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A computer teaching tool for passive cooling
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A computer teaching tool for passive cooling
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A COMPUTER TEACHING TOOL FOR PASSIVE COOLING by Alice Hui-Lin Yuan A Thesis Presented to the FACULTY OF THE SCHOOL OF ARCHITECTURE UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirement for the Degree MASTER OF BUILDING SCIENCE August 1994 Copyright 1994 Alice Hui-Lin Yuan UMI Number: EP41441 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMI Dissertation Publishing UMI EP41441 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code uest ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 UNIVERSITY OF SOUTHERN CALIFORNIA THE SCHOOL OF ARCHITECTURE UNIVERSITY PARK LOS ANGELES. CALIFORNIA 90089-0291 This thesis, written by Alice Huilin Yuan under the direction of h .er. . . . Thesis Committee, and approved by all its members, has been pre sented to and accepted by the Dean of The School o f Architecture, in partial fulfillm ent of the require ments fo r the degree of Master of Builsing Science fT“' ...... « -■ Date . ■ ■ THESIS COMMITTEE ACKNOWLEDGMENT I wish to express my sincere thanks and appreciation to the chairman of my thesis committee, Professor Marc Schiler, for his help and guidance through this research. He patiently guided me through the process of making the abstract idea into writing and computer graphics. This thesis could not be completed without his direction and support. I am truly grateful. Thanks and appreciation are also extended to Professor Goetz Schierle and Professor Pierre Koenig, for their review of the manuscript and constructive suggestions. I also would like to take the opportunity to thank my father for his emotional and financial support, which provided me a comfortable and peaceful environment for learning. Finally, Sen Yan deserves special appreciation, his support and understanding is the motivation behind the scenes. INDEX I. ACKNOWLEDGEMENT ii II. LIST OF FIGURES vi III. LIST OF TABLES viii IV. ABSTRACT ix PART ONE LITERATURE SEARCH 1 1. INTRODUCTION 2 2. CLIMATE 5 2.1 THE SUN 5 2.2 WIND 7 2.3 WATER 7 3. LANDSCAPE 10 3.1 HOT ARID AREA 10 3.2 HOT HUMID AREA 13 4. BUILDING 18 4.1 BUILDING FORM 18 4.2 BUILDING MATERIAL 22 4.3 MOISTURE EFFECT 25 4.4 INSULATION 25 5. SOLAR CONTROLS 30 iii 5.1 SHADING EFFECTS OF PLANTS 32 5.2 SHADING DEVICES 33 6. VENTILATION 40 6.1 THERMAL FORCES 40 6.2 WIND FORCES 41 6.3 WIND TOWER 48 7. EVAPORATIVE COOLING 54 7.1 DIRECT EVAPORATIVE COOLING 55 7.2 INDIRECT EVAPORATIVE COLING 56 7.3 TWO STAGE EVAPORATIVE COOLING 57 8. RADIATIVE COOLING 62 9. EARTH COUPLING 65 9.1 DIRECT SYSTEM 67 9.2 INDIRECT SYSTEM 70 PART TWO USING THE COMPUTER AS A TEACHING TOOL FOR PASSIVE COOLING 72 10. THE COMPUTER AS A TEACHING TOOL 73 11. A COMPUTER TEACHING TOOL FOR PASSIVE COOLING 76 iv 12. FUTURE DEVELOPMENT BIBLIOGRAPHY LIST OF FIGURES Fig. 2.1 The sun affects the earth’s climate 6 Fig. 2.2 Day-night heat flow between water and land 9 Fig. 3.1 Vine covered trellis shading southern exposure 12 Fig. 3.2 High crown plants shading south exposure in summer, not winter 12 Fig. 3.3 Tree layout in hot humid area 14 Fig. 3.4 Cool Breezes pass through unobstructed planting into the living space 15 Fig. 3.5 Tree funnel to enchancing breeze 16 Fig. 3.6 Venturi effect 16 Fig. 5.1 Town layout in hot areas 32 Fig. 5.2 Standard types of shading devices 35 Fig. 5.3 Sun path and overheated periods transferred to sun-path diagram 38 Fig. 5.4 Basic types of shading devices and their projection 39 Fig. 6.1 Stack effect 41 Fig. 6.2 Venturi effect 43 Fig. 6.3 Inlet openings affect the interior air flow 44 Fig. 6.4 Overhang affects interior air flow 45 Fig. 6.5 Internal divisions affect the air flow 47 Fig. 6.6 Wind tower in different regions 49 Fig. 6.7 Wind scoop in Hyderabad, Pakistan 51 Fig. 6.8 The vault roof and ventilation 53 Fig. 7.1 Evaporative cooler in New Gourna, Egypt 55 Fig. 7.2 Courtyard Housing 58 Fig. 7.3 Two stage evaporative cooling, ultilizing a rockbed for storage and heat exchange 61 Fig. 8.1 Roof pond 64 Fig. 9.1 Direct earth coupled system 68 Fig. 9.2 Indirect earth coupled system 70 Fig. 11.1 Passive cooling 80 Fig. 11. 2 - Fig. 11. 34 Solar shading 80-96 Fig. 11. 35 - Fig. 11. 57 Ventilation 98-109 Fig. 11. 5 8 -Fig. 11. 67 Radiative cooling 111-115 Fig. 11. 68 -Fig. 11. 75 Evaporative cooling 117-120 Fig. 11. 7 6 -Fig. 11. 88 Earth coupling 123-129 LIST OF TABLES Table1.1 Comparison of passive and active cooling systems 3 Table 4.1 Comparison of the rectangular and square building form 19 Table 4.2 Reflectivity and emmisivity of materials 24 Table 4.3 Overall heat transmission coefficient (U) and time lag characteristic data for homogeneous walls 27 Table 5.1 Reflectivity of materials 34 viii ABSTRACT The mission of this thesis is to create a tool for teaching passive cooling by using modern technology, such as computers, as the media. It is very important to develop research on energy conservation devices at this time because of the limited energy sources the earth can offer. In tropical and sub-tropical areas such as Taiwan, how to design a comfortable yet energy saving living environment according to the climate condition and the fact of shortage in natural energy is significant. A good living environment can rely on active strategies such as air-conditioning or heating although it will increase the consumption of energy and decrease the ability of building shelter incorporating with the natural environment, if we only depend on the active strategies. Passive strategies have been widely used in vernacular architecture. They use site planning, building shelter, and space design to lead the natural resources into the building in order to create a comfortable yet energy conserving living space. PART ONE LITERATURE SEARCH 1 1. INTRODUCTION Just as warming the living environment is important to cold climate areas, cooling is important to tropical and sub-tropical regions. Since the energy crisis in late 1970’s, people realized the limited resources we have on the earth. In summer or in tropical and sub-tropical areas, people use energy mostly on cooling. For example, in Taiwan, the peak of energy consumption happens in a summer afternoon because of excessive air conditioned buildings. Therefore, passive cooling strategies become the alternative choice to cool a space regarding to energy conservation. Even though passive strategies do not produce as rapid a result as active strategies, they solve part of the problem and protect nature. Saving energy is a main issue in using passive strategies, but passive design should provide a comfortable space in order to promote the quality of a living environment. Although there are many advantages using passive strategies, some buildings, especially those with special requirements, still need active strategies, such as mechanical equipment, to achieve the conditions required. The conditions in interior space are affected by the following factors: local climate, site, building shelter, mechanical equipment and human comfort. Regarding architectural design and usage, those above can be categorized into the following strategies: PASSIVE STRATEGIES: using site and building shelter to reduce the climatic problems, and to guide the natural sources into the building in order to reach desired interior conditions without using any mechanical equipment. Although it is not as effective as the active system, it is more environmentally conscious, and it has been practiced in vernacular architecture for a long time. ACTIVE STRATEGIES: the word "active" is the antonym to "passive". Active strategies are parastic; they basically depend on mechanical equipment, such as fans or fluid and pumps, to achieve heating or cooling. Their collector and storage are separated. HYBRID STRATEGIES: mix of both passive and active strategies. STRATEGIES ACTIVE HYBRID PASSIVE HOW mechanical equipment site planning space planning building shelter ENERGY CONSUMPTIO N more less SIZE OF BUILDINGS larger smaller TYPE OF BUILDING hospital office building hotel department store office building retail store school institution clinic residential school clinic Comparison of passive and active system table 1.1 A good living environment can rely on the active strategies, but depending on it too much will increase the annual building air- conditioning cost, and decrease the ability of a building shelter cooperating with the natural environment. The idea of passive strategies does not deny the contribution of the active, its emphasis in using the natural resources can economize energy, and thus reduce the load of the active systems. 2. CLIMATE Climate affects human comfort, building type and passive strategies. Climate is composed of three elements: the sun, wind and water. 2.1 THE SUN The sun is the greatest heat source, and it is also what we need to avoid in passive cooling. In passive cooling strategies, the sun can only be regarded as an energy source, but avoided as a heat generator. The maximum possible intensity of radiation that may be received at a particular location is determined by latitude. Those rays of the sun are received vertical to the surface of the earth pass through the minimum amount of the atmosphere. Vertical rays are not received north of the Tropic of Cancer and south of the Tropic o f Capricorn. Oblique and tangent rays have to pass through a considerable amount of atmosphere before reaching the surface of the earth [Oakley, 1961, p27] / ' ' - — "tongent ray the sun affects the earth’s climate [Oakley,1 961, p27] fig. 2.1 Since there are always humidity and clouds in the equator area, the greatest solar radiation does not happen at the equator, but the nearby two Tropics where fewer clouds and humidity exists. In the northern hemisphere, a south facing slope can gain more solar radiation than the plane in the winter; but during summer, the plane gains more sun rays than a hill slope. 6 2.2 WIND Wind is formed by moving air, when the sun warms the atmosphere, the air expands its volume and reduces the density, and decreases its pressure. In the opposite, when temperature drops, the air sinks, and the density rises, and pressure increases. The air tends to flow from high to low pressure zones. According to the air behavior, the wind is formed and grows unpredictably complex. Winds are grouped into three categories: local and regional persistent winds; global persistent winds such as the trade winds of the tropics, and maverick winds for cyclones, tornadoes and hurricanes. Local persistent winds are almost all in variable small-scale convection winds— the sea breeze, the land breeze, the mountain wind and the valley wind.[Moffat and Schiler, 1981, p38] 2.3 WATER Water is one of the most important elements in nature. It is also a great heat storage. Since water has a higher specific heat than land, it takes longer to heat up and cool down. When water changes phases, it also takes a great amount of energy. When solar radiation hits water in the early morning or late afternoon at a low angle, the radiation will not be stored but reflected by the surface of the water. However, when sunlight hits the water at noon at a high angle, the energy will be absorbed and stored in the water body. Hence, large bodies of water, such as ocean and lake, act as a big solar storage to save energy and then to release it slowly. This effect helps to stabilize the temperature. It also explains the extreme temperature fluctuation in desert areas where water rarely exists. Temperature differences between water and ground also generate convection air currents, resulting in the familiar offshore breezes which provide relief in hot climates [Moffat and Schiler, 1981, p46]. Since water has a higher specific heat than land, it warms up slower during the day. Therefore, the warmed air over the land rises, and the cooler, heavier air of the sea flows towards the land to replace the warm air which rose. At night, this process reverse. Large surfaces of water also temper extremes o f the climate by encouraging evaporation and the transfer of radiation into latent heat [Moffat and Schiler, 1981, p47]. When the water turns into a gaseous state, it draws a tremendous amount of energy from its surroundings, and the temperature drops but the humidity increases. In hot and arid areas, this is one of the most common ways to cool the environment. 8 Water has a higher specific heat than land, therefore water absorbs and releases heat slower than the land. During the day, the solar radiation is absorbed by the land rapidly, the air on land is also heated, so the air pressure is reduced, and the air rises, the denser, heavier cool air from the water flows in, and replaces the hot air. S T o K t MOK-fc * - r£ A » T .__ LoSl Day-night heat flow between water and land fig. 2.3 9 3. LANDSCAPE Landscape can affect microclimate by either the landform or the vegetation. Using landscape to save energy is a powerful tool for conservation: It controls wind, solar radiation and precipitation, tempers extremes of climate, and can save up to 30 percent of a home's total energy requirements for space heating and cooling [Moffat and Schiler, 1981, p11]. 