Tropical Architecture TROPICAL architecture is all about tackling the heat island effect.
Many confuse the term tropical architecture with a particular design style. In reality, tropical architecture is all about achieving thermal comfort through the use of passive design elements like sunshades, cavity walls, light shelves, overhangs, roof and wall insulation and even shading from large trees to block the sun. It can look very traditional, ultramodern or even high-tech. Passive design is the process of achieving this comfort level without the use of mechanical systems. Tropical architecture is all about tackling urban heat island effect. So what exactly is the heat island effect? This phenomenon is what results from cities that have very little greenery and very many concrete surfaces. The city will have 2 to 3 degrees Celsius higher temperature than that of the surrounding suburbs and countryside. Figuratively, it forms an ―island‖ of hotter land, while being surrounded by cooler land in the city outskirts. Dark-colored roofs add to the heat island effect. Some of the heat absorbed by dark-colored roofs is transmitted to the room or space below.
Basic design principles
For the Philippines, having a warm humid climate, there are a few basic design principles regarding natural ventilation to cool a home or a building. The external features of the building envelope and its relation to the site should be designed to fully utilize air movement. Interior partitions should not block air movements. Air velocity can be reduced when the interior walls are placed close to the inlet opening or each time it is diverted around obstructions. If interior walls are unavoidable, air flow can still be ensured if the partitions have openings at the lower and upper portions. This is a common strategy in the old Filipino bahay na bato, with its transom panels covered with intricate wood carvings or wood louvers. Maximize window openings for cross ventilation of internal spaces. Vents in the roof cavity can can also be very effective in drawing out heat from the room interiors. Since hot air goes upward, and cool air goes downward, openings at the top of staircases and in clerestory windows facilitate air change. It is generally cooler at night, so ventilation ventilation of internal spaces can be continuous for nighttime cooling. cooling. This means designing the building with operable windows to let hot air escape at night and to capture prevailing night winds. To supplement supplement natural ventilation, fans can be be placed at various heights and areas to increase comfort conditions. Fans are effective in generating internal air movement, improve air distribution and increase air velocities. Window openings are advisable at the body level for evaporative human body cooling. And room width should not exceed five times ceiling height for good air movement. Sunshades and and sun protection devices on openings reduce heat gain and glare, and also help in internal daylighting. Louvres that are adjustable can alter the direction of air flow and lighting. Asian houses have big roof overhangs to protect interior spaces from heat gain and g lare. Shading materials should reflect heat, and not be another source of heat. Roof insulation is a must in our warm climate. This reduces the temperature significantly inside the house.
What is "Sustainable Architecture?" Eco-housing, green development, sustainable design -- environmentally sound housing has as many names as it has definitions, but the Rocky Mountain Institute, in its "Primer on Sustainable Building", flexibly describes this new kind of architecture as "taking less from the Earth and giving more to people." In practice, "green" housing varies widely. It can range from being energy efficient and using nontoxic interior finishes to being constructed of recycled materials and completely powered by the sun. Green building practices offer an opportunity to create environmentally sound and resourceefficient buildings by using an integrated approach to design. Green buildings promote resource conservation, including energy efficiency, renewable energy, and water conservation features; consider environmental impacts and waste minimization; create a healthy and comfortable environment; reduce operation and maintenance costs; and address issues such as historical preservation, access to public transportation and other community infrastructure systems. The entire life cycle of the building and its components is considered, as well as the economic and environmental impact and performance. Basically, its an environmentally friendly house!
