A distribution system is a network designed to receive, store, maintain, distribute, or control the flow of a distribution media. A common example is a heating hot water system that consists of a pump, a tank, and an interconnected piping system for distributing hot water to terminals. 

The group IfcDistributionSystem defines the occurrence of a specialized system for use within the context of building services or utilities for built facilities. Important functionalities for the description of a distribution system are derived from existing IFC entities:

• From IfcSystem it inherits the ability to couple the built system via IfcRelReferencedInSpatialStructure to one or more IfcSpatialElement subtypes as necessary.
• From IfcGroup it inherits the inverse attribute IsGroupedBy, pointing to the relationship class IfcRelAssignsToGroup. This allows the grouping of distribution elements (instances of IfcDistributionElement subtypes).
• From IfcObjectDefinition it inherits the inverse attribute IsDecomposedBy pointing to the relationship class IfcRelAggregates. It provides the hierarchy between the separate (partial) distribution systems. For example, an electrical main circuit may be aggregated into branch circuits.

The Property Sets for Objects concept template applies to this entity under Pset_DistributionSystemCommonname as shown in table below:

The Group Assignment concept template applies to this entity as shown in table below.

For the most common case of an IfcDistributionElement subtype containing ports of a particular PredefinedType that all belong to the same distribution system, the IfcDistributionElement is assigned to the IfcDistributionSystem via the IfcRelAssignsToGroup relationship, where IfcDistributionPort's are implied as part of the corresponding system based on their PredefinedType. An IfcDistributionElement may belong to multiple systems, however only one IfcDistributionSystem of a particular PredefinedType. 

• EXAMPLE: A gas-powered hot water heater may have three ports: GAS, DOMESTICCOLDWATER, and DOMESTICHOTWATER. The heater is a member of two systems (GAS and DOMESTICCOLDWATER), and hosts one system (DOMESTICHOTWATER) at the corresponding port.

The next image illustrates a distribution system for an electrical circuit.