How to choose and use modeling software

Consulting engineers should evaluate how to select and use the right modeling software tools for a building design project

By Clark Denson and Abe Morris April 19, 2021


Learning Objectives

  • Understand the value of an owner’s project requirements and BIM execution plan, and what elements are important to include.
  • Review the benefits and limitations of modeling software tool interoperability.
  • Learn about the different use cases for building energy modeling tools, including compliance, comparison and prediction.

The scope and complexity of building design projects is broad, and there are many modeling software tools that a project team must choose from as they perform analysis and calculations, collaborate across disciplines and trades, produce construction documents and ultimately aid in the management of a building.

However, it’s critical to define project team members’ responsibilities and building performance goals, as this will determine which modeling software tools should be used, how to use them and their limitations. These tools include, but are not limited to, building information modeling, energy models and daylighting models.

These modeling tools are broadly used in the architecture, engineering and construction industry and have evolved to impact the way buildings are designed, built and operated.

Project requirements and modeling software integration

Beginning with the end in mind is the key to a successful project and requires evaluating what it means to comply with the goals of all project team members and stakeholders, providing enhanced planning and collaboration on the front end to ensure the appropriate mechanisms and processes are in place. Ideally, the goals of the owner and other project stakeholders are documented in an owner’s project requirements, which ASHRAE defines as:

“A written document that details the functional requirements of a project and the expectations of how it will be used and operated. This includes project and design goals, measurable performance criteria, budgets, schedules, success criteria, owner’s directives and supporting information.”

Examples of these requirements may include occupancy requirements, sustainability, energy efficiency, asset tagging, asset tracking and building performance criteria. From a BIM perspective, beginning with the end in mind means defining BIM authoring software selection, model integrity and level of development, as these choices impact the success of others and ultimately the overall success of the project.

A BIM execution plan that is shaped by the OPR will help guide the selection of modeling tools and define requirements, roles and responsibilities for each phase of the project. Some of the main elements in a BIM execution plan include:

  • Software and version.
  • Daylighting needs.
  • Asset/facility management expectations.
  • Collaboration/data exchange methods.
  • Level of development
  • Quality analysis/quality control process and requirements.

Software and its version are used by each trade to confirm compatibility to meet project requirements for linking and data exchange. The ability to have data shared between multiple modeling tools can have dramatic time-saving benefits. For instance, models developed in BIM tools can be used by some energy and daylighting tools without having to re-create building geometry. However, project team modelers must understand the flow of information and how the models and data they create are consumed downstream. If energy models are expected to import geometry from the BIM model, the modeler must comply with the guidelines and restrictions of the energy modeling software, otherwise the BIM geometry will not import accurately, negating the benefits of the software integration.

There is a clear time-saving synergy to simulate daylighting controls within energy simulation tools, but using that same tool to calculate other daylighting-related metrics — such as spatial daylight autonomy, annual sunlight exposure and daylight glare probability — may not always be the best choice. To provide timely and effective design assistance to architects, the best daylighting tools tend to provide cloud-based simulations and direct integration with BIM tools. The benefits of such daylighting software are significant, as the simulations take a fraction of the time of those on desktop-based software and changes to the primary BIM model are immediately reflected in the daylighting model. These daylighting tools also tend to have more detailed reporting features and are more forgiving of the precision with which the BIM model is created than in some energy modeling tools.

When an OPR includes asset/facility management requirements, it is important to understand what types of equipment will be tracked, classification schemes, naming conventions and what data related to each piece of equipment will be tracked. BIM authoring tools such as Revit, ArchiCAD and OpenBuildings Designer are designed to support model element classification systems such as Masterformat and Omniclass. Having all model elements (e.g., equipment, doors, etc.) developed with an embedded classification taxonomy allows the model elements (assets) and associated data to be organized and transferred across various software platforms while maintaining data structure and integrity.

Design firms must be prepared to support various classification systems as each owner’s asset management software is configured differently. Project stakeholders use classification systems for different reasons. For example, owners may organize and classify data for facility and asset management, while architects and engineers classify data to generate project specifications. Contractors may use classification systems for construction management, scheduling and cost estimates.