Architectural Response to Sustainability Since the Oil Embargo in the 1970‘s, there has been an increased awareness in environmental issues. Some people may look at the loss of non-renewable resources and think automobiles are the main cause. However, that is not so. It may be suprising to many that the majority of energy depletion comes from buildings. Half of the non-renewable resources that are used used are wasted by buildings buildings and homes, where as only 25% is used by automobiles (Slessor 1996, p.4). In addition, the United States citizen uses 20 times more raw materials than the average world citizen. This shock has hit the architectural field hard but there has been little done to remedy the situation. The idea of sustainable architecture is not new. As defined by Robert Berkebile, AIA, ―It is design that improves the quality of life today without diminishing it for the next gener ation.‖ (Berkebile ation.‖ (Berkebile 1993, p.109) However, sustainable architecture is hardly ever used. used. The lack of green architecture is a fault of both the client and the architect. It is the architect's responsibility to converse to the client about sustainability, but most firms do not have the resources in their files to produce beneficial or new ideas about designing sustainable buildings. Also, if an architect does wish to produce a sustainable building, the client may not want to pay the additional costs it may take to construct, and is most the time unaware of the benefits. The time has come to educate the clients about design issues such as ―sleek does not mean better‖ and ―a glass wall is not better than a concrete wall.‖ There comes a time when people have to stop worrying only about the exterior details and start worrying about the internal ones, "…It is time to stop putting the fins on the Cadillac." (Slessor Cadillac." (Slessor 1996, p.5) We as architects have valuable resources at our disposal that are more than often over looked. In addition, as designers we must change the standards of construction. We have to stop pulling details and other pre-fabricated building systems out of catalogues and use our design ability to change the way architecture runs. Architects must challenge the preconceptions behind building forms. In fact, there is still much to learn from traditional vernacular forms.
Principles of Sustainable Architecture The following nine ideas, as provided by the Hannover Principles of Architecture (http://minerva.acc.virginia.edu/~arch/pub/), should be seen as a means of improving the quality of life through environmentally friendly architecture. These points are constantly changing, so that they may adapt as our knowledge of the world evolves.
1. Insist on rights of humanity and nature to co-exist in a healthy, supportive, diverse and sustainable condition. 2. Recognize interdependence. The elements of human design interact with and depend upon the natural world, with broad and diverse implications at every scale. Expand design considerations to recognizing even distant effects. 3. Respect relationships between spirit and matter. Consider all aspects of human settlement including community, dwelling, industry and trade in terms of existing and evolving connections between spiritual and material consciousness. 4. Accept responsibility for the consequences of design decisions upon human well-being, the viability of natural systems and their right to co-exist. 5. Create safe objects of long-term value. Do not burden future generations with requirements for maintenance or vigilant administration of potential danger due to the careless creation of products, processes or standards. 6. Eliminate the concept of waste. Evaluate and optimize the full life-cycle of products and processes, to approach the state of natural systems, in which there is no waste. 7. Rely on natural energy flows. Human designs should, like the living world, derive their creative forces from perpetual solar income. Incorporate this energy efficiently and safely for responsible use. 8. Understand the limitations of design. No human creation lasts forever and design does not solve all problems. Those who create and plan should practice humility in the face of nature. Treat nature as a model and mentor, not as an inconvenience to be evaded or controlled. 9. Seek constant improvement by the sharing of knowledge. Encourage direct and open communication between colleagues, patrons, manufacturers and users to link long term sustainable considerations with ethical responsibility, and re-establish the integral relationship between natural processes and human activity.
Sustainable Designs - A compact envelope allows for very little surface area to be exposed to the external environment. Thus, providing the structure more economical when it comes to heating and cooling. - The use of a buffer zone between the core (living space) of a building and its exterior walls, such as the design of a hallway or a laundry room, helps maintain comfortable conditions internally and saves energy. - Wall types are also important. When wind hits a wall it produces a back flow at the base, which if not sealed properly or if there was a designed opening, filtration into the building will occur. This will cause much energy loss and a draft inside. - Using trees in the landscape is a great way to buffer the strong north winds in the winter. Also, a tree placed on the southern corner of a house allows for cooling in the summer and heating in the winter. - Numerous wall types are designed to be energy efficient throughout the year. Some examples of walls are the Trombe wall and water wall, which absorb heat in the winter. - Passive solar heating is the use of glazed walls in proper locations to allow sunlight to penetrate in the winter and to be blocked in the summer. This process, if done properly, will allow heating and cooling to occur during the relative seasons. - Solar panels, another use of solar energy, is an enhanced product that exploits sunlight to heat and produce clean energy. Once a mainstream product in the 1970‘s, solar panel use is minimal because of their high cost compared to the price of fossil fuel. However, in the long run, solar panels more than pay for themselves. - Earth rammed homes (a house whose walls are backfilled with earth) are of great benefit for the serious economically aware owner. These types of homes use the natural heating and cooling of the earth to maintain the internal temperature of the house. Though it may be more costly to dig out and back fill, the electric and heating bill will be very minute compared to the cost to heat and cool an average home (Achard 1993, p.54).
