Wednesday, January 19, 2011

Ancestral Puebloans: An Ancient "Passive Solar" Dwelling

The ancient Ancestral Puebloans that built this cliff dwelling were early-day urban planners and passive solar-specialists. And, they knew their geology or at least how to apply it.

Their dwellings were built to collect, store and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. This is called “passive solar” design. In today’s language, passive solar is cheap, efficient, eco-friendly and very green. For the Ancestral Puebloans, it was naturally available and made good sense.

The ancient cliff dwelling is called River House, located a few miles west of Bluff, Utah near the banks of the San Juan River. The Ancestral Puebloans lived there between 700 and 1300 AD. Notice that it is build into a massive rock-alcove that faces south, towards the sun. In winter, the low-angled sun’s rays penetrate the dwelling and keep it warm. In summer, when the sun’s rays are high overhead, most of the rooms remain in the shade and stay relatively cool. This is a classic and early example of passive solar design.

The alcove naturally formed in the rock, because it lies at the touching-point or contact between the Navajo Sandstone, a vast  windblown desert that has "turned to stone", and the underlying Kayenta Formation, made of river mud and silt. The Navajo Sandstone is an aquifer, allowing ground water to seep through it, which emerges at contacts to form springs. The Kayenta is an aquitard, slowing the flow of water within it. Over time, water weakens the overlying sandstone by dissolving its cement, allowing an alcove to form. In addition, the springs at the contact are a fresh source of drinking water in this high desert climate with low precipitation.

Here, we have not only a prime example of a passive solar dwelling, but a site also chosen to optimize the area’s most precious natural resource, water.

No comments:

Post a Comment