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Net-Zero Energy

The Solar Decathlon highlights solar energy technologies. However, our house is also more efficient that a typical home, which reduces the required size of the solar energy systems. These design features include a well-insulated envelope, high performance windows, daylighting, natural ventilation, efficient appliances, and an efficient HVAC system. It raises two questions:

We answer these questions using computer simulations of the annual energy performance of both our house and a “benchmark” house based on DOE’s Building America program. The benchmark represents a typical production home of the same size and in the same location as our home – in our case, a typical 2100 ft2 home in Boulder, CO. The benchmark has conventional appliances and lighting, 2x6 insulated walls (R-17), double pane low-e windows, and a conventional air-to-air heat pump.

Even without the building integrated solar systems or the novel HVAC system, our home would use 40% less energy than the benchmark home. Most of the savings come in heating, where more insulation, better windows, and passive design allow our home to use 73% less heating energy than the benchmark.

Energy Performance Monthly Total Energy Use in Boulder, CO

Energy consumption drops even further when the novel HVAC and solar thermal systems are included. Compared to the benchmark home with conventional water heating and HVAC, our home requires 60% less electricity to operate throughout the year.

While the Solar Decathlon houses are powered only by solar energy on the National Mall, our home is designed to be connected to the utility grid in Colorado. When the PV system The electricity generated by the PV system can either be used directly by the home or fed to the local utility grid. While there will certainly be drawing energy from the grid at night, over the course of a year in Boulder, our PV system will produce 38% more energy than the house will use. Even in Washington, D.C., the house is a net zero energy home, producing slightly more energy than it will use.