Interior and Exterior View of a Sustainable Home
Water Collection Flood water collection, and the pooling of greywater (from sink and bath) would supply a sufficient amount of water for irrigation purposes. Connecting residential greywater and storm water run-off to a centralized underground storage basin would reduce the need for clean city water. Collected water would help to irrigate residential gardens and green spaces. Gardens and green spaces cut down on neighborhood pollution and save residents money on certain products such as vegetables. (Steele 1983, p151) This would be especially useful in Emerson Park, East St. Louis because it is an area which receives a good amount of rain and it is at a lower elevation than the surrounding neighborhoods thus water collection into a basin would not be a problem. This system however would be a costly one to install, just as the light rail station was, but like the rail station I feel in the next ten to fifteen years the city will relize its benefits. For this pooling of water to be beneficial residents would need to develop green spaces which would require greywater only. Areas such as flower gardens, vegetable gardens, and mini parks are some examples of things which could use greywater. Also by creating these attractive landscapes residents could save money on products they would normally buy at the store by growing vegetables such as tomatos, apples, and watermellon.
Example of one method of greywater irrigation.
Passive Solar Housing Passive solar systems are self-sufficient buildings which rely on natural principles insted of mechanical systems to provide a non-polluting source of heating and cooling.
Introduction Passive energy is more sustainable than active energy systems because passive systems use far fewer natural resources to build and maintain. They do not rely so heavily upon gas for heating or coolants for air conditioning. Passive systems are designed so that they can take natural energy from the sun to heat a building and use specific design principles to cool a building. Passive energy systems are also cheaper than active systems because they are less susceptible to malfunction since they rely completely upon nature, rather than using mechanical equipment to produce energy. In order to create a home that will
maximize the effects of passive solar heating, a designer must take many different variables into account. Two major ideas crucial to creating effective passive solar housing are orientation andmaterials. Passive solar buildings should be oriented to receive as much southern sun as possible. In the summer, the hot sun can be blocked by using overhangs or through landscaping like large foliated trees. In the winter, sun should help heat the house because the sun angle is lower in the sky allowing more sun to hit the glazing more directly. Thought should also be given to the specifications of the windows for maximum solar gains and heat loss. By using the right building materials such as masonry or concrete and combining them with effective insulation, solar energy can be contained in the house allowing it to be comfortable year round (Desbarats 1980, 232).
Building Orientation Building orientation is crucial to maximizing energy production in a passive solar home. Because passive solar homes rely on natural sunlight to power the building's utilities, the building should be oriented on thesite in a way that will allow it to maximize the amount of sunlight. The best way to achieve this is to orient the house on the east-west axis and concentrate most of the house's glazing on the south wall. This allows the home to receive the most direct sunlight for the longest period of time (Hibshman 1983, 261). Heat travels through windows very easily, however heat does not exit as easily. Once the heat passes through the window, it breaks up and it takes much longer for that heat to exit (Button 1993, 129). This allows heat that enters a building to stay in the building for a long time. This is a helpful principal for heating a building in the winter and is the reason why windows should receive as much light as possible in the winter. However, in the summer, the hot sun can become an uncomfortable problem. To alleviate some of this heat, passive solar homes should be designed with attic fans or some sort of operable clerestory windows which can be opened to release some of the hot air when it rises. Glazing should be greatly reduced on the east and west walls and should be virtually eliminated on the north side of the home because most cold winds in winter come from the north and west (Desbarats 1980, 56). Because the house needs as much protection from these winds as possible, and glazing cannot provide this protection, windows should be eliminated. (Desbarats 1980, 28).
