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Building Energy Modeling — What do We Know?

Building Energy Modeling — What do We Know?

Posted: November 2, 2023 | Project Management

Read the full article in the November/December DCD Magazine

According to Wikipedia, energy modeling (or energy system modeling) is the process of building computer models of energy systems in order to analyze them. Such models often employ scenario analysis to investigate different assumptions about the technical and economic conditions at play. Outputs may include the system feasibility, greenhouse gas emissions, cumulative financial costs, natural resource use, and energy ef ficiency of the system under investigation.

A wide range of techniques are employed, and these models can be international, regional, national, municipal, or stand-alone in scope. Governments maintain national energy models for energy policy development, and energy models are usually intended to contribute variously to system operations, engineering design, or energy policy development.

Energy modeling has increased in importance as the need for climate change mitigation has grown in importance — the energy supply sector is the largest contributor to global greenhouse gas emissions. The IPCC Fifth Assessment Report of the United Nations Intergovernmental Panel on Climate Change posits that climate change mitigation will require a fundamental transformation of the energy supply system, including the substitution of unabated (not captured by CCS) fossil fuel conversion technologies by low-GHG alternatives. Most energy models are used for scenario analysis.

The National Renewable Energy Laboratory

The National Renewable Energy Laboratory (NREL) leads the development of physics-based modeling and simulation software tools to predict and analyze building system-level effects and performance. NREL is transforming energy through research, development, commercialization, and deployment of renewable energy and energy efficiency technologies.

Building energy modeling researchers develop multipurpose physics-based simulation software used in the prediction and analysis of building energy use. Software engines are used to support a variety of stakeholders and use cases, including:

• New building and retrofit design
• Code compliance
• Green building certification
• Qualification for tax and utility incentives
• Real-time building control and operation.

Building energy modeling software is also used in largescale analyses to inform policy decisions and help develop building energy codes. NREL is actively engaged in the areas of urban and district-scale modeling, standards, stock modeling and analysis, and building energy modeling for grid interactive efficient buildings, among others.

Featured Building Energy Modeling Software — NREL develops, maintains, and distributes EnergyPlus™, the U.S. Department of Energy’s state-of-the-art, open-source whole building energy simulation engine. EnergyPlus provides detailed and validated physics-based algorithms used by building designers and researchers to accurately model whole-building system energy performance. These models inform integrated design, early-stage and advanced R&D, standards, policy, and investment decision making.

NREL’s team also leads the development of OpenStudio®, a cross-platform suite of powerful and flexible open-source tools to support EnergyPlus, including the Radiance engine for advanced daylighting analysis. The platform includes a software development kit, scripting and workflow automation, prototype building models and standards-related model transformation tools, and a tool supporting large-scale simulation analyses.

Project Scope — NREL’s building energy modeling research is focused on:
• Continuing to update and produce a quality EnergyPlus simulation engine and OpenStudio platform
• Identifying and moving toward the next generation of building energy modeling simulation and analysis tools
• Developing and integrating building energy modeling and analysis tools to support new research and innovation in building science and energy efficiency.

About NREL: NREL focuses on creative answers to today’s energy challenges. From breakthroughs in fundamental science to new clean technologies to integrated energy systems that power our lives, NREL researchers are transforming the way the nation and the world use energy. For more information on NREL, see

The Department of Energy (DOE)

The DOE informs us that Whole-Building Energy Modeling (BEM) is a versatile, multipurpose tool that is used in new building and retrofit design, code compliance, green certification, qualification for tax credits and utility incentives, and real-time building control. BEM is also used in large scale analyses to develop building energy-efficiency codes and inform policy decisions. So what exactly is BEM? And what roles does the U.S. Department of Energy (DOE) play in the BEM industry and community?

What is BEM? — BEM is physics-based software simulation of building energy use. A BEM program takes as input a description of a building including geometry, construction materials, and lighting, HVAC, refrigeration, water heating, and renewable generation system configurations, component efficiencies, and control strategies. It also takes descriptions of the building’s use and operation including schedules for occupancy, lighting, plug-loads, and thermostat settings. A BEM program combines these inputs with information about local weather and uses physics equations to calculate thermal loads, system response to those loads, and resulting energy use, along with related metrics like occupant comfort and energy costs. BEM programs perform a full year of calculations on an hourly or shorter basis. They also account for system interactions like the ones between lighting and heating/cooling.

How is BEM Used? — BEM applications leverage its ability to answer questions that cannot be easily answered by other means. Major use cases include the following:

• Architectural Design: Architects use BEM to design energy-efficient buildings, specifically to inform quantitative trade-offs between up-front construction costs and operational energy costs. In many cases, BEM can reduce both energy costs and up-front construction costs.
• HVAC Design and Operation: Commercial building HVAC systems can be large and complex. BEM helps mechanical engineers design HVAC systems that meet building thermal loads efficiently. It also helps design and test control strategies for these systems.
• Building Performance Rating: BEM can be used to assess the inherent performance of a building while controlling for specific use and operation. Inherent performance rating is the basis for processes like code compliance, green certification, and financial incentives.
• Building Stock Analysis: BEM analysis on prototype models supports the development of energy codes and standards and helps organizations like utilities and local governments plan large scale energy-efficiency programs.

New use cases emerge as BEM becomes more powerful and easier to use.

DOE’s Goals and Roles — DOE has supported research, development, and deployment of BEM, and has itself been an active user of BEM, since the 1970s. Through the Building Technologies Office (BTO), DOE develops two significant BEM software packages, EnergyPlus™ and OpenStudio™ — both referenced previously in this article.

In addition to developing software, BTO funds the maintenance and expansion of ASHRAE Standard 140, a method of test for BEM engines. In 2016, it initiated a three year project to use national lab test facilities to generate high-resolution empirical data sets to validate selected BEM calculations at a finer granularity. Testing and validation improve BEM accuracy, help establish minimum BEM software requirements, and increase BEM stakeholder confidence.

Finally, BTO partners with organizations like the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE), the American Institute of Architects (AIA), and the International Building Performance Simulation Association (IBPSA) to support the BEM community. BTO sponsors hackathons, design competitions, and student travel to BEM conferences. It also collaboratively develops online resources for modelers like the UnmetHours peer-to-peer question-and-answer site and the AIA’s 2030 Commitment Design Data Exchange site.

These “core” activities are reviewed annually by outside stakeholders to ensure its portfolio continues to move industry forward. DOE supplements them with competitive awards that fund BEM research and deployment. These help DOE balance its portfolio, address market needs, and explore new directions.

For more information about BEM, visit