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Passive Solar Design
Passive Solar Design
Your home's windows, walls, and floors can be designed to collect, store, and distribute solar energy. This is called passive solar design or climatic design. Unlike active solar heating systems, passive solar design doesn't involve the use of mechanical and electrical devices, such as pumps, fans, or electrical controls to move the solar heat.
To understand how a passive solar home design works, you need to understand how heat moves and how it can be stored.
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Conduction: Heat transfer among stationary, vibrating molecules: Common through solids. A boiling pot’s handle warming up is an example of conduction.
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Convection: Heat transfer by the circulation of a gas or liquid. Convection is a swift way of transferring heat due to the shifting of molecules and exposing new ones to the heat source/sink continuously. The aspect of wind chill is an example of convection.
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Radiation: Heat transfer through the air from a hotter to a cooler object by means of energy waves. An object’s transmittal and absorption of radiation heat depends on its properties. A black car getting extremely hot on a sunny summer day is an example of radiation heat transfer from the sun.
- Thermal Capacitance: A material’s ability to store heat.
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Five elements of passive solar design
To design a completely passive solar home, you need to incorporate what are considered the five elements of passive solar design.
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Aperture (Collector): The large glass (window) area through which sunlight enters the building.
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Absorber:The hard, darkened surface of the storage element that warms easily by solar radiation.
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Thermal mass: The materials that retain or store the heat produced by sunlight.
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Distribution: The method by which solar heat circulates from the collection and storage points to different areas of the house.
- Control: Various methods, such as roof overhangs and thermostat control, that change as a function of time to accommodate heat absorption and transfer for comfort.
Direct Gain
Sunlight passing through windows heats people and objects directly. No special provision is made to store or circulate heat. Solar heat displaces the need for other sources of heat during the day. Room temperature swings may be large.
The Trombe wall distributes or releases heat into the home over a period of several hours. Solar heat migrates through the wall, reaching its rear surface in the late afternoon or early evening. When the indoor temperature falls below that of the wall's surface, heat begins to radiate and transfer into the room. For example, heat travels through a masonry wall at an average rate of 1 hour per inch. Therefore, the heat absorbed on the outside of an 8-inch-thick concrete wall at noon will enter the interior living space around 8 p.m.