Which energy performance metric is typically measured as part of a building's energy efficiency?

Energy use intensity (EUI) is a key metric used to assess a building's energy performance and efficiency. It is calculated as the total energy consumed per unit of floor area, typically expressed in terms like kilowatt-hours per square foot per year. EUI provides a clear, quantitative measure that allows for comparisons between different buildings or building types, making it easier to identify areas for improvement in energy management.

In contrast, while the other options offer valuable information related to a building's energy consumption or efficiency, they focus on different aspects. The building area ratio (BAR) measures the ratio of a building's total area to the site area, providing insight into land use rather than energy performance. Annual energy cost (AEC) reflects the financial expenditure on energy over a year but does not directly show efficiency or consumption relative to the building's size. Lighting power density (LPD) gauges the power used for lighting relative to the area but is a specific subset of energy use focused solely on lighting rather than overall energy performance. Therefore, EUI stands out as the most comprehensive metric for assessing energy efficiency across a building.