MEP System Implementation Guide

Quick Reference

Critical Warnings

• ALWAYS create ports on distribution elements BEFORE attempting to connect them. Elements without ports cannot participate in flow networks.
• ALWAYS create at least two ports per segment element (one inlet, one outlet). Segments are flow-through elements.
• NEVER connect two ports with the same flow direction. A SOURCE port MUST connect to a SINK port.
• NEVER use IfcDistributionSystem in IFC2X3 models. Use ifc_class="IfcSystem" for IFC2X3 compatibility.
• ALWAYS use ifcopenshell.api.run("system.add_system", ...) to create systems. NEVER use model.create_entity("IfcDistributionSystem") directly — it skips required relationship setup.
• ALWAYS assign elements to a system AFTER creating port connections. The system is a logical grouping; ports define the physical topology.
• NEVER assume system.remove_system deletes contained elements. It ONLY removes the system grouping; elements and their ports remain in the model.
• ALWAYS use ifcopenshell.api.run("root.create_entity", ...) for MEP elements, not model.create_entity(). The API sets GlobalId, ownership, and validates predefined types.
• ALWAYS pass products as a list to system.assign_system (v0.8+ convention).

Decision Tree: MEP Workflow