MEP Pressure Drop and Duct & Pipe System Calculations

Let's have a look at the native Pressure Drop calculation methods that takes place in Revit. 

For ducting, we can choose between 3 calculation methods:

1. Altshul-Tsal Equation

2. Colebrook Equation

3. Haaland Equation

It is possible to use a different calculation method for straight duct segment pressure drops, through the API, or alternatively, to download a calculation method from a third-party developer.

The Altshul-Tsal Equation provides a pressure drop for, as an example, the 225x225 duct segment, of 3.85 Pa

The Colebrook Equation provides a pressure drop for the 225x225 duct segment, of 3.81 Pa

The Haaland Equation provides a pressure drop for the 225x225 duct segment, of 3.65 Pa

We also have the ability to control what calculations will take place per duct system. When entering the type properties of a duct system, one will be able to choose between:

•       All: Both Flow and Pressure Drop calculations will take place and ducting can be sized automatically
•       Flow only – Only Flow calculations will take place and ducting can be sized automatically
•       None – No Flow or Pressure Drop calculations will take place and ducting can be sized automatically
•       Performance – No Flow or Pressure Drop calculations will take place and ducting cannot be sized automatically

Performance is a new addition to the available duct systems calculation property.  My best bet would be that this was added for large projects where considerable lag is experienced when Revit is running its calculations in the background. This will be a good option to choose when ducting is being modelled. Flow and Pressure Drop calculations can then be activated at a later stage for auto-sizing purposes. Thus: When modelling - Performance, and when designing/validating – All.

Calculations: All – Both Flow and Pressure Drop calculations will take place and ducting can be sized automatically

Flow only – Only Flow calculations will take place and ducting can be sized automatically

None – No Flow or Pressure Drop calculations will take place and ducting can be sized automatically

Performance – No Flow or Pressure Drop calculations will take place and ducting cannot be sized automatically