant and te mperature increases, relative humidity will decrease (VanWylen and Sonntag 1973). Figure 3-19 shows dew point in different tem peratures. Relative humidity (RH) is the ratio of the mole fraction of water vapo r to the m ole fraction of saturated moist air at the same temperatur e and pressure. RH is dimensionless, and is usually expressed as a percentage. Lines of cons tant relative humidity reflect the physics of air and water which are determined via experimental measurement. Relative humidity of 100% indicates that the dew poi nt is equal to the current tem perature and the air is maximally saturated with water ( VanWylen and Sonntag 1973). Humidity ratio is also known as moisture content, m ixing ratio, or specific humidity. Humidity ratio is the proportion of mass of wa ter vapor per unit mass of dry air at the given conditions (DBT, WBT, DPT, RH, etc.). It is typically the y-axis, the vertical axis, of the graph. For a given dew point, th ere will be a particular humidity ratio for which the air sample is at 100% relative humidity. Humidity ratio is dimensionless, but is sometimes expressed as grams of water pe r kilogram of dry air or gr ains of water per pound of air (Liddell and Scott) Specific enthalpy symbolized by h, also called h eat content per unit mass. It is the sum of the internal heat energy of the moist air in cluding the heat of the air and water vapor within. In the approximation of id eal gases, lines of constant enthalpy are parallel to lines of constant wet-bulb temperatur e. Enthalpy is given in joules per kilogram of air or BTU per pound of air (Liddell and Scott)

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47 Specific volume, also called i nverse density, is the volum e pe r unit mass of the air sample. The units are cubic meters per kilogram of ai r. Other units are cubic feet per pound of dry air (Liddell and Scott) Computational Fluid Dynamics-CFD Based on the contextual complexity of the physical phenomena and the needs of controlling indoor comfort, Computational Flui d Dynamics, CFD, is needed for natural ventilation system designs. The first applications of CFD were in the 1970s in building science. These codes have been used in designing natu ral ventilation systems in buildings. Simplified models can be used starting from the early stages of the design process, because the necessary calculating data are limited to only a few esse ntial parameters. It has been examined the application of CFD to predict passive airflows in buildings driven by internal heat sources and more recently assisting wind flows. CFD is based on little design steps, which are related to indoor environmental quality. It is possible to start from a simplified geometry and modify its form by little or single variations until arriving at a topologically corre ct ventilation system (Iannone 1999). FLUENT package could provide detailed air temperature, air velocity, contaminant concentration within the building or outdoor spaces. Based on long computational time and excessive computer resource require ments, the application of CFD for natural ventilated building have been limited (Wang and Wong 2006). Numerical flow mechanics (computational flui d dynamics CFD) is increasingly used for the solution of technical probl ems related to flows. At the Institute for Micro Process Engineering, the CFD software FLUENT is us ed along with the mesh generator GAMBIT. Use of the former software allows for the de velopment and optimization of a variety of microstructure devices. No prototype has to be constructed and tested in a timeand costconsuming manner.

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48 In order to simulate any flow, well know n fluid momentum equations called NavierStokes (N.S) equations should have been solv ed within the computational domain. These equations are the non-linear equa tions that obtained from th e momentum balance across the sample fluid control volume. The N.S equations in physics are one of the most complicated differential equations that govern physical phenomena. Since there is no analytical solutions for these equations for the complex geometries typi cally the N.S equations are solved numerically. The aforementioned solution is sometimes called Computational Fluid Dynamic (CFD) simulation. There are many commercial packages exist in order to solv e N.S equations. A well known commercial package is FLUENT. This packag e has been used in this study to solve N.S equations as well as energy e quation (FLUENT user manual 2006). Summary When the kinetic energy or the buoyancy driv en force of the air is used for ventilation purposes, th en this type of ventilation is typically called natural ventilation. Some of the benefits of natural ventilation beside energy and cost sa vings are improving occupant health, quality of life, and productivity. Based on the literature review, the wind towe r (badgir) has been chosen as the possible technique for natural ventilation without mechanical equipment that is examined in the case study. This technique has benefits for green buildings/sus tainable buildings which will be discussed in the results and conclusions. This technique adopts environmental energies such as wind for better natural ventilation. This technique had been used in mostly Middle East and other countries for centuries a nd it can be beneficial in new buildings. Different tools for analyzing natural ventilation have been researched to select the approach. Based on the literature review, Autodesk Ecotect, simplified calculation for air change by using psychrometric chart, and FLUENT package have been chosen as tools to model natural ventilation with a badgir. The use of the tools and their effectiveness will be discussed in the results section.

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49 Figure 2-1. Schematic of wind-driven cross ve ntilation (Source: Emmerich, Stuart Dols 2001). Figure 2-2. Buoyancy-driven stack vent ilation (Source: (Emmerich et al. 2001).

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50 Figure 2-3. Schematic of si ngle-sided ventilation (Source: Emmerich, Stuart Dols 2001). Figure 2-4. Schematic of stack ventilation with sub-slab distribution (Sou rce: Emmerich, Stuart Dols 2001).

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51 Figure 2-5. Different parts of badgir (Source: Bahadori 2008). Figure 2-6. Comparison between inside temper ature (C) and height of badgir (m) of Yazd University in Yazd, Iran, year 2003 at 3: 00 pm for 10 days period (Source: Bahadori 2008). Roof of badgir Roof of the building Badgir column Opening of badgir (wind intakes) 15 m 13 m 0.7 m 0.0 m Temperature( C) 9 10 11 12 13 14 15 16 17 18 40 35 30 25 20 15 HEIGHT (M)

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52 Figure 2-7. Space under badgir which has water re servoir (ab-anbar) located under holed slab. (Source: Romina Mozaffarian). Figure 2-8. Plan of badgirs w ith six and eight interior wall dividers (Source: Bahadori 2008). Figure 2-9. Badgir with four interior wall dividers (S ource: Romina Mozaffarian).

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53 Figure 2-10. Badgir with eight interior wall dividers (S ource: Romina Mozaffarian). Figure 2-11. Badgir in Dolat-abad in Yazd, Iran (Source: Romina Mozaffarian).

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54 Figure 2-12. Plan views of differe nt wind towers (Source: Azami 2005). Figure 2-13. Typical plan of four dir ectional wind towers (Source: Azami 2005). Figure 2-14. Flat badgir roof in Y azd, Iran (Source: Romina Mozaffarian). WoodenPieces Wooden Pieces

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55 Figure 2-15. Badgir with shed roof in Yazd, Iran (Source: Romina Mozaffarian). Dashed Line: Circula tion of air during night time Solid Line: Ci rculation of air during day time Figure 2-16. Circulation of air during th e day and night (Source: Bahadori 2008).

