SOLAR/THERMAL CHIMNEY PROCESS
HOW IT WORKS A solar chimney is a passive solar ventilation system. It is a way of improving natural ventilation within a building as well as providing heating or cooling by utilising heat from the sun to enhance the natural stack effect ventilation through a building. It is also used as a renewable power generation source. The solar chimney is a system that has been used for centuries, particularly in the Middle East by the Persians and in Europe by the Romans, for passive heating and cooling within buildings. The tall chimney is generally coated in a material with high thermal absorbency. As it absorbs heat energy from the sun during the day it increases the temperature of the air within the chimney, creating an upward movement of air within the chimney. This creates a suction at the base of the chimney. RESIDENTIAL/COMMERCIAL In a residential situation this suction can either be used for ventilation and cooling in hot weather or in cold weather the top of the chimney can be shut and a vent near the top of the chimney directing the warmed air back into the house. Thermal massing can also be used on the house side of the chimney to provide heating to the interior spaces at night time. This method of ventilation and cooling is especially useful in very hot climates with low wind where other methods like wind scoops would be unsuitable. In a residential situation a solar chimney is often used in conjunction with a geothermal heat exchanger to provide cool air into the building interior. POWER GENERATION In a renewable power generation situation either reflective surfaces are used to reflect the sun’s rays onto a central tower to concentrate the solar energy and thus increase the stack effect within the tower, or there is a large/wide greenhouse type space at the base of the tower which is used to create a upward movement of of air in the tower. This movement of air up the tower is used to drive turbines to create electricity. |
TYPICAL USES
As described above there are two main uses for a solar/thermal tower. The first is a relatively small scale thermal chimney which is used in residential and commercial buildings for heating cooling and ventilation and is often combined with a geothermal heat exchanged and used as part of a passive HVAC design. The second is a solar uplift tower which is used for electricity generation. These structures tend to be extremely large as the height of the tower and surface area of the collector are proportional to the efficiency and energy output of the system.
ADVANTAGES AND LIMITATIONS
ADVANTAGES
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LIMITATIONS
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NUMERIC PARAMETERS
The numerical parameters for a solar/thermal chimney vary greatly on the use, HVAC in a building or renewable energy production and thus a case study looking at each are presented below.
GENERAL
GENERAL
- Can convert up to 70% of irradiated solar energy into heat (typical annual average-50%)
- Life Span = 60 years + (with proper maintenance)
- Solar uplift tower collector/greenhouse - 2-6m high, covering thousands of m^2 area
- residential/commercial thermal chimney collector size - varying on amount of ventilation required / size of building
SOLAR UPLIFT TOWER
The Manzanares Chimney, Spain
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RESIDENTIAL/COMMERCIAL THERMAL CHIMNEY
Hawaii Gateway Energy Centre Natural Energy Laboratory of Hawaii (LEED Platinum)
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