Forums >> Revit Systems >> Technical Support >> AIR FLOW GOING THE WRONG WAY

dbruckman

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Joined: Tue, May 20, 2014
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I've been in Revit Architectural for years, but am just now starting to use the MEP. 

This is Revit 2015

I have set up a make up air supply system in a building, set terminals, a supply air unit, connected the whole thing up with ductwork and what I get is the total supply CFM showing at the opposite end of the systme, at the cap at the end of the line, and zero CFM at the unit outlet.  The flow is exactly opposite of what it should be.

What am I doing wrong?

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dbruckman

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I've been horsing with this for a bit, and it seems as though the sequence in which you add elements to a system is crucial to the system being able to collect data on air flow.  If you begin with an air terminal you appear to need to go all the way back to the supply unit rather than then setting duct from the air handler to that terminal.   I THINK...... or if you are adding duct from an air handler, you need to add the air terminal last. It seems to go haywire if you try to do it in parts along a run, but not in a sequence.

Still messing with it, though...not sure I get it yet.

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Gyvven

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Joined: Wed, Dec 19, 2007
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Airflow populates from the air terminal back to the mech equipment. You must define your CFM at the air terminal and it will automatically sum at the VAV or whatever equipment your hooking up to. Order of connection doesn't have anything to do with it in my experience.

The output on your equipment should be set to Calculated (with Flow linked to a parameter), the input on the air terminal should be Preset (with Flow linked to a parameter). The inlet on your equipment, if you're dealing with a VAV, should be set to Preset (with Flow linked to the same parameter as the outlet). This allows the eqipment to see the "demand" from the air terminals and feed that information further up the chain, all the way back to the AHU. (I made an autosizing VAV and Air Terminal that are in the downloads section, but I need to update them since I've made some nifty changes recently.)

Using the duct inspector, or even applying a System Color Scheme to the view, will show you the air flow at every point along the duct. The airflow at a cap and it's adjacent ductwork should always be zero, unless somebody is messing with you and turned your duct cap into an air terminal. Don't laugh, I've seen it happen.... ok, I did it.

I hope this helps, unless I completely missed the issue. If I did, upload your model and we can take a look at it and see what's happening. I won't be able to since I'm not on 2015 yet.

-Gyv

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