Editor’s note: This is the second of an eight part series.
Last week I introduced the concept of passive design using the ancient cliff dwellings of Mesa Verde (Colorado, USA) to illustrate the point. In a nutshell, the “Ancestral Pueblo Peoples” – also known as the Anasazi – chose certain cliffs that excluded the hot summer sun but welcomed its warming rays in winter.
The Anasazi first occupied the caves over 1,000 years ago. Warm in winter and cool in summer: they were no dummies. Here is what we can learn from them: design for the climate; use local materials; harness free energy.
During the 1970s as small group of hippies used these same design principles in the same region of the US Southwest but in a radically different way. Using beer cans, old tyres and soil, they built what they called Earthships. Here is what Wikipedia has to say:
“An Earthship is a type of passive solar house that is made of both natural and recycled materials (such as earth-filled tires), designed and marketed by Earthship Biotecture of Taos, New Mexico. Earthships are constructed to use available natural resources, especially energy from the sun. Earthships are designed to use thermal mass construction and natural cross ventilation, assisted by thermal draught (Stack effect), to regulate indoor temperature.”
Both the Anasazi and the hippies figured out ways to live comfortably in a climate that ranges from 40 degrees in the summer and minus 10 in the winter by using passive design. An Earthship is designed to allow low angle winter sun to reach deep inside the structure but to exclude high angle summer sun. Once the winter sun enters the structure some of it is stored in what is called thermal mass, such as an earthen floor, bricks, tiles and even the earth-filled tyre walls.
Believe it or not, thermal mass is essential for keeping these structures from overheating in the middle of winter on cold, sunny days when the temperature outside is right at the freezing point. Thermal mass acts as a battery in that it stores excess energy (in the form or heat) during the day and releases it at night. Of course the Earthships also contain plenty of insulation to hold that heat inside the structure overnight.
All of this falls into the category of passive design because it requires no moving parts such as fans or pumps, or the electricity to run them. Passive means it just happens by natural energy flows and cycles.
Earthships also employ passive cooling systems, but I see I am out of words for this week and next week’s column is all about passive cooling with examples from the tropical nation of Nicaragua.