Glass The amount as well as type of glass windows used in a house are very important considerations interms of thermal comfort, cost and efficiency. There are many different types of windows available: single, double and triple paned (Button 1993, 164) A single pane is simply one pane of glass. These are generally the worst types of windows to use. Although they are the cheapest windows available, they are not energy efficient and they allow more heat gain in summer and heat loss in winter than either the double or triple paned windows do. Double pane windows are much more energy efficient. The reason is the cold winter air passes through the first pane but then must pass through a gap of either air or Argon gas before it reaches the second pane. The reason this is helpful is because air or Argon gas provide excellent insulation and do not allow the cold to penetrate nearly as much as it would if there were only one pane. Triple paned windows work on the same principal as double paned but they are even more energy efficient because there is even an additional layer of insulation (Button 1993, 166). It is also possible to get windows with coatings such as low emissivity coatings (low-E) which help to block the suns harmful rays but still allow visible light to pass through (Button 1993, 173).
R-Values for Different Types of Glass
Thermal Mass Thermal mass is another important concept to keep in mind when dealing with energy efficient housing. It is important for these types of homes to be built with materials that have a large amount of thermal mass (Hibshman, 1983, p.48). Such materials are brick, stone and concrete. These materials are ideal because materials with a large thermal mass absorb much of the energy they receive from the sun. These materials absorb and release energy completely, but slowly. Because it takes a long time for the energy to be released after it is absorbed, a phenomenon known as lag, warm sunlight that is absorbed during the day is finally released over time at night. This is another natural phenomenon which proves helpful because it provides warmth at night when the house is the coldest and heat is necessary. Because all of the heat is released at night the floor is then cool for the next day and consequently this helps to cool the rest of the house. It is also important leave the concrete floors on the south side of the house exposed. If they are carpeted, they lose most all of their thermal mass properties. However, carpeting would be acceptable on the north side of the house because there should be almost no windows there anyway (Hibshman, 1983, p.32).
How Thermal Mass Works
Affordability in Sustainability Using Passive Solar Heating Cost is a very important factor for designing sustainable architecture. Aside from creating enviornmentally friendly architecture, sustainable architecture allows lower building and maintenance costs. Affordability goes hand in hand with sustainablity and is something which we, as designers, should concentrate on when designing the housing in East St. Louis. One way to create affordable homes is by using everyday, affordable materials to replace expensive and wasteful mechanical ones. One way this can be achieved is by using 55-gallon drums filled with water to create thermal mass, a very necessary element for passive solar heating. By placing these drums in direct sunlight, they will absorb the sun's energy and, because lag also occurs in water, they will have the same effect on the house that materials like concrete or masonry would, but without the cost (Hibshman, 1983, p.50). Another, affordable solution is to use these drums filled with water to replace water heaters. They can be placed in the roof or any other place where they will receive a lot of direct sunlight (see figure on "Sustainable Design" page). The owner can then use that water which has been naturally heated for bathing or cooking, replacing a mechanical hot water heater and greatly reducing cost (Hibshman, 1983, p.53). Another way to create affordable yet sustainable architecture is by using unconventional building techniques. One way is to use post-and-beam units instead of conventional stick framing. The posts are then anchored into the concrete. This creates a very stable framing system and also reduces costs because no 2"x4" studs are used and therefore, less wood is used. However, the most important money saving factor in this construction is the use of prefabricated wall systems. These systems are cut into 4'x8' sheets and can then be placed right in between the posts on the construction site with no wated materials used (Hibshman, 1983, p.71). This is also a faster method of construction so the labor costs will also be reduced. While these are just a few ideas more specific examples using these techniques can be found in the sited material.
Diagram showing good passive solar design
What is passive cooling? Passive cooling is the least expensive means of cooling a home in both financial and environmental terms. Some level of passive cooling is required in every Australian climate at some time of the year. As cooling requirements are dictated b y climate, distinctly different approaches to passive cooling are required for:
hot humid climates (Zone 1) where no heating is required
temperate and warm climates (Zones 2−6) where both heating and cooling are required
cool and cold climates (Zones 7−8) where heating needs are more important.
Each climate is discussed separately below. Cooling people Factors affecting comfort for people (human thermal comfort) are outlined in Design for climate and include both physiological and psychological factors. To be effective, passive cooling needs to cool both the building and the people in it. Evaporation of perspiration is the most effective physiological cooling process. It requires air movement and moderate to low humidity (less than 60%). Radiant heat loss is also important, both physiologically and psychologically. It involves direct radiation to cooler surfaces. Conduction contributes to both types of comfort and involves body contact with cooler surfaces. It is most effective when people are sedentary (e.g. sleeping on a water bed). Cooling buildings The efficiency of the building envelope can be maximized in a number of ways to minimize heat gain:
shading windows, walls and roofs from direct solar radiation
using lighter colored roofs to reflect heat
using insulation and buffer zones to minimize conducted and radiated heat gains
making selective or limited use of thermal mass to avoid storing daytime heat gains.