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56 Figure 2-17. Stairs under ba dgir columns to water reservoi r (ab-anbar) (Source: Romina Mozaffarian). Figure 2-18. Modern badgir or Kolah Farangy Badgirin Tabas, Iran (Source: Bahadori 2008).

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57 Figure 2-19. Circulation of air through a building with badgir (S ource: Bahadori 2008). Figure 2-20. Section of badgi r with dampers and small pool underneath (Source: Bahadori 2008). Ab-anbar/ Small pool

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58 Figure 2-21. Cross section of a building in Zion National Park visitor center (Source: Torcellini et al. 2002) Figure 2-22. (a)Comparisons between percentage of relative humidity and water capacity in different desiccants, (b) Comparison betw een time in hours and water capacity of different desiccants (Source: Lavan 1982). (b) (a)

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59 Table 2-1. Temperature and wind speed of outside air and badgir air (Source: Bahadori 2008 and modified by Romina Mozaffarian) Cooled Air Entering the Building from Badgir Outside Air/Ambient Air Difference of Temperature C Hour Temperature C Wind Speed m/s Temperature C Wind Speed m/s 19.8 1.5 28.7 2.5 8.9 9 20.7 1.2 30.2 2.1 9.5 10 20.4 1.5 32.1 1.8 11.7 11 20.3 1.4 32.8 1.8 12.5 12 19.9 1.8 33.3 2.1 13.4 13 20.4 1.5 34.1 1.7 13.7 14 20.7 1.4 35.6 1.7 14.9 15 21.2 1.3 37.2 1.8 16 16 20.1 1.2 36.4 1.6 16.3 17 20.1 1.4 35.8 1.9 15.7 18

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60 Figure 2-23. Evaporative cooler (Source: ASHARE 1999). Figure 2-24. CFD model (Source: Ecotect website). Figure 2-25. CFD model (Source: Ecotect website).

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61 Figure 2-26. Plots of prevailing winds from weather data, showing annual wind frequency and speed (left) and summer wind temperatures (right)(Source: ecotect.com website). Figure 2-27. Solar chimney (Sour ce: Bansal and Mathur 1993). Figure 2-28. Window openings (S ource: Bansal and Mathur 1999).

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62 CHAPTER 3 RESEARCH METHODOLOGY Introduction The purpose of this study is to im prove the environmental performance of building ventilation and temperature by using a wind towe r (badgir). Badgirs can reduce the electrical consumption of the buildings. The main focus of this study is on natu ral ventilation caused by winds. By using a badgir, outdoor air can be introduced into a building to circulate air. Secondly, tools for modeling a building with badgir are ex amined. Autodesk Ecotect, a psychrometric chart, and FLUENT packages are tools which were selected to study natural ventilation in a case study building, namely Rinker Hall in the School of Building Construction at the University of Florida. These three tools have been compared and evaluated. In this model, we are assuming that wind will pass through a wate r reservoir, which in Florid a can be the natural underground water, to reduce temperature. The hottest month of the year, July, has been selected for the study. Wind Tower or Badgir as a Speci fic Kind of V entilation Design Based on the literature review, the wind tower or badgir has been chosen as one of the best techniques for natural ventilation in buildings Badgirs have not been applied commonly in buildings for natural ventilation in United St ates. In wind tower or badgir, no mechanical conditioning system is used. Natura l ventilation caused by wind is one of the main forces used in badgirs. By designing a badgir, the outdoor air can be introduced into the building to circulate air and ventilate the building. When visiting the city of Yazd, in Iran in March 2009, it became obvious to me that a badgir is really a masterpi ece of engineering which works efficiently even now without any mechanical equipment. The we ather in Yazd was not windy in March, but the badgir system was cooling the building well. Th ere was a room under the tower of badgir with three doors to control circulate the cool air when needed.

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63 Analytical Tools for the Examination of Natural Ventilation w ith a Badgir After reviewing possible analytical tools for examining natural ventilation of a building with badgir, three tools, Autodesk Ecotect, simplified calculation based on psychometric chart and the FLUENT package, have been chosen. Thes e tools are either user friendly, low cost, or considered to be the state of the art. Autodesk Ecotect Process The following data are infor mation given in Autodesk Ecotect program for modeling a building in Atlanta climate. The Atlanta climate was the closest climate to Gainesville and was selected. Inputs Required for Autodesk Ecotect are as following. Three Dim ensional View of the building: Spec ific dimensions can be given to model the building. Figure 3-1 is the model of Rinker Hall, school of Building Construction at University of Florida with approximate dimensions in Autodesk Ecotect Program. This figure shows a three dimensional view of the building in this software. Location Data and Wind Data: Figure 3-2 s hows wind frequency in different hours. The chart on the right corner shows different hours of the day in the Atlanta, Georgia climate zone. Hourly Data: Figure 3-3 shows m onthly diurnal average of differe nt temperatures in twelve months of year. Give information to calculate thermal analysis Hottest day of July/02 has been chosen for this study. Simplified Calculations Ba sed On Psychrometric Chart By using a psychrom etric chart, the air temp erature of the badgirs intake can be found. We assume that the temperature inside the buildin g is approximately close to the temperature of the ambient air passing through water resorvoir/ ab-anbar/small pool. This temperature can be directly extracted from the psychrometric chart as follows.

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64 Input of Psychrometric Chart Average Temperature Average temperature is the average of the high and low temperatures. Based on Table 3-1, maximum temperature in July in Gainesville, Florida is 90.9 F (32.72C) and minimum temperature in July in Ga inesville, Florida is 70.8 F (21.55C). The daily average temperature is as followed: Average Temperature in July = = 80.85 F (27.14 C) Relative Humidity The rela tive humidity is a percen tage measure of the amount of moisture in the air which is compared to the maximum amount of moisture th at air can hold at the same temperature and pressure. Based on data from the National Oceanic and Atmospheric Administration, Table 3-2 indicates relative humidity (%) fo r selected city, Gainesville, FL For Rinker Hall, a relative humidity of approximately 60% has been chosen which is the afternoon relative humidity in Table 3-1. Based on Table 3-2, relative humidity the afternoon humidity, in one of the most humid times of the year, July is 60%. Dew Point Dew point is that temperature at which a moist air sample at the same pressure would reach water vapor saturation. Relative humidity of 100% indicates that the dew point is equal to the current temperature and the air is maximally saturated with water. Based on Figure 3-4, psychrometric chart, the average dew point, is as follows: Average Dew point Temperature based on Psychometric result in July= = 70.5 F (21.38 C)

