Passive Solar and Zero Energy Homes

The marriage of passive solar design with zero energy homes makes cost-effective heating and cooling possible. Solar is simultaneously the first and last thought in a zero energy home. Orientation comes first, enabling the building to take the fullest advantage of the sun. The last thought is where and how much solar hot water and photovoltaics (PVs) to put on the building to make up the last of the loads that can't be provided by the design and operation of the home. The less solar equipment required, the more cost effective the construction costs of the home.

Getting to Zero

Passive solar design is much easier to apply in new buildings than in existing homes. Virtually every zero energy house in colder climates has taken full advantage of passive solar heating potential; up to 60% of the heating load can be met through passive solar design.

Does this scene sound familiar? A culture facing an environmental crisis. Their primary building resource — wood — was in high demand for ships and buildings, making the primary heat source for comfort — charcoal — increasingly scarce and expensive. This was the situation that faced the Greeks in the 5th century B.C.E. Most of the Greek peninsula and the islands had been denuded so they were forced to import wood from faraway places. This drove the ancient architects to reevaluate how they built their buildings.

According to Socrates, "In houses that look toward the south, the sun penetrates the portico in winter, while in summer the path of the sun is right over our heads and above the roof so that there is shade." Thus was born the idea of passive solar heating and summer shading.

Looking back over American architectural history, we see that early settlers also wisely used the sun for comfort. Early Native American settlers of the American Southwest were very conscious of the movement of the sun and built their pueblos so that the community had access to the southern sun. The people of the Anasazi culture that populated the Four Corners area of Colorado, Utah, New Mexico and Arizona lived in large open caves that faced south. They built their dwellings recessed far enough from the opening that the cave roof shaded the homes in the hot summer months.

A more contemporary example is the saltbox design, favored by the early colonists in New England. Saltbox houses were oriented to the south with a two-story elevation fenestrated by windows. The north roof sloped down to one story and had few windows. This took the chill out of cold New England winters when the sun was out. In California, homes built in the Spanish colonial style had elongated east-west axes so that they faced the sun. Roof overhangs and decks the length of the house on the second floor shaded the south-facing glass in the summer.

As these examples show, until fairly recently we humans have been pretty good at living within our climatic means. But in the middle of the 20th century, with the invention and commercialization of air-conditioning, we started to lose direct contact with variations in climate and weather. After thousands of years of planning shelter around the cycles of the sun, we stopped worrying about where the sun would be located in the summer and winter sky. Why did it matter? Powerful heating and cooling systems took over, allowing builders to use essentially the same house designs in Anchorage, Alaska, as they did in Pensacola, Florida.

When energy was cheap, it was easy to rely on mechanical systems that overcame the conditions of nature. Now, as we are becoming painfully aware, volatile energy costs are making this approach obsolete. We need to look backward to see how people have traditionally lived as well as anticipate the environmental conditions that our buildings will have to endure in the future

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