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Repair Windows errors before they cause bigger problemsFix Now →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Energy usage effectiveness (EUE) is a proposed building-performance metric that divides a building’s total annual energy use by an adapted calculation of its unregulated process energy use. It is intended to add context that energy use intensity (EUI) can miss, including occupancy, space utilization, plug loads, process loads and the ventilation associated with occupant density. EUE is still a concept under investigation, not a universally adopted standard or a single mandated calculation.
What energy usage effectiveness means
Roger Chang and Drury Crawley define EUE in their 2018 Building Performance Analysis Conference and SimBuild paper as total building energy use divided by an adapted calculation of unregulated process energy use. Chang’s March 2018 summary describes the same idea more briefly as total annual energy use divided by process energy use, with the process component predicted through modeling or measured in operation.
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The distinction between those descriptions matters. An EUE calculation does not automatically mean “total meter energy divided by one directly metered process-load value.” The denominator may be an adapted, modeled value designed to make process energy comparable across buildings or operating conditions. Any published EUE therefore needs to state exactly how its process-energy denominator was produced.
In simplified form:
EUE = total annual building energy use ÷ adapted unregulated process-energy use
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If both terms are expressed in the same energy units and cover the same reporting period, the result is a ratio. The ratio has meaning only when the analyst also reports the building type, climate zone, occupancy assumptions, process-load boundary, normalization method and whether inputs were modeled or measured.
The proposal borrows the word “effectiveness” from the data-center Power Usage Effectiveness discussion, but it is not the same metric and should not be substituted for data-center guidance. Building EUE is aimed at broader building benchmarking and design decisions, where process loads and occupancy patterns vary substantially among offices, schools, healthcare facilities, retail spaces and other uses.
Why EUI alone can be an incomplete signal
EUI is commonly calculated as annual building energy use divided by floor area, often reported in kWh per square metre or kBtu per square foot. It remains useful for tracking a building against its own history or comparing broadly similar buildings. Chang and Crawley’s point is narrower: area-normalized energy does not describe every condition that determines whether a building is delivering useful service efficiently.
Utilization and partial occupancy
A building that is only lightly occupied can show a low EUI because fewer spaces, systems and schedules are being used. That low number may not represent good performance at the occupancy level the building was designed to support. Conversely, a building operating at high utilization can consume more energy while providing more usable space and service.
Occupant density and ventilation
More occupants generally bring higher ventilation requirements and greater internal gains. A densely occupied building may therefore use more total energy while using less energy per person or delivering more activity per square metre. The EUI value by itself does not reveal whether the occupancy assumptions behind two buildings are comparable.
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Plug and process loads
Computers, laboratory equipment, kitchen appliances, medical devices, manufacturing equipment and other process loads can dominate energy use in some building types. EUI records the resulting total, but it does not identify whether a high value reflects inefficient building systems or an energy-intensive activity that the building is hosting. The 2018 paper specifically identifies plug loads and process loads as factors not captured by EUI alone.
Thermal comfort and space quality
Energy can be reduced by conditioning less space, accepting uncomfortable temperatures or operating with schedules that do not meet occupants’ needs. A low EUI is not evidence that thermal comfort, indoor environmental quality or functional requirements are being met. EUE also does not measure comfort directly; it is a benchmarking ratio, not an indoor-environment score.
EUI and EUE answer different questions
| Aspect | EUI | Proposed EUE |
|---|---|---|
| Basic calculation | Total annual energy divided by floor area | Total annual energy divided by an adapted unregulated process-energy calculation |
| Primary reference | Building size | Building process-energy activity or service context |
| What it can expose | Area-normalized energy trends and broad peer differences | How much total energy is associated with the modeled or measured process-energy baseline |
| Occupancy treatment | Often implicit or handled separately | Can be represented through occupancy density, process assumptions and related ventilation rates |
| Inputs | Usually utility energy and floor area | Utility energy plus a defined process-energy model or measurement boundary |
| Comparability risk | High when building uses, schedules or occupancy differ | High when denominator definitions, normalization or process boundaries differ |
| Current status | Widely used benchmarking convention | Concept explored in the 2018 paper; no universal implementation protocol is established by the material available here |
Neither metric replaces the other. EUI is usually easier to calculate and communicate. EUE may add explanatory power when the service delivered by a building depends strongly on occupancy or process activity, but it requires more assumptions and documentation.
