AirSelect3D Blog
AHU Bill of Materials + DXF/IFC Export: What Your BIM Team Needs
Ask an AHU manufacturer what their selection software exports and you will hear "a technical data sheet and a drawing." Ask the people downstream — procurement, the production planner, the BIM coordinator, the structural engineer — and every one of them is really asking for the same missing document: a bill of materials that agrees with the drawing.
The BOM is the export nobody writes into the specification and everybody ends up rebuilding by hand in Excel. That rebuild is where errors enter, because it is the one step in the chain that no software checks.
Three audiences, one list
A BOM for an air handling unit has to answer three unrelated questions from one set of lines:
- Procurement needs the supplier's own article number and quantity — not "EC plug fan, 900 mm", but the exact catalogue reference that can be dropped into a purchase order.
- Production needs the physical build: how many casing panels of what thickness, which frame profiles, how many access doors and on which side, the drain pan orientation.
- BIM and handover need the asset data: manufacturer, model, service classification, weight, and enough identity for a COBie sheet (BS 1192-4 / ISO 19650-4) to survive into the facility management system.
A BOM that serves only procurement is a purchase order. A BOM that serves only production is a cut list. The export has to be one list with enough columns to serve all three, because the moment they diverge into separate documents, they start disagreeing.
What each line has to carry
| Field | Why it matters | Common failure |
|---|---|---|
| Supplier article number | The only unambiguous identity | Generic description, "as per drawing" |
| Description + duty | Lets a reviewer sanity-check the selection | Description without the operating point |
| Quantity | Purchase and build | Counted once for the drawing, again for the BOM |
| Section / module reference | Ties the line to a physical position in the unit | No link back to geometry |
| Mass (kg) | Structural load, lifting plan, transport | Missing, or unit total only |
| Standard / class | ISO 16890 filter class, EN 1886 casing class | Marketing text instead of the class |
| Data source | Which supplier engine produced the number | Silent defaults presented as vendor data |
That last row is the one engineers underestimate. A filter line that reads "ePM1 60%, 592 × 592 × 292, 4 off, 47 Pa clean" is checkable. The same line with a rounded "50 Pa typical" cannot be reproduced by anyone — and the same discipline that governs a technical data sheet a consultant will accept governs the BOM: a number the supplier never published should print as absent with a reason, never as a plausible default.
The BOM and the geometry are the same object
Here is the structural point, and it is worth more than any column list: the bill of materials and the DXF are two views of one component chain. Every line in the BOM is a section in the unit, and every section in the unit occupies millimetres on the drawing.
If those two are generated from separate code paths — one walking the component list, one reading a stored casing length — they will drift. Not dramatically, and not immediately. A module gets an access spacer, the 3D model grows 400 mm, the drawing follows, and the BOM keeps the old panel count. Nobody notices until the fabricator is short two panels, or until a coordinator's clash check passes against a model whose weight is 180 kg lighter than the crate that arrives.
The fix is not more cross-checking. It is that the BOM, the DXF, the IFC and the data sheet all derive from the same live geometry, recomputed on every regeneration — the same single-source rule that makes a clean DXF/IFC hand-off trustworthy in the first place.
Weight is the line item that leaves the plant room
Operating mass is the one BOM field that gets read by someone who will never open your data sheet. The structural engineer sizes the plinth and the slab from it; the site team sizes the lift. It has to be a roll-up of real component masses — coil block with water charge, fan and motor, filter frames, casing panels, dampers — not a catalogue estimate for "AHU, 5 000 m³/h."
And it has to distinguish dry mass from operating mass. A four-row cooling coil holding 40–60 litres of water is 40–60 kg that the dry figure does not show, on a component that already sits at one end of the unit rather than at its centre of gravity.
An acceptance checklist
| Check | Pass criterion |
|---|---|
| Identity | Supplier article number on every purchased line |
| Traceability | Each line references its section in the unit |
| Consistency | BOM section count matches the DXF module count |
| Mass | Per-line masses, dry and operating, rolling up to the unit total |
| Provenance | Vendor-supplied values marked as such; gaps marked as gaps |
| Freshness | Regenerated after the last component change, alongside the drawing |
| Format | Machine-readable (CSV/XLSX), not a PDF table to retype |
Run the consistency check on your current tool this week: export the BOM and the DXF for one configured unit and count the sections in each. If the numbers differ, the two documents were built by two rules, and only one of them can be right.
AirSelect3D builds the parts list, the DXF, the IFC and the technical data sheet from the same computed geometry that drives its 3D viewer — so a swapped coil changes all four at once, or none of them.
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