Passive Solar Design
With many thanks to
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.
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
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
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
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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