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65 The above temperature is close to the water te mperature in the main water reservoir, Abanbar. If the water reservoir is big enough, the water temperature would not change drastically during a 24-hour period. Air Change Calculation Volum etric flow rate = Wind speed (m/s ec) Cross sectional area of badgir (m2) Since average wind speed in Gainesville, FL is 2.5 m/sec and cross sectio nal area of badgir is 9 m2 (3 m3 m). Then, at each second 2.5 m/sec 9 m2 =22.5 m3air is coming into the building. Therefore, in 1 hr, 22.5 m3air 3600=81000 m3air is coming into the building Volume of Rinker Hall, School of Building Construction is 18,000 m3. Therefore, the amount of the fresh air coming into the building in 1 hr is: = FLUENT Package FLUENT package is another software used to obtain inform ation about natural ventilation in a building. The computational domain is divi ded into 87,037 small elements (so called mesh) to solve Navier-Stokes equations in each of these small elements. This simulation computationally is costly. The computation was performed on a 2.61 GHz desktop computer and the results converged after 8 hours. FLUENT packag e has been used to find the temperature of the building with and without the badgir detail s. In FLUENT package, the assumption is the wind passes over water reservoir before coming to the building for simplify. This temperature of the air flowing into the buildi ng after passing the water has been used as the last boundary = 4.5 volume of air per hour. =

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66 condition. Therefore, the value of 70.5 F (21.38 C) which had been calculated from psychrometric chart is imposed at the badgirs intake in FLUENT package. In order to calculate information in CFD P ackage, the following data needed to be considered for FLUENT packages. Input of FLUENT Package Average temperature: Average Temperature is the average of the high and low temperatures. Data in table 3-1 has been co llected from NOAA for Gainesville, Florida. Month of July has been selected for FLUE NT package process. Table 3-1 shows the maximum temperature is in July which is 90.9F(32.72 C) and minimum temperature in July which is70.8F (21.55 C). Wind speed: Wind speed shows the movement of air in an outside environm ent. Figure 35 shows different directions of wind in Flor ida. Figure 3-6 indicates wind direction in different months in St. Augustine Beach. St. Augus tine Beach, FL is the se lected city to get information for wind speed since it is the closet city to Gainesville, FL. Figure 3-6 shows the average wind speed (m/s) throughout the year Average wind speed in July is used for FLUENT package. Boundary condition: The Navier-Stokes (N-S) equations are the fundamental differential equations of the movement of fluid. Boundary conditions need to be defined in order to solve Navier-Stokes equations. Therefore, the value of velocity in all of the boundaries should be defined. In order to solve any differential equations, some boundary conditions and/or initial conditions need to be define d. The same role applies for Navier-Stokes equations. In order to solve N.S equations, all velocity should be defined at all boundaries. Boundaries in the Rinker Hall CFD model transl ates as any limits of our computational domain that separate the computational domain from the ambient. The effect of the ambient on our computational domain is defined at th e boundaries. Therefore, all of the walls are the boundaries of our domain. The open areas such as open doors and/or the badgir are another type of boundary. The well-known N o-Slip boundary condition has been applied on all of the walls. This boundary condition implie s that the velocity of the fluid close to the walls should be the same as the velocity of the wall (in this case the velocity of the wall is zero because all of the walls are stationary ). Because all of the openings are exposed to the ambient air, the pressure at the doors (s pecifically the open doors) is assumed to be atmospheric pressure (100,000 Pascal). The velocity of the flow at the badgir is set to be the average velocity of the wind in July. The opening of the badgir should be designed perpendicular to the wind to be able to co llect all of the kinetic energy of the wind. Flow field: The flow field is the velocity component at each point. Each point also has its own static pressure that is calculated. Computational domain: Computational Domain is the area in which N-S equations are solved. Here, the interior area of the building and badgir serve as the computational

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67 domain. The computational domain is the Rinker Hall School of Building Construction building at the University of Florida. The feas ibility of installing a badgir in order to reduce electricity consumption of the building has been studied. The goal of this research is to find if the installation of a badgir in the Rinker Ha ll School of Building Construction is able to provide cooling for the building. In this study, using the Computational Fluid Dynamic (CFD) method, the building, as is and without the badgir, is compared to the building in which the badgir is implemented. No slip boundary condition: This condition is imposed for three components of velocities: X velocity, Y velocity and Z veloci ty. This makes evident that all the velocity components at the wall have to be zero. Barometric pressure: Barometric pressure, also calle d air pressure or atmospheric pressure, is the pressure exerted by the weight of air over a given ar ea of Earth's surface. Barometric pressure is measured by an instru ment called a barometer. Low pressure areas have less atmospheric mass above their locatio n, whereas high pressure areas have more atmospheric mass above thei r location. Similarly, as elevation increases there is less overlying atmospheric m ass, so that pressure decreases with increasing elevation (Mechtly, E. 1973). Figure 3-7, shows a fifteen-year averag e mean sea-level pressure in the world map. In this figure, MSLP stands for mean sea level pressure, JJA stands for June, July, August and DJF stands for Decem ber, January, February months. Openings: There are three existing doors and openings located in Rinker Hall, School of Building Construction. FLUENT package recogn izes these doors as openings where their pressure value is set as atmospheric pressure. Pressure outlet boundary: Pressure outlet boundary condi tion has been imposed at the doors. In other words, P at the doors is at mosphere pressure. Heat flux and temperature boundary condition: The 1000 w/m2 heat flux boundary condition is imposed on the s outh wall and roof. The 1000 w/m2 value is the typical sunshine heat flux in Florida. The temperatures of other walls are set to be equal to ambient air temperature. FLUENT solves flow field (Navier-Stokes equation) for these boundary conditions. FLUENT calculates te mperature, velocities and pressure in the computational domain. Solar heating load: In northern Florida, the sun shin es from south, east and west. When sun rises from east, the west and south walls and the roof of the building are absorbing solar energy. At noon, the sun shin es vertically to the top of the building and heats the roof and the south walls, while during the evening the roof, east, and south walls absorb the solar energy. The study shows th at the sun which shines on the west and east walls was neglected because the walls are exposed to the suns rays for only a short period of the day. In the state of Florida, the maximum solar energy hitting the ground is about 1000 Watt/m2. This is assumed that the skies are clear. The average solar energy can be calculated by integrating the solar radiati on during the day. The average so lar energy was used as the heat flux boundary condition on the roof and the south walls. Though there are many