How to calculate EUE without hiding the denominator
The following workflow follows the logic described by Chang and Crawley while making the reporting choices explicit.
- Set the boundary. Define whether total energy includes electricity, purchased fuels, district energy and on-site generation, and specify the reporting period. Keep the boundary consistent with the process-energy calculation.
- Assemble total annual energy use. Use utility bills, interval meters or a calibrated building model. State whether the figure is measured, simulated or a combination. If on-site generation is involved, explain whether the numerator is delivered energy, site energy or another convention.
- Identify unregulated process energy. List loads driven by the building’s activity rather than by the base building’s regulated systems. Depending on use, this can include equipment, appliances, laboratory systems, data-processing equipment, medical equipment or production machinery. Do not assume every plug load belongs in the same category without documenting the rule.
- Choose the adapted denominator method. The denominator can be estimated from a model, derived from measured operation or assembled from both. Record schedules, equipment power, diversity factors and operating hours. An adapted calculation should be reproducible; a single unexplained meter channel is not enough for cross-building comparison.
- Decide whether to normalize process loads. The conference paper examines normalized and non-normalized approaches. Normalization might hold an activity level, occupant density or process intensity to a common reference; non-normalized values preserve the building’s observed condition. The choice changes the question the ratio answers, so report it beside the result.
- Align occupancy and ventilation assumptions. Occupant density affects both internal gains and outdoor-air requirements. Use the same occupancy basis in the process calculation and in the total-energy model, and document any ventilation-rate assumptions.
- Compute and label the ratio. Divide the total annual energy by the adapted process-energy value, then publish the numerator, denominator, units, period and method—not just the final ratio.
- Interpret against an appropriate comparison group. Compare buildings with similar uses, climate conditions, occupancy and process intensity. A ratio from a laboratory should not be treated as a direct target for a lightly occupied office merely because both have the same floor area.
Illustrative calculation
Consider a hypothetical 100,000-square-metre office whose measured annual energy use is 10,000,000 kWh. Its EUI is 100 kWh/m²-year. Suppose an adapted process-energy calculation estimates 4,000,000 kWh for office equipment and other defined unregulated loads. The resulting EUE is 2.5.
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If the analyst instead applies a documented occupancy-normalization method that produces a 5,000,000 kWh process-energy denominator, the EUE becomes 2.0 while the measured total energy and EUI remain unchanged. Neither ratio is automatically “correct” without knowing which operating question the denominator is intended to answer. This example is instructional, not a benchmark value from the 2018 paper.
What the 2018 study examined
Chang and Crawley evaluated benchmark EUE values using all 16 U.S. Department of Energy Commercial Prototype Buildings associated with ASHRAE Standard 90.1-2013. The evaluation covered ASHRAE climate zones and used a bottom-up approach rather than relying only on aggregate utility statistics.
The authors compared EUE with calculated EUI and investigated several choices that can materially change a result:
- normalized versus non-normalized treatment of unregulated process loads;
- occupant-density assumptions;
- ventilation rates associated with those occupancy assumptions;
- building type and climate zone; and
- the relationship between modeled process activity and whole-building energy.
The 16 prototypes are a defined analytical sample, not a measured performance claim about all commercial buildings. Their value is in showing why a denominator and its assumptions must travel with an EUE result.
Potential use in building design
Testing design options
During concept and detailed design, teams could calculate EUI and EUE for the same option set. A façade change, HVAC strategy or control sequence may lower regulated energy while leaving process energy unchanged. Another design may support higher occupant density or more equipment with a modest increase in total energy. Looking at both ratios helps the team ask whether a change improves the building system or simply shifts the activity assumptions.