Collaboration/data exchange methods are documented to define method and frequency of file and data transfers. When project team members are dispersed across geographic locations and behind organizational firewalls, cloud-based collaboration tools such as Autodesk BIM 360 can bring the owner, design and construction teams into a single cloud-based environment, where permissions can be assigned based on roles and responsibilities to grant and limit access to data. This mitigates the need for file transfer and allows for streamlined collaboration.

The LOD matrix assigns model element authors and LOD for each phase of the project. This ensures the model evolves properly to meet project requirements. LOD originated from AIA Contract Document G202. Over time, other organizations have adopted LOD.

For example the National BIM Standard 2013 (version 3) definition:

“LOD is the degree to which the element’s geometry and attached information have been thought through — the degree to which project team members may rely on the information when using the model.”

It is important to confirm all required parameters and fields are embedded in model elements at model inception so required data can be input at the appropriate phase of the project. For example, serial number and warranty information are not available during design, but the design BIM author will provide these parameters for future population. Manufacturer/model may be populated in design, but will most likely change in the construction phase.

The quality process and requirements are defined to ensure routine checks are performed to ensure models are compliant with project requirements.

The BIM execution plan is often helpful in identifying challenges that must be overcome. Confirming all model elements have the correct classification assigned is rarely a simple task. For example, project requirements may require light fixtures with battery packs be tracked for maintenance. For efficiency purposes, the BIM content or families may share 3D geometry for normal and emergency fixtures with an option to provide graphics and tag to indicate emergency on construction documents.

Omniclass is defined at the component and family level, requiring two separate components be loaded into the model with different omniclass numbers so the emergency and normal fixtures are classified appropriately. Consequently, as more owners look to leverage technology and implement BIM on projects for asset and facility management, design firms may have to spend time planning and change processes to meet the owner requirements.

Using modeling software to demonstrate compliance

National and state energy codes, such as the International Energy Conservation Code, ASHRAE 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings and California’s Title 24 Building Energy Efficiency Standards, all follow a similar compliance structure in that they require a project meet all mandatory and prescriptive requirements unless applicable exceptions are taken. Alternatively, if a project is unable to meet or chooses not to meet one or more of these prescriptive requirements, a performance approach that uses building energy models is required.

Energy codes have become more stringent over the years, particularly in the past 10 years (see Figure 2). Anecdotally, as prescriptive code requirements get more strict and rigid, prescriptive approach compliance tools like COMCheck are being used less often and energy modeling tools are being used more often because the performance approach provides a more flexible and potentially cost-effective means of a design team achieving its vision for the project. In this approach, energy models of the proposed design and a hypothetical baseline design are created, and if the annual energy performance of the proposed design sufficiently surpasses the baseline, the project complies with code.

Other than for energy codes, energy modeling tools are used to show compliance with beyond-code rating systems such as the U.S. Green Building Council’s LEED rating system and utility incentives such as the California Savings by Design program. In these three cases, there is a particular set of rules that the energy model is expected to follow to show compliance. For example, Appendix G of ASHRAE 90.1-2016 provides detailed rules on how to create the proposed and baseline models to show improvements in energy performance. Consequently, any project attempting to comply with Appendix G must use modeling tools that incorporate specific features.

For example, ASHRAE 90.1 requires automatic daylight responsive lighting controls for most space types. When energy modeling is used to show compliance with the standard, automatic daylight controls must be either modeled directly within the energy simulation software or through schedule adjustments determined by a separate daylight analysis. This second option can be more tedious and time-consuming, so project teams seeking compliance should consider using a modeling tool that integrates both energy and daylight simulation within the same software.

Finally, creating the baseline model has little value beyond serving as a “measuring stick” for the proposed design, so a few energy modeling tools have developed features that incorporate portions of or all of the applicable rulesets to automatically generate the baseline model. For example, EnergyGauge Summit automatically generates a baseline building when used for Florida energy code compliance. Similarly, the California Building Energy Code Compliance software provides a similar function for California Title 24. The IES Virtual Environment modeling software also can aid in demonstrating compliance with these specific codes. Hopefully more software developers will add similar time-saving features to their tools to allow modelers to spend more time developing and comparing energy-efficient, cost-effective project alternatives for proposed designs, which is the true value of the energy modeling process.

