Problem with Loss Method

[Anonymous]

Hi, 

I have problem with loss method for tee. I can set this value as specified coeficient and the write a value for each fit, but it is imposible for tee. For tee I have only 2 options: undefined and ashare. With ashare is problem, because in loss raport it gives me value: -9999. 

What can I do to set this value for tee as pecified coeficient.

Thanks for Yours replies. 

[dbutts7]

what version of Revit are you using?

tks - db

[Anonymous]

My version is Revit 2015.

[dbutts7]

OK, I just tested this by placing a couple of rectangular ducts, with a standard rectangular tee. When I select the tee, I get this:

So, I checked the help file, and this came up for the Revit 2015 R2 update release:

http://help.autodesk.com/view/RVT/2015/ENU/?guid=GUID-6708486B-6D46-49DF-8438-14EAAA6F0818

While this explains how the loss method is determined, it didn't explain why the fitting was assigned by a specific table.

doing a little more research, I found that Update Release 3 for Revit 2015 was supposed to correct this behavior, but I have R2 with update release 4, and am getting the error still.

Let me do a little more digging with Autodesk - it could be that Revit can't find the ASHRAE table definitions, which is why it's not being assigned.

Was this a new project to 2015, or one you started in a prior release? Just checking, to eliminate any other possibilities.

thanks - David B.

[Anonymous]

Thank You for Your concern.

I started this project in Revit 2015.

[dbutts7]

Thanks - I've got a case started with Autodesk, since I was able to replicate it in Revit 2015 - will post a response shortly.

thanks - db

[dbutts7]

Hadn't forgotten about this - Autodesk just got back to me, their first response said to make sure the air terminal had an airflow assigned (mine do) and that the air terminal connection is set to In. (they are). That didn't solve the problem, so I've posted a couple of file examples for them to test...will get an update back as soon as I can...

One note - I didn't encounter the problem with a new file created in Revit 2015 R2, with update 5, but the duct also didn't pick up the airflow from the terminals, if added or edited after the duct was placed. Fix one problem, find another...

thanks - db

[dbutts7]

Ok, here's an update. Check the connection on the air terminal, and let me know what it's set to on the connector for flow configuration - is it Preset, Calculated or System?

In order for the ASHRAE tables to work correctly, the connector must be set to Preset or Calculated - check this first. The out of the box families for air terminals should all be set to Preset, but check your and see if it was changed. A sample project from 2014 that was having the same error was set to System, which could cause this not to work correctly.

The file I created would allow me to to review the ASHRAE coefficent tables, but the duct would not return any airflow values, when the connector was set to system. I changed this to Preset, and the airflow correctly displayed on the duct using calculated or specific loss for the loss method.

I'm working on a blog post to more fully explain this, so stay tuned.

[dbutts7]

Now here's a couple more notes. In order for any of the fittings to use the ASHRAE tables, the system must be well formed - while it may look correct from a plan view, you need to check and makre sure all of you duct is properly connected.

Here's how I caught this - the project I was testing this out on was originally developed in Revit 2014. Since we're working in 2015, I did what anyone else would do - I upgraded the file. Has this ever happened to you - you get a warning telling you a duct or pipe has been modified in the opposite direction, and the only solution is to delete the element?

That's what happened on my test file - and some of the parts were removed, causing me to have an open system. When this happens, you'll get an incorrect or missing loss value in the duct and fittings. Also, pay attention to those warnings that show up on the context tabs for the duct/part - they'll tell you if there's an error, such as no loss defined. That's usually this first hint.

To check it, create a few 3D views and sections, checking the entire system out, using the TAB keys and views. Be aware that the disconnect may not be readily obvious - the duct may look connected, but it's not.

Try this out and let me know what you find.

thanks - David B.

[Anonymous]

Thank You for Your reply. I chcecked all issues. My airterminals have airflow configuration: Preset. Whole system is connected corectly, I am sure, because I made small example and it calculate airflows well. But in report, I still have wrong value of pressure drop for tees. If you want to see this, I attach project.

http://www.speedyshare.com/en4hY/problem-with-pressure-drop.rvt

[dbutts7]

OK, I'm downloading now, will take a look at it asap -

thanks - db