3.1 HOT-ARID AREA In a hot arid climate, the sun radiates intensely to the earth during the day. Since dry earth has a low specific heat, it gains heat very easily; however, at night, the heat retained in the soil will reradiate to the clear sky, and the temperature can drop dramatically from 110 °F to 70 °F within a few hours. Therefore, reducing heat gain during the day and controlling heat loss at night are the main goals when planning an energy efficient building in this climate zone. In any kind of passive cooling strategies, preventing solar radiation and increasing night time ventilation, which must be selective, are the two most important methods to keep down the temperature. However, in a hot-arid area, the landscape must be able to balance the extreme temperatures of day and night by blocking the hot wind and preventing any moisture loss. Vegetation and water can help to achieve these goals. The sun is a problem common to both (dry and humid) tropics. It is too hot and bright, and overheats and dries up all the surface it lights up, 10 reflecting undesirable quantities of light or transmitting undesirable quantities of heat into the interior of the dwellings [Fry, 1982, p27]. Therefore, shading is very significant in these regions. Landscape should be able to serve as a sun block. Tall, high crowned trees planted close to the home are the best. Palm trees are often chosen for this solar control [Moffat and Schiler, 1981, p81]. Vines are also a common choice for wall or roof covering to protect the structure from direct sunlight, often the south-facing fagade requires a maximum amount of shading. Since there is a water shortage in most hot-arid regions, grass is not a good choice because it requires a great amount of irrigation. Consequently, a drought- resistant ground covering is a preferred selection. On both east and west fagades, low trees or bushes are favored because of the low morning and afternoon sun. However, trees with loose structure and light foliage are desirable at the east side of the building, since they can reduce the radiation generated by the morning sun but allow the pleasant dawn light to enter. 1 1 summer high angle sun winter low angle sun Vine covered trellis shading southern exposure [Moffat and Schiler, 1981, p100] fig. 3.1 W i n t e r SUM High crown plants shading south exposure on summer, not winter [Moffat and Schiler, 1981, p100] fig. 3.2 12 One of the goals of landscaping is to prevent hot-dry winds. Cactus or a man-made screen can be used as a windbreak to guide away the undesirable winds. The windbreak needs to be placed perpendicular to the prevailing wind. The openings of the building should be protected from unwanted heat which is mainly from the sun. If there is a cool breeze, the landscape should serve as a guide to lead this breeze into the living space. The other goal is to prevent moisture loss. In hot-arid areas, water is very precious, and should be protected from direct sunlight. A pool or fountain is desirable in landscape designs of this climate. This body of water needs to be shaded to prevent evaporation by sunlight, and placed upwind from the openings of the building in order to bring the cool, moist breeze into the living space . 3.2 HOT-HUMID AREA Unlike the hot-arid region, the sky of the hot-humid climate is always cloudy and the water source is plentiful. The moist atmosphere and cloudy sky prevent the heat from reradiating out at night, hence the temperature difference between day and night is not as great as the hot- arid zone. Therefore, some strategies used in the hot-arid area can not be practiced in this region. In a hot-humid climate, the temperature cannot be reduced by evaporation because additional water in the air only adds to the discomfort [Moffat and Schiler, 1981, p95]. Avoiding heat storage and promoting ventilation to dissipate humidity are the two key goals of 13 energy-efficient design in hot humid areas [Moffat, and Schiler, 1981, p96]. In this region, high-canopied palm trees are common, and ideal for the site. Not only can they provide shade from the cruel summer sun, but breezes can pass through to the structure. It is ideal to have natural shading provided by plants, but heavy planting can produce unwanted humidity and block the desirable cooling breeze. If palm trees are chosen to be planted, they should be properly placed, otherwise they might block the welcome winter sun. Moreover, the plantation must serve as a wind channel to guide the cooling breezes into interior space. NORTH SOUTH NORTH Tree layout in hot humid area [Moffat and Schiler, 1981, p99] fig. 3.3 14 Cool breezes pass through unobstructed planting into the living space [Moffat and Schiler, 1981, p98] fig. 3.4 Using a tree funnel to lead wind toward the home can increase the wind velocity and raise the cooling ability of a light breeze. The other method to increase the wind speed is using a windbreak with narrow openings. This effect is known as the Venturi effect.” (see Ventilation chapter) 15 » . • • • . * " . / J • * ; «; . s •: ; ••• „.. ; . **"— W ^ Tree funnel to enchancing breeze [Moffat and Schiler, 1981, p103] fig. 3.5 § * 0 4 ^ 1 * • j p • • • m * « f « ^ ♦ •fastest Venturi effect: a small opening to increase wind speed [Moffat and Schiler,1981, p43 ] fig. 3.6 16 Since water and moisture are already too much for humid areas, placing a pool or fountain is not a good idea, but only brings mugginess, producing glare, and attracting insects. Ventilation is the only way to cool the building in this region. Therefore, inducing breezes towards the living area is the main concern of the design. If possible, the house should be placed on a rise in the terrain, this will increase the breeze and ventilate through the building. A paved surface is not desirable in both hot-humid and hot-arid landscapes. Any external paved areas made of concrete or stone, which absorb and reradiate heat, should be minimized, shaded, and located downwind of and as far as possible from dwellings and related outdoor areas.[Moffat and Schiler, 1981, p80] Besides changing the microclimate, landscape is also good for human health, Plants can filter and purify the polluted air. Bushes are the best choice as the natural air filter and it is better to alternate with trees in order to achieve the best result, but be careful not to block breezes away from the house. 17 4. BUILDING Buildings serve as the shelters to protect humans from natural hazards, and to provide a comfortable living environment. Therefore, the building form has to respond to the local climate in order to achieve these goals. 4.1 BUILDING FORM A square and a rectangle are the basic shape for the buildings. Usually, buildings with more surface area gain heat and lose heat much more quickly than those with less surface area. The surface to volume ratio dominates the condition inside of buildings. If a building has a large surface area, the internal condition is more influenced by the external climate than in one with less surface areas. Smaller buildings have larger skin/volume ratio than large buildings. For example, an cube has a volume of 1 ft3 and a surface area of 6 ft2. The skin/volume ratio is 6. On the other hand, for a 2'*2'*2' cube with a volume of 8 ft3 and a surface area of 24 ft2. The skin-volume ratio is only 3. A building with less surface area is dominated by its internal load, which is the heat of people, machinery, lighting and so on. Since the land cost in an urban area is much higher than in a suburban area, to optimize the usage of the entire real estate, high rise buildings become a preferred choice of developers and owners. High rise structures need to be light in weight; therefore, steel frames and curtain walls have been developed. Curtain walls are mostly glass which permits daylight to enter the 18 building. On the other hand, curtain walls act as a wrap to seal the whole building. Therefore, the skin of the building does not respond to the weather and the environment. The building interior loses contact with the surrounding environment, and the ability of using natural forces. These buildings totally depend on a mechanical system to achieve cooling , heating and some lighting. Smaller scale buildings, such as residential, have large skin/volume ratios, that permit more sunlight and natural ventilation to work inside of the space, they have more gain and loss through the skin because their skin/volume ratio is bigger. The table below shows the relationship between these two forms: BUILDIN G FORM SURFACE AREA HEAT GAIN HEAT LOSS VENTILA TION TYPE OF USE high-rise buildings office department store SQUARE less less less worse RECTAN GLE more more more better small-scale residential clinic school institution comparison of the square and rectangular building form table 4.1 19 According to the table 4.1, the buildings with less surface area are easier to control by mechanical equipment, and for passive cooling the rectangular building is more desirable. Using natural forces to cool a space in a hot area, the building form should be carefully considered. Square forms are recognized as the best building shape for preventing heat gain in summer, and eliminating of heat loss in winter, In fact there is a steady progression on the building form: in cold climates, the best building form tends to be a cubic form in order to maintain certain temperature inside. Buildings in temperate climates are best elongated along the east west direction. In hot humid climates, instead of a big building, the shelter is best broken into small parts in order to increase ventilation, and increase the building skin area to prevent heat accumulation inside. In hot arid areas, the courtyard building is the most popular form among all because the center courtyard helps to create a microclimate within the building. Olgyay's conclusions for basic house forms are different, his conclusions are: 1. The square houses is not the optimum form in any location. 2. AH shapes elongated on the north-south work both in winter and summer with less efficiency than the square one. 3. The optim urn lies in every case in a form elongated some where along the east-west direction [Olgyay, 1963, p90]. 20 HOT-ARID AREA It is difficult to generalize. For example, although the winter condition in hot, arid regions would permit an elongated house design, the heat in summer are so severe that a compromise is required and the traditional solution is a compact, inward looking building with an interior courtyard. This minimizes the solar radiation impact on the outside walls and provides cool air within the building. [Konya, 1980, p39] The courtyard is an important element in building design in a hot-arid area. It is shaded by walls, trees, or trellis to prevent direct radiation from the sun, and it usually contains a pool, a fountain, or vegetation to provide an evaporative cooling effect. Since reducing surface area can reduce heat gain, the buildings in a hot arid climate tend to be jointed together in order to achieve protection against the heat with shaded structures. HOT-HUMID AREA Since the day-night temperature difference in hot humid area is not as great as in a hot arid region, increasing shade for elimination of radiation, and augmenting ventilation to catch any available air movement are the two main goals in building design. In this climate zone, ventilation is the most effective way to cool the environment, the buildings are placed loosely in order to achieve this goal. 21 4.2 BUILDING MATERIAL Besides the building form affecting the thermal capacity, the material also plays an important role in conductivity. The amount of heat penetrating a building depends largely on the nature of the wall and roof. During the hot periods of the day, heat flows through these elements into the buildings where some of it is stored; at night, during the cool period, the flow is reversed.