Passive solar design is one of the oldest and most effective green building techniques. It literally goes back to the cave man. Cave dwellings in the northern hemisphere often had openings toward the south so that the sun could heat the interior rock during the day, and this heat was then released into the cave at night. The theory is still pretty much the same, but modern technology and building materials have made it vastly more efficient.
A home designed using passive solar principals can save huge amounts of money over the life of the home, and even better, passive solar design does not cost significantly more than standard construction. All it takes is some common sense and knowledge. This article is written from the perspective of the Cleveland, Ohio area, but the technique can be effective in almost any area of the globe with some minor modifications.
South Facing Glass
In general, glass that faces the equator will be the most effective. In the U.S., this means south. Winter time sun will penetrate the glass and the long wave radiation will become trapped in the building, warming the home. In effect, what this concept does is make your home a green house. (Pardon the pun.)
Solar Shading
To decrease summer heat gain, an overhang should be placed above the window. This will keep the hot summer sun from increasing your cooling load in the summer, while letting the lower winter sun in. This works because the sun’s height in the sky (altitude) changes from summer to winter. The summer sun is higher, and therefore hits us more directly. A solar shade over the window will block this sun and keep the heat out of your home. The winter sun hits the earth from a lower altitude, and therefore a smaller angle. These rays will go under the shade and into the building to help with heating.
Proper sizing of the shade is important to maximize the winter heat gain while minimizing summer heat gain. To properly size shades in your area, consult a sun chart. Find the sun’s altitude angle at the vernal and autumnal equinox for your area. This will be a good angle to use to size your shade. Simply draw a line from the bottom of the window at this angle, and you will be able to find the size of your shade. In the northern United States, this angle should be around 45 degrees.
Another effective way to shade south-facing windows and reap the benefits of passive solar concepts is to plant deciduous trees on the southern side of your home. The leaves will block the summer sun, and as they fall off the tree in autumn, more and more sunlight will be allowed into your house.
Thermal Storage
Passive Solar design is best when used in conjunction with the concept of thermal storage. Some materials, such as stone, tile, and concrete have a high thermal mass. This means that they have the capacity to store large amounts of heat. If the area that the sun hits during winter days is dark in color, it will absorb heat better. If it has the property of high thermal mass, the energy collected during the day will continue to be released longer into the night, helping with heating bills.
Any home that has windows on other areas than the northern side will experience some benefits of passive solar design. Understanding the concept will help you design your home in a more energy efficient manner.
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