In my journey towards creating perfect energy models with BIM, I came across many online resources from the software companies. But the common theme among those resources were all the things you shouldn’t do in order to facilitate a clean integration. That practice of avoiding errors ended up being a game of whack a mole, where errors would always arise and you’d have to constantly mitigate them. That’s why I created a modeling structure that can be followed to mitigate 100% of your errors before they happen. Leaving you confident with your model delivery process and ensuring that you remain within your allocated time budget for the task at hand.
gbXML Energy Modeling Integration
The modeling structure is comprised of 5 fundamental modeling techniques that can be used to create a perfect energy integration model every time using Autodesk Revit, listed below are the 5 techniques.
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 exterior finish edge of the insulation, which would include all the area/volume for the interior conditioned spaces.
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.
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.
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.
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.
You can learn how to use the 5 modeling techniques from the proven BIM-integration workflow I developed through my online training program. There you’ll learn how to build perfect energy models every time, while saving you time, delivering results faster and managing your design updates by leveraging the power of BIM for energy modeling. You can start by downloading my free ebook on how to integrate BIM with energy modeling. Simply sign up to my newsletter and I’ll send you the ebook to help you get started with this innovative workflow