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Passive Solar

Home Passive Solar

Passive Solar techniques produce a cooler or warmer air temperature in a building by using the sun's energy without any electrical equipment (such as solar panels). There are three main components to an effective passive solar design:

1. Direct gain - This is the most common passive solar system. Direct gain refers to the sunlight that enters a building through windows and stores heat in the thermal mass incorporated into floors or interior walls. To design a direct gain system, one needs to calculate how much window area and how much thermal mass are required to provide the desired quantity of heat for the building. In general, total direct gain glass area should be at least 7 percent, but not exceed 12 percent of the house's floor area.

Key factors for windows in a building are:

  • Glazing - (South facing glass windows): It is ideal if the windows are angled within 5 degrees of true south, however, windows angled within 15 degrees of true south work almost as well. In addition, vertical glass, as opposed to glass titled up or down, is probably the best year-round solution.

  • SunTempering is another basic of passive solar techniques that only involves increasing the number of windows on the south side. In a conventional house, about 25 percent of the windows face south which amounts to about 3 percent of the house's total floor space. In a suntempered house, the percentage is increased to a maximum of about 7 percent. Energy savings are modest with this system, but suntempering is very low cost.
  • Building or taking out overhangs can greatly change the amount of sunlight that currently shines on the window.

2. Thermal mass - This is the material that stores the sunlight during the day and releases it at night. Examples of this would be floors or walls made of adobe, brick, masonry, tile, concrete, stone, or water, Thermal mass can be built into floors, interior walls, fireplaces, or bancos. The sun does not need to hit these surfaces directly to store the heat, nor do these surfaces necessarily need to be a dark color. The thermal storage capabilities of a given material depend on the material's thermal conductivity, specific heat and density. Usually higher density materials can store more heat. Thermal mass can be costly so it is always best to look at cost to benefit ratio for thermal mass.

3. Insulation - holds the heated air inside, and cold air out. By simply opening the drapes or insulated blinds on your south facing windows during winter days, when the sun is low in the sky, you can raise the room temperature. Also, Night insulation, such as window shades, quilts or insulating drapes, improves energy efficiency dramatically.
Heat gained from the sunlight increases as it passes through glass. If you are designing a house or a remodel, talk to your architect or designer about possible passive solar choices.