Who this is for: Architects, engineers, and analysts who want to look under the hood of their modeling and energy analysis tools.
Takeaway: “Energy Analysis Models” (EAM) are used in whole building energy simulations, and gbXML is a common format for representing these models. Translating from a Building Information Model (BIM) to an Energy Analysis Model has historically been an error-prone and time-consuming process. Knowing how an EAM is built can help improve the quality of your analysis. In Autodesk’s new BPA Help, we’ve included some fundamentals on Energy Analysis Model geometry that will be of interest to both novices and experts. Start diving in here.
By: Ian Molloy, Senior Product Manager, Autodesk Building Performance Analysis;
and Adam Menter, Sustainability Education Program Manager
There are many different paths between Building Information Modeling (BIM) and Building Performance Analysis Modeling (BPA). But no matter what tools you use, getting a valid Energy Analysis Model (EAM) for whole building energy analysis is a vitally important step.
[AU PRESO: Ian Molloy will cover some of this material, and more, at his Autodesk University presentation tomorrow, Tuesday 12/3/13 from 8-9:30am: AB2260 – No Pain All Gain: Autodesk® Revit® 2014 Automatic Energy Analytical Model Creation and Analysis. Check it out!]
What is an EAM?
If you were to ask an energy analyst to describe what an EAM is in just one word the most likely response would be: geometry. Of course this is true, but, when virtually every building professional works with ‘geometry’ in some way, what is it that’s so special about the geometry of an EAM?
Basically, an Energy Analysis Model (EAM) is an abstraction of a building’s overall form and layout into a ‘computational network’ that can capture all of the key paths and processes of heat transfer throughout the building effectively.
EAM and Geometry Modeling
This post will focus on the ‘modeling’ component of whole building energy analysis. Put more precisely: we will focus on the geometric data that is contained in the gbXML schema and drives whole building energy simulations, such as that provided by Revit or Vasari through Green Building Studio – which uses DOE 2.2.
This geometry is made up of Spaces, Surfaces, and Zones – defined as follows:
- Spaces are discrete volumes (masses really) of air that experience heat loss or gain due to internal processes like occupancy, lighting, equipment and HVAC as well as exchange heat with other Spaces and the exterior environment.
- Surfaces are the paths of heat transfer to or from each Space, including between interior spaces and the exterior environment.
- Zones are groups of Spaces used to establish some commonality between those spaces – such as having the same orientation, the same function, or being served by the same HVAC system.
As you can see, EAMs are not inherently all that complex. They follow a certain set of basic concepts and only have so many parts and properties to them. The key challenge with EAMs is and has always been creating them with sufficient reliability both easily and consistently.
If you’ve had any past experience with energy simulation, either directly or indirectly, you will also likely have come across terms such as the ‘Zoning’, ‘Blocking’ or ‘Chunking’ of an EAM. Unfortunately, all of these terms can mean different things to different people. This creates a significant grey area that makes it difficult to build trust in, and scale the use of, energy analysis tools. This post is part of an effort to provide better information, and build a more precise common language, around the use of energy analysis tools.
In the Autodesk BPA Help, you can learn the basics of Spaces, Surfaces, and Zones. A few interesting takeaways include:
- Spaces don’t always need to be divided by rooms in the building – but this often does makes sense analytically. It often makes sense to further subdivide large rooms into multiple spaces when you’re modeling large rooms like open-plan offices and atria.
- The shape of spaces doesn’t matter (and isn’t accounted for). The orientation, adjacency, and type of Surfaces is what dictates heat transfer behavior.
- There can be a difference between Zones (combining spaces in gbXML code) and “zoning” (creating simplified geometry that combines rooms)
- Despite conventional wisdom, your Energy Analysis Models don’t need to be “airtight” to get valid simulation results.
Dynamic Energy Simulation Fundamentals
If you’re newer to building energy modeling, you may want to back up and learn how whole building energy simulation works.
Buildings are complex systems. Good analysis accounts for the dynamic interrelationship of a variety of factors over time. Some of these factors are: form, materials, systems, building use, and climate.
LEARN MORE at Autodesk BPA Help about the anatomy of a dynamic energy simulation with a series of schematic diagrams that build on each other.
Revit 2014, Analytical Volumes, and EAM Creation
Revit 2014 now offers an entirely new way to create an EAM automatically from Revit building elements. See our recent Revit 2014 Release News, Energy Analysis using Revit Building elements and Revit 2014 Update Release 1 blog posts for more information.
We’re very excited about this new feature for a variety of reasons. Hopefully the information in this post will help you more fully understand and appreciate it. As we continue to build Autodesk BPA Help, we will cover more on the creation of EAMs with Revit and Vasari.
Tell us what you think:
What do you think of this description of what an EAM is? Has anything been missed, overlooked or does something need clarification? What have been your experiences with EAM creation, good and bad?