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Integrating Energy Modeling with BIM in the Design Process It’s safe to say that these days’ architects are most likely using a BIM tool for architectural design. But when it comes to collaborating with the engineer or energy modeler with BIM, the models are typically never done to accommodate their needs and a large amount of time gets wasted due to rework. There are ways to adapt a model to use them for energy modeling, but most of the time it’s easier to rebuild the geometry, which seems redundant given that we're duplicating existing work. The solution isn’t to find better ways at fixing these models, but to build these models up correctly from the beginning with energy modeling in mind. For that we're going to need a volumetric modeling process, which outlines the progression of model elements through a level of detail that is required to suit energy modeling and then allow the model to progress seamlessly into detailed architectural modeling. This way the energy modeler can get involved early and provide quick feedback using an effective design process. This ebook will walk you through the proven workflow that seamlessly integrates Building Information Models in the energy modeling process which facilitates collaboration and synergy within the design team. The workflow manages the building model’s information in a way that continuously adds value by refining the building using an iterative energy simulation process with a LEED compliant energy modeling tool. This saves you time by avoiding the rework that would otherwise be necessary from transitioning to this software.
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Level of Detail The key to make this work is to define specific Levels of Detail (LOD) for each model elements. There are five levels of detail from 100 through to 500 (conceptual to as-built). The LOD is used to define a modeling tasks for model element and assign it to a model element author (MEA) to reach an outcome during a certain phase or milestone. As the design develops, various elements of the model will progress from one LOD to the next at different rates. You can use a BIM Execution Plan to organize the definitions based on your project goals and phase outcomes.
Project Goals
Daylighting Passive Cooling Passive Solar Heating Energy Efficiency
Level of Detail
100 – Volumetric and approximate area 200 – Approximate geometry 300 – Precise geometry 400 – Fabrication 500 – As-built
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Architectural Design The architectural design industry is one that has the biggest adoption of BIM tools, but so far most of the architects are using BIM to serve their own requirements. Some design teams will use BIM to collaborate, but this has typically been around the coordination of the various disciplines for clash detection. This process requires a high amount of detail (LOD 300) in order to facilitate effective coordination. Clash detection is a great BIM goal to strive for during the detailed design stage, but it has been leading designers to start modeling elements at a LOD 300 for coordination. Starting your architectural design at this LOD 300 can be cumbersome to manage at an early stage, but more importantly it skips over the opportunity of integrating the model into an energy modeling application. What ends up happening here is the architect passes off this LOD 300 model to the energy modeler, who then needs to rebuild or adapt an identical model in order to perform an energy simulation. I can teach you how to build models quickly and effectively in order to seamlessly integrate with energy modeling, but the biggest opportunity to save time and speed up energy performance feedback is to build up the model from an LOD of 0 to 150, and then migrate to 300 once the integration link is created.
Intercepting the design process at the schematic design phase to create an energy model integration link.
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Integrate, Simulate and Iterate The benefits of using energy modeling at an early stage is to inform the design and make improvements towards an objectively more energy efficient building. A BIM-integrated energy modeling workflow allows you to make those modifications in Revit and then effectively add the new elements to the energy model and compare the differences. This process enables you drive down the building load and optimize energy efficiency. The energy linked model can be quickly edited by the architect since it is designed to be simple and volumetric, which means there isn't any excessive clutter when you're performing design options. Otherwise the detailed architectural model can be linked in the integration model and the changes can be tracked and updates using the specific modeling techniques outlined in the BIM Energy Modeling Online Course.
The iterative feedback loop allows you to build and analyze a model, then re-integrate the model updates to compare results; and then further optimize the energy model by leveraging the best of both environments (modeling and simulation).
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The 5 Modeling Techniques Building a Revit model to seamlessly integrate with energy modeling can be tricky if you aren't aware of the importing guidelines for gbXML files. That's why I created the 5 fundamental modeling techniques that can be used to create perfect energy models using BIM every time.
#1 Centerline When you’re not sure where to place your model element, use the centerline of the wall. But more specifically the gbXML export process is looking for the analytical line, which an invisible barrier created at the centerlines of your walls (except for floors/roofs). If you’re working with an architectural design model, first you either adapt this model or reference it for this new energy modeling specific model, then you’ll need to place the elements in relationship to the actual architectural elements. It is best to position the analytical wall on the interior finish edge of the insulation, which would include all the area/volume for the interior conditioned spaces.
