Getting down to net zero
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7/5/2009 - 7/5/09
There are five steps to green building a net-zero home, which uses no more energy than it generates. The five steps build on each other in complexity and cost.
Thermal envelope and insulation. The goal of a good thermal envelope (the protective shell that includes walls, roof, windows, skylights, and floor) is is to keep heat in during the winter and out during the summer. Except for conservation, good insulation is the single most beneficial item to save energy in your home.
Mechanical system efficiency. Check the SEER rating for energy-efficiency when considering refrigerated-air-conditioning systems. Radiant-heat systems can be fired with a high-efficiency condensing boiler, which captures the heat from water vapor in the exhaust gases, while the vapor is condensed back into liquid water and used to heat the return water in the radiant system. These boilers also capture latent heat released during the phase change of the water from gas to liquid.
Appliances and lighting. Refrigerators, stoves, ovens, and lights use a lot of the energy consumed by a home. Energy Star appliances use up to 50 percent less energy than standard models. Gas uses less energy to heat food than electric. Your toaster oven uses less energy than your big oven. And incandescent lighting uses up to four times more energy than compact flourescent.
Active energy systems. This is the level at which the home begins to generate and harvest renewable energy, and at which the home can become net-zero. At its simplest level, it means that onsite renewable-energy sources provide all the energy needs. At its most complicated level, it means that onsite renewable energy offsets all the energy used to create the home and to manufacture and transport all of its materials or, at the extreme end, the daily energy used for commuting from a suburban location.
Solar thermal panels use the sun's heat for the home's washing machines, showers, and sinks, and can also heat the home during winter. These systems can be designed to run backwards during the summer to provide cooling.
Photovoltaic panels, which convert sunlight directly into electricity, are generally "grid-tied" - connected to the electrical grid via an inverter that conditions the solar electricity to be in phase and compatible with the commercially generated electricity. The building runs on solar electricity first and commercially generated electricity when needed. Any excess electricity is sent back into the commercial grid through a "net metering" process that essentially causes your meter to run backwards.
Certification. The fifth step is multifaceted. It refers to the many third-party methods of quantifying what performance level of "green" a particular building has achieved. LEED and BuildGreen New Mexico are two well-known systems. In each case the process begins in the design stage, evaluating site conditions and how the building relates to the site. The systems also look at water efficiency, resource efficiency, indoor air quality, site development, and solar orientation.
Energy Star is a rating given to certain homes that have qualified based on a set of energy-efficiency guidelines published by the U.S. government. It represents a basic level of effeciency over and above standard construction methods. And HERS (Home Energy Rating System) measures the performance of a particular building against a "normal" building built to standard code requirements, and gives an index rating based on energy use.
Kurt Faust is an artist, blacksmith, cabinetmaker, and homebuilder. He owns Tierra Concepts Inc. and Carpinteros with his two partners, Eric Faust and Keith Gorges. He may be reached at kurt@tierraconceptssantafe.com.