To maximize heat loss, use the following natural sources of cooling:
air movement
cooling breezes
evaporation
earth coupling
reflection of radiation.
Cooling sources Sources of passive cooling are more varied and complex than passive heating, which comes from a single, predictable source — solar radiation. Varying combinations of innovative envelope design, air movement, evaporative cooling, earth-coupled thermal mass, lifestyle choices and acclimatisation are required to provide adequate cooling comfort in most Australian climate zones. Additional mechanical cooling may be required in hot humid climates and in extreme conditions in many climates, especially as climate change leads to higher temperatures during the daytime and overnight. Air movement Air movement is the m ost important element of passive cooling. I t cools people by increasing evaporation and requires both breeze capture and fans for back-up in still conditions. It also cools buildings by carrying heat out of the building as warmed air and replacing it with cooler external air. Moving air also carries heat to mechanical cooling systems where it is removed by heat pumps and recirculated. This requires well-designed openings (windows, doors and vents) and unrestricted breeze paths. In all climates, air movement is useful for cooling people, but it may be less effective during periods of high humidity. An air speed of 0.5m/s equates to a 3°C drop in temperature at a relative humidity of 50%. This is a one-off physiological cooling effect resulting from heat being drawn from the body to evaporate perspiration. Air movement exposes the skin to dryer air. Increased air speeds do not increase cooling at lower relative humidity but air speeds up to 1.0m/s can increase evaporative cooling in higher humidity. Air speeds above 1.0m/s usually cause discomfor t. Cool breezes Where the climate provides cooling breezes, maximising their flow through a home when cooling is required is an essential component of passive design. Unlike cool night air, these breezes tend to occur in the late afternoon or early evening when cooling requirements usually peak.
Cool breezes work best in narrow or open plan layouts. Cool breezes work best in narrow or open plan layouts and rely on air-pressure differentials caused by wind or breezes. They are less effective in:
buildings with deep floor plans or individual small rooms
long periods of high external temperature (ambient or conducted heat gains above 35 –40 watts 2
per square metre (W/m )
locations with high noise, security risk or poor external air quality, where windows may need to be closed.
Coastal breezes are usually from an onshore direction (south-east and east to north-east in most east coast areas, and south-west in most west coast areas, e.g. the ‗Fremantle Doctor‘). In mountainous or hilly areas, cool breezes often flow down slopes and valleys in late evening and early morning, as heat radiating to clear night skies cools the land mass and creates cool air currents. Thermal currents are common in flatter, inland areas, created by daily heating and cooling. They are often of short duration in early morning and evening but with good design can yield worthwhile cooling benefits. Cool night air Cool night air is a reliable source of cooling in inland areas where cool breezes are limited and diurnal temperature ranges usually exceed 6−8°C. Hot air radiating from a building fabric‘s thermal mass is replaced with cooler night air drawn by internal−external temperature differentials rather than breezes. Full height, double hung windows are ideal for this purpose. Further cooling can be gained by including whole of house fans (see below).
Convective air movement The rule of convection: warm air rises and cool air falls. Stack ventilation, or convective air movement, relies on the increased buoyancy of warm air which rises to escape the building through high level outlets, drawing in lower level cool night air or cooler daytime air from shaded external areas (south) or evaporative cooling ponds and fountains.
Convection causes warm air to rise, drawing in cool air. Convective air movement improves cross-ventilation and overcomes many of the limitations of unreliable cooling breezes. Even when there is no breeze, convection allows heat to leave a building via clerestory windows, roof ventilators and vented ridges, eaves, gables and ceilings. Convection produces air movement capable of cooling a building but usually has insufficient air speed to cool people. Solar chimneys Solar chimneys enhance stack ventilation by providing additional height and well-designed air passages that increase the air pressure differential. Warmed by solar radiation, chimneys heat the rising air and increase the difference in temperature between incoming and out-flowing air.
