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This article refers to a device for ventilation. For the power generation technology, see Solar updraft tower.
A solar chimney is a way of improving the natural ventilation of buildings by using convection of air heated by passive solar energy. The solar chimney has been in use for centuries, particularly in the Middle east, as well as by the Romans.
Description
In its simplest form, the solar chimney consists of a black-painted chimney. During the day solar energy heats the chimney and the air within it, creating an updraft of air in the chimney. The suction created at the chimney's base can be used to ventilate and cool the building below. In most parts of the world it is easier to harness wind power for such ventillation, but on hot windless days such a chimney can provide ventilation where otherwise there would be none.
A principle has been proposed for solar power generation, using a large greenhouse at the base rather than relying solely on heating the chimney itself. (For further information on this issue, see Solar updraft tower.)
Solar chimney and sustainable architecture
] A Solar chimney can serve many purposes. Direct gain warms air inside the chimney causing it to rise out the top and drawing air in from the bottom. This drawing of air can be used to ventilate a home or office, to draw air through a geothermal heat exchange, or to ventilate only a specific area such as a composting toilet.
Natural ventilation can be created by providing vents in the upper level of a building to allow warm air to rise by convection and escape to the outside. At the same time cooler air can be drawn in through vents at the lower level. Trees may be planted on that side of the building to provide shade for cooler outside air.
This natural ventilation process can be augmented by a solar chimney. The chimney has to be higher than the roof level, and has to be constructed on the wall facing the direction of the sun. Absorption of heat from the sun can be increased by using a glazed surface on the side facing the sun. Heat absorbing material can be used on the opposing side. The size of the heat-absorbing surface is more important than the diameter of the chimney. A large surface area allows for more effective heat exchange with the air necessary for heating by solar radiation. Heating of the air within the chimney will enhance convection, and hence airflow through the chimney. Openings of the vents in the chimney should face away from the direction of the prevailing wind.
To further maximize the cooling effect, the incoming air may be led through underground ducts before it is allowed to enter the building. The solar chimney can be improved by integrating it with a trombe wall. The added advantage of this design is that the system may be reversed during the cold season, providing solar heating instead.
A variation of the solar chimney concept is the solar attic. In a hot sunny climate the attic space is often blazingly hot in the summer. In a conventional building this presents a problem as it leads to the need for increased air conditioning. By integrating the attic space with a solar chimney, the hot air in the attic can be put to work. It can help the convection in the chimney, improving ventilation.
Passive down-draft cooltower
A technology closely related to the solar chimney is the evaporative down-draft cooltower. In areas with a hot, arid climate this approach may contribute to a sustainable way to provide air conditioning for buildings.
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. 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. 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.)
See also
- Windcatcher
- Wind tower
- Trombe wall
- Earth cooling tubes
- Autonomous building
- Passive house
- Sustainable architecture
- Passive solar
- Stack effect
- Ventilation (architecture)
- HVAC
External links
- http://www.sxlist.com/techref/other/spac.htm
- http://www.seav.sustainability.vic.gov.au/ftp/buildings/VSII/solar_chimney.pdf
- P Olmos Ultrasonic velocity meter to evaluate the behaviour of a solar chimney Meas. Sci. Technol. (2004) 15, N49-N53.
- Clito Afonso and Armando Oliveira Solar chimneys: simulation and experiment Energy and Buildings, Volume 32, Issue 1 , June 2000, Pages 71-79.
- http://www.ecosensual.net/drm/eco/ecovent1.html
- http://www.flomerics.com/flovent/technical_papers/v46.pdf
- http://www.europeangreencities.com/pdf/activities/ConfApr2004/15.pdf
- http://www.greenbuilder.com/sourcebook/PassSolGuide3.html
- http://www.azsolarcenter.com/design/pas-3.html
- http://www.azsolarcenter.com/technology/pas-3.html
- http://www.thefarm.org/charities/i4at/lib2/aircool.htm
- http://www.nrel.gov/docs/fy02osti/32157.pdf
- http://www.nrel.gov/buildings/highperformance/zion_ee_features.html#cooltower
- Santa Clara University Kennedy Mall Commons - includes simple description and graphic of solar chimney used in a "Green Demonstration Building"* at Santa Clara University.
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"Solar chimney"