2013 and "multiple values" in ducts

[DaveDH]

We upgraded one of our projects to experiment with the ventilation & duct calcs in 2013. So far we like what we're seeing with regard to calcs (especially the duct pressure loss report), but one thing I've noticed is that, if a duct has mutliple branches attached to it, the flows (and a couple other numbers) show up as "Multiple Values" instead of the sum of the CFM. Has anyone else seen this? And know how to fix it?

[daniel.morrison]

This has happened because Autodesk has now allowed duct flows to be split when using System Colour Fill or System Inspector so you can see the differences in flow before and after the tap (this is a good addition). Unfortunately Revit now sees these multiple values and doesn't know which to report in a schedule. Hopefully it wont be too difficult in the next upgrade to allow the schedule to just the maximum value, or maybe the average, or even show split values, but as far as I know there is no solution to this at present.

[martin.schmid]

Hello-- thanks for the post. I'm curious... why would one tag or schedule the airflow of a duct? Is this a required bit of documentation for certain types of projects or specific owners/code reviewers that require it?

If looking at a schedule, and all you see is the maximum value, the pressure drop, and the length, it may not make sense how the pressure drop is derived from the flow, since the pressure drop is actually derived from the individual section's flows, not the maximum flow.

For tagging, someone could easily have been 'sloppy' in previous releases, and ended up with documentation like shown below, potentially leading to questions for clarification.

We'd like to understand how/when you need to show flow to perhaps eventually come up with a better solution than what was available in the past.

6-25-2012 1-46-42 PM.jpg

[DaveDH]

We don't show duct cfm tags on our construction docs. This would be for internal use only, on a working view, for backchecking calcs and loads, etc.

[daniel.morrison]

Similar to Dave above we would not show flows for ductwork. Maybe moreso for pipework as a design check. What we were looking to do though would be to schedule the ductwork with flows etc so we can then transfer this into our acoustic analysis software. In either case the only accurate way to show this would be to split the values in a duct/ pipe to show the different flows at each section - ie before and after a tap or stub connection, don't know how this would go in a schedule though?

[rrubert]

We need to be able to quickly see what the airflow is in a particular duct. I agree that the way that it works in 2013 is correct, however, I don't want to add actual splits in my ductwork to be able to see the airflow results (I realize that's what the system inspector is for, however, to use the system inspector to its fullest potential, you have to set the systems up correctly, and that takes a long time). So, I'm wondering if you could add virtual splits? Maybe you add some kind of functionality to the taps to make them divide up the airflow, but without showing a physical line?

The way I use the airflow, friction, velocity, etc in everyday use is like this: Say an architect calls me up and wants to raise a ceiling height. I want to quickly be able to click on the duct, see the airflow in that particular duct, and see how I can resize the duct. I will eventually care what the total duct static pressure is for sizing my fan, but at the moment, I just want to see the airflow in one particular duct, and I want to see the maximum airflow in the duct, because I want to size it for the worst case scenario.

[daniel.morrison]

.... So, I'm wondering if you could add virtual splits? Maybe you add some kind of functionality to the taps to make them divide up the airflow, but without showing a physical line?.....

In 2013, Revit must essentially do this anyway as this is how the system colour fill and the system inspector work. We just need the ability to tag and schedule it, although scheduling would be a bit more complex.

[ben.136902]

This was a mistake by autodesk. Add a feature and leave it incomplete.

[daniel.morrison]

This was a mistake by autodesk. Add a feature and leave it incomplete.

This was a operation normal by autodesk. Add a feature and leave it incomplete.

[martin.schmid]

What we were looking to do though would be to schedule the ductwork with flows etc so we can then transfer this into our acoustic analysis software.

Hi Daniel-- if you had a schedule of ductwork values with their flow, how would this help manually transcribe to acoustic analysis software? Does the software only require the size and flow? Does it not care about what is connected to what... if it does, how do you get this from the schedule?