In general, a net-zero building is a very energy efficient building that 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.
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 produced is exported to and stored in the utility grid. Later, when energy use is higher, the stored energy is able to offset the difference.
Net-zero energy relates to whole building design and sustainability, including reduced water usage. Rainwater catchment and grey water recycling help reduce the usage of this valuable resource.
Typically, there are four net-zero energy definitions that the design team and building owner can pursue. As defined by the DOE, the net-zero energy definitions are:
Net-Zero Site Energy
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
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
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
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.
A fifth definition recognizes grid-independent buildings that cannot achieve net-zero status.
Near Zero Energy
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.
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 a low-energy building with a percent energy savings goal and into the realm of a sustainable energy endpoint.
DAE can work with you to design a net zero building. To begin the process, contact us or fill out the form.