Slide Show:

Environmentally Sensitive Buildings
in the Tropics:
Design Ideas for Passive Cooling

Hari Srinivas
Emerging Trends Series E-191. June 2010 (Updated March 2023).

This is a slide presentation that outlines some of the concepts behind passive cooling to design environmentally sensitive buildings in the tropics. The approach takes two aspects into consideration in designing buildings - protection against the sun, and cooling with the wind.

The design aspects illustrated here fall under what is popularly known as "passive cooling", and explains the manipulation of a building's orientation, design, envelope, fenestrations, materials, and landscape to cool buildings in the tropics.
Cooling a building using air conditioners can constitute almost 30% of a building's annual electricity costs. This can be substantially reduced using passive cooling.

Keeping interiors of buildings cool in the tropics (defined as the land mass between the Tropic of Cancer in the north, and Tropic of Capricorn in the south) is an important design goal for not only personal comfort, but also for providing economic and environmental benefits.

Passive cooling is a method of cooling a building or device that does not use mechanical systems such as air conditioning or fans. Instead, passive cooling relies on natural processes, such as convection, radiation, and conduction, to prevent heat from entering the interior of a building or to transfer heat from the interior of the building or device to the exterior environment. As illustrated by the slides outlined below, passive cooling techniques use temperature variations during the day, flow of breeze, shade, evaporative cooling etc, in order to keep interiors cool.

Due to its low costs to construct and maintain, and almost no impacts on the environment, "passive" cooling has considerable benefits in without the use of any intermediate electrical devices or mechanical systems.

Some common techniques used in passive cooling include:

• Orienting the building to maximize shading and minimize solar gain
• Using reflective materials on the roof to reduce heat absorption
• Providing vents and openings to allow for natural ventilation
• Using thermal mass materials such as concrete or water to absorb and store heat during the day and release it at night
• Using insulation to reduce heat transfer through walls and ceilings

Passive cooling can be an effective and energy-efficient way to regulate the temperature in a building or device, especially in climates with mild to moderate temperatures.

Note: Active cooling, on the other hand, refers to cooling technologies that rely on an external device to enhance heat transfer. This can include fans and air-conditioning systems (which requires massive amounts of electricity and/or gas - cornering more than 30% of energy costs of buildings).


The area between the Tropic of Cancer in the north and the Tropic of Capricorn in the south, is considered as the "Tropical Zone." This is where, with the sun angle being about 70deg and with high temperatures and humidities, the need for passive cooling becomes critical.

In order to cool buildings naturally, or passively, there are essentially two natural elements that are manipulated - the sun itself (i.e. prevent the sun from hearing up a building's interior), and the wind (i.e. use wind flows to cool a building and accelerate evaporation of sweat from the body).

Using the sun and wind as key natural elements will mean ensuring that buildings in the tropics are designed with elements that provide shading against the sun, and using wind/breeze to accelerate evaporation of sweat to cool the body.

There are three clusters of design ideas that can be used to passively cook a building: (1) using a building layout or its different components to create shade from the sun, (2) manipulating the fenestrations - windows, doors and other openings for cross-ventilation, and (3) using a building's components in order to heat-to-cool (i.e. using heat to generate circulation of air.

As listed above, there are six design principles that can be used to manipulate building elements in order to cool buildings: (1) manipulating a building's overall orientation to the sun's angle; (2) manipulating the way a building is designed - including activities that take place within the building; (3) manipulating a building's envelope - roofs and walls; (4) manipulating a building's fenestrations - doors and windows; (4) manipulating the materials used to build a building; and finally (6) manipulating the surrounding landscape.



A building's orientation can be manipulated by ensuring that there are less windows on the east and west sides of a building, in order to avoid direct sunlight entering the building interiors and heating it up

Similarly, positioning activities within a building can lso help in keeping working or living areas cool: day-time activities can be positioned in the western part of a building (which is less heated up compared to the east), and night-time activities can be positioned in the eastern part of a building (where the setting sun in the west will not heat it up).



Designing a building with a number of corners helps to cast shadows on the walls against the sun, thus keeping the interiors relatively cooler.

Older buildings in the tropics tended to have high ceilings - this design feature was used to take advantage of "air-mass replacement" to cool interiors: hot air can raise to the top of the room, allowing cooler air to replace it below.

Building structures on raised stilts not only help in reducing disaster risks such as flooding, but also helps in cooling buildings by taking advantage of directing strong wind flows.