Modeling software for comparative design assistance

The U.S. Department of Energy has compared the multifunctionality of building energy modeling tools to that of a Swiss Army knife, but perhaps one of its most valuable use cases is that of a comparative analysis tool. When used early and often during the design process, energy modeling software is one of the best tools available to project teams when designing energy efficient, cost-effective buildings. For instance, ASHRAE Standard 209: Energy Simulation Aided Design for Buildings Except Low-Rise Residential Buildings provides a methodology for ensuring energy simulation and analysis tools are used effectively throughout the design, construction and operations of a building.

Some energy modeling tools provide simplified methods for defining heating, ventilation and air conditioning equipment capacities and efficiencies as single values (i.e., tons of cooling, energy efficiency ratio) regardless of whether the equipment is operating at full- or part-load. This method may be sufficient for preliminary analyses of simple box modeling, massing and orientation or perhaps even load reduction analyses, but caution should be taken when using these same tools for other more advanced analyses, such as HVAC system analysis and optimization, code compliance or LEED certification. In these cases, it is important (and required for code and LEED) that the modeler choose tools that account for changes in the HVAC equipment’s rated capacity and efficiency during part-load operation using part-load performance curves.

While many modeling tools come pre-installed with default curves for various equipment such as chillers and packaged direct expansion air conditioners, it is more accurate to use product-specific performance curves, particularly to provide a meaningful comparison of products whose performance varies during part-load conditions.

At present, most HVAC manufacturers’ websites enable download of a product-specific 3D model to place into the BIM model. Similarly, most lighting manufacturers’ websites have product-specific photometric files (.ies) available for inclusion in daylight/lighting simulations. Unfortunately, HVAC manufacturers’ websites do not have product-specific performance curves available for direct import in energy model tools, leaving modelers with the time-consuming and tedious task of poring over manufacturers’ performance data tables or imploring the manufacturer representatives to fill out complex data table spreadsheets for the modeler.

Fortunately, there is hope, as ASHRAE Standard 205P: Representation of Performance Data for HVAC&R and Other Facility Equipment will define a standardized method for manufacturers to readily provide this information, leading to energy modeling software developers adding features to more easily import this data.

Can modeling tools predict the future?

British mathematician and professor of statistics George Box is credited with saying, “All models are wrong, but some are useful.” To apply this in the world of building design and construction, project teams must clearly understand the owner’s expectations for using modeling tools and express the results through meaningful conclusions that inform design decisions. To illustrate this, ASHRAE Standard 90.1 Appendix G includes an informative note that describes the limitations of this energy modeling method:

“Neither the proposed building performance nor the baseline building performance are predictions of actual energy consumption or costs for the proposed design after construction. Actual experience will differ from these calculations due to variations such as occupancy, building operation and maintenance, weather, energy use not covered by this procedure, changes in energy rates between design of the building and occupancy and the precision of the calculation tool.”

Consequently, energy modelers only following the rules of Appendix G should make it clear to the building owner that the results of the compliance model may not serve as accurate predictions for utility budgeting purposes without sufficiently wide uncertainty or safety factors. If an owner desires a design-phase energy model to provide such information, modelers should seek a deeper understanding of potential building operations and incorporate a greater degree of detail into the model. Finally, the results should be provided within a range of uncertainty through a modeling sensitivity analysis, considering potential variations in factors such as occupancy, operations schedule, weather, as well as equipment control and efficiency.

Modeling software tools provide an incredible opportunity for the industry to work toward a more optimized built environment, and it is exciting in the context of what the future holds. The industry is evolving and to ensure projects are optimized for the best outcomes, and all of the project stakeholders need to understand the capabilities, benefits and limitations of the software tools used for project design, construction and building operations.

Author Bio: Clark Denson is a senior building performance engineer for Smith Seckman Reid. Abe Morris is Smith Seckman Reid’s BIM program manager.