In this article we will cover how to take an architectural model that is built for rendering purposes in SketchUp, and simplify it down to the essentials required for analysis.
For an explanation of why you are simplifying the model, see this article: Simplicity vs. Complexity -- Modeling for Energy & Daylighting Analysis in Sefaira. I highly recommend that those who are new to building performance simulation or energy modeling read this article, but the short of it is: an architectural model is typically outfitted with every detail of the building’s design with the goal of producing realistic orthographics and renderings. An energy model, however, only needs a few pieces of geometry to represent the building's performance.
Here's a video with best practices for deconstructing a detailed architectural model into an energy model. See below for step-by-step written instructions.
1. Start by setting up Sefaira scenes & layers.
Why? This will help you to keep organized throughout the modeling process by separating your Sefaira geometry from the rest of the model.
- Create a Sefaira specific layer and make it the default (Note:make sure all your detailed building elements are grouped on their respective layers.)
- Create a scene with all the detailed model elements visible
- Create a Sefaira scene
2. Next, we'll use the section plane tool to cut a cross-section at the ground floor. We want to extract the 2-dimensional lines that define the perimeter of our building.
Why? You will eventually build the ground floor surface of your energy model from the 2D lines you've pulled out of the architectural model.
3. Create a surface and extrude to the height of the building.
Why? You are starting to create the overall volume of your building.
4. Model the insets or extrusions on the building’s facade and roof. Ignore small extrusions like mullions or columns; any geometry on the building’s envelope that has a dimension smaller than ~1.5 feet can be ignored.
Why? The goal is to draw the geometry that has a big impact on the building's total volume, as well as the amount of square footage of the envelope that separates the conditioned space from the outside air. Small details will have little to no impact, and are better left out. Remember, KISS.
5. Copy up the bottom floor surface the distance of the floor-to-floor height. Adjust floor surfaces as the cross-sectional area of the exterior envelope varies.
Why? This is a simple way to build the internal floor geometry, but it's not the only way. If your floor geometry varies greatly at each level, then it may be best to draw over your architectural model.
Note in the sectional view how all building elements are modeled as thin surfaces.
6. Cut a plan view at each floor (via the process outlined in Step 2.: place the section tool at the desired location --> right-click --> create group from slice) and use the 2D lines to draw interior walls.
Why? This is another modeling tip for easily creating interior geometry, but again, it's not the only way.
Note: make sure to tag interior walls by right-clicking on the surface → Sefaira → tag as internal wall.
Pro tip: you can select an entire group or component and tag entities, rather than tagging each individual surface. If you group your internal walls as you are building them, you can select the entire group and tag as internal.
7. With the detailed model turned on in the view, draw in the windows and any building elements that provide shading (e.g. overhangs, balconies, louver systems, eaves).
Why? We are adding information about the type of materials that the envelope is comprised of. Windows have different insulation properties than walls and also let in light, so we should distinguish what is solid in the model vs. what is glazed. Shading elements will affect the solar heat gain in our building, and therefore should also be included. Drawing over the architectural model to determine approximate location and size of the windows and shading is, yet again, just one way to achieve the end result.
Note: make sure to tag windows as glazing, and shading elements as shading by right-clicking on the surface → Sefaira → tag as shading.
8. Create context buildings by selecting the roof surfaces and extruding down to the ground.
Why? The context geometry will most likely provide some sort of shading for your building, consequently affecting the solar heat gain in the space.
Note: make sure to tag context as shading by right-clicking on the surface → Sefaira → tag as shading.
9. Use Sefaira’s entity palette (click 'Show Entity Types') to ensure that all the building’s elements are assigned properly and that all faces are oriented with the proper normals, so that no red faces are showing.
Why? Up to this point you've built the building geometry properly, and now you want to make sure that each surface is interpreted as the appropriate building element. You want to make sure that your roofs are tagged as roofs, your floors as floors, glazing as glazing, etc. Sefaira's entity palette will show you how many surfaces are within each model category. You can change any surface's entity type by right-clicking on the surface --> Sefaira --> tag as....
Note: make sure to tag all geometry from your detailed model as Ignore! If your detailed model exceeds 15,000 planes, we recommend that you delete it from the Sefaira energy + daylight model altogether. This will significantly decrease the weight of your Sefaira model and ensure that the analysis is speedy.
Your Sefaira model should have as few planes as possible. You can check the total plane count by navigating to 'Model Info' and checking 'Statistics.'
Pro tip: If your architectural model and Sefaira model are in the same file, group your Sefaira model and enter into that group. Now when you look at model statistics with 'show nested components' deselected, you will see statistic about quantity of planes in just that group.
That's it, you're done! Happy Analyzing.
Here are some additional links that will help in understanding how to set up your energy model.