To understand how the flow configuration for components work, please consult the following webpage:
What we learn is that the flow configuration is function setting the property in the Revit family connector element.
In the most common scenario, a heating and cooling loads analysis on the spaces and zones in Revit results in a certain quantity of air that needs to be supplied to each space based on the supply temperature of the system (zone). In this situation where the downstream components define how much air needs to flow in the worst-case scenario, we assign the flow configuration of the diffusers as Preset. In this case, for air handling equipment, the value is set to calculate. This means the connector assumes the value of the sum (aggregate) of all the downstream connectors.
When the air handling equipment supply flow is known, then the connectors are set to System. A flow Factor allocates the percentage of the system (total) flow to each component. The factor must be between 0 and 1 and the total for the downstream system components should equal one. In this way, the system forces the diffusers to accept a value as a percentage of the flow from the air handling equipment. This second scenario typically the case when the design was made outside of Revit.
Duct sizing can be done as per normal for both scenarios.
If you need help adopting Revit or BIM in your practice, please contact Micrographics so we may be of assistance.