I find there is some confusion in the industry about Revit using ASHRAE tables for pressure losses in duct fittings. After a bit of investigation, I found the following post, which I believe should be of interest to anyone in the MEP discipline and who want to use Revit for more than just a drafting tool.
Please vote for the idea to improve Revit (posted on the same link)
Consider that the pressure drop through a tap might be a much as 40%. If this loss is not accounted for, the pipes will not be sized as required.
Some further reading on the matter:
- Specify a Pressure Loss Method
- Working with ASHRAE Tables
- Pressure Loss through Tap Always Zero
- The Building Coder – User MEP Calculation Sample
- The Building Coder – Reading ASHRAE Table Information from Elements
My advice would be to consult the pressure loss report.
If it is picked up that some duct fitting does not induce a loss on a section of the route where it should, then some compensation must be made for that. Select the element by its ID and consider it carefully.
Ten to one it is not calculating a loss factor.
Autodesk is aware of the limitation and users should vote en masse so that they have the incentive to fix it. Users should play a much more active role in giving feedback through the ideas in Revit. Your vote matters.
If you need help adopting Revit and BIM in your practice, please contact Micrographics so we may be of assistance.