[Konya, 1980, p40] The building materials and type of construction must respond to the need of maintaining internal temperatures in a comfortable range against the external conditions. Hence, the following characteristics of materials and construction should be carefully considered. ABSORPTIVITY VS. EMISSIVITY Radiation might be reflected or absorbed by an opaque area. The color and texture of the surface material gives a good indication. Solar radiation consists of visible and short infrared waves. However, most of the solar energy is concentrated in the visible wavelength, the reflectivity of material is related to the color value. The long infrared wave happens between objects at night time. For instance, During the day, the lighter the color, the less the absorptivity, and the higher the reflectivity. In other words, the darker the surface, the more heat it absorbs, and the higher temperature it gets. However, color does not indicate the behavior of a surface with regard to its emissivity or power to emit long-wave or infrared radiation and both black and white painted surface lose heat to the sky at night at equal rate. [Konya, 1980, p40] If a material's absorptivity is lower 22 than its reflectivity and this material releases the absorbed heat as thermal radiation(long-wave), it will lower the temperature of the building. The table 4.2 shows the reaction of materials to solar and thermal infrared radiation: 23 SURFACE % OF REFLECTIVITY SOLAR RADIATION % OF REFLECTIVITY INFRARED RADIATION % OF EMISSIVITY INFRARED RADIATION Silver, polished 93 98 2 Aluminum, polished 85 92 8 Whitewash 80 Copper, polished 75 85 15 Chromium plate 72 80 20 White lead paint 71 11 89 White marble 54 5 95 Aluminum paint 45 45 55 Indiana limestone 43 5 95 Wood pine 40 5 95 Asbestos cement, aged 1 year 29 5 95 Red clay brick 23-30 6 94 Gray paint 25 5 95 Galvanized iron, aged 10 72 28 Black matte 3 5 95 Reflectivity and emissivity of materials table 4.2 24 4.3 MOISTURE EFFECT Materials absorb moisture according to their hygroscopic qualities. In generalorganic substances have higher absorptive properties than inorganic materials. With increased moisture content, materials show higher heat transmittance because of the relatively high thermal conductivity of water [Olgyay, 1963, p114]. 4.4 INSULATION Insulation is most effective under steady state conditions or if the direction of heat flow is constant for long periods [Konya, 1980, p41 ]. Insulation may be categorize into two types: resistance insulation and capacity insulation. RESISTANCE INSULATION The insulation value of the material, characterized by the "U" factor (overall heat transfer coefficient expressed in Btu/hr/sq. ft), defines the heat resistance. The lower the U value, the better the insulating effect. Air is one of the best insulators because of its light weight and low thermal conductivity. Roofs and walls often contain two or three layers of air gap to reduce heat transfer. However, reducing heat transfer depends on the enclosed surface which acts as a heat transferring medium across the space. Therefore, choosing a highly reflective material such as metal foil for the air space is recommended because it can reduce thermal 25 conductivity. Also, the angle of the roof and the direction of heat flow also affects heat convection and conduction. CAPACITY INSULATION Capacity insulation is often referred to the heat storage value of a material, characterized by density times specific heat. The larger the heat storage value the longer time it takes for heat to go through the material. This period of time for material to reach an equilibrium temperature is called "time-lag". Materials with large time-lag are usually of heavy weight and higher density. 26 OVERALL HEAT TRANSMISSION COEFFICIENT(U) AND TIME LAG CHARACTERISTIC DATA FOR HOMOGENOUS WALLS MATERIAL THICKNESS INCHES U VALUE BTU/HR/SQ. FT TIME LAG HOURS STONE 8 12 16 24 0.67 0.55 0.47 0.36 5.5 8.0 10.5 15.5 SOLID 2 0.98 1.1 CONCRETE 4 0.84 2.5 6 0.74 3.8 8 0.66 5.1 12 0.54 7.8 16 0.46 10.2 COMMON 4 0.60 2.3 BRICK 8 0.41 5.5 12 0.31 8.5 16 0.25 12.0 FACE BRICK 4 0.77 2.4 W OOD 1/2 0.68 0.17 1 0.48 0.45 2 0.30 1.3 INSULATING BOARD 1/2 1 2 4 6 0.42 0.26 0.14 0.08 0.05 0.08 0.23 0.77 2.7 5.0 In the above table U value is based upon an outdoor surface conductance of 4.0, and an indoor surface conductance of 1.65 Btu/hr/sq. ft. For composite construction to the individual sums of the time lags an additional estimated lag should be added. It is customary for two layers and light construction walls to add 1/2 hour more; for three or more layers, or very heavy constructions, one hour additional lag is preferred. table 4.3 27 HOT ARID AREA In this region, since most of the buildings have to fight with the extreme climate conditions, yet keep the internal temperature within a certain temperature range. The buildings here are traditionally constructed with thick walls and roofs with very small openings to prevent heat loss at night and heat gain during the day. The buildings are usually constructed of materials such as clay or stone, since these kinds of materials are denser and heavier, the time lag is larger. By doing this, during the day the buildings can absorb solar radiation slowly, and accumulate the heat in the mass of the walls and roof, at night, the mass gradually releases the stored heat. Flat roofs are practical in this seldom raining area, but the traditional roofs in desert areas are domes or vaults shapes because these shapes have larger surface areas than their base, solar radiation is diluted and re-radiation during the night is more feasible. HOT HUMID AREA Although the solar radiation has been partially diffused by the moisture in the atmosphere in this region, shading and ventilation are two critical components of comfort. The vernacular architecture in this region is usually very open in plan and construction; however, this raises a problem that the building needs to be open all the time. The building materials must be light in weight and low in heat capacity to prevent any accumulation of the heat during the day time, and to reduce re-radiation, which can cause discomfort at night. Subsequently, both the interior and 28 exterior walls have to be minimized in order to maximize air movement through the space. The roof becomes a dominate element of a building. The roof is usually steeply sloped with thick thatch. It can provide shade for the living space below and drain the heavy rainfall, which occurs in this region, quickly and silently. The other advantage of this kind of porous roof material is that it can avoid condensation. 29 5. Solar Control The sun is the most powerful source which determines our thermal environment. Solar radiation enters the atmosphere and causes climatic phenomena on the earth, such as the wind movement and evaporation of water. In addition, solar radiation also has a decisive effect on the lives of people. The amount of solar radiation penetration through the window glazing causes the interior temperature to rise, and result in the so called the "greenhouse effect". The sun rays consist mainly of short-wave heat radiation. The incoming sunlight from transparent windows is absorbed by wall, floor surface, and furniture. Conversely, these surfaces emit long wave radiation, and since glass is opaque to the long-wave heat radiation, the heat is trapped inside the space. In tropical areas, solar radiation should be prevented from entering buildings since it is usually the source of discomfort. The following methods are able to reduce the solar heat gain through the windows: (1) orientating the building in such a way that fagades with large openings face towards the directions which receive less sunlight; (2) using special glassing which acts as heat filters; (3) Using shading devices such as screens, overhangs, louver systems, blinds, etc., in front of windows [Harkness and Metha, 1979, p37]. Well designed shading devices can control solar radiation into a space, and furthermore, the amount of lighting inside the space. Horizontal overhangs work according to the solar altitude, and vertical 30 ones work with the solar azimuth. Adjustable devices, such as louvers and blinds provide more flexibility for the sunlight entering a space. The control of solar heat gain has been a problem from long ago. The skin of the building serves as filter between the outdoor and indoor conditions. But the radiant heat is not as easily managed as other conditions, such as light, sound and air, it needs to be taken care of before it reaches the building shell. Traditionally in hot and arid areas, buildings are crowded together to provide shade to each other, and to shade narrow alleys or small public spaces in between. In hot humid areas, the shading device should combine the protection from the intensive rain while simultaneously allowing air to flow through. Therefore, verandahs, overhangs, and awnings are most welcome. In both hot arid and hot humid areas, plants which provide shade are mostly welcome. 31 In hot humid areas, loose planting allow air to flow through. In hot arid areas, houses are grouped together to give each other shade. town layout in hot areas [Konya, 1980, p49] fig. 5.1 5.1 Shading Effects Of Plants Plants around the house do not only provide a beautiful view to the occupants, but also reduces air-borne sounds with great efficiency. Furthermore, if the trees are planted densely, the thick leaves filter the air and eliminate dust. Plants also can reduces the glare. However, in hot places, plants are great for shading the house. A tree planted in front of a window does not only reduce the solar radiation entering the house, but the evaporation process of the leaves also helps to cool the air. Vines are another natural heat-control device. The cooling effect and the evaporation process makes them valuable on the walls which receive a large amount of sunshine. Both vines and trees should be carefully selected according to their shading performance and their appearance. Each tree's appearance and characteristics are different. Therefore, the shading effect also changes. For instance, existing trees and shrubs provide the simplest way to shade the low buildings, and deciduous trees are especially valuable as they do not cut out the winter sun [Konya, 1980, p45]. 5.2 Shading Devices The windows account for the greatest amounts of heat entering the building and therefore shading them offers the greatest protections [Olgyay, 1963, p72]. Therefore, for controlling the temperature inside a building, the solar radiation needs to be reduced. To reduce radiation, the window should be well protected from the sun. Inside glass shade protectors are such devices as blinds, roller shades, and curtains. The sun protector effect for glass depends on several factors: the reflectivity o f solar radiation of the applied material and its color coating, the location of the shade protection which influences the radiation the radiation and convection heat impact, and the specific arrangement of the applied shading method [Olgyay, 1963, p67]. 33 Light colors reflect the sun radiation , and the dark colors absorb it. For example; polished aluminum has 85% of reflectivity of solar radiation. Conversely, the black and matte material reflects only 3%. SURFACE REFLECTIVITY PERCENT OF SOLAR RADIATION: polished aluminum 85 white-lead paint 71 light green paint 50 gray paint 25 black matte 3 table of material reflectivity [Olgyay, p68] table 5.1 Inside shading protecting devices which are placed behind the glass, can only reflect part of the radiation , and a part of the radiation is absorbed convected and reradiated into the room. If the device is on the glass surface, part of the radiation is reflected, and part of it is absorbed, convected, reradiated into the outside and inside space. Outside shading devices release the absorbed, convected and reradiated heat to the outdoor air. Hence, location of shading device affects its effectiveness. The ability of keeping radiation out increases as it is located behind, on, or in front the glazing surface in that order. 34 There are no absolute answer to this question, different type of protector serves different function regarding to the effectiveness of shading devices. Therefore, they can only be categorized according by certain restrictions. However, shading devices give by far the most efficient performance, since by shaping them according to the changing seasonal sun-path, both summer shading and winter heat gain can be achieved [Olgyay, 1963, p63]. The most common shading devices are: the horizontal member (overhang), the vertical member (fin), and eggcrate (which is the combination of both horizontal and vertical member.) - AIM I MOtlZONlAi ftlVICI w r m Standard types of shading devices [Olgyay,1963, p73] fig. 5. 2 35 All devices have a characteristic shading mask, which represents the section of the sky they conceal. In many cases, different shading devices will leave similar masks so that several possible solutions to a shading problem will exist [Konya, 1980, p46]. Therefore, the designer can examine the need of shading area, and create a shading device accordingly. In his book Design With Climate. Olgyay has suggested the following four steps for designing the and examine shading device. StepT. To define the time when shading is needed: Data should be collected for the daily temperature changes throughout a year at the place in question. Average daily temperatures should be used with hourly or two hourly data for each month o f the year. The temperatures which fall over the bottom line of the comfort zone will define the overheated period. This can be tabulated on a chart where the hourly and monthly divisions server as ordinates. Step2: To determine the position of the sun when shading is needed: On a sun path diagram the curve lines represent the movements of the sun for the dates shown. Step3: To determine the type and position of a shading device for the overheated period: This is plotted on a protractor having the same scale as the sun-path diagram. The shading masks are independent of latitude, orientation, and time, and can be used in any situation. Most shading devices produce shading masks which can be simply resolved into one of the three basic types: vertical (fm), where the characteristic shape is bounded by radial lines; horizontal(overhang) with a mask of segmental shape, and egg- crate types, which are a combination of the first two. Step4: To evaluate the shading device: The shading mask’s dimension must be determined to ensure correct shading during the overheated period, and to allow, if necessary, some sun to penetrate during the underheated period. Step 3 and step 4 can be reversed; the required shading can be determined and as appropriate shading device then developed to suit the situation [Olgyay, 1963, p80]. 