Collections allow you to specify a number of Envelope variables on a per-facade basis, and also allows you to use these facade-level variables for Strategies and Response Curves. For example, you can use Collections to add shading to a particular facade of a building, to specify different Glazing U-factors on different facades, or to study glazing ratios on each facade independently.
A "Collection" is a group of planes in a building model. By default, The web application creates four standard pre-defined wall collections.
1. Collections Overview
Collections are available for: Facade Glazing, Walls, Override Window to Wall Ratio in the Envelope tab; and Software Shading in the Shading tab.
2. How to Use Collections
By default, collections are hidden—with the exception of Override Facade or Roof Glazing. When Collections are hidden, adjusting a variable adjusts it for all planes in your model. For instance, if you adjust the Facade Glazing U-Factor, you are adjusting the U-Factor of all glazing across all facades. To enable Collections, click on the Collections toggle, tucked underneath the title banner. Now you can edit each collection independently. For instance, you could adjust the Glazing U-Factor only for East or West facing facades.
A Note on Building Orientation
Collections are groups of specific planes in your model. If you change the building orientation using “Building Rotation” control, the Collections will also rotate. For instance, let’s say that Facade C is, by default, the South-facing facade. If you add a Horizontal Projection to the glazing on Facade C, and then rotate the building 90 degrees, Facade C (and its shading) now faces West.
3. Modules with an ON/OFF Toggle
Some modules have both an on/off toggle and Collections functionality. These modules can be turned on and off either for all collections, or on a per-collection basis.
For instance, if you “Turn on” Override Facade Glazing when collections are hidden, you are overriding the glazing for all facades in your model. But if you only want to override glazing for one facade, you can show Collections, then “Turn on” Override Facade Glazing only for that facade. The other facades will retain the glazing from the building model.
TIP: You can create strategies when a module is turned OFF. A module does not have to be “on” in order to add a variable to a strategy. This means you can investigate strategies like Brise Soleil and Glazing % without editing your baseline case.
4. How Collections are Determined
Sefaira automatically assigns each plane in your SketchUp model to a collection, based on plane normal orientation in the original model. While this approach is generally reliable, there are some potential pitfalls: normal orientation must be correct, and certain types of geometry may be misinterpreted.
In Sefaira Web App, each plane has an orientation that governs which side is inside or outside the building. In SketchUp, the orientation of the plane is described by its normal. Normals must face outward in order for each plane to be assigned to the appropriate collection. You can easily correct an inverted normal in SketchUp by right-clocking on the plane and selecting “Reverse Faces” (fig. 3). Sefaira for SketchUp can help quickly identify normals that are facing the wrong direction.
A Note on “Backwards” Geometry
In some cases “backwards facing” geometry can lead to counter-intuitive collections. A good example is the case of roof overhangs (eaves). In this case, the Web App will associate the exposed overhang plane with the opposite roof collection (fig. 4). This may produce minor inaccuracies in results. For example, the total area of Roof A will be read sightly larger because it includes the area of the eaves under roof C. When creating strategies associated with the roof, for example Roof Intergrated PV, it is worth keeping in mind the roof size increase. Alternatively, you can change the plane type to “ignore” using the SketchUp Plugin, which will remove it from all calculations.