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Indirect / Passive Air-Flow Systems Indirect / Passive Air-Flow Systems Bhujon Kang and Sky Lutz-Carillo csd Center for Sustainable Development UTSoA - Seminar in Sustainable Architecture Indirect / Passive Air-Flow Systems Bhujon Kang Sky Lutz-Carrillo main picture of presentation Why Air-Flow Matters evaporation of sweat, further cooling the body, which acounts In beginning an investigation into for 20% of the heat lost. Moving air-flow systems it is helpful to air removes moisture and provides first establish why this subject is proper conditions underwhich the important in the first place. There body can evaporatively cool itself by are three major reasons, each perspiration. Together these acount compelling in itself and as a group for more than half of the cooling proving that this subject would be capacity. unwise to ignore. These three reasons are comfort, energy and health. Comfort Air-flow plays a central role in determining the way we perceive the environment, be that outdoors or in. Air-flow is integral to the way our bodies regulate heat. Convection occurs when a fluid (gas or liquid) is heated and as a result moves from one place to another. (warm air rises in a room, allowing cool air to fall). It is also important to note that air Convection moves warm air speed has an effect on perceived away from the body, accounting comfort. Optimal air movement for for fully 35% of the heat lost from thermal comfort is 10-50 feet per the body. Air flow also facilitates minute. Lower levels feel stagnant 1 UTSoA - Seminar in Sustainable Architecture Figure 03: Comfort zone based on air velocity and tempera- ture and higher levels can be disruptive. a substantial economic cost. An (eda pg46) What these quidelines energy audit of office buildings in the consider comfortable also depends UK comparing naturally ventilated on the environmental temperature, spaces and those that are air- as seen in figure 3. conditioned (figure 05) shows a large difference in delivered energy use Energy between the two types. An even larger difference can be seen in Buildings demand a large their comparison of primary energy percentage of the energy produced use which looks at the value of in this country and around the energy at its source, accounting for world. By use building’s operational inefficiencies in delivery. This study consumption accounts for 38.9% showcases the possibilities that (figure 04) of that produced, which natural and innovative ventilation not only contributes to environmental strategies can bring to design in the degradation but possibly more Figure 05: Delivered energy use form of cost savings and abatement importantly for the owners, carries of environmental degradation. Figure 04: Energy consumption related to user groups and use Figure 06: Primary energy use 2 Indirect / Passive Air-Flow Systems Health What is Air-Flow? the earth, also known as the Coriolis Effect. ncreasingly builders, architects and In order to understand how air medical professionals are becoming flow systems work in buildings it Local aware of the prevalence of Sick is helpful to begin by exploring the Local climate data can be very useful Building Syndrome in our modern mechanisms that create global for getting a picture of the area’s buildings. This group of ailments atmospheric air circulation. By weather patterns. One way this is largely thought to be the result of tracing this thread from global information is sorted in into climate prolonged exposure to unhealthy conditions to local and then zones, each of which has its own chemicals and compounds in the air microclimate we are able to characteristics. While still fairly due to flaws in the design of heating, understand how these pieces fit general, this is a good starting point cooling and ventilation systems. together to affect our buildings. With for determining which environmental This phenomenon is a relatively this information we are better able to strategies will most likely have a new problem which comes in part decide between competing design chance at success. Below are a few from the proclivity to build buildings strategies. that allow for almost no natural air rules of thumb for various climate infiltration. Today Sick Building zones. Global Syndrome is most often seen in mechanically ventilationed buildings - Hot-humid Climates designed for the minimum level At the most basic level all air Maximize natural ventilation. Use of ventilation. In order to protect flow is movement from a zone of large openings and cross ventilation, against this measures must be taken high pressure to a zone of lower high ceilings, narrow spaces, single- to ensure appropriate air exchange pressure in an attempt of this air to loaded corridors. rates base on occupancy and use of reach equilibrium. The earth’s air space. Certain guidelines have been mass is an incredibly complex and - Hot-Arid Climates developed based on these variables dynamic