Energy Modeling

What is Energy Modeling?

Energy modeling simulates a building’s energy use, helping to inform design decisions or diagnose underperformance. Model inputs include building geometry, envelope data, including construction materials specifications, mechanical systems data and projected or actual building use and operations including occupancy, lighting, and HVAC schedules.^[1] These inputs are combined with local weather data to simulate cost-effective building designs with optimized energy performance.

Figure 1 – Three-dimensional model of the New Jersey Meadowlands Commission Center for Environmental & Science Education (Source: Rutgers Center for Green Building).

How to Implement Energy Modeling

Implementing energy modeling into a new commercial building project requires an appropriately skilled team  (see Integrated Design Process).  The architect/designer/builder should be knowledgeable about energy-efficient and green building practices. A ‘Certified Energy Professional’ can evaluate or rate the building design using energy modeling software and recommend improvements.^[2]

The necessary steps for implementing a building energy model comprise the following. First, create a model of the baseline building, which represents the building as designed (typically by some combination of the project architect and engineer).  Next, manipulate specific variables to simulate alternate scenarios of building energy performance. Many national green building certification programs require new buildings to meet or exceed a specified level of energy performance and correspondingly require energy model documentation.

For example, LEED v4 for Building Design and Construction requires project teams electing to take the performance option to demonstrate minimum energy performance through a whole-building energy simulation that compares proposed building performance to a baseline building that uses ANSI/ASHRAE/IESNA Standard 90.1–2010, Appendix G, with errata.^[3]

There are several energy modeling software applications available on the market. The US Department of Energy, through its Building Technologies Office (BTO), offers two types of energy modeling programs, which are publicly available free of charge: EnergyPlus, and OpenStudio, which uses EnergyPlus for energy modeling and Radiance,for advanced daylight analysis.

The US DOE Commercial Buildings Program website lists additional analysis tools.

Example

NJ Meadowlands Commission Center for Environmental & Science Education (CESE)

For this study, the Rutgers Center for Green Building (RCGB) utilized DesignBuilder and EnergyPlus to simulate the structure and functioning of the New Jersey Meadowland Commission (NJMC) building. DesignBuilder was used to construct a three-dimensional architectural and engineering model. This model contained information on all of the materials and systems included in the actual building, to the extent that the model permitted. Once this computer model was constructed, EnergyPlus was used to simulate the weather conditions, energy use, heating and cooling needs, occupant activities, and all other pertinent variables to create a virtual model of the building’s structure and activity that is as close to that of the real building as possible. The output from this model provided an estimate of the annual energy consumption by system as well as the heat loss/gain throughout the building. After completing the base model according to the building as designed, the study team ran multiple simulations while substituting in different equipment and materials.

Benefits

Energy modeling facilitates comparison of building design alternatives and assists in determining the most cost-effective path for meeting energy performance goals over the life cycle of the building. Energy modeling also supports green building certification and code compliance. When used early in the design process, energy modeling reduces redesigns and subsequent delays later in the project – a significant benefit.^[4] HOK, an architectural and engineering firm, tracked how quickly modeling pays for itself in a variety of commercial building types over a multi-year study and found that the energy modeling payback is typically 1-2 months.^[5]

Costs

For large buildings, energy modeling costs can run from $30,000 to $200,000, depending on the level of analysis, and design complexity including choice of energy efficiency strategies.^[6]  The upfront cost of an energy model may be spread out across the life-cycle of the building or even during only the design phase, as noted above.

Resiliency

Energy modeling identifies and evaluates green building strategies that enhance building resiliency. While energy modeling typically uses historical weather data, specific, regional, and forward-looking climate data can be used in energy models to inform resilient building design.^[7] For example, in the NJMC study mentioned above, the team ran an energy model scenario according to low-emissions mid-century predictions of climate change developed by the Northeast Climate Impacts Assessment (NECIA).^[8]

Energy modeling that takes into account resiliency objectives may include specific design inputs to address increasing heat, more intense precipitation, or rising sea levels. The NYC Mayor’s Office of Resiliency and Recovery’s Climate Resiliency Design Guidelines provides resilient design strategies including, cooling and shading buildings, improving the efficiency of building envelopes, utilizing green roofs and landscape elements, planning for increased failure or reduced efficiency of electrical or mechanical systems, and providing passive solar cooling and ventilation features.^[9]

^[1] US DOE Office of Energy Efficiency and Renewable Energy – Emerging Technologies. 2018. “About Building Energy Modeling.” https://www.energy.gov/eere/buildings/about-building-energy-modeling (accessed June 11, 2018).

^[2] ASHRAE Building Energy Modeling (BEM) Professional Certification https://www.ashrae.org/professional-development/ashrae-certification/certification-types/bemp-building-energy-modeling-professional-certification (accessed June 13, 2018).

^[3] USGBC – LEED v4 for Building Design and Construction. Updated April 6, 2018. EA Prerequisite: Minimum Energy Performance, Page 66. https://www.usgbc.org/resources/leed-v4-building-design-and-construction-current-version (accessed June 13, 2018).

^[4] Amber Wood and John Lisman. 2017. “The Benefits of Early Stage Energy Modeling.” USGBC-Colorado. https://www.usgbc.org/articles/benefits-earlystage-energy-modeling-usgbc-colorado (accessed June 12, 2018).

^[5] Roth, Amir. 2016. “The Shockingly Short Payback of Energy Modeling.” US DOE Buildings. https://www.energy.gov/eere/buildings/articles/shockingly-short-payback-energy-modeling (accessed June 12, 2018).

^[6] Roth, Amir (2016). “The Shockingly Short Payback of Energy Modeling.” US DOE. Office of Energy Efficiency and Renewable Energy https://www.energy.gov/eere/buildings/articles/shockingly-short-payback-energy-modeling (accessed June 12, 2018).

^[7] NYC Mayor’s Office of Recovery and Resiliency. April 2018. Climate Resiliency Design Guidelines. Version 2.0. Page 4. http://www1.nyc.gov/assets/orr/pdf/NYC_Climate_Resiliency_Design_Guidelines_v2-0.pdf (accessed June 11, 2018).

^[8] Krogmann, U., Minderman, N., Senick, J. and Andrews, C.J. “Life-Cycle Assessment of the New Jersey Meadowlands Commission Center for Environmental and Scientific Education Building.” 2008. Prepared by Rutgers Center for Green Building for New Jersey Meadowland Commission. At http://rcgb.rutgers.edu/wp-content/uploads/2018/06/LCC-Final-Report-5-21-08.pdf (accessed June 19, 2018).

^[9] NYC Mayor’s Office of Recovery and Resiliency. April 2018. Climate Resiliency Design Guidelines. Version 2.0. Page 9-19. http://www1.nyc.gov/assets/orr/pdf/NYC_Climate_Resiliency_Design_Guidelines_v2-0.pdf (accessed June 11, 2018).