Using Passive Solar Heating in Your Home
Although passive solar heating is best incorporated into a house during the initial design, the concepts of passive solar heating can also be used when remodeling or adding to your home. Window design, and glazing choices in particular, are critical factors for determining the effectiveness of passive solar heating in a home. In heating climates, large south-facing windows are used, as these have the most exposure to the sun in all seasons.
Windows can also be located to provide solar heating in cold climates or avoid solar heating in hot climates. In cold climates, large south-facing windows allow significant solar energy into the house and also provide daylighting; properly sized overhangs can prevent overheating in the summer. In hot climates, north-facing windows can provide daylighting without heating the house.
East- and west-facing windows generally cause excessive heat gains in the summer and heat losses in the winter, and are usually sized small. Although overhangs are impractical for east- and west-facing windows, vertical shading can be used, or trees and shrubs can be strategically located to shade the windows. Landscaping has other benefits, including natural cooling and protection from the wind.
Windows can now be designed for a number of purposes. Some windows are designed to let the sun's heat in while insulating against the cold, and are ideal for south-facing windows in cold climates. Others are designed to reject the sun's heat while providing insulation, and are ideal for all windows in hot climates and east- and west-facing windows in moderate climates.
Thermal mass such as tiles, masonry, or even water-filled walls provides a means of storing the solar energy that enters through the windows. Built into the floors and walls near the south-facing windows, thermal mass will absorb solar energy during the day and keep the house from overheating. At night, the thermal mass will release the heat, keeping the house warm.
An alternate approach is to locate a thermal mass wall on the south-facing side of the house, with glazing on the exterior, separated from the wall by only a few inches. The wall absorbs heat on the sun-facing side and releases it slowly into the living space over the course of the day. Although the wall will block the sunlight, daylighting can still be achieved through narrow windows located above the thermal wall.
For thermal mass to be effective, air must circulate freely through the house to carry the heat from the thermal mass to the places where it is needed. Fans are sometimes used, but natural convection will often circulate the air sufficiently. For instance, a central staircase provides an effective means for allowing hot air to rise, and to complete the circuit, vents between the upper and lower floors along the exterior walls will allow cooler air to flow back to the thermal mass. Doors must be left open for this approach to work.
U.S. Department of Energy - Energy Efficiency and Renewable Energy
