down-draft chimney/power station

The principle is to allow water to evaporate at the top of a tower, either by using evaporative cooling pads or by spraying water. Evaporation cools the incoming air, causing a downdraft of cool air that will bring down the temperature inside the building.^[5] Airflow can be increased by using a solar chimney on the opposite side of the building to help in venting hot air to the outside.^[6] This concept has been used for the Visitor Center of Zion National Park. The Visitor Center was designed by the High Performance Buildings Research of the National Renewable Energy Laboratory (NREL).

The principle of the downdraft cooltower has been proposed for solar power generation as well. (See Energy tower for more information.)

An energy tower (also known as a downdraft energy tower because the air flows down the tower) is a tall (1,000 meters) wide (400 meters) hollow cylinder with a water spray system at the top. Pumps lift the water to the top of the tower and then spray the water inside the tower. Evaporation of water cools the hot, dry air hovering at the top. The cooled air, now denser than the outside warmer air, falls through the cylinder, spinning a turbine at the bottom. The turbine drives a generator which produces the electricity.

The greater the temperature difference between the air and water, the greater the energy efficiency. Therefore, downdraft energy towers should work best in a hot dry climate. Energy towers require large quantities of water. Salt water is acceptable, although care must be taken to prevent corrosion.

The energy that is extracted from the air is ultimately derived from the Sun, so this can be considered a form of solar power. Unusually, this form of solar power also works at night, because air retains some of the day's heat after dark. However, power generation by the Energy tower is affected by the weather: it slows down each time the ambient humidity increases (such as during a rainstorm), or the temperature falls.

A related approach is the solar updraft tower, which heats air in glass enclosures at ground level and sends the heated air up a tower to drive a turbine at the top. Updraft towers do not pump water, which increases their efficiency, but do require large amounts of land for the collectors. Land acquisition and collector construction costs for updraft towers must be compared to pumping infrastructure costs for downdraft collectors. Operationally, maintaining the collector structures for updraft towers must be compared to pumping costs and pump infrastructure maintenance.

Zion Visitor's Center

courtesy of: 

wikipedia