37 w t > H I M i B A f i p i l l i r N i a n i l l t l , 44# N , {•*. A . )5* *. l*f. » .« + r * + A f. m t w m a/ A fW t nllW e ii<m #*k W - MU»1, FU'U*. ><* N. Laf. N«« 4#*H. la*. Sun path and objection. Overheated periods transferred to sun-path diagram [Olgyay, 1963, p80] fig. 5.3 3 6 6. VENTILATION »QtltC*C4( lettutt IM7MVMVM<VA9M ^:.v:>v.:.>y«v/.sV/A i mmzm a * *W «•**»#>*« Iw m»M D*.t<«<«)ww4t«M t» *. m m iM *•» Basic types of shading devices an d their projection. [O lgyay, 1963, p81] fig. 5.4 Ventilation plays an important role in passive cooling systems. It does not only supply fresh air for human health, but it also cools the building structure, removes the perspiration from human skin, and keeps inhabitants comfortable when the interior temperature is higher than outdoor. Air movement is caused by a difference in air pressure. A pressure difference is caused by the external wind flow (wind force) or the temperature gradient between indoor and outdoor (thermal force) [Givoni, 1976, p281]. Either cause can act alone or in conjunction. 6.1 THERMAL FORCE-CONVECTION Hot air is less dense than cool air. If the indoor air is warmer and therefore less dense, the indoor vertical pressure gradient is less than the outdoors. This means that inside there is an excess pressure at any level above the opening and a depression below it, and these differences increase with vertical distance from the aperture. The indoor air cannot flow out, however, as no aperture is available where the pressure differences exist. When different openings are provided at different heights and the indoor temperature is again higher than outside, the pressure difference is formed in such a way that excess indoor pressure builds up at the upper opening, where air will flow outwards, while a depression is created at the lower level, inducing an inward flow. When the indoor temperature is lower, the positions are interchanged and flow direction reversed [Givoni, 1976, p281]. Olgyay also points out that the larger the temperature difference, and the greater the distance between vertical 40 inlet and outlet openings and the greater the size, the more vigorous the air flow. This phenomenon is the so-called "stack effect.” [Olgyay, 1963, p111]. W A R M A IR W A R M A IR CO O L AIR / COOL A IR CO O L A IR i Stack effect fig 6.1 6.2 WIND FORCES Wind results from different air pressures. Air tends to move from a higher pressure zone to a lower pressure zone. In summer or tropical areas, the cooling comfort of sufficient speed is of more importance than the volume of air change. For ventilation, window openings and the interior divisions have a great effect on the wind speed and air circulation inside a space. Window Openings 41 Basically the window opening has an effect on how much air flows through a shelter; however, the position and the size of the opening decide how the air will circulate inside of the space. In order to let air flow through a space, both inlet and outlet openings are required. Inlet openings control the amount of air flow, and the outlet openings direct the air stream. When a building is placed in an air stream, air piles up against the windward side of the wall, and creates a high pressure zone. On the opposite side of the building, the leeward side, the air pressure is relatively low. Since air tends to flow from high pressure to the low pressure zone, placement of openings is most effective when inlets face a high and outlets a low pressure area. According to Givoni, when the wind angle is perpendicular to the inlet window, the ventilating ability of a traditional cross-ventilation room with window on the opposite walls does not work as well as rooms with windows placed on adjacent corner walls [Cook, 1989, p59]. Givoni also points out that if windows are positioned 45 degrees to the wind direction, the average indoor air velocity is increased and better indoor air circulation is also provided [Konya, 1980, p52]. The size of inlets also affects the air speed. As mentioned above, the inlet should be related to the flow pattern in order to catch the incoming air movement. In addition to that, the attachments, such as overhangs and blinds, of the inlet openings are also important elements to direct the flow pattern. The interior air velocity can be increased if the outlet is larger and the inlet is smaller, which is known as the "Venturi effect." Conversely, if the outlet is smaller than the inlet, the interior space will receive less benefit from the 42 openings since the air velocity is increased mostly outside and downstream of the building. Venturi Effect [Lippsmeier, 1969, p 199] fig. 6.2 Ideally the air-stream should benefit the occupants at sitting to standing height in a living room, and sleeping height in a bedroom (especially in hospitals) [Lippsmeier, 1969, p197]. Figures 6.3 indicates the relationship between air flow and the position of inlet openings: a. High inlet placement without equal outside wall surface exerts upward forces, resulting cooling in the wrong place. b. Inlet opening in the middle equal wall surfaces results in pleasant flow pattern. c. Inlet opening at the bottom of the wall results in the flow sweeping the floor surface. Inlet openings affect the interior air flow fig. 6.3 The attachments of windows, such as overhangs or blinds, also affects the direction of the air movement inside of a space. An overhang does not only work for shading, but placing it in a different position results in a different air flow effect. An overhang at ceiling height intercepting and diverting air masses toward the inlet improves the ventilation effect. Similar solid overhangs, when placed directly above the window opening, cause the air to flow toward the ceiling because they eliminate the outside pressure effects from above. Since the air bypasses the living zone, this effect is unfavorable. The same overhang modified by a slot equalizes the pressures, thereby lowering the flow pattern to a more useful level [Olgyay, 1963, p110]. 44 a b c a: The overhang collects the air flow which otherwise would escape, and enhances incoming flow effect b: The solid overhang blocks the air pressure above and directs the flow upward away from living zone. It is an unfavorable effect, c: A gap between the overhang and the building equalizes the external pressure and creates a desirable flow pattern. Internal Division An unobstructed straight flow ensures the speediest air movement. Placing furniture or partitions in an air stream reduces the air velocity and changes the flow pattern. Therefore, arranging internal divisions should be carefully considered according to the flow pattern. The laminar flow stream is bordered by turbulent eddies which causes a slow cartwheel motion in a relatively stagnant air mass surrounding the flow [Olgyay, 1963, p106]. Partitions affect flow patterns only when they are placed in the air stream. Placing partitions in the air flow stream will slow the movement, and reduce the ventilative ability. Overhangs affects interior airflow fig. 6.4 45 Based on Givoni's research, the velocity is the lowest when the partition is in front of or near the inlet window, as the air has to change direction upon entering. But better conditions are obtained when the partition is near the outlet [Givoni, 1976, p303]. 46 g- a. The unobstructed air flow passes through a one-zone room. 47 b. The partition parallel to the flow pattern does not change the air movement. c. The partition perpendicular to the flow has great effect on the air movement. d. The upper room is not ventilated, and the ventilative ability of the flow gets weaker in the lower room. e. The upper room has sufficient ventilation, and the lower room receive no air movement. f. The route of the air movement is decided by the shortest distance between inlet and outlet openings. Therefore, room A receives most of the airflow and the ventilation of room C is the smallest. g. When a wall placed perpendicular to the air flow, the air movement does not enter the rear room. [Cho, 1989, p72] Internal division affects the airflow fig 6.5 6.3 WIND TOWER The idea of a wind tower is to catch unobstructed higher level breezes, it is popular in hot arid areas, such as the Persian Gulf states, North Africa and Pakistan. In some locations, where wind is mainly from one direction, the tower forms a scoop with only one opening facing that direction. In areas where wind is from several directions, the tower has openings in all directions. The wind tower functions in the following manner: The air entering the tower from the windward opening with positive wind pressure coefficient, leaves through any opening which has a pressure coefficient smaller than that at the windward opening. That is, part o f the air which has entered the tower is lost through other tower openings, (which has negative pressure coefficient) and the rest enters the house. The portion entering the house may be partially cooled by the structure, if the structure has stored a sufficient amount of coolness from the night before. When the air flows over moist surfaces, it is further cooled evaporatively. During the night, when air is flowing through the tower and the house, the ambient air coolness is also stored in the building mass. With heavy 48 structures this energy storage plays an important role in providing thermal comfort during the following day.[Bahadori, 1985, p119] S H H H I - S^sr/crs 7 M A J - c c tc s . 2 > r D/rfCT/4 '6 TV, if AAVY* W i / * e n A r r JM E A S O T C X f/z i'// '/>/ * $ _ /~ a ' r v - /.ec J S .1 /TV ir ;.\ £ > J.'OC/'S E i/ee ir k'^isrss s irs'i t f4 fiS nun < < ro" rE 'JTL ■ A D 7C0) f)> V C S /O C P Jr/M ' TEAS' /y tr C h 'T S T fs 'r /s r A /V {uses s/ a cs /s e e '» ) U -/T /S m v a 'a s c o re s S'a e T/:/.r/<rT' b e s r f t r:s //>*/ c hfss//> scooss H E A R T , Wind towers in different regions [Wang, p59] fig. 6.6 49 On the other hand, when the wind comes from the opposite direction of the wind tower opening, a negative pressure will be formed in front of the tower openings, the air cycle will reverse: the interior hot air will be pulled out through the tower opening, and the cooled air will flow in from lower level openings. When the outdoor air is cooler than the indoor air, the wind tower also serves as a device for the stack effect. That is, when the hot air rises, and the cool air enters from outside at the lower level openings. According to Nkuo’s thesis, Passive Cooling Methods for Mid to High-Rise Buildings in The Hot Humid Climate of Douala. Cameroon. West Africa, “ ...the wind scoop can be used in a hot humid climate mainly to ventilate the interior environment, and to flush the buildings of excessive heat, more than to cool or lower the temperature of the air [Nkuo, 1989, p44].” The disadvantages of the traditional wind towers are: 1. Dust, insect and sometimes small birds, can enter the buildings. 2. A portion of the air admitted in the tower is lost through other tower openings and never enters the building. When the tower has only one opening facing the wind all the air entering the tower enters the house. 3. The amount of coolness which can be stored in the tower mass is generally limited (due to small mass and low specific heat o f the energy- storing material), and may not be enough to meet the cooling needs of the building during a hot summer day. Or the exposed surface area of the energy storing material may not be sufficient to allow a high rate of heat transfer. 4. Even in buildings with basements, where the air is made to flow over moist surfaces, the evaporative cooling potential of the air is not fully utilized. In hot, arid climates evaporative cooling is a very effective process for providing thermal comfort. In fact, because of this effectiveness, and due to their relatively low initial and operating costs, 50 electrically driven evaporative or desert coolers have now become very popular in Iran, even in cities which have traditionally employed wind towers. 5. Wind tower do not find any application in areas with very low wind speeds.