Concept of Solar Chimney
Solar chimney is also referred to as thermal chimney. Simply, solar chimney can be defined as an upright tube that makes use of solar energy to augment natural ventilation in buildings. It consists of a black tinted tube. Solar chimneys are essential in improving natural ventilation of buildings by using a convection of air heated by reflexive solar energy. It improves buildings’ ventilation by providing a cooling effect and fresh air at times when the sun is too hot (Quarchining, 2010). Solar energy heats the chimney and the air inside, generating an updraft of air in the chimney. The suction generated at the bottom of the chimney is used in ventilating and cooling of buildings. The fundamental elements of a solar chimney are the solar collector area, the main ventilation shaft, and the inlet and outlet air openings.
Concepts have been established for solar power generation using green house. This is where heat is absorbed from underground other than heating the chimney. Solar chimneys are tinted so that they can absorb heat easily from the sun. Once the air in the chimney is heated, it goes up drawing cold air from underground through the heat exchange tubes (Schlaich, 1995). This is illustrated in the diagram below.
Source: Quaschning, V., 2010. Renewable Energy and Climate Change. Oranienburg, Deutschland: Wiley-IEEE
From the above diagram, the solar chimney absorbs hot air through a geothermal heat exchange to supply inert home cooling. It is illustrated from the diagram that the air that enters the heat exchange tube is at 950F. Once the hot air enters the tube, the temperatures go down to 550F. It is evident from the diagram that the heat exchanged caused the reduction in temperatures thus providing a cooling effect to the building illustrated in the diagram above.
Solar chimneys are used for ventilation. Solar energy heats up air inside the chimney, making it rise up. This absorbs cool air from the bottom part of the building, which is used to ventilate buildings such as homes and offices. Air absorption through a geothermal heat exchange can also be used in ventilating a particular area such as a composting toilet (Sukhatme, 2008). Natural ventilation can be generated by providing vents in the upper parts of a building letting warm air rise by convection. Concurrently, cooler air can be drawn in through vents from the lower parts, providing a cooling effect to the building.
Natural ventilation process can be improved by making use of a solar chimney. This is where the solar chimney is placed at a higher level than the rooftop of a building. For better results, the solar chimney should be constructed against the building wall facing the sun. Heat absorption from the sun can be augmented by making use of a glassy surface on the side facing the sun.
Larger surface areas of a solar chimney gives way for more effective heat exchange with air that is required for chimney heating. Heating of air within the chimney increases convection and the amount of air that flows through the chimney. Openings of vents in the chimney should not face the direction of prevailing winds (Smith, 2005). To maximize the cooling effect of a building, the incoming air should be guided through underground tubes before it is allowed in the building.
Solar chimney functioning can be improved by incorporating it with a trombe wall. The added advantage of this design is that the system can be reversed during cold season to provide solar heating effect instead of the cooling effect. In addition, the functioning of the solar chimney can be improved by incorporating it with the attic space. This is because the attic air space helps convection in the chimney improving ventilation. The use of solar chimney that is integrated with attic air spaces improves natural ventilation and passive cooling strategies of buildings. They help in reducing the amount of solar energy required in heating up the chimney, carbon dioxide emission and it reduces pollution.
Passive downdraft cool tower
The evaporation downdraft cool tower is a technology that is closely correlated to solar chimney. In areas with hot climate, this system provides a sustainable air conditioning for buildings. The standard of the system is to allow water evaporate at the top of the tower by using evaporative cooling pads. Evaporation cools incoming air that causes a downdraft of cool air that reduces temperature inside the building (Vogel & Kalb, 2010). Airflow can be augmented by constructing a solar chimney on the opposite side of the building. This is because it helps in letting out air from the building. Passive downdraft tower is shown in the diagram below.
Source: Smith, P F., 2005. Architecture in a Climate of Change: A Guide to Sustainable Design. Neerijnen, GL: Elsevier
Solar chimneys are said to have a low conversion rate of solar heat collected into electricity. It is for this reason that the chimneys are not efficient. This is a disadvantage of making use of solar chimneys. The advantage associated with solar chimneys is that they are cheap and have low maintenance costs.
Quaschning, V., 2010. Renewable Energy and Climate Change. Oranienburg, Deutschland: Wiley-IEEE.
Schlaich, J., 1995. The Solar Chimney: Electricity from the Sun. Fellbach, Deutschland: Axel Menges.
Sukhatme, 2008. Solar Energy: Principles of Thermal Collection and Storage. New Delhi, Delhi: Tata McGraw-Hill.
Smith, P F., 2005. Architecture in a Climate of Change: A Guide to Sustainable Design. Neerijnen, GL: Elsevier.
Vogel, W. & Kalb, H., 2010. Large-Scale Solar Thermal Power: Technologies, Costs and Development. Troy, NY: Wiley-VCH.