Moving toward Zero Energy Homes in California

12/01/04

"Green" House Effect Makes Sense in the Golden State Key Features of the 21st Century.

Most homeowners would enjoy a house that pays its own energy bills. Many are willing to pay more for the features that can make it happen, if the home meets their standards of comfort, convenience, and indoor environmental quality. In California, where residents have experienced severe droughts, natural disasters, and energy shortages, energy-efficient homes that are friendlier to the environment will appeal to many.

The U.S. Department of Energy’s Building America Zero Energy Homes initiative has collaborated with the National Renewable Energy Laboratory (NREL), Centex Homes, Davis Energy Group, and the Florida Solar Energy Center (FSEC) to build three innovative, energy-efficient homes in northern California: one "first-generation" demonstration home in Livermore and two "second-generation" model homes in San Ramon. These high-performance homes were built to meet the criteria for homeowner satisfaction and environmental friendliness.

The 21st Century Performance Home in Livermore

In 2002, Centex Homes built the 3,080-ft2, one-story 21st Century Performance Home in the Los Olivos development of Livermore, California. The house is a demonstration model for energy efficiency and renewable energy technologies. For the past two years, its owners have been strong advocates for these complementary technologies. A large part of that advocacy stems from the utility bills they have submitted to Davis Energy Group for the past two years. They have yet to pay for electricity—the roof-mounted solar panels generate 100% of the home’s annual net electrical energy. And the home uses about 45% less natural gas for space and water heating than comparable homes in the area.

The owners have also become "meter watchers." When they first moved into the home, they wanted to cover the electrical meter, which is located in the hallway, with a picture. Now they like to check it periodically to see what they’re using. If the use seems a bit high, they find something they can turn off to save energy. And they can also see how the photovoltaic system works: on a sunny day the solar cells can generate power; on a cloudy day or at night the house draws current from the electrical grid. From October 2002 through September 2003, the photovoltaic system generated 104% of the electrical energy the house needed.

The home’s architectural and energy features—from walls to windows to appliances—work together to use energy efficiently and to maintain a high level of comfort and satisfaction. A shining example of energy savings is the home’s air conditioning. During the summer of 2003, when the area experienced record temperatures of 100°F or higher, the home’s two air conditioners operated for a total of only 8.9 hours. Several features made this possible:

  • The tile roof and attic insulation help keep the upper part of the house cool.
  • Generous overhangs on the south, east, and west windows reduce the solar gains during the summer.
  • The insulated concrete foundation—rimmed with polystyrene—and the tile and hardwood floors help keep surfaces cool.
  • The cellulose insulation in the building envelope helps prevent thermal leaks.
  • The high-efficiency windows help with insulation and reduce solar glare.
  • The NightBreeze ventilation system automatically monitors the outside air and distributes it via ductwork to cool the house at night. This minimizes the need for air conditioning during the day. It runs quietly and is controlled by a thermostat.
  • A weather sensor on the outside of the house allows the prediction of the next day’s weather to the computer-controlled variable-speed fan, which provides cooling airflow accordingly.

The house has a solar water heater, which produces about 50% of the energy required for the domestic hot water. There is also an instantaneous tankless gas water heater that serves as a backup when the solar heat is unavailable. It uses about 70% less gas than a typical storage water heater. In addition, motion sensors in the kitchen and bathrooms activate a pump when someone enters the room so hot water is available whenever it’s needed.

The experience in Livermore taught the builder how to integrate these energy efficiency systems into production buildings. According to Jeff Jacobs, project manager at Centex, "The Livermore house gave us the opportunity to learn how to integrate these systems into a mainstream options package for a production home. We are now ready to offer that package, which we call PowerSave, to the general public at Lunaria and Aventura in San Ramon."

For the complete article please go to: http://www.eere.energy.gov/buildings/building_america/