Passive Solar Home Design
By Kenton Shepard
Passive design is home design which uses natural methods of heating and cooling which require few or no mechanical devices and minimal or no consumption of other fuel.
Heating
Passive solar heating uses the sun’s energy to heat a home. Typically, the home is designed and oriented to collect sunshine through large, South-facing windows. Sunlight shines into the home onto materials with high thermal mass, such as concrete, masonry or stone, which absorb sunshine and store it as heat, slowly releasing it over time to warm the home interior.
Active solar heating uses the sun’s energy to heat a home, but heat is distributed through the home with the help of mechanical equipment such as fans, requiring the use of some electricity.
Source: Kenton Shepard
South-facing windows with overhangs to shade them from summer sun
Cooling
Heat always moves toward a cooler material. For this reason, homes can also be passively cooled by opening the home at night and allowing thermal mass material to radiate its heat to the cool outside. During the day, the home is kept closed, windows are shaded and heat in the home will be absorbed by the thermal mass material.
The Five Design Elements
To qualify as a passive solar design, a home must have five elements…
- The Aperture- serves as a solar collector to collect sunlight. Typically, the aperture consists of large windows which face within 30 degrees of South.
- The Absorber- is the surface of the thermal mass serving as the heat storage material. Absorbers will be more efficient if they’re dark-colored, since light colors reflect sunlight and dark colors absorb it as heat.
- The Thermal mass- is the storage medium which stores heat and releases it slowly. Concrete, water, brick, masonry, stone and gravel are commonly used for this purpose. Thermal mass materials are usually floor or wall materials near windows.
Source: Kenton Shepard
Thermal mass is provided by a (pink) concrete wall heated by sunlight shining through large, South-facing windows.
- Distribution- is the method by which heat stored in thermal mass is transferred throughout the home. In strictly passive homes, heat moves through the home by conduction, convection or radiation. Active solar homes will use mechanical devices such as fans and blowers.
- Control Devices- are devices which control the functions of features in the home. An example would be roof overhangs which shade windows during the summer to prevent unwanted solar gain, but which allow sun to shine in during the winter to warm the home, or deciduous trees which shade windows in the summer but allow winter sunlight to pass through when they lose their leaves. Other examples are sensors and switches which operate pumps, fans, vents or mechanical window shading devices.
These design elements are incorporated into the home using the following design approaches…
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Direct gain- sunlight shines into the home to warm thermal mass incorporated into the floors or walls.
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Indirect gain – sunlight shines onto a high thermal mass wall which in turn radiates its heat to the home interior.
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Isolated gain- sunlight shines through windows to warm a particular part of the home such as a sunroom or greenhouse.
Other design elements in passive solar design are…
Insulation and air sealing- homes which limit air leakage and are well insulated retain more heat, which lowers heating costs. Auxiliary heating and cooling systems are usually required in areas which experience extremely high and low temperatures.
Window Heat Gain and Loss Control Devices
- Operable shutters
- Operable insulated window coverings
- Operable awnings
Advantages to Passive solar
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Conventional heating equipment size can be reduced.
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Large windows provide natural light.
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Large windows reduce lighting costs.
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reduced heating costs
SOURCES FOR FURTHER INFORMATION
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