We recently covered ways to rethink your approach to modeling building performance in the Abundance Blog post, You May Want to Rethink Your Energy Model. In that post, we talked about using energy modeling as a design tool, and ASHRAE Standard 209 supports exactly that. Initially published in 2018, ASHRAE Standard 209 is an energy simulation-aided design standard that defines consistent energy modeling procedures to quantify the impact of design decisions as they are being made. In this post, we will cover our takeaways from ASHRAE Standard 209 to help make the case for changing up the typical approach to energy modeling.

The Status Quo

To understand why you need modeling as part of the design process, you must first understand the status quo approach, which is to produce a model no earlier than Design Development (DD). With this approach, the model is created using the existing design and system selection, with only minor improvements available to the project team because so much of the design is already set. This ineffective method of modeling does not offer the ownership and project teams the same opportunities to reap the greatest benefits from the energy model. As illustrated in Fig. 1 below, the greatest opportunity to impact building performance is at the project start, which diminishes over time as the design progresses.

And at the same time, the effort required to implement these increasingly limited performance improvements only grows with time. Simply put, to get the greatest impact with the least amount of effort, start energy modeling early.

Figure 1. Relationship Between Time & Level of Effort/Performance, Jason Glazer & Erik Kolderup, IPBSA – USA Summer Meeting St. Louis

Recognizing the common practice of starting energy modeling late in the project, and the practice’s tendency to inhibit improved building performance, ASHRAE Standard 209-2018 was created.

Before we get into the standard, it’s important to note that while ASHRAE Standard 209 refers to energy efficiency features/tradeoffs as “Energy Efficiency Measures”, or EEM for short, here we will refer to these as Energy Conservation Measures or ECMs. This better aligns with the terminology used by our building performance team, although both terms are used interchangeably throughout the industry.

ASHRAE Standard 209-2018

ASHRAE Standard 209-2018 was developed to help project stakeholders and designers get the most value out of energy modeling, while also defining best practices to achieve performance objectives. While the Standard includes some general conditions, it does not require absolute compliance and can be tailored to suit the needs of any project. The Standard was created with high-performance building programs like LEED or Green Globes in mind and is recommended for used by architects and owners when defining a project’s scope of work to guarantee a uniform and effective approach to energy modeling.

Energy Modeling Cycles

The ASHRAE 209-2018 standard is comprised of a set of general requirements and eleven modeling “cycles”. Of the eleven cycles, seven coincide with the design phase, three with construction, and one with post-occupancy. Each cycle has its own set of unique modeling goals and analysis approach, based on the applicable project phase. Only two cycles are required by the Standard (Cycle #3 and at least one other design phase cycle), and the intent is to incorporate additional cycles for the project’s success as necessary. The cycles defined by the Standard are:

Design phase
    • Modeling Cycle #1 – Simple Box Modeling (Recommended)
    • Modeling Cycle #2 – Conceptual Design Modeling (Recommended)
    • Modeling Cycle #3 – Load Reduction Modeling (Required)
    • Modeling Cycle #4 – HVAC System Selection Modeling (Recommended)
    • Modeling Cycle #5 – Design Refinement (Recommended)
    • Modeling Cycle #6 – Design Integration & Optimization (Recommended)
    • Modeling Cycle #7 – Energy Simulation-Aided Value Engineering (Recommended)
Construction phase
    • Modeling Cycle #8 – As-Designed Energy Performance
    • Modeling Cycle #9 – Change Orders
    • Modeling Cycle #10 – As-Built Energy Performance
Post-occupancy phase
    • Modeling Cycle #11 – Post-Occupancy Energy Performance Comparison
  • Project-specific data should be used in place of assumptions or simulation software defaults when it is available.
  • A dedicated energy charrette is strongly recommended, and in some cases required, as part of the goal-setting process and integrative project team approach.
  • A detailed Owners Project Requirements (OPR) document is strongly recommended, and in some cases required, and should clearly define energy performance and sustainability goals, financial criteria for decision making, and individual system performance goals.
  • Include cost information when evaluating energy measure alternatives to ensure short-term and long term-costs are considered. Construction costs are also necessary to better identify cost savings realized from the downsizing or elimination of building systems (i.e. heating and cooling systems).
  • A thorough quality assurance process must be implemented to review input and output data from the model after each cycle.

As our approaches to sustainable, high-performance buildings evolve, so should our process of designing, constructing, and operating these buildings. Energy modeling is a critical component of the design process, and ASHRAE Standard 209-2018 is an excellent tool to help project teams get the most value out of their energy model and energy consultant.

Are you implementing ASHRAE Standard 209-2018 on your projects? Are you interested in learning more? We’d love to hear from you!


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