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A Passive Solar BuildingJohn and Alice Carpenter spent a good portion of their monthly income to heat their two-story colonial-style house last winter. They took steps to eliminate drafts and block up leaks, but their energy bill was still high. John and Alice considered installing an active solar system, but the cost was too high and it would take years before they saw any payoff. Then they heard about passive solar techniques from a friend.

Solar energy is often perceived as being the alternative energy source of the future. In fact, a simple and less expensive form of it, passive solar energy, has been in use for centuries.

Solar energy systems don't have to be complicated or expensive to do an effective job of conserving energy. Passive solar systems, unlike active ones, require no significant mechanical equipment and operate without any external power. Instead, they rely on natural heat movement through convection, conduction and radiation.

No matter what type of passive system you install, each includes the same elements which must all work together for the system to be successful. The most obvious component is the collector, a large glass (or plastic) area that sunlight passes through. Next is the absorber, a dark surface that sunlight strikes after it passes through the collector. Now that you've collected heat, you must distribute it. This is accomplished using natural methods of heat transfer, though some "hybrid" systems use fans, ducts, and blowers to boost air movement. Lastly, you must have a control, or heat regulation device, which helps prevent overheating in summer and heat loss during sunless periods. Also, your passive system may include heat storage in the form of materials that absorb and hold heat well, such as masonry or water.

One of the most important steps in a passive solar installation is orientation, or the positioning of your house in relation to its environment. For the most effective use of passive solar techniques, your house should face due south.

The Greeks realized this and used passive solar successfully to heat and cool their homes. They learned to build their homes to take advantage of the sun's energy when wood became scarce. They believed that exposure to the sun was healthy and building their homes facing south was best.

A typical Greek house had a south-facing portico similar to a covered porch, where the sun could enter during the winter and be kept out during the hot summer when it was high overhead. Earthen floors and adobe walls absorbed much of the solar heat and a low wall was also constructed between the pillars to keep out drafts. Unfortunately, they had no glass, so they had to rely on a completely passive system, letting their architectural design and the sun do all the work.

The Romans not only copied the Greeks but advanced their ideas by designing buildings for different climates. They used clear window coverings such as glass to enhance the solar effect. The most innovative use of solar energy was in the public baths of ancient Rome. The Baths of Caracalla, one of the largest, held over 2000 at a time. The hot baths, or caldarium, faced the winter sunset to get as much solar heat as possible. The whole south wall of the bath house was glazed with glass. These giant windows trapped so much heat by late afternoon that bathers would "broil" from it.

The Romans, like the Greeks, thought solar heat to be healthier than artificial heat. Doctors considered the sun therapeutic for many ailments. Solar architecture became such a part of Roman life that sun rights guarantees were were written into Roman law.

A passive solar house uses no mechanical devices, such as motors, pumps, or fans to distribute heat. A well- designed solar home functions in harmony with the local sun and weather conditions, with spaces and components arranged so that heat transfer is primarily by natural convection and radiation. The result is an efficient and livable building, with side benefits of increased brightness and more comfortable surroundings. To make the house even more energy efficient, it can be partially buried and constructed of thick adobe. A top tier of windows can heat the rear of the house, while stone walls behind large windows provide heat for the front.     

A sunspace is a partially or totally glazed room that is added to the south-facing wall of a house. Unlike a conventional greenhouse, a sunspace is well caulked and weather-stripped, and includes materials for storing solar heat.

Solar heat is collected through the sunspace windows, which are angled equal to the latitude plus 15 degrees (any tilt in the range of 45-60 degrees works well for most locations). It's then absorbed and stored by masonry or water-filled containers that can be positioned and sized in a variety of ways. These include a masonry wall separating the sunspace from the main building, 55-gallon drums inside the  sunspace, and potting beds. Also, a water wall can take the place of the masonry wall, or a rock storage bed can be added either below the sunspace or in the adjoining basement of the main house.     

According to recent studies, well designed sunspaces can provide up to 60 percent of your home's heating requirements during the winter. This percentage varies depending on the square footage of the sunspace glazing. local climate, and the heating requirements of your house.    

There are over 100,000 passive solar homes throughout the country. Not all were custom-built; many are part of vast subdivisions in California and New Mexico. However, just as many can be found in cold northern states like Wisconsin. They take all forms from log cabins to townhouses. Some are even pre-fab units made in a factory and shipped to the building site.    

By combining age-old passive solar technology with today's "smart" houses, the most effective means of conserving energy can be had.

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