Designing a structure with a central courtyard (as in many Asian vernacular architectural styles) can provide the advantage of air pressure differences: As air flows on top of the roof, it creates low-pressure area that sucks in air from the high pressure interiors of the structure. This draws cooler air into the interiors, cooling them.

Central courtyards have another benefit similar to the "Air-mass replacement" mentioned in Slide 9 above: the courtyards heat up during the day and hot air raises up, drawing in cool air from the surrounding area into the buildings.



Building a "false" ceiling, especially under sloping roofs will trap an air pocket in between, which will function as an effective insulation against heat transmitting to the interiors. Similarly, insulation materials in the roof itself, will also help in keeping heat out and interiors cool.

Providing large overhangs for roofs, on all sides possible, provides shade that prevents walls from heating up. This shading consequently keeps interiors cool. In traditional buildings, these overhangs are usually included within a porch or verandah that wrapped aroud the entire building on all sides. (A deep overhang also protects from rain damaging the walls and other parts of a building)

Many cultures in the tropics build their buildings to have roof ponds that helped increase the humidity (especially in dry regions), and keep interiors cool. "Green" roofs - usually with grass or kitchen gardens planted on the roofs - are also used to cool interiors of buildings.

In order to make maximum use of wind breezes, a wind "scoop" or baffle is sometimes used to direct wind into the interior of a building, thus increasing the ventilation of the buildings and keeping them cool. This baffle may indeed be another part of the building itself. and its position would depend on the prevalent wind directions for the site.



Enclosing windows on the outside with shades as illustrated above can reduce the direct sunlight that enters the interiors, keeping them cool. Such shades can also be designed in the form of louvers, which allow wind to flow through, but keep the sun out.

Cross-ventilation is the process where air enters a particular space though one window and is then channeled out through another window. This in-out flow of air through a room keeps it ambiently cool, and also facilitates evaporation of sweat from the body.

Cross-ventilation, as explained in the previous slide, can be both horizontal, but also vertical. Air entering from a door or window is drawn out of a room through windows placed high up in the walls - keeping interiors cool (more so because hot air raises and flows out through these high and small windows).

As with central courtyards shown in Slide 11 above, a "wind tower" takes advantage of low air pressures resulting from air flowing at its top, to draw the hot air from the higher pressure air in the rooms below to create an air flow, which cools the interiors. (In cases of high exterior wind flows, these towers also function reversely as an inlet for air flows into the interiors - a "windcatcher" as it is called in the Persian Gulf area).

The "Venturi Effect" is usually used to explain fluid flows through narrow spaces. This phenomena can also be used to explain air flows through a room: Air is drawn through a larger inlet window and is forced out of a room through a smaller outlet window, which helps in cooling the interiors.



Passive cooling techniques also include the manipulation of building materials. For example, light porous rock or brick can be used for walls, which would act as an effective heat insulation (due to the air pockets trapped within their structure). Such walls can absorb heat and radiate it out through openings in the roof eavesThe area where a roof extends a small way past the wall of a building is usually referred to as the eaves.

Double walls, with an air layer trapped in between the walls, can also act as an effective insulation - reducing the amount of heat that is radiated through walls into the interiors.



Landscaping the area surrounding a building is a visually pleasing solution that also sustainably contributes to passive cooling: By trees that provide shade, and grass and shrubs that absorb reflected radiation from the ground. Other landscaping elements such as water bodies also help in keeping buildings cool. The "Wind Scoop" idea illustrated in Slide 16 above can also be created using scrubs and hedges, channeling wind flows into a building.

The key element that runs through the ideas presented in the slides above is "passive" - it does not require complex mechanical systems and technologies, or expense of energy, but only manipulation of existing design aspects of buildings to cool them, particularly in the tropics.

The ideas use nature itself as a model for cooling buildings - an important requirement since we spend more than 80-90 percent of our time indoors, whether at home or at work.

It is interesting that many of the above ideas are drawn from traditional and vernacular architectural systems. For example, the wind tower illustrated in Slide 20 is commonly called a "windcather" in the Persian Gulf and used extensively in traditional (and increasingly modern too) buildings.

Ultimately, it will be not one technique - but a combination of these ideas - that will best help in achieving the goals of passive cooling.

Note: The use of water (for example through evaporation, heat sinks, and heat conduction) for passive cooling is not explored in detail in the above slides, and needs to also be incorporated in any comprehensive solution for cooling.

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