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I have a generic round elbow and discovered the way it calculates pressuredrop makes no sense under some circumstances. it is the oob elbow:
At a given flow outside the below distinct angles: no pressuredrop and no loss method used
At 30°: pressurdrop is 0.0503 and it uses CD3-18
At 45°: pressuredrop is 0.0669 and it uses CD3-17
At 60°: pressuredrop is 0.0874 and it uses CD3-16
At 90°: pressuredrop is 0.0208 and it uses CD3-11 by default, but also offers CD3-12 and so on (s. picture)
This is a problem with all kind of fittings. In this example of a round elbow, it uses mitered elbows, which has higher pressuredrop. As an optimist i say this isn't too bad since it is more conservative. But the fact the 90° defaults to have a lower pressuredrop than the 30° fitting doesn't make sense. Even if i don't know a value is correct, seeing something illogical like that makes me nervous. Also the fact that it is zero at unusual angles isn't good, but knowing it I can adjust to that.
I opened the family but did not see a way to set the type of fittings it uses and the connectors are type "fitting". Since I use Revit to get at least a reasonable number, I like to resolve this or at least improve. Here my questions and ideas and I wonder if someone has ideas:
- are there families that work better or more reasonably?
- When it gives me multiple ASHRAE fittings to choose (90° in this case), is there a way to set that default in the family? I don't want to manually adjust that for every fitting.
- Is there a family editing option to fix that or to assign calculated pressuredrops to the connectors? I envision i could create my own calculation with k-values or something to make it work.
- In the project it gives me the option to use a "specific coefficient". But how can that be fixed tot he family?
I'm willing to put in time to build or edit families so they work a bit better. but fittings seem to be a black box. There is an old thread from 2013, but links in there are outdated.
There is talk about using a fitting schedule to see or assign the CD values. But I wasn't able to create a duct fitting schedule that shows any such values (even with all parameters included)
Solved! Go to Solution.