Windcatcher

[edit] Introduction

A windcatcher, also known as a windtower, is an architectural element used for natural ventilation. Windcatchers are traditional in Persian architecture, as well as in Ancient Egypt, and can be found across the Middle East.

They generally take the form of small towers installed on top of buildings, although they can be found in several different shapes and structures. The towers draw air from outside into a building, providing natural ventilation in hot, arid and humid areas. Windcatchers were typically built facing away from the wind to try and prevent ingress of blown dust and sand.

Windcatchers are passive systems that require no energy for operation.

[edit] Design

The direction of airflow at that specific location will determine the windcatcher design. Windcatchers can be one of the following:

[edit] Uni-directional

If wind tends to blow from one side only, then it will be built with one downwind opening, without openings in any other directions.

[edit] Bi-directional

These windcatchers tend to be more efficient for airflow circulation and have better performance. They serve two functions – to blow and suck air into a building.

[edit] Multi-directional

These tend to be either four, six or eight-sided windcatchers, and are bigger and taller than the two types above. The exact height and structure of each opening depends upon the specific region’s climate.

[edit] Cylindrical

This is the most technical form of windcatcher and achieves better performance than the other types.

The dimensions of a windcatcher depend on the following:

• The flow rate required for thermal comfort.
• Building dimensions.
• Materials used in the building (a windcatcher will tend to be built from the same material as the building on which it will be installed).
• The region’s typical wind weather conditions.
• Building security.

[edit] Components

The following components comprise a typical windcatcher:

• Head: Includes a moving column opened and closed either manually or electronically. This helps prevent rainwater ingress.
• Column: Fixed in place and can be installed on a rooftop (flat or inclined) using bolts.
• Windows: Installed at the lower end of the column to control airflow.
• Wind vane: Can be installed to detect the wind direction.

[edit] Functions

Windcatchers can function in a number of different ways.

[edit] Downward airflow

When using a windcatcher to try and cool the inside of a building, a tall, capped tower with a uni-directional opening. This ‘catches’ wind on one side and brings it down into the building via the tower. While the air is not cooled by the windcatcher itself, the rate of airflow provides a cooling effect.

[edit] Upward airflow using wind

Windcatchers can may be used in combination with an underground canal, known as a qanat. The tower’s open side faces away from the prevailing wind, and when hot air is drawn down the tower into the qanat it is cooled by coming into contact with the earth and cold water. The building is cooled by this air that is then drawn back up through the windcatcher.

[edit] Upward airflow

In environments that experience minimal wind, or where a qanat is impractical, a windcatcher can be used to function as a solar chimney which allows hot air to travel upwards and escape from the top of the building. In this way, large buildings – especially those constructed with thick adobe to provide good heat transmission resistance – can be kept at chilled temperatures during hot periods.

[edit] Windcatcher with wetted columns

Water is sprayed uniformly on the surface of a column which is constructed of materials such as unglazed ceramic conduits stacked on top of one another. By doing so, the column is dampened, and the effect of evaporative cooling delivers cooler air to the inside of a building.

[edit] Windcatcher with wetted surfaces

This is proposed for use in areas of typically low wind speeds. It works by using pads made from a series of straws or cellulose placed at the apertures on top of the windcatcher. Water is continually sprayed onto them, meaning that the air that flows through is evaporatively cooled. Due to its subsequent density increase, a downward circulation of air is achieved.

[edit] Limitations

Some of the limitations of conventional and traditional windcatchers include:

• They can allow the ingress of small animals, birds or insects.
• The head of windcatchers is fixed and doesn’t rotate with air flow direction.
• In regions with very low wind speed they have limited application.

[edit] Related articles on Designing Buildings Wiki

• Cross ventilation.
• Humidity.
• Natural ventilation.
• Passive building design.
• Solar chimney.
• Stack effect.
• Thermal comfort.
• Types of ventilation.
• Ventilation.
• Wind energy.
• Windmill.
• Wind turbine.