[Bahadori, 1985, p119] Despite the disadvantages described above, A wind tower (or wind scoop) is still a popular device in hot arid areas for bringing wind into a space, and to circulate the air inside the building. For example, in Hydrabad, Pakistan the wind scoop system has demonstrated the 120°F outdoor temperature can be decreased to 95°F in the indoor environment [Wang, 1990, p58]. Wind scoop in Hydrabad, Pakistan [Wang, 1990, p38] fig. 6.7 51 Increasing roof surface helps increase the rate of heat lose. In many hot arid areas, curved roof are widely chosen over flat roofs. Despite that the curved roof is structurally stronger than the flat one; however, more importantly curved roofs increase the ability of heat transfer, hence are easily cooled. Warm air gets less dense, then rises within domes or vaults away from living space, and since the hot air is kept within the curved roof, the heat transfer from the roof is minimized. Although a curved roof absorbs about the same amount of the sun’s energy as a flat roof, there is a greater convectional heat loss in the former due to the movement of the air across the roof [Clark, 1980, p201]. As the velocity increased when the air flows over a curved roof, the pressure decreases. The reduction of the pressure will then draw the hot air out of the dome, then the cooler air enters from the lower openings to enhance the cooling inside the space. 52 The dom e roof and ventilation [Brown, 1985, p99] fig. 6.8 53 7. EVAPORATIVE COOLING Evaporative cooling has been practiced in hot arid areas, such as Egypt and Persia (now Iran), for centuries. Records dating back to 2500 BC. show that the Pharaohs of Egypt employed servants to fan air over large earthen jars filled with water. The water seeping through the porous walls of the jars constituted a wet surface which provided cool air when the water evaporated converting sensible heat to latent heat [Al-Qahtani, 1987, p51]. The concept of evaporative cooling is that, when warm air passing over water evaporates the water and, as a significant amount o f heat is absorbed in the process, the air is cooled. The evaporated water is retained in the air thus increasing its humidity: for this reason, evaporative cooling can only be used in relatively dry climate, and is found in desert, composite and Mediterranean zone [Konya, 1980, p57]. Evaporative cooling can be categorized into direct and indirect methods: The direct method placed the devices inside buildings to generate coolness directly by the evaporative effect. Whereas, the indirect method placed the devices outside near the building to provide coolness to the interior space indirectly. The temperature of the walls and the roof are reduced, and the heat conduction through the building shell is also diminished, or the buildings are cooled by the air flow. 54 7.1 Direct Evaporative Cooling Evaporation cooling does not work alone, it always works in conjugation with ventilation. For example, in New Gourna Egypt, a porous jar is placed inside of a six-foot wind catcher, so when the breeze passes over the wet surface of the jar, it brings out the moisture, evaporates it and decreases the interior temperature about 4 °C. Prcvaling breeze coded room .charcoal screen SECTION THROUGH EVAPORATIVE COOLER USED N EGYPT Evaporative coo ler in New Gourna, Egypt [Al-Q ahtani, 1987, p52] fig . 7.1 55 Simply placing a damp straw matting on a wood frame in front of a window on the path of an air flow, when a breeze passes through it, the matting does not only filter the dust, but also cools and humidifies the incoming air as well. Cunningham and Thompson used modern technology to elaborate on this idea by created a system consisting o f a down draft passive evaporative cooling tower attaching to a building. At its top, vertical wetted cellulose pads, 10 cm. thick (CELdek), were installed. A plywood "X " baffle at the top o f the tower catches the wind and directs it downward. Water is distributed at the top o f the pads, and is collected at the bottom by a sump and recirculated by a pump. On the opposite side o f the building, a solar chimney was built in order to enhance the cooled inflow through the cooling tower and the building. Outdoor air flows down the cooling tower through the building to the attic and then out through the solar chimney [Givoni, 1991, p3067]. According to Cunningham and Thompson's experimental data, the performance of this system is outstanding. For example, At 4 pm on Aug. 23, 1985, the exterior temperature was 40.6°C but the tower outgoing air temperature was 23.9°C and the interior temperature was only 24.6°C. 7.2 Indirect Evaporative Cooling There are some good examples of traditional indirect evaporative cooling. The most typical and effective one is the 56 courtyard house, which is formed by a waterbody (either a still pool or a fountain) and some planting. A waterbody, such as a pool or a fountain in the path of an air flow, which will enter the building, can help cool the interior space. To assure the moistened air will enter the desired space, the pool or fountain must be protected by two or three walls, and shaded, which keeps the direct sun out and prevent water to evaporate excessively. A fountain (or a spray pool) is more effective than a still pool o f the same size and has the additional advantage that is not only cools the air but can also " wash" i t : the water droplets stick to dust particles in the air, which can then no longer remain in suspension[Konya, 1980, p57]. Usually, trees and flowers are planted around the fountain. This does not only provide a beautiful setting, but also creates some shade, and increases the relative humidity of the courtyard. Basically The courtyard house is a popular building form in hot and arid areas. It is also an ideal form for creating its own micro climate. Windows facing the courtyard are usually larger to insure most of the benefits, such as the cooler breezes, beautiful views, and moisture, from the waterbody and the plants. On the other hand, windows on the outer side of the building are relatively small in order to prevent the hot air and dust from entering the house. 57 Courtyard Housing fig. 7.2 An alternative method is to cool the building by keeping the outside walls moist. Exposed exterior building surfaces that are heated by direct sunshine or hot ambient air can be cooled effectively and inexpensively by spraying them with water. As the water evaporates, it draws most o f the required latent heat from the surface, thus lowering its temperature. The surfaces can be sprayed intermittently , since it is only necessary to keep the surface moist [Cook, 1989, p93]. A flat roof also can be permanently covered with a layer o f water an inch or two deep instead o f sprinkling. However this is less effective as the solar radiation heats the roof space through the water. In any case, the evaporation and thus cooling occurs outside o f the building structure. A further difficulty is to keep the water moving, 58 otherwise it could provide a bedding-ground for mosquitoes and other insects [Lippsmeier, 1969, p213]. 7.3 Two Stage Evaporative Cooling Conventional two-stage evaporative cooling is accomplished by precooling air without humidification in an indirect cooler (stage 1)and then evaporatively cooling the dry air coming from stage 1 in a direct evaporative cooler (stage 2). Thus its temperature is still further reduced, although at the expense o f significantly increased humidity ratio[Cook, 1989, p92]. A rock bed can be used as a thermal storage and heat exchanger, It has been used effectively in two-stage evaporative cooling systems, There are two kind of systems: thermal storage and desiccant. The thermal storage capacity of a rock bed has been widely used in the day-night system. At night, the direct evaporative cooler lowers air temperature to a nocturnal and wet-bulb, and that cool and humid air is then used to lower the temperature of a rock bed which is consisted of non absorptive rocks. During the daytime, the surrounding air reaches higher temperatures. External air then enters through the cool, moisten rock bed. the air becomes cool and moist. This system only works in hot arid climates. Otherwise the air moving through the rock bed gets very humid due to change of relative humidity. Furthermore, this idea has been used for the seasonal two- 59 stage evaporative cooler, In winter the rock bed is required to be large in order to store the required coolness, In summer, the warm air can be cooled by the rock bed before entering the building. In addition, the rock bed has been used for another function in humid areas, where the day and night temperature differences are small. The day-night rock bed does not work effectively under these conditions. The alternative way is using the rock bed as a desiccant. The rock bed must be heated to dry the rocks. When the external humid air passes through the bed, the moisture within the air is absorbed by the rocks. The dried air then can be cooled through an evaporative cooler or simply another rock bed with moist, and lower temperatures. 60 K h M W m « Tw o-stage evaporative cooling, utilizing a rock bed fo r storage and heat exchange [S tein ,1986, p371] fig. 7.3 However, the two-stage evaporative cooler is not recommended due to its low efficiency and performance. 61 8. Radiative Cooling The sky, or rather the outer space beyond the atmosphere is the only heat sink outside the planet Cosmic space is the climate absorber that balances the energy inputs from our sun as well as all other sources. Energy transfer to the sky is exclusively by radiation [Cook, 1989, p4]. In fact radiative activity is the only way that the earth can lose its heat in order to stabilize the temperature. The sun pours its energy on the earth at a rate of about 1.5 x 10A19 kJ (1.42 x 10A19 Btu) per day. The average surface temperature is approximately constant over a number of years. It is obvious that a similar amount energy per day must escape [Cook, 1989, p138]. Partially the solar radiation converts into energy by photosynthesis. Some radiation reflects back to space as a visible spectrum. But most of the energy is absorbed by the surface of the earth, the ocean, and the air. However, the energy absorbed eventually will radiate back into the universe in the form of thermal infrared radiation. Although radiative cooling is usually referred to as "nocturnal radiation," the process of infrared heat transfer is occurring both day and night. At daytime the rate of the incoming energy is larger than the outgoing radiation, the effect is usually ignored. Radiative cooling can only happen under clear skies. Clouds will absorb energy outflow and reradiate it back to earth. Therefore, the heat does not escape out but rather accumulates in the atmosphere. In addition, low warm clouds produce more infrared radiation than high cold clouds [Cook, 1989, p145]. Hence, radiative cooling is most effective in hot arid climates, such as the desert area, but rarely with clouds. 62 A roof pond is the most well known radiative cooling system today. The roof pond idea had been carried out by Harold Hay in 1965, Hay used the roof pond with movable installation to provide both winter heating and summer cooling. This "Skytherm" concept was patented in 1971. By using "Thermo ponds" on the roof, in thermal contact with the metallic ceiling / structural roof deck, and by covering the ponds by movable insulation, Hay proved that, under suitable climatic conditions, comfortable conditions can be maintained indoors by covering the ponds with insulating panels during the day in the summer, and during the night in the winter [ Cook, 1989, p94]. An experiment conducted in Phoenix, Arizona discovered that the room temperature would remain within a few degrees o f the ceiling temperature throughout the entire year. The pond temperatures were moderate because when radiation transfers most o f the heat from the occupants to the ceiling in summer, or vice versa in winter. The temperature differential can be very small compared with that required in convection cooling or heating [Cook, 1989, p 95]. Any radiative system must have a radiator element, a thermal storage element, and the means for transporting heat between these elements and the interior of the building. Roof ponds represent efficient radiative cooling designs for several reasons: (1) the radiator element is horizontal, and is thus exposed to the coolest part o f the sky dome; (2) the radiator is integral with the thermal storage element, eliminating heat transfer fluids and heat exchanger losses; and (3) the cool storage 63 element is in direct radiative contact with the interior o f the building through the metal ceiling [Cook, 1989, p170]. heat radiate out at night | cool air remains inside Roof pond for cooling fig. 8.1 By reversing the process, that is, by closing the insulation at night, and opening it during the day, the roof pond converts into a passive solar heating system to help the building absorb the maximum amount of the solar radiation, and to prevent loss the minimum amount of loss of long wave radiation at night. 