create duct system after ducts are drawn?

[HVAC-Novice]

I know i should first place the diffusers and VAV boxes and create a duct system before I draw ducts. Same for VAV boxes and AHU.

But somehow I started deleting and re-doing the systems AFTER I drew the ducts. When a VAV box or diffuser are connected to the duct, I can't create a system. the only way I see is to disconnect the duct from the diffuser and the discharge of the VAV box to be able to select both into a system. So i basically need to delete the duct pieces, create my system, and then make new connections. this obviously is tedious

Is there a way to create duct system without having to delete and re-create the duct connections to and from diffuser/VAV box?

When I click a diffuser already connected to a duct, the "create duct system"doesn't even show up. Once i delete the duct connecting to the diffuser, the "create duct system" is available. but as long as the VAV outlet is connected to a duct, it isn't available to be picked as "equipment"

[Chris.Aquino]

what version of revit are you using?

In 2013, you can create new systems in the Project Browser by duplicating and modifying an existing system.

perhaps a short video would be helpful in showing your workflow.

[HVAC-Novice]

I'm not quite sure where int eh system broweser you can duplicate systems? I use 2014.

i ended up just disconnecteng the duct fromt he terminal/VAV boxes and manually re-created the VAV systems. At least the AHU now has the VAV boxes as sub systems.

But i noticed the cfm are not always added correctly. See attached system browser. Some VAV systems correctly add the difuser rates to the VAV box, and the VAV system has that same flowrate. But some VAV systems jsut double that number (see circled).  Something must be wrong....

I also would like to lsit the VAV ssytem names in order... like VAV 1, VAV 2. right now it orders by family name (the VAV box familiy), which isn't useful.

I have the strong feeling I did soemthing wrong somewhere. i looked at the proeprties of the VAVboxes and families and they show correct flows.

[HVAC-Novice]

I still have the problem that my system flows don't add properly and that may also cause other problems (duct pressure loss report etc.).

I don't see how in the system browser I would duplicate or edit the systems. right-clicking on any of the systems lets me delete them, see properties (but that doesn't really let me change much). How would this be done?

what i like to do is now (after I drew all my ducts) re-assign all components to systems. the only way to do that seems to manually disconnect the duct from diffuser and VAV-box discharge and manually create each system, and then re-create the ducts. I was hoping there is a better way.

thanks in advance.

[chunky2k]

Well am not 100% sure

but hover your mouse over a duct, click TAB until the whole duct system is selected, then i think you can create new system for that

and then you can add equipment to the system and so on

try it and let me know

[HVAC-Novice]

I'm able to select the duct system as you say. but i miss he part where I get to the point of creating a new sysem?

[chunky2k]

well am not 100% sure but i tried this

i have a project which i drew all the package unit manually, drew all the duct and inserted all the diffusers manually

now i put the mouse over the duct, i made 6 tabs click (to select the whole system) after that i just clicked on it

now a new tab will appear on the right side (Duct system) there you can click edit system and then add equipment and so on

2 notes :

1. if you made 5 tabs (as in my project) the selection of the system is not as 6 tabs

2. it is better to remove all the diffusers then edit the system

i hope it is the answer you are looking for

reagrds

[HVAC-Novice]

Thanks. I'm able to select a VAV system with 2 tabs using your method. but there is no tab or anything showing up that lets me create a duct system.

what am I doing wrong?

[chunky2k]

hello there

well am not really an expert, but i guess since the duct is already drawn, in this case theoretically the "System" is created, i guess all you have to do "if not done" is only add equipment to the system !!

for me as i draw, i create the duct manually, beacause no matter how the Revit is smart, sometimes it is not doing the work you need exactly

reagrds

[Bill.Knittle]

What Chris is referring to is that Revit 2012 and up allow you to create more "Types" of Duct and Pipe systems. If you expand the Families branch in your "Project Browser" you will see a "Category" for Pipe Systems and Duct Systems. When you expand either category you will see the system "Family" Pipe System or Duct System. If you expand either family you will see the "Types."

Now, The "Types" that come out-of-the-box represent each of the main "System Classifications" within Revit. For example, there is a pipe system Type called Hydronic Supply. This system Type is based on the Hydronic Supply system classification. Therefore, if you need a pipe system Type called "Chilled Water Supply" you'd duplicate Hydronic Supply and rename it to "Chilled Water Supply." Chilled Water Supply is now classified as a Hydronic Supply system.

To duplicate an existing Type, you can:

1. Right-click on one of the existing Pipe/Duct System Types in the Project Browser and select Duplicate.
2. Double-left click on one of the existing Pipe/Duct System Types in the Project Browser and select Duplicate.

The key to making it all work is that the connectors in your families must be assigned to the same System Classification as the System Classification your new System Type is based on. Otherwise, you won't be able to assign your pipe, equipment, etc... to the correct System Type.

