Net Zero and Net Positive Strategies
Summary
A zero energy building is an efficient building whose annual energy use is offset by renewable energy, and the definition depends on how energy is counted. DOE counts source energy, so the accounting basis, fuel use, and boundary should be fixed before design targets are set.
Cols
Scope
- DOE definition (2015): an energy-efficient building where, on a source energy basis, actual annual delivered energy is less than or equal to the on-site renewable energy exported
- Source energy: counts upstream losses from generating and delivering power; DOE uses national-average ratios so no building is credited for its utility's efficiency
- Site basis: an earlier version counted energy at the site; a site-based zero building produces at least as much as it uses in a year
Selection
- Effect of source basis: one unit of electricity generated on site, usually by solar PV, avoids more than three units of source energy
- Fuel use: the DOE definition allows in-building fuel combustion, which differs from Living Future Institute zero energy certification
- Verification: matching annual production to use is not the only check; verify performance in operation
- Strategy order: reduce loads first with envelope and passive design, then supply the remainder with on-site renewables
Sources
- Green Building Advisor: the Department of Energy chooses a definition for net zero, https://www.greenbuildingadvisor.com/article/the-department-of-energy-chooses-a-definition-for-net-zero
- U.S. Department of Energy: zero energy buildings definition, 2017 BTO peer review, https://www.energy.gov/sites/prod/files/2017/04/f34/2017 BTO Peer Review - Informational Panel - Zero Energy Buildings - Definition.pdf
- RMI: new DOE definition of zero-energy buildings, https://rmi.org/blog_2015_11_05_new_doe_definition_of_zero_energy_buildings_is_a_base_hit_not_a_home_run
- Wikimedia Commons: Net-Zero Energy Residential Test Facility (NZERTF) in the snow (14531301000).jpg, by National Institute of Standards and Technology (Public domain), https://commons.wikimedia.org/wiki/File:Net-Zero_Energy_Residential_Test_Facility_(NZERTF)_in_the_snow_(14531301000).jpg