Right-Sizing Energy Modeling: A Practical Guide to Level of Detail (LoD)

In modern building projects, building energy analysis has become an important tool for architects, engineers, and designers. It helps them understand how a building will use energy and how design choices can affect comfort, energy costs, and overall performance. By studying these factors early, teams can create buildings that are more efficient and easier to operate in the long run.

As energy modeling becomes more common in the building industry, professionals are also facing new challenges. Projects often come with tight deadlines, complex designs, and high expectations for performance. Energy modelers are expected to provide clear results quickly, even when many parts of the design are still changing.

One of the biggest challenges is deciding how much detail to include in an energy model. If the model is too simple, the results may not be accurate enough to guide decisions. But if the model includes too much detail too early, it can slow down the work and make the process harder to manage.

To help solve this problem, many professionals follow structured guidance such as ASHRAE/IBPSA Standard 209-2024. This updated standard explains how to match the level of detail in an energy model with the stage of the design. By doing this, modelers can focus on the information that truly matters and avoid adding details that do not improve the results.

Keeping Energy Models Simple When Needed

Today’s design software makes it easy to move detailed three-dimensional building models into energy modeling tools. While this technology can be helpful, it can also lead to a common mistake.

Sometimes modelers add extra detail simply because the software allows it, not because the analysis needs it. This can create models that take longer to run and produce results that are harder to understand. When too many details are added early in the design process, the model may include information that will soon change.

During early design stages, buildings are often still evolving. Room layouts may shift, windows may change size, and the building shape may still be under discussion. In these situations, simpler energy models are often more useful because they allow designers to compare ideas quickly.

The best approach is to match the model’s detail to the goal of the study. A simple model can help compare building orientation or window size, while a more detailed model may be needed later to study system performance or meet building regulations. Adding detail step by step helps keep the modeling process efficient and useful.

Understanding the Right Level of Detail in Energy Models

Key Parts of a Building Energy Model

The updated Standard 209-2024 explains that every energy model is built from several important parts. These parts represent the main factors that influence how a building uses energy.

These elements include weather conditions, the building’s shape, zoning, walls and roofs, windows, lighting systems, equipment loads, heating and cooling systems, hot water systems, and building occupants. Each of these elements can be described with different levels of detail depending on the purpose of the model.

Lighting is a good example. In a basic model used during early design, the modeler might use one lighting power value and one schedule for the entire building. This simple approach is often enough when the goal is to compare different building shapes or sizes.

As the project develops, the lighting model can become more detailed. Designers may add lighting power for each space, different schedules based on how rooms are used, and lighting controls that turn lights on or off automatically. In very detailed models, they may even consider how heat from lighting affects the indoor environment.

It is also important to remember that not every part of the model needs the same level of detail at the same time. For example, when studying heating and cooling systems, the HVAC system and room zoning may require more detail, while lighting and equipment loads can remain simple. This focused approach saves time and keeps the model easier to manage.

Energy Modeling Through Different Design Stages

Standard 209-2024 also describes several modeling cycles that match different stages of the building design process. Each cycle has a specific goal and requires a different level of detail.

The first stage is called Simple Box Modeling. At this point, only basic information is needed. This includes the building location, total floor area, number of floors, and general building type. A simple box shape can represent the building. This model helps teams perform early studies and compare general ideas.

The second stage focuses on Conceptual Design Modeling. During this stage, the model begins to include more geometric detail. Designers may study building orientation, window size, and wall performance. Heating and cooling systems are still represented in a simple way, but the model provides useful insights for early design choices.

As the project moves forward, more detail is added in later stages. These stages include reducing heating and cooling loads, selecting HVAC systems, improving design details, and optimizing building performance.

By the final stage of design, the energy model becomes highly detailed. It may include equipment performance data, system controls, schedules, and other operating conditions. These detailed models help engineers understand hourly energy use, identify possible problems, and estimate energy costs and emissions.

Conclusion

Energy modeling has become an essential tool for designing better buildings. As buildings aim for higher energy performance and lower environmental impact, the need for accurate modeling continues to grow.

The guidance in ASHRAE/IBPSA Standard 209-2024 helps professionals manage this process by encouraging the use of the right level of detail at the right time. Instead of creating very complex models from the start, designers can begin with simple models and add more detail as the project develops.

By understanding the key parts of energy models and following clear modeling stages, teams can work more efficiently and still produce reliable results. This balanced approach ensures that energy modeling remains a practical and valuable part of the building design process.