Passive solar heating and cooling was omitted from the interesting article on "Building Green" (C&EN, July 16, page 11). This technique can save 50% of the heating and cooling costs of a home in the Philadelphia area without the use of expensive photovoltaic cells.
Such a house would be oriented toward the south with large windows on the south and small ones on the north, large eaves that keep out the summer sun but allow the low winter sun to come in, day lighting, some concrete or masonry to store daytime heat overnight (for example, a fireplace or floor), and a light-colored roof. The insulation and other features of Leadership in Energy & Environmental Design (LEED) should be included. See www.eere.energy.gov/RE/solar_passive.html or "Passive Solar Energy Book" by Bruce Anderson and Malcolm Wells, which can be downloaded from the Internet without charge.
The building code of Davis, Calif., has included passive solar heating and cooling since 1976. The code summarizes the research that supports the concept but does not require the specific features mentioned above. It sets a maximum amount of energy that can be used by a residence, an amount that can't be met without the use of passive solar heating and cooling.
The 1982 amendment states that this code had been simple, cheap, and effective. The California Energy Commission extended this code to the entire state in 2005. Extension of this code to the entire country would save huge amounts of energy.
Albert S. Matlack