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68 simplifying assumptions in this study, the resu lts allow an understa nding and confirm the effectiveness of the implementation of the badgir. Badgir Model Information in FLUENT Package Rinker Hall, School of Building Construction at University of Florida, is a m odel for FLUENT package. The dimensions of the building have been obtained from the floor plan of the building. Figure 3-8 shows the dimension of a m odel used in FLUENT package in meters. For simplicity, educated assumptions were used in the model. Figure 3-9 shows computational domain (Rinker Hall) and th e elements that have been used in this study. There are some assumptions which have been considered in this study. Assumptions are as follows: Interior walls: The interior walls have been neglected in this study. Openings: It was assumed that there are 3 open doors in this building and the opening at the badgir. Velocity components: All veloc ity components are set to be zer o at the walls. At the inlet of the badgir the velocity is set to be equal to the wind velocity. Pressure: The pressures for the doors are set to be as atmospheric pressure. Air Temperature at badgirs: In FLUENT pack age, it has been assumed that the badgirs intake already passes through water reservoi r/ab-anabar which is underground water in Florida for simplicity of the model. Therefore, the value of 70.5 F (21.38 C) has been imposed at the badgirs intake in FLUENT package. Boundary condition: Since the energy equation is coupled with the momentum equations (N.S), the boundary conditions for the energy eq uation have to be defined in all of the boundaries. Heat flux: The heat flux at the roof and the south wall set to be as the average heat flux of the sun during the summer. Temperature: The temperature of the other walls is set to be equal to ambient temperature. Direction of Sun: The Rinker Hall School of Building Construction at the University of Florida is an example of a bu ilding in hot and humid climate. Sun shines from south west in Florida. In the CFD model, the sun shines toward the roof and the south walls of the building. Shades are therefore on north side of Rinker Hall. In order to design a badgir;

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69 precise information about the wind speed at th e certain time (daily average or monthly average) must be extracted from statistical weather data. Height of badgir: In order to design the height of the badgir to wer, it is important to know the arrangement of nearby buildings as well as surrounding tall trees. Since tall trees or buildings may dissociate the wind speed and power, towers height should be taller than the neighbor buildings or trees. The entrance of th e badgir should be loca ted perpendicular to the average wind direction to collect the maximum amount of air possible. Dimensions of badgir: The speed of the air inside the building should be in the certain range to produce comfort airflow for people. According to ASHARE, the velocity of 0.5 < V < 2(m/s) is acceptable (ASHARE 1999). As a result, we will continue our design based on 2.5 (m/s) winds in the main corridor. We will assume that this speed of the wind in the main corridor would maintain the comfort Veloc ity limits in the hall and smaller rooms. This assumption helps us to design the ba dgir entrance dimensions using continuity equation. In fluid mechanics, continuity e quation (conservative of mass) applies on a control volume which may have many inlets a nd outlets. Continuity equation says that the amount of mass entering a domain should be e quivalent to the amount of mass leaving control volume. Mathematically, continuity equation assuming a constant density of air can be express as: A1V1=A2V2 Where, A1 is the cross sectional ar ea of the badgir intake. V1 is the wind speed entering badgir which can be found from the statistical weather data at the certain times. A2 is the cross sectional area of the main corridor (10.8 m2). V2 is the desired air speed in the main corri dor which is 2.5(m/s), as discussed before. Solving Eq. 1 for the unknown badgir intake cross s ectional area: 1 22 1V VA A So, )(64.8 )/(5.2 )/(2)(8.102 2 1m sm smm A This is a rough estimate of the cr oss sectional area of the badgir.

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70 Since the area to perimeter of square is the maximum for ar bitrary rectangular, the most effective shape of the badgir is square. In order to have 8.64 m2 cross sectional area, the dimension of the badgir should be almost .T he height of the badgir tower above the roof assumed to be 6 m. The schematic of the badgir is shown for any initial assumptions. Figure 3-10 shows the dimensions and wind speed assumptions for badgir Model in FLUENT package. Figure 3-11 shows the floor pl an of Rinker Hall which was used in the CFD Model. Figure 3-12 is the picture of the entrance of the Rinker Hall School of Building Construction.

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71 Figure 3-1. Three dimensional view of a simplified Rinker Hall in Ecotect Software (Source: Romina Mozaffarian). Figure 3-2. Locational Data and Prevaili ng winds (Source: Romina Mozaffarian).

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72 Figure 3-3. Hourly temperatures (Source: Romina Mozaffarian).

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73 Table 3-1. Maximum and Minimum Temperatur e in Gainesville, Florida (Source: Nationa l Oceanic and Atmospheric Administration 2001and modified by Romina Mozaffarian) Normal Daily Temperature (F) Gainesville, FL YRS JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANN 30 66.2 69.3 75.1 80.4 86.5 89.9 90.9 90.1 87.4 81 74.4 68.1 79.9 30 42.4 44.7 49.9 54.7 62 68.4 70.8 70.6 68.1 59.2 51.1 44.4 57.2 Table 3-2. Average Relative humidity (%) (Source: NOAA 2001 and modified by Romina Mozaffarian) FLORIDA Years JAN FEB MARAPR MAYJUN JUL AUG SEP OCT NOV DEC Annual M= Morning A= Afternoon M A M A MA MA MA MA MA M A M A MA MA MA MA M A GAINESVILLE (%) 18 18 90 60 90569153915191508856 89 59 90 609664936193609162 91 58

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74 Figure 3-4. Psychrometric chart (S ource: truetex.com website and Modified by Romina Mozaffarian).

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75 Figure 3-5. Wind directions st ate(Source: windfinder websit).

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76 St. Augustine Beach (AUGUSTIN) Stats based on observations taken between 10/2006 1/2009 daily from 7am to 7pm local time. Month of year Jan Feb Mar Apr MayJun JulAug Sep Oct Nov Dec SUM 01 02 03 04 05 06 0708 09 10 11 12 1-12 Dominant Wind Dir. Wind probability > = 4 Beaufort (%) 34 34 40 46 56 37 17 28 55 51 44 29 39 Average Wind Speed (kts) 9 10 10 11 12 9 8 9 12 12 11 9 10 Average Air temp. (C) 16 17 18 20 24 26 2828 27 24 19 18 22 Select Month ( Help ) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Wind direction Distribution (%) Figure 3-6. Wind direction local (Source: windfinder website).