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Making scenarios explicit
Designers should model at least the occupancy and process scenarios that drive the brief: expected average occupancy, peak occupancy, equipment schedules and any high-load spaces. Reporting a single EUE based on one schedule can create false precision. A scenario table that shows the denominator and ratio for each case is more transparent than one “design EUE” with no operating context.
Supporting early decisions
EUE is most useful early when it exposes a mismatch between the intended service and the energy model. If a project’s process loads are unknown, the right response is to improve the brief or use a clearly labeled proxy—not to present a highly precise ratio. The metric should inform design optimization, not replace load calculations, comfort analysis or code compliance checks.
Potential use in operations and commissioning
The paper discusses tracking real-time EUE as a possible way to optimize part-load system performance. In an operating building, interval energy data could be paired with occupancy and process-activity data to show when whole-building energy is diverging from the activity being served. That could help a commissioning team investigate schedules, simultaneous heating and cooling, controls, or equipment that remains on when process demand is low.
This is a potential application, not an established operational standard. Reliable use would require functioning meters, a stable process-energy definition, time-synchronized occupancy or activity data and a method for handling missing or anomalous readings. A sudden ratio change may indicate a controls problem, a change in occupancy, a new piece of equipment or a denominator-data error; it is not a diagnosis by itself.
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For portfolio analysis, EUE could provide another way to group buildings by the service they deliver rather than by floor area alone. A portfolio owner might examine offices, hospitals and laboratories separately, then compare normalized and non-normalized results within each group. Such analysis could reveal where a high EUI is largely explained by process intensity and where base-building systems appear inefficient relative to the same activity level.
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The conference paper also discusses possible relevance to outcome-based code frameworks. In that setting, an EUE-like measure could help connect measured operational energy with the activity a building supports. Any code use would require an adopted definition, verification rules, treatment of changing occupancy and enforcement procedures. The paper does not establish those rules or demonstrate broad regulatory deployment.
Common interpretation errors
Treating every denominator as equivalent
A directly metered process load, a modeled equipment schedule and an occupancy-normalized estimate are not interchangeable. Put the denominator method in the result name or reporting note.
Comparing unlike buildings
Climate, building type, operating hours, occupant density and process equipment can all change the ratio. Cross-building rankings without those qualifiers can reward a favorable assumption rather than better performance.
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Using EUE to claim comfort
Neither a low EUI nor a favorable EUE proves that temperatures, humidity, air quality, lighting or acoustics meet the project’s requirements. Pair energy metrics with indoor-environment measurements and occupant outcomes.
Ignoring process-load changes
A tenant fit-out, new server room, expanded kitchen or laboratory installation can alter the denominator and numerator. Recalculate or restate the baseline when the building’s activity changes.
Assuming a universal target
The available paper explores benchmark values but does not provide a universally valid pass/fail threshold. A target must be tied to a building type, climate, occupancy scenario, process definition and purpose.
Implementation checklist for project teams
- Write the energy boundary and reporting period before collecting data.
- Separate regulated building-system energy from defined unregulated process energy in the model or meter map.
- Document equipment schedules, diversity assumptions, occupant density and ventilation rates.
- State whether each input is measured, modeled or normalized.
- Publish the numerator, denominator and resulting EUE together.
- Report EUI beside EUE rather than substituting one for the other.
- Use a comparison set matched for building use and climate zone.
- Revisit the baseline after major occupancy, equipment or operating-schedule changes.
- Use EUE as evidence for investigation, not as a stand-alone comfort, code or commissioning verdict.
What readers should call EUE today
The most accurate description is “a proposed building benchmarking metric.” The 2018 conference paper provides a technical definition and explores how EUE might support design optimization and portfolio analysis. It also considers operations and outcome-based codes as possible applications. The material available does not establish broad adoption, a governing standard, or one universal calculation protocol.
For a project team, the practical lesson is straightforward: retain EUI for area-normalized reporting, then add EUE when the building’s energy story depends on occupancy and process activity. The credibility of the result rests less on the ratio’s decimal precision than on a transparent, reproducible denominator and clearly stated operating context.
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