passive solar systems
Solar energy is a radiant heat source that causes natural processes upon which all life depends. Some of the natural processes can be managed through building design in a manner that helps heat and cool the building. The basic natural processes that are used in passive solar energy are the thermal energy flows associated with radiation, conduction, and natural convection.


 
A passive solar system is a non-mechanical solar heating and cooling system. Solar radiation passes through an opaque, surface and heats a space, such as masonry walls and floors, absorbs and stores excess heat, which is released to the space when interior temperatures fall. When sunlight strikes a building, the building materials can reflect, transmit, or absorb the solar radiation. Additionally, the heat produced by the sun causes air movement that can be predictable in designed spaces. These basic responses to solar heat lead to design elements, material choices and placements that can provide heating and cooling effects in a building.

Since passive solar systems involve structural components of the house, they are often considered applicable only to new construction. But a passive system can be added or "retrofitted" to a house to' provide a good percentage of the home's heating and cooling needs.

All passive solar homes have these common elements:

  • Collection - To collect solar energy, double-glazed windows are used on the south-facing side of the house. 
  • Storage - After the sun's energy has been collected, some heat is immediately used in the living spaces and some is stored for later use. The storage, called thermal mass, is usually built into the floors and / or interior walls. Mass is characterized by its ability to absorb heat, store it, and release it slowly as the temperature inside the house falls. Concrete, stone, brick, and water can be used as mass. 
  • Distribution - Heat stored in floors and walls is slowly released by radiation, convection and conduction. In a hybrid system, fans, vents, and blowers may be used to distribute the heat. 
Passive solar systems rules of thumb:
-The building should be elongated on an east-west axis.
- The building's south face should receive sunlight between the hours of 9:00 A.M. and 3:00 P.M. (sun time) during the heating season.
-Interior spaces requiring the most light and heating and cooling should be along the south face of the building. Less used spaces should be located on the north.
-An open floor plan optimizes passive system operation.
- Use shading to prevent summer sun entering the interior. 
The four basic approaches that serve to classify passive systems are distinguished according to how they gain solar heat. With Direct Gain, the solar radiation enters a room directly through large areas of south-facing glass. For Indirect Gain, the solar radiation is intercepted by an absorber and storage element (e.g., a wall) that separates the south-facing glass from the room. And for Isolated Gain, the solar radiation is captured by a separate space such as a sunspace or atrium. Thermosyphon is another word that describes the natural movement of air or water due to differences in temperature.

There are several types of passive solar systems.The most common are:
1. Direct gain 2. Indirect gain
3. Isolated systems 4. Thermosyphon sytem