Also referred to as a thermal chimney, a solar chimney provides a natural way of improving the ventilation of buildings by making use of the convection of passive solar energy heated air. As we all know, earth temperature is on a rise and would keep on increasing until we reduce greenhouse gases from the atmosphere. In this project we are using solar energy which actually a main source of heat on earth to not only for ventilation but also for cooling the building or a house. When incorporated in a building, it helps reduce the energy used by mechanical means. Solar chimneys have been in existence for ages not only in the Middle East, but also in Europe.

Natural ventilation simply means that the air flow in an area is changed without using any additional means e.g. a fan . In this project, we are using simple concept of difference in pressure where air moves from higher pressure to low pressure area.

As shown in Figure 1, the solar chimney provides passive home cooling by drawing air through a geothermal heat exchange process. As we all know, hot air rises. The solar chimney utilizes this concept whereby the air in the chimney gets heated up by the solar energy and rises up, thereby drawing air from the room.
For proper functionality, the chimney has to be taller than the building and should place strategically in the building in a direction facing the sunlight.

Figure 1: Solar Chimney’s principle of operation

How does it work?

A solar chimney works on the principle that as hot air rises, so when chimney gets heated by the sunlight, air inside the chimney starts to get warmer and lighter; due to which it moves outside leaving vacuum behind and because of this, a weak negative pressure is formed which causes an air flow from the building and towards the chimney. In order to improve the efficiency in heat absorption, the chimney should be painted black and it is also advisable to use materials which are high absorbers of heat. These materials include tinted glass, insulating glazing and black frames. It is also important to design the size of the chimney appropriately as the large the chimney the more is its effectiveness.

Another important consideration is how to achieve the suction effect by funneling the cool air towards the solar chimney’s base. There are two methods that are usually applied;

1. As shown in figure 1, cool air is channeled into the house by making use of a pipe buried in the soil. As the soil heats up the air in the pipe, the hot air moves inside the house and up the chimney thereby drawing cool air in the house, resulting into ventilation.

2. The second method uses the windows that are at the lowest level of the building to capture cool air and funnel it inside the building

Integration of solar chimneys with other technologies

Though they can be used as stand alone, solar chimneys have been integrated with other technologies to improve the ventilation of houses. These technologies include;

  • Based on the roofs of the building.
    • Gable roofs can be suitably designed to integrate with solar chimney by forming the roof solar collectors as shown in figure 2. On hot days, the roof structure induces natural air circulation through some gaps and openings. Roof configurations include the single pass roof solar collector and double pass solar collector.

Figure 2: Solar thermal collectors on the roof of a building

  • Based on the walls of the building
    • These include wall solar collectors (also known as Trombe wall) which are basically vertical channels attached to the building’s exterior as shown in figure 3. When the solar heats up the surface of the channel, an air flow is triggered by the temperature differences between the ambient and the collector.

This configuration however has two main drawbacks.
  • Due to its nature, it causes significant heat losses in cold or cloudy days thus causes discomfort to the occupants of the building
  • During very hot days, massive inputs which can be undesirable.

Figure 3: Modified Trombe wall

Advantages of a solar chimney

  1. Helps to improve ventilation especially when it is hot and still outside
  2. Since it is a quiet method, it improves the quality of the air in a room without resulting into noise pollution
  3. It can be used during the night as well to increase the ventilation rates
  4. Reduces the reliance on wind driven ventilation and also can help to reduce energy costs incurred as a result of using electrical fans etc.
  5. It allows the ventilation of small and narrow places

References/important links
1. Zhai, X. Q., Song, Z. P., & Wang, R. Z. (2011). A review for the applications of solar chimneys in buildings. Renewable and Sustainable Energy Reviews, 15(8), 3757-3767.

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