64 9. EARTH COUPLING The earth coupling, or so called earth sheltered, underground architecture has existed for a long time, but the scientific interest in earth coupling was initiated in the 1970's due to the energy crisis. For thousands of years, people have lived in earth sheltered structure in many places around the world. One o f the most well-known American examples is that provided by the ancestors of the Pueblo Indians of the Southwest. Before 300 AD., most of their dwellings were built beneath earthen mounds; later they built their homes in cliff sides in the region that is now Arizona, Colorado, and New Mexico. For many centuries the cliff dwellings provided both secure defense and protection from extremes in temperature [Boyer, 1980, p4]. Another famous example is in the Shanxie Province of China where the largest subterranean community in the world is located. Ten million people live in caves in response to extreme climatic conditions in that region. Not only residential buildings are earth sheltered, but the entire community, including government offices, schools, and factories are all constructed underground. Despite the aesthetic potential, earth sheltered architecture also serves many functions, such as preserving the environment, acoustical isolation, land-use benefits, reduced maintenance, fire protection (only for heavy timber, masonry, and concrete constructions), protection from earthquakes , nuclear attack and fallout, also defense from storm and 65 tornado. The cost of earth coupling buildings and energy conservation are also the other attractions [ Sterling, 1982, p13~20]. The main concern of constructing an earth sheltered building is focused on its energy saving potential. The earth can serve as a heat sink for the building in most regions. The soil temperature is relatively steady That is, during the summer it remains at a lower temperature than the ambient air temperature. During the winter, the soil temperature is higher than the air temperature. People have long acknowledged that in hot climates the temperature of the ground is usually cooler than the ambient air temperature. If the ground is shaded, the temperature is reduced even more. Basically, the ground's temperature depends on two factors: one is the seasonal change of the surface temperature, the other is the constant temperature at a depth of several meters [Wang, 1990, p54]. Experiments in Israel and North Florida can have verified that the earth average surface temperature can be lowered by about 14.5-18°F (8-10°C) below the summer temperature of exposed soil. The difference between the ambient maximum air temperature can be up to 27°F(15°C) in mid-summer; this provides a potential to use the earth as a heat sink for the buildings [Wang, 1990, p54]. The earth’s surface temperature reaches highest during summer because of the intensive solar radiation. This condition can be changed by planting vegetation, the reflectivity of the surface, and the diffusivity of the soil. With a high diffusivity heat is easily changed between the surface and the layers below, and this results in small surface temperature 66 fluctuations. Wet soil has a higher diffusivity than dry soil; hence, the wetter the s o il, the smaller the diurnal range of the surface temperature, and the faster the propagation of heat through the ground in the day time [Wang, 1990, p55] There are two passive cooling systems of earth-coupled structures. They are identified and defined as direct and indirect systems. 9.1 Direct System In a direct earth-coupled system, the building interior space is thermally coupled to the subsoil by conduction through the building envelope. In most earth sheltered buildings this occurs only through the walls and the floor [Cook, 1989, p200]. 67 c ;-v> V •<^&£c£g££fci£sV : I - •;.y - rr- v^ - ^ .:; * > * i § . % n I; *1 I i ** r. T -V ^ £ • • : ■ > ■ : . . . - *•; :"i: V . J . ^ - - , *. v ® is & '0 1 ^ ■ / # Totally Atrium or 1 Side 2 Sides 3 Sides Underground Courtyard Open Open Open Plan Types Chamber Types m z m s m s_as ifeuJS&Es^ s s s r "True* Atrium or Hillside Side "Nonearth* Underground Courtyard Elevatlonal Penetrations Roof Berm Types "True* Atrium or Berm Side "Nonearth* Underground Courtyard Elevational Penetrations Roof Building Sections y ^ 1- ^ ,i * v ________________ / " ■ ■ i» nyv^ii> ‘iU*HH i*Yvir k f a ^ w . . . ■ *•*«........... Nonvisible Roofscape Mound Partially Completely Visible Building Elevations Visible Direct system [Boyer, 1980, p8] fig. 9.1 In the temperate zone, the direct earth-coupling system can be regarded as the earth cooling system. Since the earth is a great thermal storage, it stores the excessive heat in the soil during the summer, then releases it during winter, and vice versa. According to Kenneth Labs, the rate o f cooling to the earth is never great [Cook, 1989, p200]. Therefore, most earth-sheltered buildings are more popular in colder regions. 68 However, in tropical regions, the earth temperature around the building may exceed 78°F (26°C) and therefore supplies heat rather than absorbs heat from the interior [Cook, 1989, p201]. This condition is not expected even in the most overheated areas in the United States. Ground treatment is very important in earth-sheltered buildings. In order to overcome the overheating problem, methods like shading the roof with vegetation, or ground pavement are used. In hot arid regions, the vegetation may not be a viable solution to control the ground temperature. Therefore, roof ponds (see Evaporation chapter) and irrigated gravel beds over the soil can be applied. In the irrigated gravel bed application, the gravel cover serves to shade the soil itself and to modify and reduce heat transfer to the soil as a result of modification in the soil-to-air heat transfer coefficient [Boyer, 1980, p113]. In hot humid areas, the type earth-coupled structures should be carefully selected since ventilation is very important in reducing the moisture in the air, and to prevent condensation on walls and floors. 9.2 Indirect System In an indirect earth-coupled system, the interior space is coupled by (air) convection to a heat exchanger in the soil; the system may be open, as in the case of buried earth-air heat exchange pipes through which intake air is drawn, or closed by circulating indoor air through a 69 buried pipe loop,[Cook,p200] Since this kind of cooling mainly depends on the earth contact, therefore, pipes (or tubes) need to be deep enough and have certain lengths to enhance heat exchange between air and earth. In order for air coming into the pipe, the opening should be carefully planned. According to Mechanical and Electrical Equipment for Building by Benjamin Stein, John S. Reynolds and William McGuinness, the earth tube needs to be 8 to 12 inched in diameter, buried 5 to 10 feet deep, and 100 to 200 feet long [Stein, 1986, p197]. COOL TUBE indirect system [Boyer, p102] fig. 9.2 Indirect earth-coupling systems using open-loop earth-air heat exchangers to temper outdoor air introduced to the interior the relative warmth of the ground (relative to the outdoor air). Under such circumstances, the earth heats the incoming air in wintertime, but never to a degree approaching comfort temperatures; therefore, it cannot be considered a heating system in the same sense as a space heating system. Nor will it be as effective as an air-to -air heat recovery system. 70 As a result, passive indirect coupled system also are used almost exclusively for cooling [Cook, 1989, p201]. Earth coupling is only good for dry climates. In hot humid areas, condensation might occur in the earth contact wall, and fungus might grow inside of the earth tube. Hence, the earth coupling system is not an effective strategy. 71 PART TWO USING THE COMPUTER AS A TEACHING TOOL FOR PASSIVE COOLING 72 10. COMPUTER AS A TEACHING TOOL Computers were first introduced as a rare and extraordinary piece of equipment used for special assignments by small groups of people. Because of recent development In technology, computers now are not beyond reach, but step into everyone’s life. Computers are widely used in business, industry, government agencies and schools. Computers have been used in teaching for quite a period of time. Instructional computing is basically any use o f computing techniques within the classroom. It can be drill and practice on fundamental concepts using computer program in a given discipline. It can be a tutorial dialog in which a computer program provides tutorial assistance in a more sophisticated manner than just drill, it can be problem solving in which computer programs are written to solve discipline oriented problem. It can be simulation in which a computer program may model a real world situation. Or it can be testing: letting the computer program ask the question, check the answer, and record the performance [Hernandez- Logan, 1982, p22]. There are advantages of using computers in teaching: Instructional computers free instructors of repetitive tasks, they provide individualized instruction and let the student progress in his own path. Furthermore, an 73 interactive program can make learning an active experience because the computer can wait for students to take action. Architecture department mostly uses computer graphic to design structure (CAD) and also has programs to simulate energy flows in a building (DOE2). These programs required students to have some knowledge in order to input information for computer to model or simulate. For teaching the basic concepts of a certain subject, a different kind of program must be designed. Teaching students about the subject of environmental control is especially important today because of the limits of natural energy. I chose the subject of passive cooling since in most areas, such as Taiwan, the peak of consumption of electricity is on a summer afternoon due to air conditioned buildings. Therefore, with conscious designing, we can avoid many problems. In order to achieve this goal, architectural educators must put more emphasis on it. Design fields are arguably the academic disciplines in which art and science are mostly closed married. Technical and social issues must be rigorously studied with the rational brain’s attention to detail, while the creative brain must be allowed flights of imagination. Frequently, architectural education has coped with the difficulties of integrating these widely different needs by teaching them separately, unintentionally 74 encouraging students to view them as incompatible [Brown and Novitski, p162]. Graphic presentation is undoubtedly a strong way of communication, which can be regarded as a universal language that no other language can compare. Since most architectural students have very strong graphic visualization, pictorial elucidation is the most effective way of teaching students these theories. Animation can be regarded as an upgraded pictorial presentation. It tells the sequence of an event. Computers are also able to act as a multimedia display device, which combines vedio, sounds, CD ROM and more. This is a powerful tool to assist teaching because in the future computer might imitate the real world situation, and make learning more interesting, and realistic. Computers are the tool of the future, it has been widely use in many institutes, business, and public services. Creating computer teaching tools is an essential thing to do for the education in tomorrow. 75 11. A COMPUTER TEACHING TOOL FOR PASSIVE COOLING The process of making this program went through many stages. First comes the literature research, which is recorded in the first part of this thesis, the second step is making a story board which contains the story line and key frames for each section, then the final goal of this thesis is to produce a computer program which explains the passive cooling strategies and practical applications. In order to achieve the goal, I decided to work on Macromind Director software which is described as a mature animation program for Macintosh computer. According to Srdja Hrisafovic’ thesis, he described the software as followed: “This software allows you to move through the program in different directions using the ‘button technic’, Advantages at this software are possibility of using colors in creating the cast members, key frames are connected by animation and there is a possibility of using sound effect.” Besides the technical part of this thesis, this computer is divided into five categories: they are solar shading, ventilation, radiative cooling, evaporative cooling and earth coupling. Each category is then divide into introduction and applications. 76 The system of this program are as followed: Passive Cooling Solar Shading Introduction Sun path and overheated period Shading device and projections: overhang-case study fin-case study eggcrate-case study Landscape: deciduous tree high crown tree Reference Ventilation Introduction Thermal force (Convection) Wind force and openings: size of openings position of inlet overhang at the inlet Wind tower: convection single direction wind tower multi direction wind tower Reference Radiative Cooling 77 Introduction Roof pond— case study Reference Evaporative Cooling Introduction Direct evaporative cooling Indirect evaporative cooling: courtyard spray roof Reference Earth Coupling Introduction Direct earth coupling (earth contact) Indirect earth coupling (earth tube) Reference This teaching tool consists of five categories of passive cooling strategies, each category includes a verbal description, an animated introduction, and specific applications. Although five categories are placed in an order in this program, users are free to choose their own directions. Users can exit anytime to the main menu, and choose any of the five categories which are parallel to one another. 