The increase in natural convection from these measures enhances the draw of air through the building.
Source: Green Builder Solar Guidelines (Residential) Solar chimneys enhance ventilation. Evaporative cooling As water evaporates it draws large amounts of heat from surr ounding air. Evaporation is therefore an effective passive cooling method, although it works best when relative humidity is lower (70% or less during hottest periods) as the air has a greater capacity to take up water vapour. Rates of evaporation are increased by air movement. Pools, ponds and water features immediately outside windows or in courtyards can pre-cool air entering the house. Carefully located water features can create convective breezes. The surface area of water exposed to moving air is also important. Fountains, mist sprays and waterfalls can increase evaporation rates.
Photo: Sunpower Design Ponds pre-cool air before it enters a house. Mechanical evaporative coolers are common in drier climates and inland areas where relative humidity is low. They use less energy than refrigerated air conditioners and work better with doors and windows left open. Their water consumption can be considerable. (see Heating and cooling) Earth coupling Earth coupling of thermal mass protected from external temperature extremes (e.g. floor slabs) can substantially lower temperatures by absorbing heat as it enters the building or as it is generated by household activities.
Earth coupling utilises cooler ground temperatures .
Passively shaded areas around earth-coupled slabs keep surface ground temperatures lower during the day and allow night-time cooling. Poorly shaded surrounds can lead to earth temperatures exceeding internal comfort levels in many areas. In this event, an earth-coupled slab can become an energy liability. Ground and soil temperatures vary throughout Australia. Earth-coupled construction (including slab-onground and earth covered or bermed) utilises stable ground temperatures at lower depths to absorb household heat gains. Passive cooling design principles To achieve thermal comfort in cooling applications, building envelopes are designed to minimise daytime heat gain, maximise night-time heat loss, and encourage cool breeze access when available. Considerations include:
designing the floor plan and building form to respond to local climate and site
using and positioning thermal mass carefully to store coolness, not unwanted heat
choosing climate appropriate windows and glazing
positioning windows and openings to enhance air movement and cross ventilation
shading windows, solar exposed walls and roofs where possible
installing and correctly positioning appropriate combinations of both reflective and bulk insulation
using roof spaces and outdoor living areas as buffer zones to limit heat gain.
Integration of these variables in climate appropriate proportions is a complex task. Energy rating software, such as that accredited under the Nationwide House Energy Rating Scheme (NatHERS), can simulate their interaction in any design for 69 different Australian climate zones. While the NatHERS software tools are most commonly used to rate energy efficiency (thermal performance) when assessing a house design for council approval, their capacity, in ‗non -rating mode‘, as a design tool is currently under-used. Seek advice from an accredited assessor (Association of Building Sustainability Assessors orBuilding Designers Association of Victoria) who is skilled in using these tools in non-rating mode. Envelope design — floor plan and building form Envelope design is the integrated design of building form and materials as a total system to achieve optimum comfort and energy savings.
Heat enters and leaves a home through the roof, walls, windows and floor, collectively referred to as the building envelope. The internal layout — walls, doors and room arrangements — also affects heat distribution within a home. Good design of the envelope and internal layout responds to climate and site conditions to optimise the thermal performance. It can lower operating costs, improve comfort and lifestyle and minimise environmental impact. All Australian climates curr ently require some degree of passive cooling; with climate change this is expected to increase. Varied responses are required for each climate zone and even within each zone depending on local conditions and the microclimate of a given site.
Maximise the indoor−outdoor relationship and provide outdoor living spaces that are screened, shaded and rain protected.
Maximise convective ventilation with high level windows and ceiling or roof space vents.
Zone living and sleeping areas appropriately for climate — vertically and horizontally.
Locate bedrooms for sleeping comfort.
Design ceilings and position furniture for optimum efficiency of fans, cool breezes and convective ventilation.
Locate mechanically cooled rooms in thermally protected areas (i.e. highly insulated, shaded and well sealed).
