Passive Solar Heating
From Swikipedia
Introduction
Passive solar heating is a building design in which solar energy provides a significant portion of the heating without fans or pumps. In such a design, the building itself serves as the solar collector and heat storage system.
Brief Description
Passive Solar Heating is the most cost effective means of providing heat to buildings. In particular, it makes use of the building components to collect, store, and distribute solar heat gains to reduce the demand for space heating. It does not require the use of mechanical equipment because the heat flow is by natural means (radiation, convection, and conductance) and the thermal storage is in the structure itself. Also, passive solar heating strategies provide opportunities for daylighting and views to the outdoor through well-positioned windows.
For designing a passive solar heated structure, tow basic elements are required: a south facing exposure of transparent material (glass, plastic) to allow solar energy to enter; and a material to absorb and store the heat (or cool) for later use.
Passive Solar Heating Design Considerations:
For constructing a building with a passive solar heating design, there are some considerations like:
1. Site Considerations: The performance of any passive solar energy design building is strongly impacted by the site and the siting of the building in relation to its surroundings. Therefore, one has to take into consideration the site and its surroundings so as to maximize the solar gains in winters and minimize them during summers.
2. Building Shape and Orientation: Different building shapes and orientations can be designed to perform efficiently by combining effective glazing, solar exposure, and shading into the building form. This efficiency can be enhanced by variations in the placement of interior spaces and by the use of such options as clerestories and skylights. Depending upon the site, topography, and shape of the available space, orientations other than east and west may be desirable. However, for most climates, an east-west axis is the most efficient for both heating and cooling.
3. North Walls: The building should be shaped in a way, so that, the roof slopes downward from the south to the north wall. This reduces the height of the north face of the building and therefore the area through which heat is lost. This also allows sunlight to reach more area of north side outdoor spaces.
4. Indoor Space Planning: Habitable spaces that are most occupied and have the greatest heating and lighting requirement should be arrayed along the south face of the building. Rooms that are least used (closets, storage areas, garages) should be placed along the north wall where they can act as a buffer between high use living space and the cold north side.
5. Entryways: Entries account for great deal of heat loss especially in small structures (such as during opening/closing of doors/windows, heat seepage through doorframes etc.). To reduce both direct and infiltration losses, entryways should be recessed or protected against the direct force of prevailing winds.
6. Windows: For the most part, window areas on east, west and north facing walls should be kept as small and as minimal as is consistent with interior requirements and should be recessed and all should be double-glazed. Windows are the least effective heat flow inhibitors of a building's shell, both in terms of letting heat out in the winter, and letting heat in the summer.
7. Combining Systems: Many times it is desirable, or even necessary, to use more than one passive heating design strategy. For instance, the use of a thermal storage wall may block a beautiful view while a direct gain design in the same south wall may create intolerable glare and have a tendency to overheat. In such cases the two designs can be used side by side or in any other configuration (a thermal storage wall on each side of a direct gain window). It is essential, however, to properly size this combination in order to maintain quality control and avoid undesirable temperature fluctuations.
8. Reflectors for Passive Solar Heating: If partial shading is problematic, collection of solar radiation can be greatly enhanced by the use of reflecting devices. Solar collection can be increased 30-40% when reflectors are used with either vertical, horizontal, or sloping glazing. For greatest efficiency, the angle of a reflector in relation to the collecting surface must be carefully selected.
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