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77 Table 3-3. Wind Speed (m/s) (Source. windfinder website) FLORIDA YRS JAN FE B MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANN GAINESVILLE (m/s) 23 6.8 7.3 7.6 7.1 6.7 5.9 5.5 5.2 6 6.1 6.2 6 6.4

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78 Figure 3-7. 15 year average MSLP ( mean sea level pressure), JJA (June, July, and August) and DJF (D ecember, January and February) m onths (Source: William M. Connolle).

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79 Figure 3-8. Rinker Hall model in meter in FL UENT package (Source: Romina Mozaffarian). Figure 3-9. Computational domain (Rinker Hall) and the elements that were used in this study (Source: Romina Mozaffarian).

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80 Figure 3-10. Badgir (Source: Romina Mozaffarian). Figure 3-11. Rinker Hall first floo r plan (Source: Roya Mozaffarian). 3m 3m 3m Wind 2.5 (m/s)

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81 Figure 3-12. Rinker Hall main en trance (Source: Roya Mozaffarian).

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82 CHAPTER 4 RESULTS AND ANALYSIS Introduction Based on the literature review and methodol ogy, inform ation regarding badgir has been summarized in Table 4-1. Table 4-1 is the result of information fo r designing a badgir in hot and dry climate and hot and humid climates. This information is based on researches of typical badgirs in Iran. The dimensions of opening in badgi rs need to be calculated based on square feet of a building. Similarities between Wind Towers/Badgirs of Buildings in United States and Middle East w ith New Techniques Wind tower in Zion Park is an example of applying badgir in Un ited States. In this building, honeycomb media is located at top of th e tower. Water pumps in this system, and then evaporates. Since evaporated air is denser than am bient air, it drops through the tower and enters the building. This cool air cools the building. This system is very similar to the buildings with badgir and dampers which are locat ed in Yazd, Iran as well. In badgirs with dampers in Iran, there is a pump which directs the extra water from small pool or ab-anbar to top of the building. A fountain located on top of clay surface on top part of badgir use the extra water and keeps the dampers wet. When the air gets wet through dampers, evaporates and gets cool. Colder air has higher density than outside air and this causes circulation of air inside the bu ilding. Air enters to the building and cools the building (Bahadori 2008). Benefits of Badgirs in Green Building/Sustainable Building The following are the benefits of having badgirs in green buildings. Cooling the building without using any elec trical equipm ent (natural ventilation). Having natural lighting through th e openings of the badgir.

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83 Using the cold space underground for storing food instead of a refrigerator, especially in winte. Using natural materials like adobe, dried m ud bricks for building badgirs for high heat storage capacities and fo r sustainable building. Autodesk Ecotect, Simplified Ca lculation and FLUENT package Three too ls, Autodesk Ecotect, simplifie d calculation from psychrometric chart and FLUENT package, were used to find a tool for an alyzing a building with a badgir. The results of Autodesk Ecotect are not detailed for a speci fic building with speci fic dimensions. Also, Autodesk Ecotects output is not detailed for natural ventila tion of a building with badgir. Simplified calculation based on psychrometric chart is not as detailed as a FLUENT package. It has an approximate result without considering f acts such as wind speed a nd temperature of walls of buildings. In FLUENT package the temperatur e of walls and wind speed are considered for boundary conditions. The following are the results of Autodesk Ecotect, simplified calculations from psychrometric chart, and FLUENT package. Autodesk Ecotect The results of given inform ation to Aut odesk Ecotect software are as follows. Monthly diurnal averages: Figur e 4-1 shows Monthly temperature, beam solar, diffuse solar, wind speed and zoned temperature are being shown in different colors. Weekly Summary: Figure 4-2 shows weekly av erage temperature. Different colors of temperatures indicate different temperatures. Monthly Rainfalls: Figure 4-3 shows rainfalls in different months of years in mm. Comparisons of Different Wind Data: Figur e 4-4 shows wind data in average wind frequency, average wind temperature, average relative humidity and average rainfall throughout a year. Monthly Wind Data: Figure 4-5 shows wi nd frequency in all different months. Daily Data: Figure 4-6 shows hour ly operational profile from 1s t day of January to 31st of December. It shows the result of temperatures relative humidity, direct solar radiation,

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84 diffuse solar radiation, average wind speed outdoor, average cloud c over and average daily rainfalls in different hours of day. Weekly Data: Figure 4-7 shows weekly data of average temperature, maximum outdoor temperature, minimum temperature, relative humidity, direct solar radiation, diffuse solar radiation, average wind speed, average cl oud cover and average daily rainfall. Data for Strongest Wind in Hourly Data: Figure 4-8 shows monthly Diurnal averages in different temperatures in a year. By looking at the figure, in month of July highest temperature, relative humidity, direct solar, diffuse solar are being graphed. Thermal Comfort: Figure 4-9 shows thermal comfort in mean radiant temperature. Export the model to CFD, DOE-2, gbxml and DXF files. Simplified Calculations of Air Change Based on the m ethodology reviewed in the previ ous chapter, the daily average temperature in Gainesville, Florida in July, the temperature of air passing through water reservoir, and the air change rate has been calculated. Based on these, we are assuming that the building with the badgir has an indoor air temperat ure of 70.5F (21.38 C), which is the temperature of the air passing through water reservoir/ab -anbar. Also, we are assuming a building without a badgir has a temperature of daily average temp erature of ambient air in Gainesville, Florida in July which is 80.85F (27.14 C). The difference between these two temperatures is 10.35F (-12.03 C). The result shows a building with ba dgir has a lower temperature than a building without badgir. The humidity is not being considered. Result of temperature difference = 80.85 F70.5 F= 10.35 F (-12.03 C) FLUENT Package Results of Building with Badgir In Figure 4-10(a, b), contours of the velocity and the flow streamlines in the building are depicted. This figure shows that the wind is ente ring the badgir with a ve locity of 2.5(m/s), the average velocity of the wind in Gainesville, Ju ly. Then the wind circulat es in the building and

