EUI Calculator - Energy Use Intensity

What is EUI (Energy Use Intensity)?

Energy Use Intensity (EUI) is a metric that expresses a building's energy use as a function of its size. It is calculated by dividing the total energy consumed by the building in one year by the total gross floor area of the building. EUI is expressed in units of energy per square foot per year, typically kBtu/ft²/yr in the United States or kWh/m²/yr in metric countries.

EUI serves as a standardized metric that allows building owners, managers, and energy professionals to compare the energy efficiency of different buildings regardless of their size. A lower EUI indicates a more energy-efficient building, while a higher EUI suggests there may be opportunities for energy savings.

How to Calculate EUI

Calculating EUI involves three simple steps:

1. Gather energy consumption data: Collect all energy bills for your building over a 12-month period. This includes electricity, natural gas, fuel oil, propane, district steam, and any other energy sources used by the building.
2. Convert to common units: Convert all energy types to a common unit, typically kBtu (thousand British Thermal Units). Use these conversion factors:
   • 1 kWh = 3.412 kBtu
   • 1 therm = 100 kBtu
   • 1 gallon of fuel oil = 138.5 kBtu
   • 1 gallon of propane = 91.5 kBtu
   • 1 MWh = 3,412 kBtu
   • 1 GJ = 947.8 kBtu
3. Divide by floor area: Divide the total annual energy consumption (in kBtu) by the total gross floor area (in square feet) to get the EUI.

Example Calculation

Let's calculate the EUI for a 50,000 square foot office building:

• Annual electricity consumption: 800,000 kWh = 2,729,600 kBtu
• Annual natural gas consumption: 5,000 therms = 500,000 kBtu
• Total energy: 3,229,600 kBtu
• EUI = 3,229,600 ÷ 50,000 = 64.6 kBtu/ft²/yr

Why is EUI Important?

EUI is important for several reasons:

• Benchmarking: EUI allows you to compare your building's energy performance against similar buildings in your region or nationwide.
• Identifying opportunities: A high EUI relative to similar buildings indicates potential for energy savings through efficiency improvements.
• Tracking progress: Monitoring EUI over time helps you track the impact of energy efficiency measures.
• Compliance: Many cities and states now require buildings to report their EUI as part of benchmarking and disclosure ordinances.
• Real estate value: Buildings with lower EUI often command higher rents and property values due to lower operating costs.
• Sustainability goals: EUI is a key metric for tracking progress toward carbon reduction and sustainability targets.

Factors That Affect EUI

Several factors influence a building's EUI:

Building Characteristics

• Building type: Different building types have vastly different energy needs. Hospitals and data centers typically have high EUI due to 24/7 operations and specialized equipment.
• Age of building: Older buildings often have higher EUI due to less efficient systems and envelope construction.
• Building envelope: Insulation levels, window quality, and air sealing significantly impact heating and cooling loads.
• Building systems: HVAC efficiency, lighting systems, and plug load management all affect energy consumption.

Operational Factors

• Operating hours: Buildings that operate 24/7 will naturally have higher EUI than those with limited hours.
• Occupancy density: More people per square foot means more lighting, ventilation, and equipment needs.
• Equipment and processes: Special equipment like commercial kitchens, server rooms, or manufacturing equipment add to energy use.
• Maintenance practices: Well-maintained equipment operates more efficiently.

Climate and Location

• Climate zone: Buildings in extreme climates (very hot or very cold) require more energy for heating and cooling.
• Weather patterns: Unusually hot summers or cold winters can cause EUI variations year to year.

EUI Benchmarks by Building Type

Understanding typical EUI values for different building types helps put your building's performance in context:

Low EUI Buildings (Under 50 kBtu/ft²/yr)

• Warehouses and storage facilities
• Efficient residential buildings
• Parking structures

Medium EUI Buildings (50-100 kBtu/ft²/yr)

• Office buildings
• Schools and universities
• Retail stores
• Hotels (limited service)

High EUI Buildings (Over 100 kBtu/ft²/yr)

• Hospitals and healthcare facilities
• Full-service hotels
• Restaurants
• Supermarkets
• Data centers
• Laboratories

Strategies to Reduce EUI

If your building has a high EUI, consider these strategies to improve energy efficiency:

Quick Wins

• Adjust thermostat setpoints and schedules
• Turn off lights and equipment when not in use
• Replace incandescent bulbs with LEDs
• Clean or replace HVAC filters regularly
• Seal air leaks around windows and doors

Medium-Term Improvements

• Upgrade to ENERGY STAR certified equipment
• Install programmable or smart thermostats
• Add occupancy sensors for lighting control
• Improve insulation in accessible areas
• Commission or retro-commission building systems

Major Upgrades

• Replace old HVAC systems with high-efficiency equipment
• Install a building automation system
• Upgrade windows to high-performance glazing
• Add renewable energy systems (solar panels)
• Conduct a deep energy retrofit

EUI and Building Codes

Many jurisdictions now incorporate EUI targets into building codes and policies:

• Benchmarking ordinances: Cities like New York, Chicago, and Seattle require large buildings to annually report their EUI.
• Building performance standards: Some cities are implementing requirements for buildings to meet EUI targets or face penalties.
• Energy codes: New construction must meet increasingly stringent energy codes that effectively limit EUI.
• LEED and green building certifications: These programs use EUI as a key metric for evaluating building performance.

Frequently Asked Questions

What is a good EUI for an office building?

A good EUI for an office building is typically between 50-75 kBtu/ft²/yr. Buildings achieving ENERGY STAR certification often have EUI values below 70 kBtu/ft²/yr. High-performance green buildings may achieve EUI as low as 30-40 kBtu/ft²/yr.

How do I convert EUI from kBtu/ft² to kWh/m²?

To convert from kBtu/ft² to kWh/m², multiply by 3.155. For example, 50 kBtu/ft²/yr = 157.7 kWh/m²/yr.

Should I use site EUI or source EUI?

Site EUI measures energy as delivered to your building and is useful for understanding your building's direct energy consumption and costs. Source EUI accounts for energy losses in generation and transmission and is better for understanding environmental impact. ENERGY STAR Portfolio Manager reports both values.

Why does my EUI vary from year to year?

EUI can vary due to weather differences, changes in occupancy or operating hours, equipment additions or removals, and changes in energy rates that affect behavior. Weather-normalized EUI can help account for temperature variations.

Can I compare EUI across different building types?

While technically possible, comparing EUI across different building types isn't particularly meaningful since different uses have vastly different energy needs. A hospital with an EUI of 200 might be performing excellently, while an office with the same EUI would be performing poorly.