system in constant flux, Minimize natural ventilation. Use to address this issue. (figure 07) but at its base two things drive this small air flow openings. system. The first is solar radiation heating different regions of the earth - Temperate Climates at different rates. This differential Make dual use of radiation and heating between the poles and wind effects, cross ventilation. Use the equator is what creates jet southern openings. Figure 07: Air flow rates streams and trade winds which act to circulate and equalize this - Cool Climates imbalance. The second thing that Use southern windows, small drives this system is the rotation of openings on other exposures Figure 08: Frequency of SBS Figure 09: Global air circulation Figure 10: Wind rose 3 UTSoA - Seminar in Sustainable Architecture Wind rose data can easily be found uplift breeze. Mountains and other which illustrates normal local wind types of variable terrain can also speed and direction for different create wind screens and pockets parts of the year. This information is of turbulence. Additionally the no doubt useful but it has its pitfalls presence of vegetation such as trees as an authoritative viewpoint. and bushes should be considered, as they can be very successful at deflecting wind. Micro-Climate Micro-climate takes a look at the Principles: Natural Ventilation specific conditions on a given site. At this scale topography and As we have learned all air flow is adjacencies to water and vegetation the result of pressure differentials. is considered. Recognizing There are a few main ways that particular configurations inherent this occurs in relation to buildings. in the site can drive many of the Wind pressure, in which the exterior important early design decisions. air flow creates high and low air One important feature to be aware of pressure zones on the building and is the cycle of sea and land breezes stack effect in which heat rising on which move air across land that is the interior of the building seeks close to large bodies of water. In this to escape and draw in cooler air. cycle, as the land heats up, the air Wind pressure acts on a building in around it heat and rises, which draws two major ways, the first and most air inland across the cooler water. commonly used is cross ventilation. Then at night when the land cools The second is Venturi effect. more quickly, the opposite happens and air flows from the land toward Wind pressure the water. A diagram of this process can be seen in figure 11. The All air flow is the result of pressure presence of mountains also has a differentials. Wind pressure is the profound effect on air flow. Mountain result of wind blowing against and/ breezes can occur when mountains or past a building. Pressures on heat up faster than the air at the the building surfaces come from the surrounding altitude, creating an change in momentum when air is deflected or its speed is reduced. Positive pressure is created on the windward side and negative pressure on the leeward side, resulting in air flow from positive to negative pressure zones. Orienting with the long axis perpendicular to the prevailing warm weather breezes produces the greatest pressure differentials Venturi Effect: The reduction in fluid pressure that results when a fluid Figure 11: (A)Sea Breeze (B)Land breeze Figure 12: Wind pressure diagram 4 Indirect / Passive Air-Flow Systems flows through a constricted section to flow out of opening at the top of Qualitative information includes of pipe. The fluid velocity must the building and draw in air near the calculation techniques for defining increase to allow the same volume ground. climate parameters. So, design of air to pass through the constricted guidelines and criteria for natural opening. The Bernoulli Principle This effect is at its maximum ventilation include recommendations explains the inverse relationship in the winter when the greatest and rules like the followings. between speed and pressure, temperature differences exist and meaning that this creates a drop Building Location and Layout in pressure due to the increase in - Mountain and hill sites speed. - By the sea, a lake or a large river - Urban site This phenomenon can be used to Landscape Design - Wind deflection - Funneling and acceleration of air The Form of the Building Envelope - Building Height. Figure 13: Venturi Diagram - The Roof Form - Aspect Ratios - The Corrugation of the Building Envelope Figure 15: Stack Effect Configurations only minimal ventilation is required. Figure 14: Venturi Effect on Hannover Pavilion In warm conditions, temperatures can be deliberately elevated to draw air out of a building (usually at induce greater pressure differentials. the roofline) using the movement of the outside air. Stack Effect: The molecules of warm air are moving at a faster rate, are more agitated and therefore create more space between these Figure 16: Stack Effect diagram molecules.
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