Manually or automatically connect equipment to create a system, or assign equipment to existing systems.
This video demonstrates the following:
When you create a system in Revit MEP, you create a logical relationship between related elements in a project. For example, a supply air system might include duct, fittings, diffusers, and mechanical equipment. As you place elements in the model, they are assigned to a system classification based on their duct and/or pipe connectors. You can select a group of elements, specify a system type, and enter a system name.
For example, a supply diffuser is assigned to the Supply Air system classification. You can select a group of diffusers and assign them to the Supply Air system type. You can change the automatically generated system name, if desired. If the default system types don't meet your needs, you can create custom system types by duplicating and renaming an existing one.
Next, you select the equipment that provides the air supply for the system and is necessary for computing its pressure drop. In this example, a heat pump is added to the system. Notice that the heat pump has more than one system classification, and it is assigned to the same system as the diffusers: 3rd Floor Supply Air.
You can manually connect equipment and diffusers by placing the ductwork yourself, or you can use the Generate Layout tool to have ductwork added automatically.
Creating systems in Revit MEP enables you to have the layout in your design generated and sized automatically.