Green Your Crib: Harness Sun Power Passively

Dennis Allen at his home in Santa Barbara
Paul Wellman

Green building strategies save energy, improve health, and are good for the planet, but they cost more. At least that’s the common belief — but what’s the reality?

Take the case of a passive solar-designed residence, an ancient energy-harnessing system that goes back to the Egyptians, Greeks, Romans, and Anasazi of the American Southwest. Homes are built with an opening on the south side to collect the solar power, the building’s shell stores solar heat in the winter, and simple shading keeps the interior from overheating during the summer.

These three elements — windows, building mass, and shading devices — are found in almost every modern home. Consequently, passive solar design adds no extra cost to a home during construction, with the possible exception of a minor increase related to how the summer sun is shaded. When put together effectively, this strategy offers great comfort and a superb return on investment.

Creating a tight, well-insulated shell with high performance windows is critical. The windows must both insulate and allow infrared solar rays to enter. The shell needs appropriate mass to dampen temperature swings, absorbing the heat when sunny and releasing it back into the living space at night. Thermal mass can be provided by concrete or tile floors, interior masonry or plaster walls, brick fireplaces, stone countertops, double layers of drywall on walls and ceilings, or even solid material furniture.

Shading can be provided by fixed elements (trellises, roof overhangs, window eyebrows), strategically placed deciduous trees, or moveable awnings (manual or motorized). Movable shades are most effective because they can be adjusted according to sunshine irrespective of time of day or season of year. The ease of use and modest cost make motorized awnings my preference.

Can passive solar design work for existing homes? Yes, but modest remodeling will most likely be required. Insulation and weather stripping may need to be added, but these are universally considered good expenditures. Many houses on the South Coast have windows facing south, often for the view, so installing a few high-performance units in these openings, although not inexpensive, can greatly enhance heating efficiency and comfort. Costs vary widely for adding thermal mass, but adding effective exterior shading is usually easy and relatively inexpensive.

My own home is a passive solar house, and in our five years there, we’ve never turned on the heater. The inside temperature varies at most 1.5 degrees in 24 hours, whether the outside temperature is in the 30s or 90s. Year-in and year-out, the temperature stays within a 68-81 degree range. We have no air conditioning. The house is comfortable, quiet (thanks to no mechanical equipment), and healthy; plus we have no heating or cooling bills.


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