Nomenclature – Defining Zero Energy Buildings
Definitions of key terms applied to the zero energy building definitions.
Annual: Covering at least one period of 12 consecutive months for all energy measurements.
Building: A structure wholly or partially enclosed within exterior walls, or within exterior and party walls, and a roof providing services and affording shelter to persons, animals or property.
Building Site: Building and the area on which a building is located where energy is used and produced.
Building Energy: Energy consumed at the building site as measured at the site boundary. At minimum, this includes heating, cooling, ventilation, domestic hot water, indoor and outdoor lighting, plug loads, process energy, elevators and conveying systems, and intra-building transportation systems.
Campus: A group of building sites in a specific locality that contain renewable energy production systems owned by a given institution.
Delivered Energy: Any type of energy that could be bought or sold for use as building energy, including electricity, steam, hot water or chilled water, natural gas, biogas, landfill gas, coal, coke, propane, petroleum and its derivatives, residual fuel oil, alcohol based fuels, wood, biomass and any other material consumed as fuel.
Energy: The capacity for doing work. Energy takes a number of forms that may be transformed from one into another, such as thermal (heat), mechanical (work), electrical or chemical. Customary measurement units are British thermal units (Btu), joules (J) or kilowatt-hours (kWh).
Exported Energy: On-site renewable energy supplied through the site boundary and used outside the site boundary.
Geothermal Energy: Deep-earth heat used for either electricity generation or thermal energy.
On-site Renewable Energy: Includes any renewable energy collected and generated within the site boundary that is used for building energy, and the excess renewable energy could be exported outside the site boundary. The renewable energy certificates (RECs) associated with the renewable energy must be retained or retired by the building owner/lessee to be claimed as renewable energy.4
Portfolio: A collection of building sites that contains renewable energy production systems owned/leased by a single entity.
Renewable Energy: Energy resources that are naturally replenishing but flow-limited. They are virtually inexhaustible in duration but limited in the amount of energy that is available per unit of time. Renewable energy resources include biomass, hydro, geothermal, solar, wind, ocean thermal, wave action and tidal action. [from DOE’s U.S. Energy Information Administration Glossary]
Renewable Energy Certificate (REC): Represents and conveys the environmental, social and other non-power qualities of one megawatt-hour of renewable electricity generation and can be sold separately from the underlying physical electricity associated with a renewable-based generation source.
Site Boundary: Line that marks the limits of the building site(s) across which delivered energy and exported energy are measured.
Site Energy: Same as building energy.
Source Energy: Site energy plus the energy consumed in the extraction, processing and transport of primary fuels such as coal, oil and natural gas; energy losses in thermal combustion in power generation plants; and energy losses in transmission and distribution to the building site.