Tropical Design Module 4: Passive Cooling

Passive Cooling

A cooling system using a building’s design and construction to maintain a comfortable temperature within the building.

Passive design is essentially low-energy design achieved by the building’s particular morphological organization rather than electro-mechanical means.

Passive Cooling Techniques

1. BUILDING CONFIGURATION, SITE LAYOUT and SITE PLANNING
Example : A building can be protected from direct sunlight by placing it on a location within the site that utilizes existing features such as trees, terrain etc.

2. BUILDING ORIENTATION
Example : In tropical countries such as the Philippines, it is best to place service areas in the west and east facing sides of the building because these sides are exposed to direct sunlight.

3. FACADE DESIGN
Use of Double-layered façade
Use Low-emissivity glass (Low-E glass)
Use of Insulation

4. CROSS VENTILATION
The circulation of fresh air through open windows, doors or other openings on opposite sides of a room

STACK EFFECT / CHIMNEY EFFECT
The tendency of air or gas in a shaft or other vertical space to rise when heated, creating a draft that draws in cooler air or gas from below

5. SUNSHADING DEVICES
VERTICAL TYPES
Vertical Sun Shades are generally used on the East-Facing and West- Facing Sides
of a building
EGGCRATE TYPES
Combination of Horizontal and Vertical Shades

WIND ANALYSIS
Wind direction: Desirable and undesirable winds in each of the climatic zones depend largely on local conditions. Any breeze in the lower latitude (tropical and arid climates) is beneficial for most of the year.
Cross ventilation: Cross ventilation is far more important in the tropics than in temperate zones. The theoretical strategy for blocking or inducing wind flow into a building is based on local prevailing wind conditions. Generally, for the tropical zones as much ventilation as possible is desired.

Influences on Built Form
1. Zoning for transitional spaces -the traditional spaces used for lobbies, stairs, utility spaces, circulation, balconies and any other areas where movement take place. These areas do not require total climatic control and natural ventilation is sufficient. For the tropical and arid zones, the transitional spaces are located on the north and south sides of the building where the sun's penetration is not as great. An atrium can also be used a transitional space.

2. Use of atrium
In the tropical zone the atrium should be located so as to provide ventilation within the built form. In the arid zone the atrium should be located at the centre of the building for cooling and shading purposes.

Influences on Built Form
1. Form: Optimum building form for each climatic zone. Research has shown that the preferred length of the sides of the building, where the sides are of length x:y, are: tropical zone - 1:3

Analysis of these ratios shows that an elongated form to minimize east and west exposure is needed at the lower latitudes.

2. Orientation: Orientation as well as directional emphasis changes with latitude in response to solar angle. Building's main orientation for tropical countries would have a directional emphasis on an axis 5deg north of east

3. Vertical cores and structure The arrangement of primary mass can be used as a factor in climatic design as its position can help to shade or retain heat within the building form. For the tropical zone, the cores are located on the east and west sides of the building form, so as to help shade the building from the low angles of the sun during the major part of the day.