Random Analytical Surface Geometry

[Anonymous]

 Hi all, please help me out here. I have been struggling with this issue for a couple of weeks and I would absolutely appreciate it if you could help me understand why this is happening.

Traditionally we were building eggshell geometry from the building floorplan in SketchUp for energy analysis, but we are now trying to make a transition to using Revit gbXML export. There have been challenges.

As you see in the screenshots below, analytical spaces seem to be defined correctly, but analytical surfaces are plagued with strange intrusion bits - #1,2,3,5 are those. #4 is the contact face between the bathtub and the floor, and I don't understand why it should be turned into an "air gap". 

These problems seem universal - they happened in other building models of mine as well. I've attached the Revit file for your reference. If you could please help me understand, it would be an amazing help. Thanks in advance.

Seungyeon

[Anonymous]

Hello,

When you perform an energy analysis on a building model, the energy model shows analytical surfaces with gaps and jagged edges.

Issue: Small gaps and jagged edges make little or no difference to the analysis and exist primarily to improve analysis performance.

The areas of analytical surfaces used in the energy analysis are approximations of the surfaces of the model elements. The automatically generated energy model may contain gaps between analytical surfaces and jagged edges. These features of the energy model may look unusual, but they do not affect the accuracy of the results of the energy simulation.

In the Energy Settings dialog, the Analytical Surface Resolution option allows you to specify how precisely analytical surfaces match the surfaces of the building elements they represent. A smaller resolution value may align the analytical surface areas more closely with the surface areas of building elements. However, the change will result in an energy simulation that takes longer to complete but is not noticeably more accurate.

Solution: This issue does not require any action.

You can visit this url for more information : http://help.autodesk.com/view/RVT/2016/ENU/?guid=GUID-3BB183C2-8F74-4016-8094-D7046C3EC683

If my answer solved your problem , Please Kudo  and Accept as solution.

Thanks

[Anonymous]

Thanks for your reply Salah.

I understand what you mean, and it's a totally valid feedback for the post..But I realize I did a poor job at explaining my point.

Ultimately my goal is to import gbXML into a third party energy analysis tool, in my case OpenStudio plugin within SketchUp, and proceed with energy analysis without spending too much time manually fixing the shell geometry. If I were to do that, I need to export watertight geometry from Revit. I understand gbXML itself can handle "reasonably closed" geometry, but third party energy analysis tools will give fatal errors and quit the simulation when the geometry vertices do not coincide. My issue is that every time I export gbXML to SketchUp, my analytical surfaces are sloppy and nothing close to being watertight, making me spend too much time on manual repairs.

I have done some research and do all the "best practices" for the export, but the result is still sloppy. Here's the checklist:

- Turn on the “Areas and Volumes” option.
- Make columns non-room-bounding.
- Assign rooms to all areas, including lifts, risers, and voids.
- Ensure room limits are sufficient for each room to have a bounding element or another room at the top and bottom. (In general, set upper limit to floor above.)
- Remove all room separation lines that do not separate two areas.
- Ensure that two or more room-bounding walls have not been placed in parallel and in contact with each other. Do the same for floors and roofs.
- Resolve any warnings about overlapping walls and room separation lines.
- Resolve any issues with overlapping rooms.
- Change function of external walls and ground floors to “exterior”.
- Ensure all areas have a floor.
- Make half-height internal walls non-room bounding. If there are different rooms on either side of the wall use a room separation line to mark the boundary between them.
- Ensure that roof footprints are sufficient to cover the areas below.
- Where possible, replace bay windows with windows directly in the main wall.
- Use the “Automatically Imbed” option to place curtain glazing within walls instead of making holes in the wall’s profile

Below are some screenshots of gbXML export of the Revit Architecture Sample. I would love to know what I'm missing in order to get the watertight geometry that OpenStudio likes. I'm also very curious as to why the two narrow skylights appeared.

Maybe this is the limitation of Revit's analytical geometry and I'm asking for the impossible. But if anyone has a suggestion please share and help!

Best,

Seungyeon

[Ian_Molloy · Accepted solution]

Hi Seungyeon,

I think you did a good job describing the problem. In short different tools and workflows have different requirements and so its a very challenging topic to fully appreciate. 

Salah was 100% correct with respect to the information about the 'new' way we create an energy model (gbxml) from Revit. Your issue and experience sounds like it is related to the 'older' room/space based gbxml export. The new way is significantly more scalable, robust and accurate i.e. it works with real arch models from concept to detail. The old method is far more sensitive to the arch model and as a result you generally have to remodel the building or model a very specific way which somewhat defeats the purpose and is not very BIM like.

Unfortunately neither of these methods will guarantee you an airtight model, certainly not without remodeling the building. In simple terms this is mainly due to the fact that 1) real architectural models do not contain watertight conditions and so it is near impossible to solve it automatically and 2) energy simulation engines such as DOE2 and EnergyPlus do not actually require closed shells and it only accounts for a very small % geometric accuracy which is ultimately undone by manual remodeling.

We run these new models through EnergyPlus all the time so if its failing in OpenStudio you should likely talk to the OpenStudio team about it to see if they can fix it.

I hope this helps.

Regards,

Ian

[Anonymous]

Thank you for your kind input, Ian.

1) Could you explain to me the difference between the "new" and "old" way of gbXML exporting? Is the "new" way not a room/space based scheme? If it is indeed different from the way I did it, could you please explain to me the process?

2) In terms of the watertight geometry required by softwares, I think it's really the interfaces, in my case OpenStudio, that are fussy with non-closed shell. Energy Plus would be okay with it, but unless I'm going to bypass the interface, I'm always going to need watertight geometry, don't I?

Thanks in advance 🙂

Best,

Seungyeon

[Ian_Molloy]

You are very welcome Seungyeon.

The following is a brief explanation of both methods:

1. The 'old' way requires you to place rooms or spaces, set and check heights, sliver space tolerances and navigate a whole host of modeling dos and donts. The basic method essentially draws a 2D floor plan using the rooms/spaces and then extrudes them by heights and cuts them by room bounding elements. It actually works very well if you model VERY cleanly but its take a lot of learning and practice. In most models however you can get all kinds of strange artifacts that will cause the simulation to fail or worse, be wrong. 

The 'new' way does not require you to place rooms/spaces (but if present can use their data), it identifies 'analytical spaces' from wherever architectural elements essentially create separate volumes from 'reasonably enclosed' elements (not perfectly watertight - gaps and overlaps are actually expected). It works with conceptual massing all the way through to detailed elements, Furthermore you can actually visualize the energy model more easily in Revit (go visibility/graphics -> analytical model categories -> see analytical spaces and analytical surfaces.

The new energy model creation is pretty well documented here:

http://help.autodesk.com/view/RVT/2017/ENU/?guid=GUID-3242666F-501E-434C-A584-9DEE71BB632E

I also did a webinar just recently with one of our resellers and I cover it there too, demo starting at around 16 minutes in:

https://www.youtube.com/watch?v=KD8jCpSUwJY

As for item #2, yes each interface has its own requirements. Most expect you to model the building in that tool and some / few support import gbxml but all handle it differently with different tolerances. If you can determine where the failures are occuring someone on the OpenStudio development team may be able to help you.

Regards,

Ian