#2 Simplicity If elements export their analytical surface according to their centerlines, then creating consistent element thicknesses throughout the model is key to ensure quality. I’d recommend using a round and even number on the small side, for example: 100mm or 2”. This makes it easy to offset to and from the centerline, and allows you to work within the architectural design frame.
Shaft walls are drawn flush all the way up.
Align the edge of floor/roof with the centerline of walls.
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#3 Precision The precision in which you place model elements is very important, sometimes being off by a few millimeters can cause an error in the integration. What I mean by off is when you’re laying out walls and you don’t snap them in place, they simply ‘look in the right spot’. Applications such as IES VE having healing algorithms that mitigate these small issues, but other tools may not. Although you can still make this work, this just means that some tools are more forgiving than others with the level of precision for your BIM project.
Connect curtain walls to their mid-points, as well as walls and space separation lines.
#4 Completeness The model elements are being recognized within the integration process (reading the gbXML file) by their space adjacencies. This means the software only knows that the wall is an exterior wall because the wall surface is exposed by the ‘outdoor’ and not another space. In order for this process to properly identify all the elements and convert them to their designation, spaces/rooms need to be completely enclosed within every volumetric area in the model.
Place plenum spaces on intermediary levels, such as level 1.9.
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#5 Hierarchy W Lastly if you want to remember how to execute each one of these fundamental modeling techniques, you’ll need to follow a structure. I start off by laying out the wall elements from the most rigid and complex to the most simple and flexible. I’ll start off with the exterior walls, then curtain walls, then core/shaft walls and interior walls. The process of building a model can still be organic, but when you intersect these walls together or need to modify certain areas, you can always come back to the hierarchy of importance. Following this structure will give you the confidence that you’re building up the model right the first time, instead of always second guessing yourself on how you’ve placed a certain element below/above… you will just know you’ve placed it right by following a system that works.
Geometry Integration Once the building geometry is successfully integrated, the thermal templates, building constructions and HVAC systems are assigned in order to start running an energy simulation. When merging new model elements, these steps are repeated using the same templates to generate comparative energy analysis results.
Importing a new/modified gbXML file flattens out the existing model (typical with all applications).
Once the gbXML file is imported, export it from IESVE to a Geometry file and then merge geometries.
TRACE can merge data from different gbXML files.
Space schedules can be exported from Revit and used to assign thermal templates.
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Energy Simulation The goal of using BIM for energy modeling is to run the energy simulation and use those results to drive the building load down. A managed BIM integration process allows you to incorporate design updates and maintain an accurate and up-to-date energy model for quick feedback.
Getting Started with Existing Models There are 2 ways you can approach an existing model. The first is by adapting the model using the modeling techniques discussed above, but I would only recommend this for advanced users or simple/small projects. If you’re new to the BIM-integration process or have a large/complex project, it can be faster and easier to start building up a new model, using the existing one as a reference.
Export the model to CAD (from Revit),
Build up each model element.
Import each plan/elevation into a new project,
The reason from importing ‘X-refs’ in Revit is for simplicity and clarity. The imported CAD files are small and won’t bog down your model and they are easy to hide/remove layers. It also makes it easy to place the wall in relationship to where the actual architectural wall is.
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BIM-Integrated Energy Modeling Workflow, Online Course If you want to avoid all your integration errors and receive best practices for each model element, you can sign up to our on-demand online course at www.trailloop.com (follow the link for a coupon code) and learn how to implement and master the BIM for Energy Modeling workflow.
This course will help you in the following area:
Save time from the production of energy models by avoiding rework,
Deliver quick feedback during an integrated design process and engage the engineering team earlier,
Receive LEED credit performance feedback earlier,
Perform design iterations by managing design updates,
Interoperate from Revit to IESVE, TRACE 700, OpenStudio, and other tools accepting gbXML integration.
This course will help you plan your energy analysis feedback to your team during each phase, while reporting on the performance of your project goals. You’ll be able to capture the positive gains of these building features and prepare accurate building loads in order to right size the systems through the design development phases.
Course details
33 learning modules
Certificate of completion for 8 Continuing Education hours
Lifetime access
5 hours of step-by-step video tutorials with paced downloadable exercises
30-day money back guarantee
About the Instructor Jean Carrière, CET, LEED Green Associate Jean is the President and Building Performance Technologist for Trailloop with extensive experience using building information modeling with building simulation applications. He has taught BIM and energy modeling at post-secondary institutions in Ottawa and Toronto, and has spoken at conferences throughout North America. His background is in architectural technology, Passive House science, and project management, with a focus on energy optimization within a BIM virtual environment.
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