Thermal mass Thermal mass is the storage system for warmth and ‗coolth‘ (the absence of warmth) in passive design. Climate responsive design means positioning thermal mass where it is exposed to appropriate levels of passive summer cooling (and solar heating in winter). Badly positioned mass heats up and radiates heat well into the night when external temperatures have dropped. As a rule of thumb, avoid or limit thermal mass in upstairs sleeping areas. In climates with little or no heating requirement, low mass is generally the preferred option. (see Thermal mass) Earth-coupled concrete slabs-on-ground provide a heat sink where deep earth temperatures (at 3m depth or more) are favourable, but should be avoided in climates where deep earth temperatures contribute to heat gain. In these regions, use open vented floors with high levels of insulation to avoid heat gain.
In regions where deep earth temperatures are lower, consider enclosing subfloor areas to allow earth coupling to reduce temperatures and therefore heat gains.
Windows and shading Windows and shading are the most critical elements in passive cooling. They are the main source of heat gain, via direct radiation and conduction, and of cooling, via cross, stack and fan-drawn ventilation, cool breeze access and night purging. (see Glazing;Shading) Low sun angles through east and west-facing windows increase heat gain, while north-facing windows (south in tropics) transmit less heat in summer because the higher angles of incidence reflect more radiation.
Source: Association of Building Sustainability Assessors (ABSA) Relationship between sun angle and heat gain.
Air movement and ventilation Design to maximise beneficial cooling breezes by providing multiple flow paths and minimising potential barriers; single depth rooms are ideal in warmer climates. Because breezes come from many directions and can be deflected or diverted, orientation to breeze direction is less important than the actual design of windows and openings to collect and direct breezes within and through the home. Use casement windows to catch and deflect breezes from varying angles.
Source: Dept of Environment and Resource Management, Qld For breeze collection, window design is more important than orientation . Wind doesn‘t blow through a building — it is sucked towards areas of lower air pressure. To draw the breeze through, use larger openings on the leeward (low pressure or downwind) side of the house and smaller openings on the breeze or windward (high pressure or upwind) side. Openings near the centre of the high pressure zone are more effective because pressure is highest near the centre of the windward wall and diminishes toward the edges as the wind finds other ways to move around the building.
Airflow pattern and speed for dif ferent opening areas.
In climates requiring winter heating the need for passive solar north sun influences these considerations; designers should strive for a balanced approach. The design of openings to direct airflow inside the home is a critical but much overlooked design component of passive cooling. Size, type, external shading and horizontal/vertical position of any openings (doors and windows) is critical — as shown in the diagrams below.
Source: Steve Szokolay Airflow pattern for windows of different opening height. Louvre windows help to vary ventilation paths and control air speed. Consider installing a louvre window above doors to let breezes pass through the building while maintaining privacy and security. In climates requiring cooling only, consider placing similar panels above head height in internal walls to allow cross-ventilation to move the hottest air. Position windows (vertically and horizonally) to direct airflow to the area where occupants spend most time (e.g. dining table, lounge or bed). In rooms where it is not possible to place windows in opposite or adjacent walls for cross-ventilation, place projecting fins on the windward side to create positive and negative pressure to draw breezes through the room, as shown in the diagram below.
Use fins to direct airflow. Design and locate planting, fences and outbuildings to funnel breezes into and through the building, filter stronger winds and exclude adverse hot or cold winds.
Plant trees and shrubs to funnel breezes.
Plant trees and shrubs to funnel breezes. Insulation Insulation is critical to passive cooling — particularly to the roof and floor. Windows are often left open to take advantage of natural cooling and walls are easily shaded; roofs, however, are difficult to shade, and floors are a source of constant heat gain through conduction and convection, with only limited cooling contribution to offset it. Insulation levels and installation details for each climate zone are provided in Insulation and Insulation installation. Pay careful attention to up and down insulation values and choose appropriately for purpose and location.
In climates that require only cooling or those with limited cooling needs, use multiple layers of reflective foil insulation in the roof instead of bulk insulation to reduce radiant daytime heat gains while maximising night-time heat loss through conduction and convection. This is known as the one-way insulation valve. Reflective foil insulation is less affected by condensation and is highly suited to cooling climate applications as it reflects unwanted heat out while not re-radiating it in. Roof space Well-ventilated roof spaces (and other non-habitable spaces) play a critical role in passive cooling by providing a buffer zone between internal and external spaces in the most difficult area to shade, the roof.
