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Passive Solar Design
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Much of what is presented in this article deals specifically with Austin, TX, but much of it can be applied to solar design elsewhere, as well.

Passive solar design refers to the use of the sun's energy for the heating and cooling of living spaces. In this approach, the building itself or some element of it takes advantage of natural energy characteristics in materials and air created by exposure to the sun. Passive systems are simple, have few moving parts, and require minimal maintenance and require no mechanical systems.

Operable windows, thermal mass, and thermal chimneys are common elements found in passive design. Operable windows are simply windows that can be opened. Thermal mass refers to materials such as masonry and water that can store heat energy for extended time. Thermal mass will prevent rapid temperature fluctuations. Thermal chimneys create or reinforce the effect hot air rising to induce air movement for cooling purposes.

Wing walls are vertical exterior wall partitions placed perpendicular to adjoining windows to enhance ventilation through windows.

Passive design is practiced throughout the world and has been shown to produce buildings with low energy costs, reduced maintenance, and superior comfort. Most of the literature pertaining to passive solar technology addresses heating concerns. This information is useful and relevant in our area; however, cooling issues, which are equally important in Austin, are less well documented. Key aspects of passive design include appropriate solar orientation, the use of thermal mass, and appropriate ventilation and window placement.

Consideration of high humidity is a key issue in Austin. For example, a basic passive cooling strategy is to permit cooler night air to ventilate a house and cool down the thermal mass (this can be brick, stone, or concrete walls or floors, or large water containers) inside the house. The thermal mass will absorb heat during the day; however, excessive humidity will reduce the cooling effect from the cooler thermal mass. Interior design elements of a home in our region also play a strong role in the effectiveness of passive cooling. For example, carpets, drapes, and fabric-covered furniture will absorb moisture from humid air, forcing the air conditioner to work harder to remove humidity.

As a design approach, passive solar design can take many forms. It can be integrated to greater or lesser degrees in a building. Key considerations regarding passive design are determined by the characteristics of the building site. The most effective designs are based on specific understanding of a building site's wind patterns, terrain, vegetation, solar exposure and other factors often requiring professional architectural services. However, a basic understanding of these issues can have a significant effect on the energy performance of a building.

The cost of passive design elements can run the same or slightly more than conventional building costs. This assumes that design services are used in both approaches - passive solar design and conventional design. Interior thermal mass materials such as stone and brick generally add to the cost of a home but can also be considered aesthetic enhancements.


There is not a financing issue unless the house does not include mechanical cooling. Lenders feel that the resale value of a home is reduced if mechanical cooling is not present.

There is a basic understanding and acceptance in regards to passive heating among a large number of persons who have relocated here from colder regions. Passive cooling approaches are not well known.

According to the Energy Code, there are limitations on the amount of glass a building can have (25% if double-pane). It is normally not necessary to exceed that amount in order to achieve significant passive solar energy in Austin. However, this amount can be exceeded if an approved computer analysis shows that more glass will improve the energy use pattern in the building.

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