NET-ZERO ENERGY STRUCTURES
In general, a net-zero building (ZEB, zero-energy building) produces as much energy as it uses over the course of a year. The concept is that buildings can meet all their energy requirements from low-cost, locally available, non-polluting, renewable sources. These buildings are very energy efficient. For a pictorial example of the systems in a net-zero energy structure, click here.
Net-zero buildings can use traditional energy sources from the local utilities when on-site generation does not meet the building loads. When the on-site generation is greater than the building's loads, the excess electricity is exported to the utility grid. By using the utility grid to account for the energy balance, excess production can offset later energy usage.
Net-zero energy relates to whole building design and sustainablity. This includes reducing water usage. Rainwater catchment and grey water recycling help reduce the usage of this valuable resource.
Typically, there are five net-zero energy definitions that the design team and building owner can pursue. These definitions were developed by the National Renewable Energy Laboratory of the U.S. Department of Energy to use as design goals. These goals are intended to take the mind set from designing
low-energy building with a percent energy savings goal and into the realm of a sustainable energy endpoint. From the
DOE's website below are the five net-zero energy definitions:
Net-Zero Site Energy - A building that produces at least as much energy as it uses in a year, when accounted for at the site. The measurement time frame is annual.
Net-Zero Source Energy - A building that produces at least as much energy as it uses in a year, when accounted for at the source. "Source energy" refers to the primary energy required to generate and deliver the energy to the site. To calculate a building's total source energy, imported and exported energy is multiplied by the appropriate site-to-source conversion multipliers.
Net-Zero Energy Costs - A building where the amount of money a utility pays the building's owner for the energy the building exports to the grid is at least equal to the amount the owner pays the utility for the energy services and energy used over the year.
Net-Zero Energy Emissions - A building that produces at least as much emissions-free renewable energy as it uses from emission-producing energy sources annually. Carbon, nitrogen oxides, and sulfur oxides are common emissions that net-zero energy buildings offset.
Near Zero Energy - A building that produces at least 75% of its required energy through the use of on-side renewable energy. Off-grid buildings that use some nonrenewable energy generation for backup are considered near zero energy because they typically cannot export excess renewable generation to account for fossil fuel energy use.
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