Five Elements of Passive Solar

Passive solar technologies use sunlight to get energy without the use of active mechanical systems. Passive solar systems convert sunlight into usable heat and cause air-movement for ventilation. As contrasted to active solar systems, which use a significant amount of conventional energy to power pumps or fans, passive systems tend to us a small amount of conventional energy for the use of controlling dampers, shutters, or other devices which enhance the solar energy collection, storage, and use.

A home’s windows, walls, and floors can be designed in such a way to collect, store, and distribute solar energy in the form of heat during the winter and reject solar heat during the summer months. Some passive solar homes are heated almost entirely by the sun, while others are designed with south-facing windows which provide some fraction of the heating load. The design of a passive solar home is what distinguishes it from a conventional home.

In order to design a completely passive solar home, the incorporation of the five elements of passive solar design is necessary.

Source US DOE

The first element is the aperture, the large glass area, usually a window, through which sunlight enters the building. Typically, the aperture faces within 30 degrees of true south and should avoid being shaded by other buildings or trees between 9 a.m. to 3 p.m. each day during the heating session. The absorber, a hard, darkened surface of the storage element, is the second element of the design. The surface sits in the direct path of the sunlight, which hits the surface and is absorbed as heat. The third element is the thermal mass: the materials that retain or store the heat produced by the sunlight. Unlike the absorber, which is in the direct path of the sunlight, the thermal mass is the material below or behind the absorber’s surface. The distribution, the method by which solar heat circulates from the collection and storage points to the different areas of the house, constitutes the fourth element of solar design. In a strictly passive design, three natural heat transfer modes will be used: conduction, convection, and radiation. However, in some applications, fans, ducts, and blowers help with the distribution of the heat throughout the house. The final element of the design is the control. During the summer months, roof overhangs are used to shad the aperture. Other elements can be used to control the under- and/or overheating include electronic sensing devices, operable vents and dampers, low-emissivity blinds, and awnings.

While other elements go into the designing of a passive solar home, such as the window location or air sealing, these five elements constitute a complete passive solar home design. Each element serves its own function; however, all five must work together for the design to be successful.

Source (Info and Images): US Department of Energy


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