Building performance metrics: beyond energy use intensity

In July and August last year, we focused on the process for energy roadmaps and noted the importance of establishing a baseline for a building’s energy performance. The process involves reviewing utility bills and developing an energy balance, defining the various energy sources and identifying the major energy consuming systems. Once developed, the baseline can be used to benchmark against other facilities of a similar type and occupancy.

Read more: Creating a comprehensive energy roadmap, Part I and Part II

The most common benchmarking metric is the energy use intensity (EUI), expressed as energy per square foot per year (kBtu/ft2/yr), and it results from a fairly simple calculation of the total annual building energy use divided by the gross building area, as defined by the ANSI/ASHRAE Standard 105-2014: Standard Methods of Determining, Expressing and Comparing Building Energy Performance and Greenhouse Gas Emissions. The EUI metric is widely used in the built environment, and it is the basis of multiple industry standards and energy conservation incentives. However, metrics considering other factors than floor area may be selected, depending on the owner’s goals and concerns, including:

  • Btu per employee: typical for office buildings
  • Btu per unit of product: typical for assembly plants
  • Btu per pound of product: typical for manufacturers
  • Btu per number of beds occupied: typical for hotels or hospitals

Data center operators have their own metrics to evaluate how efficiently a data center uses energy, including power usage effectiveness, data center infrastructure efficiency and water usage effectiveness.

While these metrics are very useful in comparing a facility’s energy performance to peer buildings, one of the drawbacks to these metrics is that energy cost is not considered. An important and useful benchmark to consider is the energy cost intensity (ECI), which is the cost of energy used annually per square foot of conditioned space. This metric can identify key targets for cost and energy efficiency measures and is crucial to financial management and planning.

In addition, the above-mentioned metrics do not accommodate the operating and maintenance costs associated with the building’s systems. Consider the cost of water and water treatment associated with heating, ventilating and air conditioning (HVAC) systems. Two facilities can have the same EUI; however, one may require significant water consumption and chemical treatment for an open loop condenser water system, while the other building employs air-cooled chillers. The operating costs associated with such systems should be evaluated when analyzing overall system costs for an owner.

Even though EUI is a common tool used in benchmarking, it is important for energy managers and engineers to be familiar with other metrics and cost considerations to help their clients establish energy goals and make the most impactful budget decisions related to their facilities and systems.

To learn about benchmarking with these metrics, contact Imane El Ghazouani at