Passive Cooling Techniques for Buildings in Hot and Humid Climate

Paarth Arka Project

To be comfortable, buildings in India require some form of cooling during summer and monsoon season. There are many ways in which passive cooling can be achieved without the use of mechanical cooling systems. This includes relying on methods such as orientation, ventilation, effective window placement, shading, insulation, thermal mass and heat reflective treatments. Increasingly, residential properties in Lucknow are being built using passive cooling principles that provide thermal comfort, are environment friendly and are also less expensive.

We have described some passive cooling strategies that can effectively keep your house cooler without using expensive mechanical cooling systems.

Building Orientation

Proper building orientation can provide maximum benefits from cooling breezes in hot weather and shelter from undesirable winds in cold weather. A wind rose diagram can be used to see which winds to take advantage of or avoid. Generally, orienting the building so that its shorter axis aligns with prevailing winds will provide the most wind ventilation, while orienting it perpendicular to prevailing winds will provide the least passive ventilation. Sun diagrams can also help immensely in determining where and when sunlight enters a building, allowing the architect to accurately design sun shades, placement of verandahs, kitchens and bedrooms. Successful orientation rotates the building to minimize energy loads and maximize free energy from the sun and wind. 

Cross Ventilation

The strategy of cross ventilation relies on wind to pass through the building across oppositely placed window openings. These openings, located on opposite sides of the space are called the inlet and outlet. The sizing and placement of the inlets and outlets will determine the direction and velocity of cross ventilation through the building. Generally, movement of air from a smaller opening into a larger one increases the wind velocity as it acts as a funnel. 

Correct Windows Design

Adequate size and number of window openings are critical parameters in the passive cooling technique. Large windows allow more air to flow in removing moisture from the air. The location of the opening is equally important in building design. Usually, in a tropical climate like that of India, south east facing windows are most preferable as this is the direction where the prevailing winds blow. 

Shading

A properly designed shading system can effectively contribute to minimizing the solar radiation that induces overheating. Shading both transparent and opaque surfaces of the building envelope will minimize the solar heat gain in both indoor spaces and building’s structure. By shading the building structure, the heat gain captured through the windows and envelope will be reduced. Permanent shades can be used on all walls and windows to exclude solar access and rain. The entire building can also be covered with a fly roof. The outdoors of the building can also be planted with large trees and structures that prevent the direct sun rays to enter the building envelope. 

Heat reflective roofs

Roofs painted in white or special pigments can effectively reflect more sunlight from the surface. Such paints are very thick, thus preserving the roof surface from UV rays and chemical damages. Roofs can also be constructed with gentle slopes that increases the solar reflectance. Green roofs are also an effective way to keep the temperatures of the interiors as low as possible. 

Thermal Insulation

Thermal Insulation is achieved through a combination of materials, which retard the flow of heat into the building. The materials can be adapted to any size, shape or surface, and forms. Insulating the building envelope will decrease the amount of heat transferred by radiation through the facades. In context of passive solar design, insulation can be used together with thermal mass. Thermal mass is a dense material that can store and radiate heat. Insulation allows a warm building to stay warm and a cool building to stay cool. Some materials that can be used for insulation include Structure Insulated Panels (SIPS), Insulated Concrete Forms (ICF’s) etc. Green roofs can also act as a thermal insulator. 

Thermal Mass

Heat gain modulation of an indoor space can be achieved by the proper use of the building’s thermal mass as a heat sink. The thermal mass absorbs and stores heat during daytime and returns it to the space during night. As a general rule, thin tall buildings encourage natural ventilation and utilize prevailing winds, cross ventilation, and stack effect. Thinner buildings increase the ratio of surface area to volume. This will make utilizing natural ventilation for passive cooling easy. 

On the other hand, an elongated floor plan will make natural ventilation difficult and may require mechanical ventilation. Tall buildings increase the effectiveness of natural ventilation as wind speeds are faster at greater heights. This improves not only cross ventilation but also stack effect ventilation.