Well-ventilated roof spaces form a buffer between internal and external areas. Ventilators can reduce the temperature differential (see Passive heating) across ceiling insulation, increasing its effectiveness by as much as 100%. The use of foil insulation and light coloured roofing limits radiant heat flow into the roof space. Use careful detailing to prevent condensation from saturating the ceiling and insulation. Dew-points form where humid air comes into contact with a cooler surface, e.g. the underside of roof sarking or reflective foil insulation cooled by radiation to a clear night sky. (seeSealing your home)
Source: COOLmob Using ventilation to cool the roof space. Hybrid cooling systems Hybrid cooling systems are whole house cooling solutions that employ a variety of cooling options (including air conditioning) in the most efficient and effective way. They take maximum advantage of passive cooling when available and make efficient use of mechanical cooling systems during extreme periods. Fans Fans provide reliable air movement for cooling people and supplementing breezes during still periods. At 50% relative humidit y, air movement of 0.5m/s creates maximum cooling effect; faster speeds can be unsettling. As noted above, air speeds up to 1.0m/s can be useful in higher relative humidity, but prolonged air speeds above 1.0m/s cause discomfort. Standard ceiling fans can create a comfortable environment when temperature and relative humidity levels are within acceptable ranges. In a lightweight building in a warm temperate climate, the installation of fans in bedrooms and all living areas (including kitchens and undercover outdoor areas) significantly reduces cooling energy use.
Source: Adapted from Ballinger 1992 Air movement relative to f an position. Fans should be located centrally in each space, one for each grouping of furniture. An extended lounge/dining area needs two fans. In bedrooms, locate the fan close to the centre of the bed. Because air speed decreases with distance from the fan, position fans over the places where people spend the most time. (seeHeating and cooling) Whole of house fans
Whole of house or roof fans are ideal for cooling buildings, particularly where cross-ventilation design is inadequate. However, they do not create sufficient air speed to cool occupants.
Source: Breezepower Whole of house fans should be positioned centrally, e.g. in the roof, stairwell or hallways. Typically, a single fan unit is installed in a circulation space in the centre of the house (hallway or stairwell) to draw cooler outside air into the building through open windows in selected rooms, when conditions are suitable. It then exhausts the warm air through eaves, ceiling or gable vents via the roof space. This also cools the roof space and reduces any temperature differential across ceiling insulation. Control systems should prevent the fan operating when external air temperatures are higher than internal. Drawing large volumes of humid air through the roof space can increase condensation. A dew-point forms when this humid air comes in contact with roof elements (e.g. reflective insulation) that have been cooled by radiation to night skies (see Insulation andSealing your home for ways to mitigate this). Whole of house fans can be noisy at full speed but are generally operated in the early evening when cooling needs peak and households are most active. If run at a lower speed throughout the night, they can draw cool night air across beds that are near open windows, provided doors are left open for circulation. On still nights this can be more effective than air conditioning for night-time sleeping comfort.
What Is Green Architecture and Green Design? Definition: Green architecture, or green design, is an approach to building that minimizes harmful effects on human health and the environment. The "green" architect or designer attempts to safeguard air, water, and earth by choosing eco-friendly building materials and construction practices. Green architecture may have many of these characteristics: Ventilation systems designed for efficient heating and cooling Energy-efficient lighting and appliances Water-saving plumbing fixtures Landscapes planned to maximize passive solar energy Minimal harm to the natural habitat Alternate power sources such as solar power or wind power Non-synthetic, non-toxic materials Locally-obtained woods and stone Responsibly-harvested woods Adaptive reuse of older buildings Use of recycledarchitectural salvage Efficient use of space
While most green buildings do not have all of these features, the highest goal of green architecture is to be fully sustainable. Also Known As: Sustainable development, eco-design, eco-friendly architecture, earth-friendly architecture, environmental architecture, natural architecture
Links
http://business.inquirer.net/19613/tropical-architecture http://www.eslarp.uiuc.edu/arch/ARCH371-F99/groups/k/susarch.html http://www.yourhome.gov.au/passive-design/passive-cooling http://architecture.about.com/od/greenconcepts/g/green.htm