78 The first strategy is Solar Shading, or Solar Control (fig. 11. 1 — 11. 34). After clicking the button of Solar Shading, a verbal description of the entire content is shown on the screen, then users can go to the introduction, which reveilles problems causing by excessive solar radiation, and proposes possible solutions. Shading devices are the most effective solution to control solar radiation, the applications concentrate on how to determine overheated period and relations of shading devices and shading masks. Landscape also helps reduce the unwanted solar radiation, so examples of deciduous trees and high crown plants are located in this section. References are available in each section. 79 * KvtfSE < ? * « THE U SS E j KED TOPIC ^ % - ________________________ n\ U N LIKE AN ACTIVE SYSTEM, A PASSIVE SYSTEM DOES NOT SEPARATE THE COLLECTOR AND STORAGE. AND IT DOES NOT USE FLUID AND RUMPS OR FANS (WHICH ARE PARASITIC} r o COO?, A SPACE. IN TEEMS OF ENERGY EFFICIENCY, PASS IV E COG UNO SYSTEMS PROVIDE AN OPPORTUNITY FOR VENTlLATjON H O U G H TiU A S S T V ? ■YE L \N K i \Y D C R A D IA TIV E COOLING EAR1H coxw i m a bO LA R SiiADIJMG THE SUN IS THE MOST POWERFUL OBJECT WHICH DETERMINES OUR THERMAL ENVIRONM ENT THE SOLAR RADIATIO N ENTER ING THE ATMOSPHERE CAUSES C LIM A TIC PHENOMENA ON THE EARTH. IN TROPICAL AREAS THE SUN IS A SOURCE OF DISCOMFORT, THEREFORE, IT SHOULD BE PREVENTED FROM GETTING INTO THE BUILDING W ITH PROPER UNDERSTANDING OF THE SUN'S PATH, OVERHEAT ED PERIOD, AND SHADING MASKS OF SHADING DEYICES, ARCHI TECTS CAN M AKE THE APPROPRIATE DECISION ON SOLAR CON TROL, AND PROVIDE THE M A X IM U M COMFORT |f-r D v - *C\ D - - Id IT fig.11.1 &11.2 80 SOLAR SiiALiJNO S U L A R SiiAi> UN O *i REFERENCE c !!!!? n \u !!!} to*f 3t*ys in tto room & 5 f- m u -. 'illi; 1 , 1 fig. 11.3 & 11.4 p i i l i i i i l t f t in 81 'U /M M A ii. 82 SO j LA R S H A iiilN U *; REFERENCE SO j LA R SH A D JUNG SUN PATH A DIAGRAM SHOWING THE PATH OF THE SUN IN THE SKY DOME AS PROJECTED ON TO A HORIZONTAL SURFACE. OVERHEATED PERIOD THE TIM E WHEN SHADING IS NEEDED TO BLOCK OUT THE SUN IN ORDER TO KEEP THE UNW ANTED R A D IA TIO N AWAY fig. 11.7 & 11.8 83 SOLAR S HAD UNO SUMMER SUN PATH S O LA R SH A D UNO * REFERENCE SUMMER SUN PATH fig.11.9 & 11.10 84 S G LAR 311 AD 1N G S O L A R S H A D I N G SOLAR SHADING '< \ - '' ? • v 'Sf' < S ' ^ ^-z- .v," ^ U N i^vm s ^ s/4 m i % ; w? f s PT ' y j /■ :;, aa; // s s s , f v • * .. . * &04&f - S ' S ' '& SOLAR SHAD IN G <rtwy^ .j, <v X -> * X -^ ' < - * * ^ * * * * V * *£* * ' , ,-•, * ■ ::v-;.l V A T U ® g V .'::? '--^ }* £ ? * ? { > ' S ,-< -s AA . ■ i’ S ' S S s j T S - ? ', - ' - S -S '- S ,' .'?' ?:vfi paTji B s M t a m A SRUWi?-<0 T.IJ ? f. FATIJ. OF T;.= F SUfc • H*. Sfc.'r ■•O^f: AS i ' X ' O ^ C T f X ; OM TO A iXOX< t l . O H X A \ . S U R F A C r fig. 11.13 & 11.14 86 S O L AR S11A J J 1 In G X - < f " / / > s s S * W ‘ K X l? X i5 H N C E K A A M R Lt MIAMI A T I T U D E : 0 D E G R E E N O R T H J V E R t t E A T E D P E R I O D C A M O E M S U M M E R 6 A M O I M E O U I N O X l i i A M 6 P M W I N P E P S P A D H - i O I S N E E D E D T O B L O C K 0 - - T • E h ' > KEEP THE U H % H T K I.i RADIATION A WAT S H A D I N O M A S K S A R E A C O N V F n T i O N A f . J Z F . 0 G E O M E T R I C D E S C R I P T I O N . T H E R E F O R E , T R E Y A R E I N D E P E N D E N T O F L A T I T U D E , O I U E N T A T I O N A N D T I M E T H E S H A D I N G M A S H C A N B E U S E D I N A L L K I N D S O P S I T U A T I O N S O N C E I T H A S B E E N P L O T T E D F O R A S P E C I F I C D E V I C E T H E R E A R E T H R E E B A S I C T Y P E S O P S H A D I N G D E V I C E S 1 . H O R I Z O N T A L O V E R H A N G S : M A S K S A R E T Y P I C A L L Y F L A T C U R V E S 2 . V E R T I C A L F I N S : M A S K S A R E T Y P I C A L L Y B O U N D E D B Y R A D I A L L I N E S ; B G O C R A T E T Y R E S : T H E C O M B I N A T I O N O F H O R I Z O N T A L V E R T I C A L D E V I C E S . A N D T H E I R M A S K S A R E A C O M B I N A T I O N O P T H E T W O fig. 11.15 & 11.16 SO LAM SH A D 1.N G b H A D ip IG B-p y kX c H an Siti&KDmG D 'K y K 1 '. O Y h J U H A W r: ISO PfZO M TAl HIIW + < 1 - i:KO)K-ni!OS O H WiBiJGW 7 K P ;> !1 B P A T T i fig. 11.17 & 11.18 88 SOLAR SHADLNG f a f a t o z t , * W & / s * - < SHADING IAASK. Ob' HORIZONTAL OVERHANC SOLAR SHAD 1x4G M ttK H K R g M C E mm?^ .......... • i—v.- L i / 1 U S AIR FORCE ACADEMY, COLORADO SPRINGS, COLORADO DESIGN, ARCHITECT: SKIDMORE. OWINGS S r . M ERRILL fig. 11.19 & 11.20 89 £>Oj LA R S H A D IN G 2 ♦ REFERENCE O V - - FIN VERTICAL SHADING DEVICE § ■ W M 1 9 fifa l] FIN: VER TICA L SHADING DEVICE fig. 11. 21 & 11.22 90 SHADING MASK FOR THE VERTICAL FINS &QJLAK. b iiA U ii^ C ;* FIN VERTICAL SHADING DEVICE fig. 11. 23 & 11. 24 91 EGGCRATE: HORIZONTAL AND VERTICAL COMBINED SHADING DEVICE EGGCRATE: HORIZONTAL AND VERTICAL COMBINED SHADING D EVICE fig. 11. 25 & 11.26 92 biiA D iiN C i SHADING MASK OF THE EGGCRATE DEVICE EGGCRATE: HORIZONTAL AND VER TIC A L COMBINED SHADING DEVICE HIGH COURT B U ILDING , CHANDIGARH, IN D IA DESIGN, ARCHITECT: LE CORBUSIER 93 b O L r AR b 11A i> 1 IN O PLANTS DO NOT ONLY PROVIDE BEAUTIFUL YIEWS AROUND THE HOUSE, BUT ALSO PROVIDE SHADE WHEN PLANTS AB SORB SOLAR RADIATIO N AND CAST SHADOW, THE RADIATIO N EVAPORATES WATER FROM PLANTS THIS PROCESS CONVERTS SUNLIGHT INTO H U M ID ITY, AND IN HOT ARID AREAS, PLANTS ACTUALLY LOWER THE AM BIENT AIR TEMPERATURE £ fig. 11. 29 & 11.30 94 b O L A R SHAijiiNiU '* ■ K M FK H EN C E b KJ L A K b 1.1 A iJ 1iM O fig. 11.31 & 11.32 95 2 SOJLAR SiiADii^U b O L A k bHADLNCr & tt£ r£ :V K N -< :* H REFERENCE: BROWN, G Z , 1985; SUN. W IND AND LIGHT , JOHN W ILEY AND SONS HARRNESS, EDWARD L. AND METHA. MADAN L, 1979, SOLAR R A DIATIO N CONTROL IN B U ILD IN G , APPLIED SCIENCE PUBLISHER LTD. O LG YAY, VICTOR; 1963, DESIGN W ITH C L IM A T E : PRINCETON U N IVERSITY PRESS MOFFAT, ANN SIMON AND SCHILER, MARC, 1981, LANDSCAPE DESIGN THAT SAVES ENERGY; W IL LIA M MORROW AND COMPANY INC ! > N O V - 5 S -- fig. 11.33 &11.34 96 The ventilation category ( fig. 11. 35 -11. 57) concentrates on how local winds form and what people can do to increase air flows into the living areas for maximum comfort. Just like the other categories, this section starts with a verbal description of different causes of air flows. The introduction contains animations of two typical local winds: sea/land breezes, and mountain/valley winds. Three applications are applied here: thermal force (convection or stack effect), wind forces and wind tower. Thermal force ventilation is known as convection, and the typical example is the stack effect. Wind force ventilation is related to the inlet and outlet of air flows; therefore, three segments are developed here: size of the openings, position of the inlet, and attachments of the inlet. Wind towers are a popular device in hot arid areas, they are for convection, and for bringing wind into living space (single direction wind towers and multi direction wind towers). A case study of the wind tower in Yazd, Iran follows. 97 VENTILATION fig. 11.35 & 11. 36 98 VENTILATION * REFERENCE WATER/LAND WIND 1 " o ' " • mrs&mcrKm WATER BAS A HIGHER ST 3 : 0 3 ECO 3 I3 5 AT TO AH Tf3 E EA.RT3 I. THESHIFORE, WATER TAKE" LONGER TO HEAT UP AND TO COOL DOWH. Ot3 R 3NG TEX 3 3 DAY TX3E 5 KART 3 X GETS WARM. AH'£ 3 SO X : « 0 3 3S THE3 5 AIR OVER JT TUia WARM AIR RISES. THEN THE COOLER AND HEAVIER AIR FROM THE S3 5 A TAJC.BS ITS PLACE. AT HIOHT, IF THE X.AHE) COOL 3 DOWN SUFFICIENTLY THE PROCESS REVERSES VENTILATION -j# WATER/LAND WIND • REFERENCE c mTRopucrroM WATER HAS A 3 X3 GEIE5 R SPXCtFIC 1 3 EAT THAN THE EARTH THBBEPORE, S' WATER TATES LONGER TO HEAT UP AND TO COOL DOWN > - DURING THE DAT. THE EAR '(15 GETS WARM. AND SO DOES THE A 3 R OYER 5. IT THIS WARM AIR RISES, THEN THE COOLF.R AND HEAVIER AIR FROM T 3 0 2 SEA TARES FI'S EL AC 3 1 AT N 3 GE3 T, 3 'F T 3(E LAND COOLS 3 >OWH L. SUFFICIENTLY, THE PROCESS REVERSES fig. 11.37 & 11. 38 9 9 VENTILATION S I M O U N TA IN ,‘VALLEY W IND IH T K ^ J C T K m VENTILATION *. REFERENCE r A V * M O U N TA IN /V A L LE Y W IN D H'J IOE c / - » v c ~ ■X" 'I*'.. * ? « » > fig. 11.39 & 11.40 1 0 0 VHNTTLATION M REFERENCE i l l ! VKNTILAllON fig. 11.41 & 11. 42 nrmw&L HiE&MAL (C O m V C TJOK) < : > v 101 VENTILATION it SIZE O F OPENINGS INLET = OUTLET INLET >OUTLET wtmf Form er: & fig. 11.43 & 11. 44 102 V RNT I 1., A T I O N *6 SIZE of openings • reference B INLET - OUTLET THE AIR SPEED REMAINS UNCHANGED INLET >OUTLE I VELOCITY INCREASES OUTSIDE O F THE BUILD ING mms fdkci & opmrnc# IH 1.KK U IJ T L K I VELOCITY INCREASES RIGHT AFTER ENTER ING THE BUILDING : : : • . : : • . . $ - - - ' • POSITION O F INLETS VS - ■ : : . : ;■ i VKNTIIAI * REFERENCE InLCT= U U T L C I INLET HIGHER THAN OUTLET W D F C S V & K &rnmmmmrn ormmas INLET LO W ER THAN OUTLET fig. 11. 45 & 11.46 103 INLET = OUTLET LEVEL AIR FLOW , PA3SES THROUGH THE LIVING AREAS INLET HIGHER THAN OUTLET THE AIR FLOW IS MAINLY COOLING THE CEILING SPACE, WHICH IS NOT DESIRABLE. THE AIR FLOW SW EEPS THROUGH THE FLO O R SURFACE, AND BLO W S THROUGH THE LIVING S P A C E INLET LO W ER THAN OUTLET VENTILATION « OVERHANG5 I" WJWP F C kC E & O Y E ttJ H A J N C S A T CEILING HEIGHT SOLID OVERHANG ABOVE THE INLET OPENING L. SOLID OVERHANG A3 ABOVE. BUT WITH A SLO T fig. 11.47 & 11. 48 104 VENTILATION * REFERENCE 5 * 07EHHAHGS OYEKNANG AT CEILING HEIGHT O YER HANG AT CEILING HEIGHT INTERCEPTING AND DIVERTING AIR M ASSES TOW ARD THE INLET IMPROVES THE VENTILATION EFFECT IMIS 511UA11UM CAUSES AIR FLO W S TOW ARD THE CEILING. SINCE THE O Y ERHANG ELIMINATES THE OUTSIDE PRESSURE FRO M ABO VE THE FLOW BY PA SSES THE LIVING AREA, THEREFORE, IT'S NOT FAVORABLE SOLID OVERHANG ABO VE THE INLET OPENING oFFtmum THE SLOT EQUALIZES THE PRESSURES, THEREBY LOWERING THE FLOW THROUGH THE LIVING ZONE SOLID OVERHANG A S ABOVE, BUT WITH A SLO T L VH.NTIL ATI ON m tm m w m fig. 11.49 & 11. 50 105 VENTILATION 1 = CONVECTION D!JT;ilfiG XHT J>AX X X M X ! , VOiKM I HE ROOT iS HEATED S ? THE SD K . THE SNTEHIOR HOT A lii OS SU C K ED O U T E Y TH ii STACK E F E E C T . w«m i owi*:r VENTILATION * SINGLE DIRECTIONAL WIND TO W ER wmv TO W E R VENTILATION p r; * REFERENCE $ MULTI DIRECTION AI. WIND TO W ER Y m n Y Q Y W IH i> tO W & •n tm ijm tti fig. 11.53 & 11. 54 107 VENTILATION WUW T O W K R VENTILATION W IND TOWER, YA ZD , IRAN DESIGN, ARCHITECT: UNKNOW N fig. 11. 55 & 11.56 108 VENTILATION fig. 11.57 109 Radiative cooling (fig. 11. 58 - 11. 67) uses skies as a huge heat sink, which helps to balance the temperature of the earth. As other sections, radiative cooling section opens with a verbal elucidation, which gives a brief idea of radiative cooling. The introduction graphically explains how the solar radiation accumulates in soil during the day, and how the radiation escapes from the earth to skies at night. The reradiation only happens under a clear cloudless sky. The most well known application of radiative cooling is the roof pond developed by Harold Hay. It is the only system performs perfectly for both passive solar and passive cooling. The cast study shows the actual building using the roof pond idea. 1 1 0 R A D IA T IV E C O O L IN G * R E F E R E N C E fig. 11. 58 & 11.59 in RADIATIVE COOLING : .V S TjaTRODtfCTrOKT MOVABLE INSULATION ^ A T E R W RLACK -^J tA a T K : METAL CELLING HELPS THERMAL CONDUCTION fig. 11.60 & 11. 6 1 1 1 2 RADIATIVE COOLING ROOF FOND CLO SE THE INSULATION DURING THE DAT T O AVOID SO LA R RADIATION RADIATIVE COOLING * REFERENCE FOR. COOLING c ROOF POND O PEN THE INSULATION AT NIGHT IN O R D ER TO ACCELERATE THE RADIATIVE . THE RADIATIVE COOLING EFFECT ^ I f e v . fig. 11.62 & 11. 63 113 R A D IA T IV E C O O L IN G ♦ R E F E R E N C E R O O F FO N D * * ^ RADIATIVE COOLING * REFERENCE JROOF POND fig. 11.64 & 11. 65 c 114 RADIATIVE COOLING ROOF FOND ATASCADERO RESIDENCE, ATASCADERO, CALIFO RNIA DESIGN, ARCHITECT HAROLD HAY & KEN HAGGARD RADIATIVE COOLING R E F E R E N C E fig. 11. 66 & 11.67 115 Evaporative cooling (fig. 11. 68 -11. 75) is a popular passive cooling strategy in hot arid areas. When warm air passes over a body of water it evaporates the water, and the water absorbs a great amount of energy, so the air will becomes moist and cool after the process. This is clearly explained in the introduction section. The applications focus on direct and indirect methods in evaporative cooling. The direct method placed cooling devices inside of buildings to produce cooling effect. Conversely, the indirect method placed devices outside of buildings to cool interior space in a roundabout way. The example of direct method has been practiced in Egypt and other regions for a long time, and it is quite effective. There are two indirect evaporative cooling methods are applied here, one is the courtyard building, which is a popular form in Mediterranean areas, the other is the spray roof, which draws heat from buildings to produce cooling effect, a bibliography is also provided. 