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Predicting Natural Processes in Design with Passive Solar Walls

CalFinder Solar’s growing collection of articles about solar design includes an introductory article about passive solar walls. This article expands on the basics described in that piece, Smarter Homes Have Passive Solar Walls.

GreenBuilder.com says that:

“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. 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 home.”

GreenBuilder’s extensive feature on solar energy informs readers that passive solar energy means that mechanical means are not employed to utilize solar energy. Rules of thumb for passive solar systems include:

  • 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.

In an article for Energy Bulletin called Retrofitting for Passive Solar, by Douglas J. E. Barnes, one technique described for use on new homes is the trombe wall:

“From the outside, a trombe wall looks like a window built over a wall, but it is a very effective passive solar technique. A thermal mass wall is built then covered with glass to trap the heat it stores. Thermal siphons are another retrofitting option. To save money, you can make your own out of easily found materials. To do so, you would construct an insulated box with a black piece of corrugated steel inside and a glass top. Solar powered fans can be used to increase the air flowing through a thermal siphon.” Illustrations showing these and other passive solar options accompany the article.

Toolbase Services talks about combining the positive attributes of a traditional system with the energy-saving benefits of solar energy. This resource gives summarized tidbits including:

  • The walls of precast concrete passive solar homes are made from concrete panels, cast in a factory, and assembled on site, which saves time at the construction site.
  • The National Renewable Energy Laboratory (NREL) performed energy modeling on a precast concrete home and found the home used less than one-third of the annual heating and cooling energy of a home built to Council of American Building Officials (CABO) Model Energy Code standards.
  • The home studied by NREL consists of four-inch thick, precast concrete exterior and interior walls situated on an uninsulated slab-on-grade foundation with a conventional wood-frame roof assembly.

Taking all this information into account, consulting with a qualified solar energy builder or contractor in your area is possibly the best place to begin the process of determining the type of passive solar walls that are most efficient and appropriate for you home.

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