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85 leaves the building from the open doors. It can be seen that when the wind entering into the badgir due to the growth of the boundary layers at the wall, the mean velocity of the wind increases to 4.5 m/s (see Fig.4-10(a)). This may not be good since the wind speed under the badgir would be greater than th e comfort speed. However, if th is wind was distributed in the whole building using ducts and dampers, a more uni form flow in the building could be attained. It should be considered that the badgir would not work if the doors or wi ndows are kept closed since the flow of air coming into the building should have a way to go out. Therefore, in order to have an effective badgir, either doors should be kept open all the time or openings or vents connecting to the outdoors have to be included in the design. Figure 4-11 (a, b) shows contours of the pressure and stream lines of the flow in the building (Fig. 4-11.b is another view of Fig. 4-10.b). In this figure it can be seen that when the wind enters the badgir (see Fig. 411.b), it hits the other wall of the badgir and makes a high pressure region of 14 kilopascal (see Fig. 4-11.a). The low pressure of 0 and -1 kiloPascal at the doors can be noticed in Fig. 4-11.a. Since the pressure at the doors is set to atmospheric pressure, the zero gauge pressure can be noticed at those regions. Figu re 4-11.a is more advanced computation model if all interior walls take into the account. The pressure drops in the building due to the existence of barrier s such as interior walls. Figure 4-12 shows the contours of the temperature which is the most interesting variable in the building. In order to be able to model the buoyancy effect in the flow field, the air assumed to have the properties of an ideal gas. Therefore the density of air is de creasing with increase in temperature according to the ideal gas equation of st ate. All of the temperatures scales in Figure 4-12 are in Kelvin. Figure 4-12 cl early shows that the roof has th e highest temperature since the heat flux of sun is coming from the roof. Howeve r, it is interesting to note that the roof

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86 temperature has a maximum value far from the ba dgir column. This indicates that since the air flow is slow far from the badgir column, there is not enough flow to remove heat from the roof. By integrating the temperature over the vol ume and dividing it to the volume of the building the average temperature of air inside of the building with th e badgir has been found. The average temperature for a building which uses a badgir is 296.0450 K (or 73.4 F or 23 C). As we have mentioned before, the simulati on assumes that the air has already passed through an ab-anbar that acts like a heat sink to the ground with an almost constant temperature and the air temperature has already reached to dew point temperature. Experimentally this condition can be achieved by wetting walls of the badgir as has been mentioned in literature review. If we want to compare two buildings with a nd without a badgir, the average temperature in the building seems to be the best criteria. Ev en though humidity comparison is also important, the effect of the temperature on human co mfort is not as important as humidity. Results of Building without Badgir In order to model the build ing without the badgir, the sam e geometry and boundary conditions have been considered and the only difference is that the intake of the badgir is replaced with a wall. Since the wall (no slip boundary condition) does not let air flow penetrate into the building, there would be no external flow for air circulation. In another words, the only driving force in the building wit hout badgir is the buoyancy force of the air. This means that, for example, the density of air in th e vicinity of the hot walls is d ecreasing and this fact produces a buoyancy force that moves this part of the air upward. Figure 4-13(a, b) depicts the c ontours of the pressure and one slice of the temperature in the building without badgir. This figure (4-13.a) shows that the contour s of the pressure are uniformly lies on each other. In fluid mechanics this type of flow c onfiguration is called

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87 stratified flow. Since there is no external wind, fl ow velocities are small compared to the flow inside of the building with the badgir. Since the buoyancy force of the hot air is upward, it can be seen that the maximum pressure is at the highest part of the building in the badgir column and roof. Figure 4-13.b shows that the air in vicinity of the roof is hotter than other parts mainly due to the heat transfer from th e hot roof into the building. Figure 4-14 (a, b) shows the cont ours of the temperature and the flow streamlines and the x-velocity counters on a slic e of the building without a badgir. Figure 4-14.b shows a complicated pattern of flow of air. However, th is configuration of flow field is the result of buoyancy force. In Fig. 4-14.b it can be seen that roof temperature is high mainly due to the sun. The roof temperature is uniform in this figure si nce the flow movement is slow in this building while with the badgir (Fig. 4-12) showed a large variation in roof temperature. By integrating the temperature over the volum e and dividing it into the volume of the building the average temperature of air inside of the building without a badgir has been found. The average temperature for a building without a badgir is 307.7 K (94.46 F or 34.7 C).

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88 Table 4-1. Requirements for typical badgirs in different climate regions Weather Conditions Hot and Dry Climate Hot and Humid Climate Cross section of badgir Square Square Rectangular Hexagon Octagon Size of the roof 1.64 ft x 2.62 ft 3.28 ft x 3.28 ft 2.30 ft x 3.60 ft 1.64 ft x 0.50 ft 3.94 ft x 1.97 ft Height of badgir 9.84 ft-16.4 ft 5.91 ft-16.4 ft More than 16.4 ft Roof shape of badgir Flat Flat Shed Size of each Opening of badgir(Minimum) 7.9 Inches 7.9 Inches Wall divider between each opening of badgir 3.1 Inches -3.9 Inches 3.1 Inches -3.9 Inches Wooden cradling Every 6.56 ft Every 6.56 ft Orientation of badgir Direction of wind Direction of wind Material of badgir Mud-brick Plaster/ Brick with Plaster of cob(clay and straw) Lime Plaster

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89 Figure 4-1. Monthly diurnal averag es (Source: Romina Mozaffarian). Figure 4-2. Weekly summary (S ource: Romina Mozaffarian).

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90 Figure 4-3. Monthly rainfalls (Source: Romina Mozaffarian). Figure 4-4. Prevailing winds (S ource: Romina Mozaffarian).

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91 Figure 4-5. Prevailing winds (S ource: Romina Mozaffarian). Figure 4-6. Hourly operational prof ile (Source: Romina Mozaffarian).

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92 Figure 4-7. Weekly data (S ource: Romina Mozaffarian). Figure 4-8. Monthl y diurnal averages (Source: Romina Mozaffarian).

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93 Figure 4-9. Thermal comfort (S ource: Romina Mozaffarian). (a) (b) Figure 4-10. Velocity contours of the building with Badgir (a). Streamlines of the air flow (b) (Source: Romina Mozaffarian).

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94 (a) (b) Figure 4-11. Static Pressure cont ours of the building with badgir (a ). Streamlines of the flow (b) (Source: Romina Mozaffarian). Figure 4-12. The temperature contours in the building and the volume average of the temperature in the building with ba dgir (Source: Romina Mozaffarian).

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95 (a) (b) Figure 4-13. The pressure contours in the build ing (a) and the temperatur e counters in one slice of the building without badgir (b) (Source: Romina Mozaffarian). (a) (b) Figure 4-14. The temperature contours in the building (a). Stre amlines and x-velocity counters in one slice of the building without ba dgir (b) (Source: Romina Mozaffarian).

