Analyzing Model Outputs

Analysis of energy model outputs serves two main roles.

1. Verifying the quality of the model—An output review can help verify model quality and confirm that the model represents your intended inputs.
2. Answering design questions and providing insights—BEM can be extremely effective at providing guidance on design decisions throughout all phases of a project, and at developing strategies to meet performance targets.

Timescale of output results

Bar chart illustrating monthly energy consumption by fuel type and their contribution to whole-building energy use intensity (EUI). (Source: IBPSA-USA BEM Workshop)

Output results are available at different timescales. Each is useful for different types of model analysis, and collectively enable a thorough analysis of a building's performance.

Annual output results

Annual outputs for building energy models typically provide a comprehensive overview of yearly energy consumption, costs, and other performance metrics.

Monthly output results

Pie chart and bar chart illustrating energy consumption by end use. (Source: IBPSA-USA BEM Workshop)

Monthly outputs offer a more detailed breakdown, highlighting variations throughout the year.

Timestep output results

Timestep outputs are reported at specific intervals, often hourly or even smaller. Analyzing these outputs offering a view of energy usage and system behavior over time. Individual timestep results are useful for evaluating instantaneous loads, or system demand.

Granularity of output results

Output results are also available at different levels of granularity.

Whole-building-level outputs

Whole-building outputs in energy models encapsulate overall performance metrics like total energy consumption, costs, and environmental impact. Whole-building-level outputs may be further broken down by fuel type (electricity vs. gas), or end use.

Zone-level outputs

Line plot illustrating variation of zone temperatures over the course of the year (top image) and over the period of a week in the summer and winter (bottom images). (Source: IBPSA-USA BEM Workshop)

Zone-level outputs focus on individual spaces within the building. These outputs may include space temperatures, comfort settings, or energy consumption of equipment within a particular space.

System-level outputs

Line plot illustrating variation in heating and cooling coil loads over the course of a year. (Source: IBPSA-USA BEM Workshop)

System-level outputs analyze the performance of HVAC, lighting, or other building systems, offering a detailed understanding of each system's contribution to overall energy usage.

Other levels of granularity

Some BEM software tools allow for tracking performance using "meters" which allow you to group various items together. This can be useful for evaluating performance of a particular section of a building. One example may be to evaluate the performance individual residential units in a multifamily building.

Useful metrics

This section lists useful energy model outputs, and the following sections cover how to apply them to verify model quality and answer design questions.

Several outputs will be important for nearly every project:

• Electricity and gas consumption by end use - annual and monthly
• Peak electric demand by end use - monthly
• Energy cost by source - annual
• Air handler peak cooling and heating demand - annual
• Chilled water and hot water loop peak loads
• Unmet heating and cooling load hours

These additional outputs can also be useful when checking the quality of the model as well as with providing insights into building performance:

• Energy consumption by source - hourly or sub-hourly
• Air handler cooling and heating demand - hourly or sub-hourly
• Chilled water and hot water loop demand - hourly or sub-hourly
• Peak cooling and heating loads by component, e.g. walls, roof, window solar, etc.
• Air handler hourly data: supply air flow, outdoor air flow, supply air temperature, cooling coil load, heating coil load, fan power
• Chilled water and hot water loop hourly data: flow, load, supply temperature, return temperature
• Zone air temperature

Output reports that summarize inputs and equipment capacities are useful for verifying the model and are produced by some simulation programs:

• A list of zones that summarizes load inputs such as lighting power, occupant density, plug load, and floor area
• A list of envelope components with performance values such as U-factor and SHGC.
• Description of air handlers including autosized airflow, cooling capacity and heating capacity as well as efficiency.
• Description of chilled water and hot water loops including autosized capacity and efficiency.

Presenting the results

Energy modeling results have little value if decision makers do not understand them. When presenting results to owners and design teams here are two recommendations.

• Focus on answering design questions rather than presenting simulation results
• Present information visually

The overview below includes several examples of energy model results presented graphically but for much more detail and guidance on presenting results relevant to specific design tasks, please visit the Learn by Design Task section of this site.

• Overview: Presenting results visually
• Tutorial: Presenting an input summary
• Overview: Types of charts
• See also:
  • Learn by Design Task
  • Project Stasio
  • Architect’s Guide to Building Performance (AIA)

Review and analysis to verify model quality

Even a simple box model presents many opportunities for unintended inputs. An output review can help verify model quality and confirm that the model represents your intended inputs

• Tutorial: Review and analysis to verify model quality
• Tutorial: Compare inputs and outputs to common "rules of thumb"

Analysis to provide answers and insights

BEM can be extremely effective at providing guidance on design decisions throughout all phases of a project, and at developing strategies to meet performance targets. An overview is provided below, but for much more detail and guidance on using BEM to inform specific design tasks, please visit the Learn by Design Task section of this site.

• Overview: Analysis to provide answers and insights
• See also:
  • Learn by Design Task
  • Presenting results visually

Accuracy and Uncertainty

Building energy simulation programs are quite accurate when we provide accurate inputs. That can be a challenge for many cases, especially for early design models when many assumptions are necessary.

Often, during the design process, the focus of BEM analysis is comparing alternative design options. The relative performance of different designs is less sensitive to those assumptions, assuming that assumptions are consistent between the alternative models.

However, if the goal is to calculate an estimate of absolute energy consumption, then precise inputs are very important, and if the inputs align with real-world design and operation, then models can produce very accurate results.

Read more about Accuracy and Uncertainty.