Energy Use and EUI

Understanding the Terminology

Patrick Chopson avatar
Written by Patrick Chopson
Updated over a week ago

A building's energy use refers to the energy required to operate and sustain the project once it's occupied. The metric is commonly measured in Energy Use Intensity (EUI), to calculate EUI you run an energy model. By calculating the energy a building consumes annually, architects can better predict the projects' utility cost as it is directly linked to a building's energy consumption.

Key Energy terminologies

  • Energy Use Intensity (EUI) - refers to the energy required to operate and sustain the project once it's occupied. The metric is expressed as the energy per square area per year (kBtu/ft2/yr for IP, kWh/m²/yr for Metric).

  • Site Energy - is the amount of heat and electricity consumed by a building as reflected in your utility bills. Looking at site energy can help you understand how the energy use for an individual building has changed over time. Site energy may be delivered to a building in one of two forms: primary or secondary energy.

  • Source Energy - represents the total amount of raw fuel that is required to operate the building. It incorporates all transmission, delivery, and production losses of transportation involved in getting the energy source to the building, as well as the energy used in operations. By taking all energy use into account, this assessment of energy provides a complete overview of the energy efficiency in a building.

    Site vs. Source Energy -
  • Primary Energy - is the raw fuel that is burned to create heat and electricity, such as gas or fuel oil used in onsite generation. A full list of fuel types can be seen here.

  • Secondary Energy - is the energy product (heat or electricity) created from a raw fuel, such as electricity purchased offsite from the grid or heat received from a district steam system.


An energy model is a series of equations used to calculate the heat flow into and out of a building. It measures the amount of energy that must be expended in order to maintain the ideal level of indoor comfort.

Since the "primitive hut", humans have always sought ways to improve their shelters and make even the most hostile environment livable. Whether their building strategies were designed to combat hot/cold/wet/dry climates, or locations with poor air quality, high winds, seismic events, or resource scarcity, humans have found solutions to build ever-evolving shelters. Today, building science continues this tradition with the development of rules and equations to combat these classic struggles as well as address the demands of the modern world (ie. economy and budgets, growing populations, technologies, hyper-specialized building typologies, human rights, and most importantly -- climate change). By Identifying how climate and environmental conditions create an asymmetry to human comfort, a building can be machined to meet the demands via energy consumption and expenditure, along with a collection of active and passive design strategies.

Calculation Method

Another name for energy modeling is the Heat Balance Equation Method. This might be a familiar term as this is typically used to describe the engines used to run different energy performance simulations. cove.tool uses the ISO 13790 Standard heat-balance engine for the baseline energy analysis page (analysis.tool) and EnergyPlus for the loadmodeling.tool. cove.tool has validated both software's using the industry-standard testing procedure known as the ASHRAE Standard 140 report, which can be provided upon user request.

One of the biggest advantages that cove.tool has over its competitors is automation. With four basic inputs (location, energy code, building type, and geometry) the platform prepopulates the entirety of your prescriptive baseline energy model. Check out how we automate baseline assumptions and which standards we follow for each field in this article. The same process is followed in international locations using equivalent standards or climate zone mapping, read more here. First-time energy modeling? Check out this step-by-step article to set up your first cove.tool project. Snapshots of the Baseline Energy Page Below.


Q. Does cove.tool calculated Source and Site Energy?

The EPA has determined that source energy is the most equitable unit of evaluation. However, the EUI represented in the tool & reports is Site energy consumption. This is the total energy used within the bounds of the site and doesn't include transmission losses, fuel factors, etc. This scope of energy is best for understanding the impact design decisions will have on your building's energy efficiency (ex. Orientation, Massing, Facade Strategies, Material selection, HVAC strategy, and more). The energy may represent both primary (fossil fuel) and secondary (electricity, steam) energy, but that depends on your selected energy type on the baseline energy page (show below). For more information on source energy, check out this article from Energy Star. For more detailed information on source energy, read Portfolio Manager Technical Reference: Source Energy.

Q. How to lower my EUI?

Check out this article for immediate tips. When running an energy simulation one must understand the toll each design decision will take on altering the EUI. Depending on the building assembly, glazing percentages, active and passive strategies implemented, loads, and costs can drastically spike and leave building owners and tenants paying millions more annually. Knowing the EUI values of design decisions and other iterations, one can get the best value for performance. To learn more about the breakdown of EUI, check out this article.

Q. Can I see my energy results in units other than EUI (kBtu/ft2/yr)?

Yes, if your project is in a location that uses the Metric System (SI) the energy usage results will display in kWh/m2/yr (tutorial here). Both of these metrics are 'specific' annual energy consumption. To see your 'total' annual energy you can multiply your EUI by your building's floor area to get kWh/yr (IP) or kWh/yr (SI).

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