1 1 6 EVAPORATIVE COOLING EVAPORATIVE COOLING IS ALWAYS IN CONJUNCTION WITH VENTILATION, THF CONCEPT O T* F.YAPOR ATIVE COOLING IS THAT WAKM AIR PASSING OVER WATER EVAPORATES THE W A T E R AMD A S A SIGNIFICANT A M O U N T OF HEAT IS A B « SOBFD IN THE PROCESS, THE AIR IS COOLED. THE EVAPORAT ED W A T E R fS RETAINED IN THE A I R THUS INCREASING ITS HUMIDITY FOR THIS REASON. EVAPORATIVE COOLING CAM ONLY BE U S E D IN RELATIVELY DRY CLIMATES EVAPORATIVE COOLING METHODS CAM BE CATEGORIZED INTO T W O TYPES ONE IS DJPFCT, THE OTHER IS INDIRECT BVAPOR ATIVE COOLING # REFERENCE iNTRODUCTlON J J i N IN N fig. 11. 68 & 11.69 117 EVAPORATIVE C * R E F E R E N C E COOLING ro B iv o fs Jf&£ FiJ-tSfc VTT3J V A T !:3 ? L iT iN O S I-A C E < > : X: DIRECT EVAPORATIVE COOUKC COOLIN G R VAPOR/1 DIRECT EVAPORATIVE COOITTNO >v •Y iiH S S P A C E fig. 11.70& 11.71 118 EVAPORATIVE COOLING * R E F E R E N C E INDIRECT EV'ARORATIYE COOLING OCCURS WHEN DEVICES ARE PLACED OUTSIDE OP NEAR THE BUILDING TO PROVIDE COOLNESS TO TEE INTER/OR SPACE. INDIRECTLY. THE TEMP ERATURE Or WALLS AND ROOF ARE REDUCED. AND THE HEAT CONDUCTION THROUGH' THE BUILDING SHELL IS ALSO D IM I NISHED, OR THE. BUILDING IS COOLED BY THE AIR BLOW THE TYPICAL EXAMPLE OP EVAPORATIVE COOLING BY AIR FLOW IS THE COURTYARD HOUSE THE SPRAY ROOF METHOD IS THE EXAMPLE WHICH USES EVAPORATIVE COOLING TO REDUCE THE HEAT OR THE /.HOLDING SHELL EVAPORATIVE COOLIN G S* C O U R TY A R D H O U SE R E F E R E N C E fig. 11.72 & 11. 73 INDIRECT EVAPORATIVE COOLING INDIRECT EVAPORATIVE COOLING 119 EVAPORATIVE COOLING INDIRECT EVAPORATIVE COOLING EVAPORATIVE C O O LIN G # 8jEFjK3?KNCE REFERENCE AL-QAHTANI, TURKIHAIF, 19S7, A PASSIVE COOLING FOR RESIDENTIAL B U IL D IN G IN THE EASTERN PRO VINCE DESERT IN SAUDI A R A B IA . UN IVERSITY OF SOUTHERN CALIFORNIA MASTER OF B U ILDING SCIENCE THESIS COOL. JEFFERY, 1989; PASSIVE CO O LING ; THE M IT PRESS GIVON I, B.; 1991; ’ M ODELING A PASSIVE EYAPORATIVE COOLING T 0 ¥ E ; SOLAR WORLD CONGRESS, INTERNA TIO NAL SOLAR SOCIETY, VOL. : < PART 1 fig. 1 1 . 74 & 11.75 120 Earth coupled systems (fig. 11. 7 6 -1 1 . 88) have been practiced for centuries. The earth surface temperature changes according to the season, but at certain depths, the temperature remains at the average annual temperature. The applications are categorized in the direct and the indirect system. The direct system is the so-called earth contact, or earth shelter, which use the earth as a heat storage, when the ambient air temperature is higher than the earth temperature, the heat of the warm air will be absorbed by the earth. Conversely, when the ambient air temperature is lower than the earth temperature, the heat of the earth will then enter the space through conduction. The indirect application is also known as the earth tube, the interior space is coupled by (air) convection to a heat exchanger in the soil; the system may be open, as in the case of buried earth-air heat exchange pipes through which intake air is drawn, or closed by circulating indoor air through a buried pipe loop [Cook, p200]. Since this kind of cooling mainly depends on the earth contact, therefore, pipes (or tubes) need to be deep enough and have certain lengths to enhance heat exchange between air and earth. 1 2 1 The earth coupled systems are mostly used in arid regions. In humid areas, condensation might occur in the earth contact wall, and fungus might grow inside of the earth tube. Hence, the earth coupling system is not an effective strategy for habitable spaces in humid regions. 1 2 2 THE EAP.Tfi SERVE’ S AS A H£AT SINE. FOR BUILDINGS IN MOST REGIONS. THE SURF AC E-SOIL TEMPERATURE CHANGES ACCORDINU TO THE SEASON, BUT AT CERTAIN DEPTHS. THE SOIL TEMPERATURE REMAINS STEADY YEAR ROUND AT THE AVERAGE ANNUAL TEMP EE A TUBE. THERE TO RE. DURING THE SUMMER THE EARTH TEMPERATURE IS LOWER THAN THE AIR TEMPERATURE, AMD IN WINTER, THE EARTH TEMPERATURE IS Hi GHEE THAN THE AiR TEMR- EAIUEE. THERE ARE TWO KINDS OF FAR.TNCOUf’LING SYSTEMS THE D IR £C T S ' Y STEM. OR SO-CALLED EARTH CONTACT SYSTEM. AND THE INDIRECT SYSTEM, OR EARTH TUBE. o *-f y c -v c j t ro' jfm x INTRODUCTIO N fig. 11.76 & 11. 77 123 an DEG RBF. F m m &m tz y s DfRECT E A R TH covn.m^ fig. 11.78 & 11. 79 124 A 7 7 'T ' * DIRECT Em m COUPLING . . 3 0 D E G R E E ¥ 1 :? a V' 'T ?t r xA T r » T mEBcr EAKTH £0XiFU3ff£ * REFERENCE 'M 1 I (I fig. 11. 80 & 11.81 125 > v T f T 7 T T> T I XT n DIRECT EA-imr C O U P E IM G $ K C - A J > c vita'j ^ ,-m# t& .s&£*;t$R: m 9 H M M — IS ROUSSELOT HOUSE, AUSTIN, TEXAS DESIGN. ARCHITECT: COFFEE & CRIER fig. 11.82 & 11. 83 126 A' < :■ * * fr m REFERENCE ZAtmt couPLiae ^ p t h ' rv '> i !!• > ■ ? rzyn * REFERENCE 1N1>IKC.C i E&R TH c o m i s 80 DEGREE F fig. 11.86 & 11. 87 128 BOYER, LESTER L AND GRONDZIK. WALTER T.; 1987; SARTlI.SKO.-XE!?.TECiiNOJ.;OGY, TEXAS A S r. M UNIVER SITY PRESS CLARK KENNETH N AND FAY LORD, PATRICIA. 1980. DESERT HOUSING. ARIZONA BOARD OF REGENTS STEIN BENJAMIN, REYNOLDS. JOHN S AND MG GUINNESS WILLIAM J.; 1986; MECHANICAL AND ELE CTRfCAL EQUIPMENT FOR BUILDINGS, JOHN WILEY AND SONS STEP IMG RAYMOND. 1982; EARTH SHELTERED RESIDENT 1AL DESIG N M.AMUAL, VAN REINHOLD COMPANY LTD 12. FUTURE DEVELOPMENT Passive strategies are a direction for environmental control, the idea needs to be carried on through educators and architects. This teaching tool, which gives the general ideas of the subject, is for beginners. There are two major directions that I would like to see in the future development of this subject: one is the continuation of this tool, and the other is an expert program. Since this teaching tool presents the topic in a narrative way, in the future, a series of programs are needed to be developed and attached to the tool in order to give users more freedom. For example, in the overheated period section, users now can only see the example of Miami, but in the future, users should be able to choose the locations. The other way to extend the ability of this tool is by connecting it to other applications or related programs, or connect to simple simulations of building input by the user. The expert program is the other direction, it tells the user what to do or what not to do. A rough outline of the expert program is attached for those who are interested to develop an expert program: EXPERT SYSTEM I. Name of the city: ( location, altitude, longitude) II. Geomorphic: 1. How do you describe the site in general? A. hilly: which direction is the slope facing? how many degree is the slope? B. desert C. valley D. plane E. river F. lake G. ocean H. city with buildings around 2. How do you describe the site specifically? A. trees: a. how many? b. heights? c. direction? d. how far from the site? B. bushes: a. how many? b. heights? c. direction? d. how far from the site? C. buildings: a. how many? b. heights? c. direction? d. how far from the site? III. Climate ( already stored under the name of the city) or 1. temperature? 2. rainfall? 3. wind: a. from where? b. speed? VI. Building Type 1. hospital Active 2. department store 3. hotels 4. office buildings Hybrid 5. retails 6. school institution 7. clinic 8. residential Passive V. Occupancy: 1. How many people in the space? 2.1. What kind of activity: A. sleep B. clerical work C. substantial heavy work D. short athletic or 2.2 . Input the people schedule VI. Building: 1. Total area of the lot? 2. Total area of the building? 3. Total volume of the building? 4. How many zones desired? A. rooms=? B. heat generating rooms=? 5. Desired building form? OUTPUT************************************************************** I. BUILDING SHELL: 1. How thick is the wall? 2. insulation? yes or no, what kind? 3. Roof form: pitched/flat if pitched, slope=? 4. Roof material: 5. Should the base be lift from the ground? Yes/No if yes, how high? 6. Should the house be earth sheltered? Yes / No if yes, how deep? 132 II. Window Openings: 1. north window area : north wall area =?% 2. east window area : east wall area= ?% 3. west window area : west wall area= ?% 4. south window area : south wall area=?% 5. how height is the window? 6. light shelf needed? 7. sky light? 8. glaze type?( transmissivity) 9. window form? III. Shading ( Overhang): 1. width of the overhang=? 2. where to place it? 3. vertical or horizontal? IV. Interior Space: 1. wall: A. should there be openings between ceiling and interior wall? B. how many zones should the space be divide? C. interior material: (reduce absorptivity) 2. Vertical space:( stack effect) A. stair tower B. thermal chimney 3. Ceiling height=? V. Building Surface vs. Volume surface/volume ratio ACCESSORIES ********************************************************** I Fence: 1. height=? 2. material?( porous material) II. Atrium 1. the area for the atrium=? 2. fountain or pool needed? at what side? According to the building. III. Wind Tower: 1. height? 2. how big is the opening? 3. what is the shape? 133 BIBLIOGRAPHY 134 BIBLIOGRAPHY Al-Qahtani, Turki Haif; 1987; A Passive Cooling System for Residential Building In The Eastern Province Desert In Saudi Arabia: University of Southern California Master of Building Science Thesis; 1987 Bahadori, Mehdin; 1985; "An Improved Design Of Wind Towers For Natural Ventilation And Passive Cooling"; Solar Energy :Vol. 35 No.2 p119-129; 1985 Boyer,Lester L. and Grondzik, Walter T.; 1987; Earth Shelter Technology: Texas A&M University Press Brown, G.Z.; 1985; Sun Wind and Light: John Wiley And Sons Brown, G.Z. and Novitski, Barbara-Jo; 1987; “Combining the technical and Artistic”; Machine Mediated Leamingp; Vol. 2 No.1 & 2; p 161-172; 1987 Cho, Chen-kuan;1989; A Study on Passive Strategies in Hot Humid Climate: Master’s Thesis at Cheng-Kung University in Taiwan Clark, Kenneth N. and Paylore, Patricia; 1980; Desert Housing: Arizona Board of Regents Cook, Jeffery; 1989; Passive Cooling: The MIT Press; ISBN:0 262 03147 7 Fry,Maxwell and Jane Drew; 1982; Tropical Architecture in The Dry and Humid Zones: Robert E. Krieger Publishing Company, Florida Givoni, B.; 1976; Man, Climate and Architecture; Applied Science Publishers Ltd.; London Givoni,B; 1991;“Modeling a Passive Evaporative Cooling Tower”; 1991 Solar World Congress: International Solar Society; Vol.3 part 1; 1991 135 Harkness, Edward L. and Metha, Madan L.; 1979; Solar Radiation Control in Building; Applied Science Publisher Ltd; London Hemandez-Logan, Carmela; 1982; Computer Support for Education; R & E Research Associates Inc. ISBN.0-88247-645-9 Konya, Allan; 1980; Design Primer for Hot Climates; Architectural Press Ltd., London Lippsmeier.Georg; 1969; Building In The Tropics; Verlag Georg D. W.. Callwey, Munchen Moffat, Ann Simon and Marc Schiler; 1981; Landscape Design That Saves Energy; William Morrow and Company Inc.; ISBN:0688-0031- 2 Nuko, Lucy; 1989; Passive Cooling Methods for Mid to High-Rise Buildings in the Hot Humid Climate of Douala. Cameroon. West Africa: University of Southern California Master of Building Science Thesis Oakley, David; 1961; Tropical Houses: A Guide to Their Design: B.T. Batsford Ltd. London Olgyay, Victor;1963; Design With Climate: Princeton University Press Saini, Balwant Singh; 1980; Building in Hot Dry Climate: John Wiley &Sons; ISBN: 0 471 27764 9 Stein,Benjamin, Reynolds, John S., and McGuinness, William J; 1986; Mechanical And Electrical Eguipment For Buildings; John Wiley And Sons Sterling, Raymond; 1982; Earth Sheltered Residential Design Manual; Van Nostrand Reinhold Company Ltd.; ISBN: 0-442 28678- 3 136 Wang.Hsi-Cheng; 1990; A Cross Ventilation Study On A Building With Skip-Stop Corridors: University of Southern California Master of Building Science Thesis 137
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Asset Metadata
Creator
Yuan, Alice Hui-Lin
(author)
Core Title
A computer teaching tool for passive cooling
Degree
Master of Building Science
Degree Program
Building Science
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
engineering, architectural,OAI-PMH Harvest
Language
English
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Digitized by ProQuest
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Schiler, Marc (
committee chair
), Koenig, Pierre Francis (
committee member
), Schierle, Gotthilf Goetz (
committee member
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https://doi.org/10.25549/usctheses-c20-300887
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UC11258968
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EP41441.pdf (filename),usctheses-c20-300887 (legacy record id)
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300887
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Yuan, Alice Hui-Lin
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University of Southern California Dissertations and Theses
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The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...
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engineering, architectural