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96 CHAPTER 5 CONCLUSIONS When the kinetic energy or the buoyancy driv en force of the air is used for ventilation purposes, the type of ventilation is typically called natural vent ilation. There are m any different configurations which exist in or der to create effec tive natural ventilati on. This study focuses on natural ventilation caused by outdoor winds. In other words, the kinetic energy of wind is used to circulate air inside of the building. There are specific design requirements requiring consideration in the desi gn of a badgir in any building. Badgirs are made up of three parts, the roof, the body, including openings, and the columns of the badgir. Table 4-1 is the result of information for designing a badgir in hot and dry climate and hot and humid climates. This information is based on researches of typical badgirs in Iran. The dimensions of opening in badgirs need to be calculated based on square feet of a building. Based on the literature review, the following are recommendations for designing and constructing badgir s in United States. The components of badgirs are the roof, the opening of badgir and column of badgir. Based on literature, in hot and dry climates in United States, interior wall dividers are square (4 interior walls), recta ngular (4 interior walls), hexagon (6 interior walls) and octagon (8 interior walls). Figure 2-14 shows the badgir with six and eight interior wall dividers. Figure 215 shows four interior wall divi ders. Based on literature, in ho t and humid climates, commonly four interior wall dividers are suggested in Unite d States. Height of badgi rs can change based on different climates. Height of ba dgirs in hot and dry climates is 9.84 ft to 16.4 ft, 5.91 ft to 6.89 ft. Height of badgirs in hot and humid climates are usually 9.84 ft to 16.4 ft or even taller than 16.4 ft. The taller the badgir is, the ability to direct the wind incr eases. Adobe/cob/mud brick was one of the main materials in badgirs structure which was available locally in ancient countries like Iran. Adobe is a natural building material made from sand, clay, and water, with some kind of

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97 fibrous or organic material ( sticks, straw, dung), which is shaped into brick using frames and dried in the sun. Using natural materials that are available locally is one of the concepts of sustainable building or green building. Natural m aterials such as br ick and adobe brick that have high heat storage capacities are be ing suggested to be used to c onstruct buildings with badgir in hot and dry climate regions. These materials ha ve high heat absorption capacity (Biket 2001). The opening of badgirs between each wall divider which had been shown in Figure 2-5 is 7.9 inches which can be applied for badgirs in Un ited States. 3.1inches to 3.9 inches are the dimension of wall divider between each opening of badgir. These are approximate dimensions which can be changed based on the dimensions of badgirs. Directions of badgirs depend on direction of winds. Direction of winds in each region is different which has to be considered before designing a badgir in a building in United States. Badgirs in hot and humid climates like Florida can use the natural wate r underground as a water reservoir to cool the building. In hot and dry climates like Nevada, a small pool can be designed underground to pass the air over and reduce the temperature of outside air. Three tools, Autodesk Ecotect, simplified cal culations based on the psychrometric chart, and a FLUENT package, are used to find the best tool which can give a best result for natural ventilation of a building with ba dgir. The FLUENT package is the most detailed and precise tool. The result of Ecotect did not have the capabi lity to provide comparative temperature data. The simplified air change model shows that the av erage indoor temperature of a building with a badgir is about 10.35 F (-12.03 C) cooler than a building without a badgir. Results of the FLUENT package shows that the average indoor temprature of a building with a badgir in Gainesville is almost 11.7 C (53.06F) (accordin g to Fig. 4-12 and Fig.4-14), lower temperature than a building without badgir. The reported resu lts are rough estimates which include the main

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98 features of the flow field and temperature. Even though the results ar e hopeful, it must be considered that there were many simplified assump tions applied in these si mulations. In order to have a more realistic comparison, future studi es must be conducted in further detail. Recommendations for future studies are: 1. The ab-anbar can be included in the simulation. In this study, the effect of the ab-anbar is explicitly extracted from the psychrometric chart and the obtained air condition is used for the badgir intake. 2. The effect of the interior walls can be includ ed into the simulation. In this study, interior walls were neglected. 3. Transient simulation can be performed by im posing variable wind speed and sun heat flux in 24 hrs. In this study the maximum sun heat flux and wind speed were used in the simulation. 4. Performance of the badgir can be compared to many other configur ations that can be employed for natural ventilati on. For example, the coupling of solar chimney in order to drive air and underground water for c ooling proposes can be used. 5. Badgir can be compared with other type of green technologies. For example, the performance of the badgir can be compared to the commercial solar chiller performance for cooling proposes. 6. In the most advanced study, the series of th e badgir as the flow driver, desiccant for dehumidification, and the ab-anba r for cooling with the coupli ng of solar panels in order to dry wet desiccants can be studied and the implementation cost can be compared to the commercial HVAC systems or solar chillers.

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LIST OF REFERENCES Allard, F., (1998). Natural Ventilation in build ings, London, UK. ASHRAE Standard ( American Society of Heating, Refrigerating and Air-Conditioning Engineers). ASHRAE 62.1-2007, Ventilation for A cceptable Indoor Air Quality Atlanta, GA. ASHRAE Standard (American Society of H eating, Refrigerating and Air-Conditioning Engineers). (1999b). ASHRAE 62-1999, Ventilation for Acce ptable Indoor Air Quality, Atlanta, GA. ASHRAE Standard (American Society of H eating, Refrigerating and Air-Conditioning Engineers). (2004). ASHRAE 55-2004, Thermal Environmental Conditions for Human Occupancy. ASHRAE (1999). ASHRAE Standard 62-1999. Ven tilation for Acceptable Indoor Air Quality. Atlanta, GA. A'zami, A., (2005). Badgir in traditional Irani an architecture. Proceedings, International Conference: Passive and Low Energy Cooling for the Built Environment, Santorini, Greece. Bahadori, M. and Dehghani, A. (2008). Wind towe r, a master piece of Iranian engineering, 1st Ed.,Tehran, Iran. Bansal, N. K., Mathur and Bhandari .(1993). Solar chimney for enhanced stack ventilation". Building and Environment, 28 (3),373-377. Bansal, N K, Mathur, Rajesh, Bhandari.(1999). A study of solar chim ney assisted wind tower system for natural ventilation in buildings, Building and Environment 29(4), 495-500. Biket,a. Architectural Design based on Climatic Data. yldz technical university. BRECSU. (2000). Energy Conusmption Guide 19: Energy Use in Offices. Garston, Watford, UK, British Research Establishment Conservation Support Unit. Busby, Perkins and Will (2005). Gurtekin-Celic presentation. Natural Ventilation. Chastain, J.P., Colliver, and P.W. Winner. (1987). Computation of discharge coefficients for laminar flow in rectangular and cylindrical openings. ASHRAE Transactions 93(2B):2259-2283. Chastain, J.P. (1987). Pressure gradients and the location of the neutral pressure axis for lowrise structures under pure stack conditions. Unpublished MS thesis, Department ofAgricultural Engineering University of Kentucky, Lexington KY.

