Offset Shells:  How to Fix and Avoid the Issue

Offset Shells: How to Fix and Avoid the Issue

A common issue encountered by developing eQuest users working on geometrically complex energy models is the matter of Offset Shells. After investing many hours developing shell and zone geometries through the eQuest wizards, you may find the resulting 3D view has one or more shells out of alignment from where you expected them to land, relative to each other.

This post is intended to help address how to fix Offset Shells when they arise. We’ll also cover some best practices to avoid this issue in the first place.

Part 1 – How to Fix Offset Shells

Here is an excerpt from a community support thread on the [equest-users] mailing list, which initiated this guide, and a copy of the model files attached alongside the prompt – you can pull down a copy to follow along with the fix:

I’m having an issue right now when drawing in the Wizard. I am working on a multi-story building and I am trying to line each floor up correctly when drawing the shells. I have selected to draw the floor directly above, and I align the CAD file with the background as it should be. However, when moving on to the Detailed Mode, the floors are offset and I cannot get them back to the way they were.

For this example, the 4th shell (as labeled) which is “in-alignment” with those above it is “correctly” positioned. The shells below are offset, and so appear out of alignment:

The goal is to shift the shells so they all perfectly overlay/underlay.  I’ve indicated in green an axis to which the corners of the 2nd and 3rd shells will be moved to.

First, navigate to wizards and open up the 3rd shell (“1st Floor”) custom footprint screen.  We want this to shift a moderate amount to align with the 4th shell (“2nd Floor”).  I have marked up this screenshot to draw attentions to the drop down dialog for background overlays:

If I select the “2nd Floor” shell in the indicated dropdown dialog, the selected shell footprint appears in blue within the vertex editor. Backgrounds selected in this manner can be “snapped” to for defining new vertices in the active shell, but are not selectable for editing.

Note the active (Cyan-colored) vertex. I can observe 2 vertices I’d like to align, as marked up.

From this state, you can create a new vertex from the existing/activated (cyan) vertex by clicking and dragging it. With polygon snapping turned on, drag a new vertex to where you want that point to be on the overlaid shell footprint.  When you finish, the information in the bottom of the Custom Building Footprint window will tell you exactly what that vertex’s shift is in X/Y dimensions:

Jot this information down for immediate reference.  Shell 3 Shift: dX = 2.1 , dY = -5.7

Rinse and repeat with the 2nd Shell (“Basement”), again overlaying the “correct” 4th shell (“2nd Floor”)

This case is a little more extreme. Shell 2 Shift: dX = 23.5 and dY = 1.8

Armed with this info, we can complete our efforts in the wizards and enter the detailed mode.  If you realize this sort of problem before you are finished with wizard-level edits, I would advise holding onto these shifting notes, and focusing on completing wizard efforts first. Once you are comfortably finished with wizards and have entered detailed mode edits, we can quickly revise the FLOOR (read: wizard shell) inputs for X and Y by the noted deltas:

In detailed mode, the X, Y, and Z coordinates for your wizard shells can be found and revised as inputs specific to each FLOOR. You can view and edit these values from the Building Shell tab, by either double clicking on a FLOOR in teh component tree, or else using the spreadsheet view tab below the “ribbon” along the top:

  • To recap:
    • Shell 2 Shift: dX = 23.5 and dY = 1.8
    • Shell 3 Shift: dX = 2.1 and dY = -5.7

Example: Wizard-generated X input for Shell 2 was -33.0. By adding dX = 23.5, we arrive at -9.5.

This screenshot illustrates entering the input changes as an algebraic expression, from the spreadsheet view. Expressions are not required, but being done to help drive home the process.

Finally, check your work in 3D view – looks pretty okay!

Part 2 – Best Practices to Avoid Offset Shells

When I have fairly complex shell layouts for a project, I have been able to consistently avoid the matter of Offset Shells through a few strategies:

  1. Before starting geometries in the wizards, make sure all your CAD references for multi-level and campus buildings are origin-aligned.  Put another way: If you were to copy one CAD reference onto another using the origin as a common reference point, the plans should should align with precision
  2. After defining the first shell, ensure the following are specified in the first screen for every subsequent shell:
    1. Position this shell:  via Coordinates
    2. Tick the box for Exact Site Coordinates
    3. Leave X and Y at 0.0 (matching the first shell’s default)
    4. Provide a Z value as needed to ensure the shell is the right height from the ground (relative to the first shell).  Note that below grade floors for a given shell’s Z-coordinate will extend downward, from that elevation, and so should be negative values.
  1. It’s never a bad idea to finish the wizards just to check your work in the 3D view – you can always hop back in to make corrections!

Hope this helps!

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