The importance of sustainable practice in building design has reached a critical point. The time is now for us to design buildings that aren’t just energy efficient, but those that have positive impacts on our environment, climate, and lives. To do that, we must move our performance needle from simple goals of energy reductions and efficiency to more lofty goals for net zero or net positive energy generation and the elimination of fossil fuels. Achieving these goals requires that we know how our buildings are likely to perform over time. We need to understand and predict our buildings’ energy use intensity (EUI).
What is EUI?
Energy use intensity (EUI) is an indicator of the energy efficiency of a building’s design and/or operations. It is an absolute value expressed as the total energy used in a building per square foot, per year (kBtu/sf/yr). EUI can be thought of as the miles per gallon rating of the building industry. It is used to set a target for energy performance before beginning design and show the actual measured energy use of an existing building. Doing so allows us to compare our design against national benchmarks and other similar buildings and helps us determine reduction strategies and calculate the amount of renewable energy systems needed to power and operate our buildings.
Generally, a low EUI indicates good energy performance; the lower your EUI, the better. However, EUI without context is just a useless number. EUI always varies by building type – airplane hangars, hospitals, schools, and office buildings all have different EUI baselines. It is also important to note that just because two buildings have the same EUI and site energy use, it doesn’t mean they carry the same environmental impact. They may have different emissions and global warming potential (GWP) based on their location and energy source mix. For strict comparison and compliance performance, we are most interested in a building’s site EUI, but when trying to determine a building’s full performance, emissions, and GWP, we must also take a building’s source EUI into consideration.
Why should I measure my EUI?
It’s easier to control and improve that which we measure. Quantifying for the sake of quantifying is pointless, but there’s value in using the data to improve our decision-making, our designs, and our buildings’ performance. With states and cities adopting performance-based codes, the ability to track and understand your building’s energy use becomes important from initial design through operations.
How to get started
There are a few ways to determine your building’s EUI. If you have an existing building and access to the utility bills, simply divide the total energy consumed by the building in one year (measured in kBtu – you may need to convert from kwH and therms) by the gross floor area of the building. You can then see how your building compares to other buildings of the same type by looking at Energy Star’s Portfolio Manager tool or the commercial buildings energy consumption survey (CBECS) database.
If you are interested in determining an energy benchmark for your building prior to or during the design phase, there are additional sources you can use. EnergyStar’s Target Finder is a free and simple, easy-to-use benchmarking tool, as is Zero Tool. With just some barebones information about your building, each of these tools can provide you with a benchmark for your building type, your building’s baseline on code compliance, and can help you set targets for energy reduction and performance in a matter of minutes.
Practical application of EUI
At this point you are ready to develop and test your design – comparing strategies for holistic energy reduction and building performance through early and iterative energy modeling. Predictive modeling helps you to quickly determine the best and most cost-effective design strategies to reduce energy consumption and increase the energy performance of your project. It also allows you to perform climate and site analysis for your project to determine if and how much on-site renewable energy production makes sense for your building. It always makes sense to reduce one’s energy load as much as possible before determining the amount of renewable energy systems needed to power that load. Why pay more for building and renewable energy systems than needed?
If you have signed on the AIA 2030 commitment (a goal to reach net zero energy and carbon neutral by 2030), you can easily track your building’s predictive and operational energy within the AIA DDX platform for your entire portfolio. If you haven’t joined the AIA 2030 commitment, you can still track your building’s performance through EnergyStar’s Portfolio Manager platform.
Of course, knowing a building’s predicted or measured EUI doesn’t specify where or how that energy is being used in a building. An extension of determining a building’s EUI is determining where specific reduction opportunities exist within the building and its systems. This can be achieved through metering and sub-metering of particular systems (lighting, HVAC systems, pumps, plug loads, etc.) to gain a more complete understanding of where and how energy is being used in the building. This becomes especially important in high performance buildings where plug and process loads can represent as much as 30% to 50% of the electrical load for the building.
Mead & Hunt has begun using Cove Tool’s analysis and load-modeling tools. The analysis tool allows us to determine and track EUI targets from the earliest stages of design and test how design decisions impact energy performance, daylighting, water use, carbon reduction, and cost. It also allows us to track the potential impact, benefit, and value of on-site renewable energy production. The load-modeling tool allows us to perform more robust energy modeling required for compliance reporting.
A deep understanding of your client’s business, operations, and IT needs will help to define energy targets early and improve building performance. Knowing and tracking EUI – and in fact using it as a design tool – helps improve building design, performance, and continued operations over a building’s lifetime. It’s a critical step on the path to Net Zero and Net Positive energy performance for buildings.
Key points to remember
- Buildings are a collection of interrelated systems that behave like living entities. Building performance is affected by decisions from early design through operation.
- Before starting design, determine the Site Energy Use Intensity (EUI) baseline for the building type and set a target Site EUI for your building.
- Use energy modeling to compare design alternatives. At key points in the design process, you can use the results to calculate the Site EUI of the proposed building and check whether you’re on track to meet your energy target or need to revise the design.
- Adopt the AIA 2030 Commitment and use EUI to document the energy performance of your projects. Through the 2030 Commitment, you can evaluate portfolio wide energy performance of your firm’s projects and see where your Firm stands in relation to others in your region and nationwide.
- Understand your client’s operations and IT needs to identify hidden areas of energy use.
- Meter and sub-meter your building systems to quantify energy use and opportunities for reduction.
Resources for EUI benchmarks, targets and energy modeling
- 2003, 2012, and 2018 Commercial Building Energy Consumption Survey, known as CBECS, and available at https://www.eia.gov/consumption/commercial/.
- Energy Star provides median Source and Site EUI numbers for many building types.
- ZERO Tool establishes benchmarks as a starting point in establishing energy performance targets for design.
- AIA’s Architect’s Guide to Building Performance – Integrating performance simulation in the design process.
