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Net-Zero Energy Building Definitions

In general, a net-zero energy building produces as much energy as it uses over the course of a year. Net-zero energy buildings are very energy efficient. The remaining low energy needs are typically met with on-site renewable energy. On this page you will learn about specific definitions and their design implications.

Types of Net-Zero Energy Buildings

The National Renewable Energy Laboratory, one of the U.S. Department of Energy's national laboratories, has developed a number of specific definitions for net-zero energy buildings (NZEBs). The design team's goals will determine which definition it uses. Each type of NZEB has value in reducing energy impacts. A building may meet multiple NZEB definitions, increasing its merit as an NZEB.

For more information, see Zero Energy Buildings: A Critical Look at the Definition (PDF 477 KB). Download Adobe Reader. Following is a summary of the definitions:

Net-Zero Site Energy — A building that produces and exports at least as much renewable energy as the total energy it imports and uses in a year, when accounted for at the site. The measurement time frame is annual.

Net-Zero Source Energy — A building that produces and exports at least as much renewable energy as the total energy it imports and 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 renewable 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 and exports at least as much emissions-free renewable energy as it imports and uses from emission-producing energy sources annually. Carbon dioxide, nitrogen oxides, and sulfur oxides are common emissions that NZEBs offset.

Design Implications

During the design phase, the team should determine which net-zero energy definition to pursue based on the project goals and the values of the design team and building owner.

For example, building owners typically care about energy costs and may work to achieve the net-zero energy costs definition. Organizations such as the U.S. Department of Energy are concerned with national energy numbers, and are typically interested in reaching net-zero source energy. A building designer may be interested in site energy use for energy code requirements. Finally, those who are concerned about pollution from power plants and the burning of fossil fuels may be interested in reducing emissions.

Learn more by reading Zero Energy Buildings: A Critical Look at the Definition (PDF 477 KB). Download Adobe Reader.