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100 Chastain, J.P. (2000) Design and Manage ment of Natural Ventilation Systems. Department of Agricultural and Biological Engineering Clemson University. Dols, W. S. and Emmerich, S. J. (2003) Natural Ventilation Design and Analysis Software. National Institute of Standards and Technology, Gaithersburg, Architectural Energy Corporation Boulder, Colorado ECOTECT: Ventilation and Air Flow. (Feb. 21, 2009). Emm erich, S.J., Dols, and Axley. (2001). Natural Ventilation Review and Plan for Design and Analysis Tools. NISTIR 6781, National Institute of Standards and Technology Colorado. Emmerich, Steven J., Persily, Andrew K. and Stuart Dols, W., (2003) Impact of Natural Ventilation Strategies and Design Issues for California Applications, Architectural Energy Corporation Boulder Colorado. Fluent Inc., (2006). Fluent 6.3.26 Users Guide. Lebanon, NH. Frej, B., (2005). Green Office Buildings: A Practical Guide to Development.Washington, D.C. Green Building Studio.U.S. department of energy, < http://apps1.eere.energy.gov/buildings/tools_directory/software.cfm/ID =440/pagename_ submenu=/pagename_menu=materials_components/pagename=subjects> (Feb. 21, 2009). Heikkinen, J. and Heimonen. (2000). Hybrid Ventilation Expectations Among Finnish Designers and Decision Makers. Healthy Buildings. 2, 511-516. Heiselberg, P. (1999). The Hybrid Ventilation Process Theoretical and Experimental Work. Air Infiltration Review. 21(1), 1-4. Heiselberg, P. (2000). Design Principles for Natural and Hybrid Ventilation. Healthy Buildings., 35-46. Horstmeyer, S. (2006). "Relative Humidity, The Dew Point Tem perature, A Better Approach." < http://www.shorstmeyer.com/wxfaqs/humidity/humidity.html> (June, 8, 2009). Iannone, F. (1999). Natural Ventilation and Sustainability: D esigning with Computational Fluid Dynamics. Dipartimento di Architettura e Urba nistica Politecnico di Bari Via Orabona, 4 70125 Bari, Italy. Iannone F. (1999). Displacement Natural Vent ilation Systems Design in large rooms, Simplified models and Numerical evaluation for architectural design. Ancona University.

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101 Kleiven, T. (2003). Natural Ventilation in Buildi ngs: Architectural concepts, consequences and possibilities. Thesis for the degree of Doktor Ingeni or at Norwegian University of Science and Technology. Kleiven, T., (2003) Natural Vent ilation in Buildings: Architectural concepts, consequences and possibilities. Department of Architectural Design, History and Technology, March 2003. Lavan, Z.,Jean-Baptiste Monnier, Worek, W. M. (1982). "Second Law Analysis of Desiccant Cooling Systems". Journal of Solar Energy Engineering Lim b, M. J. (2000). Duct Cleaning: An Anotat ed Bibliography. Coventry, England, AIVC. Li, Y. (2003).Indoor and outdoor air quality. Indoor Air Quality. Hong Kong. McEneaney. (2005). Santa Monica Green Build ing program, conserve today, preserve tomorrow.< http://greenbuildings.santa-monica.org/mainpages/sitemap.html.>(Sep. 15, 2007) Mechtly, E. (1973). The International System of Units, Physical Constants and Conversion Factors. National Aeronautics and Space Administration Washington, D.C. Mendell, M. J., Fisk, et al. (1996). Elevated Symptom Prevalence Associated with Ventilation Type in Office Buildings. Epidemiology, 7 (6): 583-589. MWPS-7. (1995). Dairy Freestall Housing and Equipment 5th ed., Midwest Plan Service, Agricultural and Biosystems Engin eering Department, Iowa State University, 122 Davidson Hall, Ames IA 50011-3080. Nall, D. H. (2004). Looking across the water: Climate-adaptive buildings in the United States and Europe. In The Construction Specifier 57, 50 56. NOAA (2001). Comparative Climatic Data", National Climatic Data Center Roulet, C, Germano, M., Allard, F., Ghiaus, C. (2002). Potential for Natural Ventilation in Urban Context: An Assessment Method. Proceedings, Indoor Air Movement and Natural Ventilation. Sateri, J. (1998). A Proposal for the Classi fication of the Cleaniness of New Ventilation Systems.th AIVC Conference Ventilation Technologies in Urban Areas, Oslo, AIVC. Sanjay and Chand, P. (2008). Passive C ooling Techniques of Buildings. India., Vol. 4 No. 1, 37-46 Szikra, C. (2000). Hybrid ventilation systems Australia. Torcellini, P., Judkoff, R.,and Hayter, S. (2002). Zion National Park Vis itor Center: Significant Energy Savings Achieved through a WholeBuilding Design Process. California.

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102 Unified Facilities Cr iteria (UFC). (2004). Cooling Bu ildings by Natural Ventilation. VanWylen, G., Sonntag, R (1973). Fundamentals of Classical Thermodynamics John W iley and Sons. p. 448. Wong, P.C., Prasad a, D., Behnia M. (2006) A new type of double-skin configuration for the hot and humid climate. Energy and Buildings. Vol. 40, 1941.

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103 BIOGRAPHICAL SKETCH Rom ina Mozaffarian was born in Tehran, Ir an. She enjoyed at a young age and continues to enjoy artwork, oil-painting, and pencil drawin gs. She studied computer engineering at the University of Tehran (Azad University), and she maintained an intense interest in mathematics. After moving to the United States in 1999, she chos e to combine her interest in art and math by studying architecture. She received her Associat e in Arts degree from Miami Dade Community College in 2003. She continued her major at Fl orida Atlantic Universi ty and received her professional bachelors degree in architectur e degree in 2006. During the three years spent studying at Florida Atlantic Univers ity, she also worked at architect ural firms to gain experience. Her interests and experience led her to pursue study in building construction. She then began graduate school in building cons truction at the University of Fl orida, continuing to work for architectural firms in Gainesville, Florida. Late r, she began teaching as a teaching assistant for a graphic communications in construc tion course at the University of Florida. Romina Mozaffarian received her master of science in building cons truction in the summer of 2009. Then, she plans to begin working for a construction company to apply her knowledge of both construction and architecture.