[Bill.Knittle]

One thing I would look at is the VAV's properties. There might be a ratio parameter in there doubling the aggregated flow from the downstream Air Terminals. The OTB parallel fan units have a ratio parameter which dictates the inlet flow based on the discharge flow.

[HVAC-Novice]

I'm not sure I want to create a new duct system type. I'm fine just using the standard "supply" type. At least i don't think this is my problem here. What I want to do is create duct systems after i drew the ducts.

But I only can create a duct system (starting with VAV systems) when I select a diffuser that is not connected. And I only can add VAV boxes to the VAV duct system when the VAV boxes are disconnected on the discharge side. When they are still connected, I can't select them as long as they are physically connected. the only workaround is to delete the duct connecting the diffusers and the discharge of VAV box and re-connect after the VAV system is created.

all the other options with tabbing etc. don't seem to work since they don't bring up the "create duct system" command.

I now see why they want you to create systems before drawing ducts.

My only workaround now seems to be to re-do everything (disconnect diffusers, VAV boxes and create systems). Except Revit now decided to crash every time I select an AHU...

[Bill.Knittle]

Did you check the VAV family in the Family Editor to see if there is a Formula doubling the Flow value? I would start there. When I look at your VAV networks in your System Browser snap-shot, everything looks normal except that the the flows double.

The Air Terminals and their VAV are your secondary systems. The VAVs and the AHU are your primary system. I would select a VAV and edit the Duct System. Check to see if you can make the AHU the equipment.

The only other thing you can do is Delete the logical systems in the System Browser and rebuild them from the ground up. I wouldn't blow away the ductwork to solve a logical system issue.

I've attached an image from my Revit MEP families course I teach. Take a look at it. It's a great graphic to understand the logic.

[Bill.Knittle]

To help understand what is happening, I should reiterate a few things. Connectors are what make the world go around in Revit MEP. On the Duct side of things, We use (of course) Duct Connectors. A Supply Diffuser has a Duct Connector on it and it is set to the System Classification "Supply Air." The VAV typically has two Duct Connectors (1 inlet & 1 discharge) both set to the System Classification "Supply Air." The System Classification tells the device or equipment which logical systems it can take part in. Therefore, when you draw duct away from the VAV it automatically creates a logical Supply Air system. When you duct to the diffuser, the diffuser is added to that VAV's logical Supply Air system by means of the physical connection. Inside of each Duct Connector is also a Flow Configuration. When this is set to Calculated, it tells Revit that this Connector will be the upstream source and that all downstream Flows connected to it will be totaled here. When I put an AHU in and draw duct away from its supply discharge, another logical system is created. When I duct from the VAV inlet and tap into the duct coming from the AHU, the VAV is added to the AHU's logical system. This is Revit's way of automatically generating the logic. It does a good job but, it's 50% complete in terms of truly showing the distribution's hierachy.

The Preset Flow from the Air Terminal is propagated to the discharge on the VAV. The discharge on the VAV propagates the aggregated Flow to its inlet. Finally, the inlet Flow is propagated to the discharge on the AHU to be aggregated. The logical systems look like Image 1.jpg.

The only thing that I need to do is tell each logical system, who is the true equipment from the devices. I do that by editing the Duct System. The issue in Image 1 is that the VAV takes part in both logical systems so I need to be careful here when assigning it as the Equipment. When I select the VAV and edit the Duct System, I get an option to choose which of the two logical systems I want to edit. See Image 2.jpg .

• First, I want to edit Mechanical Supply Air 1 (the VAV and Air Terminal) and make the VAV the Equipment.
• Finally, I want to pick the VAV again, edit the Duct System, select Mechanical Supply Air 2 (the AHU and VAV), and make the AHU the Equipment .

The System Browser will now display the true hierarchy of information. See Image 3.jpg. Notice that the ratio in the VAV is reducing the overall flow upstream by 0.2. This is because the VAV also has a Return Air connector on it for a Plenum Return. So, It does not require the full flow from the AHU its diffuser is demanding.

[smyyousef]

Sterling Job, Now wonder if u just do some discharge of Ur simplification way and reiterate similar about the  Return and  exhaust systems, 

this will be benefiting and completing 

lots of thanks

[smyyousef]

My main problem now is that Select Equipment won't select the AHU of any type (here i got Fan Module front Discharge Up) , i tried this in all situations, i removed the ducts, delete the prev system and started every thing back again every time it gives me Non selected in the equipment's window in the option bar, I also noticed when i place a VAV box on the view and look at the property pane i see its System Classification assigned to supply, return air even before any duct connection, on the contrary when i place an AHU it always gives me System Classification: "Undefined.Power" .. so what to do to make this AHU cooperative