BaseQuantities Export MEP

[GCP]

Hello everyone,

We are currently modeling the electrical model using the MEP Designer in ArchiCAD 29.

When exporting the IFC file, the BaseQuantities (Qto Sets) of the elements (i.e. CableCarriersSegments) are not being exported even though this option is enabled in the IFC-Export settings.
Does anyone know why this might be happening? Is this an ArchiCAD bug, or am I possibly missing a detail? I know some Quantities (i.e. Weight) will no be exported but Length or CrossSectionArea should be exported.
I do not want to create the Qto sets manually with the property settings since it is not a Property Set.
Thank you in advance for your help.

[Laszlo Nagy]

Can I ask if this is in Ac27 or Ac29? In the text, you state Ac29, but in your signature, there is Ac27 indicated.

Also, can you tell exactly what IFC Properties are included in this IFC Base Quantities category? ( I am assuming you checked the "IFC Base Quantities" checkbox in the Data Conversion Dialog in the IFC Translator?)

By the way, there could indeed be some limitations here because all MEP elements in Archicad are created using library parts, mayn of which may not be solid elements, and as such, they may not have quantities that need solid geometry to be generated (like volume, for example).

[GCP]

Hello Laszlo,

please forgive my very late reponse. I am using AC29 (I havent updated my inforamtion since).
The BaseQantities that need to be included are those corresponding to the IFC4 ADD2 Data-Scheme. You asume well, I do have the check box activated in the IFC-Translator.
Your explanation about the library parts makes sense and explains why no BaseQuantities are exported.

Thank you.

[Laszlo Nagy]

@GCP,

I looked into this with my buddy Claude (AI), to see what's going on with this situation, if there's anything we can do about it. In short: Archicad 29 (tested on 29.2.1, same in 30) does not seem to export IFC base quantities for MEP elements. With "IFC Base Quantities" on and using IFC4 export, walls, doors and windows get their Qto_...BaseQuantities sets in the exported IFC file, but IfcDuctSegment and IfcPipeSegment (the ones I tested) get none.

I found a few limitations on the Archicad side:
- MEP cross-section data (size, wall thickness) are GDL array parameters, which the IFC Property Mapping cannot map to IFC properties.
- Ducts and pipes are exported as zero-thickness shells (the outer face of the sheet/tube) plus a second shell for the insulation, so wall thickness and material are not in the file.

Workaround: post-process the IFC with Python (IfcOpenShell). I tested this on straight ducts, pipes and bends, and it gave me correct results:
- Length = distance between the two connection ports (IfcDistributionPort), as IFC4 defines it.
- Gross cross-section and outer surface area from the exported shell; insulation thickness and volume from the difference between the two shells.
- Net cross-section and weight need wall thickness and material: define them as Archicad properties per MEP type and map them to an IFC property, or use defaults (e.g. EN 1057 wall thickness by outside diameter for copper pipes).
- Write the standard sets (Qto_DuctSegmentBaseQuantities, Qto_PipeSegmentBaseQuantities, etc.) into a new IFC file, using the official IFC4 templates.

Note: for pipes, IFC4 GrossWeight is the empty pipe and NetWeight includes the contained fluid.

Here is a test result for a single straight rectangular Duct Segment (I modified the default insulation thickness of 30mm to 100 mm), viewed in the IFCLite Viewer. Claude AI helped me with testing everything and generating the Python script. 

PS.: The summary was written by Claude.

[Laszlo Nagy]

Here is the zipped Python script that Claude created for me. If you open the script you will find some explanation at the beginning and instructions on how to use it. Please note that for this to work you will have to have Python installed on your computer.

If you use Claude Desktop you can continue working on it and you can ask it to help you develop it further if you need to because it doesn't handle all cases. It just handles the cases for the straight duct and pipe segments that I used for these tests.

For everything to work you would have to create those properties in the property manager. You would have to map them to IFC properties that you would have to create. You would also have to cover all possible cases, like pipes with different materials or different types of insulation materials, and so on and so on.