Passive Solar Building Designs

By: Brandon Cross

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Passive solar building designs which are a part of Green Building designing, exclude the use of active energy consuming systems like mechanical ventilators, photovoltaics etc. to maintain interior thermal comfort throughout the year. Instead, passive solar designs take advantage of principles of thermodynamics, climatic conditions and the sun’s travel path to greatly reduce heating and cooling needs of a building’s interior. Taking note of thermal comfort levels of humans special attention is directed at the specific site and location where a building/dwelling is to be constructed, solar orientation and climatic conditions to determine exact placement of glazing and shading elements and incorporation of thermal mass for maintaining interior thermal levels. All relevant factors need to be carefully integrated which involves extensive scientific calculations to arrive at the ideal solution. However, things have become easier through computer modelling and other related technology now available to create passive solar designs for substantial energy savings without compromising on functionality and aesthetic appeal.

To achieve twin goals of energy saving and human thermal comfort simultaneously, passive building design primarily takes into consideration the seasonal variations in the sun’s path during the daytime which in turn is related to the inclination of the earth’s axis of rotation with respect to its orbit. The sun has a unique travel route for any given latitude. Between winter and summer there is a difference of 47 degrees in the altitude of the sun at noon. This difference is at the core of passive solar designing. Combining this information with the local climatic data (HDD/CDD) reflecting heating and cooling requirements in the area it is possible to determine the time periods during the year when solar heat gain will benefit thermal comfort and when it needs to be blocked by suitable shading arrangement.

Solar heat transfer in buildings takes place through the roof, walls, doors, windows and floors of a building. By strategically placing suitable items like reflective, glazing and shading devices that restrict heat transfer occurring through radiation/convection/conduction it is possible to control the amount of solar gain entering a particular building over the year. Shades, shade screens, movable shutters and window quilts etc are items used in passive solar designing in order to meet immediate and/or daily solar gain and insulation requirements. The most important part of passive solar designing is the arrangement of rooms in the building. Generally for residential units living areas need to face the solar noon. Sleeping quarters are located on the opposite side.

It is possible to apply passive solar design concepts for achieving substantial reduction in heating bills in many suburban homes without perceptible chance to their appearance or usability and also enhance interior thermal comfort levels. There is just a need to ensure good siting, intelligent window positioning, and some amount of thermal mass in the living area, good insulation and a supplementary source of heat that can be a solar water heater connected to a central radiator. In the daytime sunrays falling on the walls will heat up the thermal mass, which will radiate the heat back to the interior as the temperature starts to fall in the evening. This may pose problems in summer but can be overcome by external shading arrangements and a radiant barrier and air gap to prevent undesirable summer solar gain.

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Brandon Cross is a Perth building designer providing residential and commercial design services for West Australian clients.

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