What is a Solar Chimney?

Solar chimneys are also referred to as thermal chimneys. Solar chimneys are used as a natural, non-electric, way to ventilate and therefore help cool buildings. Solar chimneys are not a new idea, they have been used for centuries for ventilation purposes.

The simplest solar chimney is made from brick or metal and then painted black. The black exterior color helps the chimney collect more heat from sunlight. The sunlight, or solar energy, heats the air inside the chimney. The principle behind the ventilation process is simple. Heat rises. As the air inside the chimney warms it will rise and move out of the top of the chimney. As this air moves out, the air inside the building is drawn into the chimney. The movement of this air produces ventilation. The new air that has been drawn into the chimney heats and continues the process.

The chimney must be placed in a position higher that the roof of the building it is ventilating to allow the air inside the chimney to be hotter than air inside the building itself. The process of ventilating this way is referred to as natural heat convection. The heat rising and leaving the chimney creates an updraft that circulates the air.

Solar chimneys can also be a part of a larger system. Duct work can be installed inside a building to draw air through underground systems. Underground the duct work is at a cooler temperature than the air outside. An intake duct is placed at a distance from the building and air will be drawn through this system by the solar chimney. Air that passes through the underground duct will cool and provides cooler air entering the building. This is a natural and electricity free way of providing air conditioning.

The amount of cooling and ventilation the solar chimney provides depends on many characteristics and conditions. The material the chimney is made of, the location of the chimney and the chimney's size all effect the amount of air it will draw from the building. The size and location of the ventilation ducts are also important in the air flow provided. Solar chimneys will not reduce the amount of humidity in the air but can make the air more comfortable.

Solar chimneys are also being used as a source of power generation. Air drawn through these chimneys is being used to turn wind turbines for the generation of electricity. This process can be very beneficial to areas that have large amounts of heat and not enough wind for the use of regular wind turbines.

References:
　
http://www.answers.com/topic/solar-chimney

http://www.findportablesolarpower.com/solarenergy/solarchimney.php

http://www.math.purdue.edu/~lucier/The_Solar_Chimney.pdf