In Revit we can specify a Schematic wall construction which is applied to all walls/vertical mass surfaces, determined to be an exterior wall by the energy analysis model (EAM) creation algorithm. While the list has a fairly large number of wall constructions to choose from, it is possible create custom selections. That is the topic of today's post.
For early energy analysis efforts, selecting a wall construction/assembly from a list is a lot easier than developing a Revit wall type with the proper layers, R-value, and thermal mass properties. The only catch is this is a single selection that applies to all exterior walls... which is almost always acceptable when doing early comparative analysis for passive strategies such as massing, WWR, orientation.
In this post I will show the same results, first from a Revit wall type with thermal assets, and then using the custom Schematic Type option within the Energy Settings dialog.
The specific wall construction used will be an R-50 passive house design. Similar to what we are using on a project right now, here at Lake|Flato.
Revit Wall Type Example, First
Let's see how this wall construction could be developed in Revit using a wall type with thermal assets. Per the image below, each material can have a Thermal Asset assigned, which is them multiplied by the thickness to derive the R-Value and Thermal Mass. Notice the total values here; R-52.0412 and Thermal Mass: 3.2022.
No, when we create the energy model, and select one of the analytical exterior wall surfaces, we see the same values in the Properties pane; R-52.0412 and Thermal Mass: 3.2022.
Now, lets look at how we can turn this same wall type into a custom option within the Energy Settings dialog, allowing use to apply this construction to any exterior wall in Revit for the sake of energy simulation.
GBXML Export
The first step is to export this sample project to GBxml from within Revit. Then, using Microsoft XML Editor, trim out everything except the main xml shell and the components related to our R-50 wall.
Next, you will find this file, C:\Program Files\Autodesk\Revit 2022\en-US\Constructions.xml and make a backup copy. Then, you will copy/paste the custom data, from above, into this file. If you mess up the xml file, the Schematic Types dialog will not work, and appear totally blank, as shown below.
But, when done correctly, you will see your new option in the list!
And, when you create the EAM the analytical exterior wall surfaces will have the same values. Keep in mind, this method will apply to any Revit wall type that Revit determines is an exterior wall, when using its voxel algorithm to create the EAM.
Here are both models within Insight... the results are the same, as expected.
In the run, we can see the BIM Setting (i.e. triangle) on the graph is correctly positioned to the far right. This is because this is a better performing wall than the built-in options, which you can see in the next image and discussion below.
For reference, here is a definition of the hard-wired wall types used within Insight; see image below and click here for more related info. These options are using a properly derated R-value.
Notice the following basic options:
- Uninsulated
- Two wood stud options; R-11.66 and R-36.75
- Two metal stud options: R-5.766 and R-17.126
- Two high mass options: R-4.02 and R-28.91
- One SIP: R-37.27
Fun stuff!
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