When Calculation is selected in the left panel, the right panel displays 3 tabs that control calculation methods for pipe pressure drop and flow.
For closed loop hydronic piping networks, Revit can analyze flow and pressure drop values for supply and return loops. To see the results when analysis is enabled in the model, select a pump and view the values in the Properties palette. For more information on setting the pump to display the results of the flow and pressure drop analysis, see Classification.
A network may contain a direct return loop or a reverse return loop.
Enable this option to perform analysis in a background process so you can continue working in the model. Clear the option to disable the analysis.
You can specify the calculation method used when calculating pipe pressure drop for straight segments. On the Pressure Drop tab, select a Calculation Method from the list. The options are: Colebrook Equation or Haaland Equation. The details of each calculation method are displayed in the description area.
You can specify the calculation method used when converting from fixture units to flow. On the Flow tab, select a Calculation Method from the list. The details of each calculation method are displayed in the description area. If third party calculation methods are available, they will display in the drop-list.