Pressure Drop CalculationI got an call from a client last week asking about some of the calculations that Revit MEP does.

I am trying to get results for Duct Pressure drop in Revit MEP.

Can you please share your ideas, as how can I achieve this?

This post has some additional information but is based on the Revit MEP calculation white paper from Autodesk.Revit MEP Duct Sizing calculations

Revit MEP computes pressure losses in ductwork based on the geometry and roughness of the ductwork, air

density, and air viscosity. Values for Air Density and Air Viscosity are specifiedin theMechanical Settings.

Roughness is specified in the type properties for duct/duct fitting component families.

The following example shows how Revit MEP calculates the pressure drop for a 100 foot segment of 36"x24" duct carrying air flow of 12,000 CFM. Pressure drop is defined as:

This values checks with the Hydraulic Diameter parameter shown in the Properties of the Duct in Revit:

The velocity is based on the cross sectional area:

After determining the friction factor, the pressure drop can be calculated:

The value for the calculated pressure drop matches the value found in the ducts properties in Revit MEP.

Posted byScott Briskat6/01/2010 04:06:00 PMSpecify a Pressure Loss Method for Fittings and Accessories for Duct and PipeJan 22, 2015|In-Product View

You can specify a pressure loss method for fittings and accessories for duct and pipe in the Properties palette.Third party developers can create calculation methods installed as add-ins to take the place of default calculation methods within Revit.To specify a loss method1. Select a duct or pipe fitting or accessory.2. In the Properties palette, for Loss Method, select a pressure loss method from the list.For duct, the default loss methods are: Coefficient from ASHRAE Table Specific Coefficient Specific Loss Not DefinedFor pipe, the default loss methods are: K Coefficient from Table Specific Coefficient Specific Loss Use Definition on Type Not DefinedNote: Specific Loss and Specific Coefficient are not available when a fitting or accessory with more than two connectors is selected, because there is more than one pressure loss on the fitting or accessory. Third party developers can develop additional loss methods for fittings and accessories which may appear in this list.3. When Specific Coefficient or Specific Loss is selected, you can specify a value for the selected loss method. For Loss Method Settings, click Edit.4. In the Settings dialog, specify a value for the selected Loss Method.Note:If a duct system is well-connected, the Pressure Drop parameter will report the pressure drop value of this fitting or accessory. If the fitting or accessory has more than one path (more than two connectors), Pressure Drop will display as empty. Note that the Pressure Drop value will include the pressure drop for connectors. For example, an accessory connector has a built-in pressure drop parameter, unlike a fitting. The final pressure drop on an accessory is the sum of the two pressure drop values.