Passive solar building design

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Passive solar building design involves the modeling, selection and use of appropriate passive solar technologies to maintain the building environment at a comfortable temperature through the sun's daily and annual cycles. As a result it also minimises the use of active solar, renewable energy and especially fossil fuel technologies.

Passive solar building design is only one part of thermally efficient building design, which in turn is only one part of sustainable design, although the terms are often used erroneously as synonyms (passive solar design does not relate to factors such as ventilation, evaporative cooling, or life cycle analysis unless these operate solely by the sun).

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[edit] Key concepts

The available technologies can be categorised into various categories from which design choices can be made. These include three basic ways for harnessing the sun's energy, and several other techniques:

[edit] Direct solar gain

Direct gain involves using the positioning of windows, skylights and shutters to control the amount of direct solar radiation reaching the interior spaces themselves, and to warm the air and surfaces within the building. The use of sun-facing windows and a high-mass floor is a short-cycle example of this. John Hait's "Passive Annual Heat Storage" (PAHS) method is an example of an annualized solar approach primarily using this path.

Direct solar gain systems suffer because historically there were no reasonably priced transparent thermally insulating materials with R-values comparable to standard wall insulation. This is now changing in Europe, where superinsulated windows have been developed and are widely used to help meet the German Passive House standard.

[edit] Indirect solar gain

Indirect gain, in which solar radiation is captured by a part of the building envelope designed with an appropriate thermal mass (such as a water tank or a solid concrete or masonry wall behind glass). The heat is then transmitted indirectly to the building through conduction and convection. Examples of this are Trombe walls, water walls and roof ponds. The Australian deep-cover earthed-roof, innovated by the Baggs family of architects, is an annualized example of this path.

In practice indirect solar gain systems have suffered from being difficult to control, and from the lack of reasonably priced transparant thermally insulating materials.

[edit] Isolated solar gain

Isolated gain, involves passively capturing solar heat and then moving it passively into or out of the building using a liquid (for example using a thermosiphon solar space heating system) or air (perhaps using a solar chimney), either directly or using a thermal store.

Sun-spaces, greenhouses, and "solar closets" are alternative ways of capturing isolated heat gain from which warmed air can be taken. In practice it has been found that some owners use these structures as living spaces, heating them with conventional fuels and therefore significantly increasing, rather than reducing, the environmental impact of the building.

Don Stephens' "Annualized Geo-Solar" (AGS) heating is an annualized example of this option, which offers the advantages of preventing over-heating when living spaces are already deemed warm enough, and of extending time-delays until such heat will be desired.

[edit] Other passive solar design techniques

  • Building position - Based on the local climate and the sun's positioning (determined using a heliodon), the entire building can be positioned and angled to be oriented towards or away from the sun (according whether heating or cooling is the primary concern), overshadowing from other structures or natural features can be avoided or used, and the building can be set into the ground using earth sheltering techniques.
  • Building properties - The shape (and consequently the surface area) of the building can be controlled to reduce the heating or cooling requirement, and the use of materials properties to reflect, absorb, or transmit energy (for example using visible colour) is also a consideration.

Although not classified as a passive solar technology, the use of thermal insulation or superinsulation is invariably employed to reduce heat loss or unwanted heat gain.

[edit] The development of the passive solar house

Passive solar building design dates back into antiquity and has remained a traditional part of vernacular architecture in many countries [1]. However in the developed world, if these techniques were continued by some rural populations and enthusiasts, they were largely ignored by the construction industry until towards the end of the 20th century.

Despite this lack of general enthusiasm, passive solar technologies were refined and developed during the 20th century, boosted a little by the 1973 oil crisis, and their application has been aided by the development of computer modelling techniques and a number of pioneering passive solar buildings.

At the start of the 21st century the subject has been receiving greater interest due to concerns over global warming.

[edit] Engineered passive solar houses

Although earlier experimental solar houses were constructed using a mixture of active and passive solar techniques, the first engineered passive solar houses of the modern era were built in Germany after World War I, when the Allies occupied the Ruhr area, including most of Germany's coal mines. These designs were studied in the United States, but had little influence on builders.

The first consciously passive solar house in the US [2] was designed in 1940 by George F. Keck for a Chicago area real estate developer named Howard Sloan. Keck had designed an all-glass house for the 1933 Century of Progress Exposition in Chicago and was surprised to find that it was warm inside on sunny winter days, even though the furnace hadn't been installed yet. Keck was not aware of the research being done elsewhere on solar architecture, but he gradually started incorporating more south-facing windows into his designs for other clients, and by 1940 he had learned enough to design a passive solar house for Sloan.

Sloan built a number of passive solar houses in the 1940s, and his publicity efforts influenced a number of other builders during the postwar housing boom (Sloan is also credited with popularizing the term "solar" to describe his houses). But some builders of that era didn't realize that the houses were designed to face south, and many were built facing other directions, which hurt their reputation. Critics also pointed out that windows and doors weren't always properly sealed. Public interest declined by 1950 due to cheap oil and general prosperity, until it was revived after the 1973 oil crisis.

Edward Mazria's book 'The Passive Solar Energy Book' published in 1980, was an important milestone from which interest in this field developed.

[edit] Levels of passive solar energy use

Pragmatic: A house can easily achieve 30% or better cost reductions in heating expense without obvious changes to its appearance, comfort or usability[citation needed]. This is done using with good siting and window positioning, small amounts of thermal mass, with good but conventional insulation and occasional supplementary heat from a central radiator connected to a water heater. Sunrays may fall onto a wall during the daytime, which will radiate heat in the evening.

Annualized: Historically, most "passive solar" approaches have depended on near-daily solar capture and storage, only expected to maintain temperatures through a few days and nights. These are now termed "short-cycle passive solar". More recent research has developed techniques to capture warm-season solar heat, convey it to a seasonal thermal store for use months later during the cool or cold season. This is referred to as "annualized passive solar." This requires large amounts of thermal mass. One technique buries water-proof insulation in 7-metre skirts around the foundation, and buries loops of plastic pipe or ducts under the foundations and slab. The "skirts" of insulation prevent heat leaks from weather or water.

Minimum machinery: A "purely passive" solar-heated house would have no mechanical furnace unit, relying instead on energy captured from sunshine, only supplemented by "incidental" heat energy given off by lights, candles, other task-specific appliances (such as those for cooking, entertainment, etc.), showering, people and pets. The use of natural air currents (rather than mechanical devices such as fans) to circulate air is related, though not strictly solar design.

Systems sometimes use limited electrical and mechanical controls to operate dampers, insulating shutters, shades or reflectors. Some systems enlist small fans or solar-heated chimneys to start or improve convective air-flow. A reasonable way to analyse these systems is by measuring their coefficient of performance. A heat pump might use 1 J for every 4 J it delivers giving a COP of 4, a system that only uses a 30W ceiling fan to heat an entire house with 10 kW of solar heat would have a COP of 300.

[edit] Noted solar-designers

[edit] See also

[edit] External links

[edit] References

  1. ^ The lost skills of sustainable design
  2. ^ Ken Butti and John Perlin. A Golden Thread: 2500 Years of Solar Architecture and Technology=1980.


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