The Meaning of Zero Energy and Carbon Neutral Buildings
Energy Minute: As we go from discussing energy efficient buildings, to zero-energy and zero-carbon buildings, the definitions steadily become less clear. What exactly to the terms "Zero Energy" and "Carbon Neutral" mean when applied to buildings? (podcast)
April 19, 2008
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Music by Chris Keister
Transcript
An energy efficient building is one that uses less energy than the typical new building. In the U.S., it can achieve an Energy Star rating from the Environmental Protection Agency, just like a refrigerator. Close to sixteen hundred commercial buildings earned the Energy Star label in 2007.A net zero energy building is one that's not only efficient, but gets some of its energy from on-site sources. A grid-tied building with solar power can sell excess electricity during a sunny day and buy it from the utility at night. In the course of a year, the building buys no more energy than it sells back. That much is clear, but there are differences of opinion over whether to count for example the embodied energy in the building materials, or the energy that'll be consumed to one day demolish the building.
A net zero carbon building, or carbon neutral building, is one that causes no increase in CO2 emissions. Just being a net zero energy building isn't enough. That's because there are carbon emissions to count from manufacturing the building materials, transporting them to the site, and constructing the building. But not everyone agrees on that, either.