What is a Net-Zero Energy Building?

Did you know that commercial and residential buildings account for approximately 40% of the total energy and 70% of the electricity consumed in the U.S. and Europe?

You may have heard the term Net-Zero Energy Building or Zero Energy Building (ZEB) but what exactly does this mean?  In short if a structure generates, through renewable resources such as wind, solar, bio-fuels and resident hydro-electric, as much or more than it consumes, the building can be considered a ZEB.  There are unfortunately a number of caveats in this over-simplified definition.

Ferreira Construction

Ferreira Construction

The first building in the U.S. to label itself a ZEB is located in Branchburg, NJ, the headquarters for Ferreira Construction.¬† Although the building produces enough electricity for it’s day-to-day operations, is still in fact does consume natural gas.¬† To be fair, the radiant heating system deployed reaches 95% efficiency and the building touts 530 metric tons of avoided emissions (the volume of approximately 100 cars) in the first year alone.¬† Ferreira’s achievement should not be belittled but the building is hardly net-zero according to the preceding definition, so why the confusion?

The National Lab Renewable Energy Laboratory of the U.S. Department of Energy can shed some light on the issue.¬† According to their 2006 report, Zero Energy Buildings: A Critical Look at the Definition, ZEB’s can be broken down into 4 categories; net-zero site energy, net-zero source energy, net-zero cost energy, and net-zero energy emissions.¬† If a building meets the criteria for any one of these then it can be called a ZEB.

We should also keep in mind that net-zero is referring to net-zero annually and that a times in the course of a year a building may use traditional energy sources to supplements its energy needs.¬† A new term emerging is Energy Autarkic, coming from the word autarky meaning self-sufficient.¬† This is the Holy Grail of ZEBs, an energy autarkic building can be disconnected from public energy sources because is can maintain it’s own energy needs at ALL times.¬† It is unrealistic to achieve such a state in commercial buildings except in very rare circumstances, however individuals who are really committed have achieved this in their residences.

Other terms you may hear are Near-Zero Energy and Ultra-Low Energy when referring to buildings.¬† Regardless of the variety of terms and the gray areas in the definitions, what is important and encouraging is that the movement is wide spread.¬† These terms are becoming sales monikers used by developers of both commercial residential buildings and as we all know, when “Going Green” becomes profitable things move fast!

Sources: 1, 2

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