Energy Use Intensity (EUI) can be defined as the annual energy consumption of a building (from all fuel sources) relative to the building’s total area. EUI is expressed in kBtu/sf/yr and is a common metric used to benchmark the energy performance of buildings vs. their peers. The EUI is often treated as an energy “score” with a lower number representing less overall energy use.
Source EUI considers the energy lost between the energy source and the end-use. This includes mining/extraction, processing, and transporting energy to a building. Source EUI is a good way to measure the total environmental impact of energy use in a building. Site EUI, on the other hand, is much simpler to calculate, considering only the energy consumed by the building. Site EUI is a good tool to use for benchmarking the energy use of one building vs. other similar buildings.
Generally speaking, the more energy-efficient a building is, the lower its EUI will be. However, the EUI for commercial and institutional buildings in the U.S. varies significantly. Climatic conditions, type of occupancy, and hours of operation all have an impact on energy consumption, as well as the products and systems used for the building’s envelope, lighting, water heating, and HVAC systems.
In addition to serving as a benchmark or an energy score, the EUI is often used as a goal to guide the design of a building. In fact, the first step in designing a Net Zero Energy building is generally setting a goal for the building’s energy consumption. The ASHRAE Advanced Energy Design Guides recommend the following target Site EUIs (kBTU/sf/yr) for Net Zero Energy projects:
ASHRAE Advanced Energy Design Guide for Small to Medium Office Buildings 2019
ASHRAE Advanced Energy Design Guide for K-12 School Buildings 2018
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