Revit MEP

Reply
Member
CM-Black
Posts: 5
Registered: ‎07-28-2010
Message 1 of 17 (3,279 Views)

Duct Fitting & ASHRAE Table

3279 Views, 16 Replies
07-28-2010 08:35 AM

If I create a custom duct tee fitting, how do I associate it with one of the pre-loaded ASHRAE Tables?

Mentor
lawrencerobinson5
Posts: 175
Registered: ‎05-30-2008
Message 2 of 17 (3,270 Views)

Re: Duct Fitting & ASHRAE Table

07-28-2010 09:57 AM in reply to: CM-Black

Go to http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=13092938&linkID=9243140 for a family creation guide.  Start on page 141, it's a guide on creating a flange family that uses look up tables.  This will show you how to link parameters to the look up tables.

 

Lawrence

Member
CM-Black
Posts: 5
Registered: ‎07-28-2010
Message 3 of 17 (3,265 Views)

Re: Duct Fitting & ASHRAE Table

07-28-2010 10:09 AM in reply to: lawrencerobinson5

The ASHRAE tables are a type .tbl file and are not accessed in the same way as a .csv lookup table.  The ASHRAE tables provide a loss coefficient for the fitting to determine the pressure drop thru it.

Employee
martin.schmid
Posts: 1,297
Registered: ‎11-16-2005
Message 4 of 17 (3,230 Views)

Re: Duct Fitting & ASHRAE Table

08-02-2010 02:38 PM in reply to: CM-Black

The C:\Program Files\Autodesk\Revit MEP 2011\Program\Ashrae\ASHRAE.xml file is used to determine which tables the fitting might be associated with... then, based on the tables that suit the rules defined in the .xml file, you can select a specific table.  If there are no tables listed in the ASHRAE table param of a fitting instance, then I suspect that the fitting in question doesn't meet the rules defined by the various tables. 

 

What kind of fitting are you creating?  Is it similar to one of the fittings listed in ASHRAE Handbook 2009, chapter 21 (pg 26...) or some other table that you find in the C:\Program Files\Autodesk\Revit MEP 2011\Program\Ashrae folder? 



Martin Schmid, P.E.
Product Manager - Revit MEP
Architecture, Engineering, and Construction
Autodesk, Inc.

Member
CM-Black
Posts: 5
Registered: ‎07-28-2010
Message 5 of 17 (3,208 Views)

Re: Duct Fitting & ASHRAE Table

08-04-2010 10:47 AM in reply to: martin.schmid

I want the standard "Round Tee with Transition - Beveled" fitting to only associate with the SD5-12 Table.  For some reason that table isn't even selectable and it defaults to the SD5-10 table.

 

Another problem is that the fitting only works when the Ds dimension (downstream side of the main) is smaller than the upstream side.  Sometimes you may not want to transition the duct to a smaller size.

 

How are the fittings evaluated to determine which tables apply?  I don't see any parameters in the fittings that then associate with the ASHRAE tables.

Contributor
peterworley
Posts: 16
Registered: ‎01-13-2010
Message 6 of 17 (2,865 Views)

Re: Duct Fitting & ASHRAE Table

12-31-2010 12:37 PM in reply to: CM-Black

Can anyone explain this? 

 

What and where is the parameter that links each fitting to its respective loss table?

 

I understand that there is an *.xml file and that there are *.tbl files but how are the fittings linked to these files?

 

Regards,

Pete

Employee
martin.schmid
Posts: 1,297
Registered: ‎11-16-2005
Message 7 of 17 (2,831 Views)

Re: Duct Fitting & ASHRAE Table

01-04-2011 07:55 AM in reply to: peterworley

Let me explain by an example of how this works, using the ‘Rectangular Elbow – Radius’ fitting.

 

Insert the fitting… there are no ASHRAE tables listed in properties because the tables are generally specific to ‘Supply’ or ‘Return’.  There is also ‘Common’, but the Revit doesn’t let you select a ‘Common’ one since you can’t select a ‘direction’ specific one since the direction is not yet known.  For this particular fitting, the may not matter at all, but in the general case for reducing/enlarging fittings, etc, this is at least somewhat necessary.

 

Now, using additional ductwork as necessary, connect the fitting to a supply air terminal.

 

Now, the ASHRAE Table list is populated with a list of entries.  The first one that defaults for me is SR3-1, probably due to the order in the XML file (but I didn’t verify).  If you look at the XML for this entry, you see the following, with several Formulae used to validate if this ‘Table’ applies to the fitting.  I.e., there are checks for the angle (theta), width ratios and height/width ratio.  If you modify the fitting to invalidate any of these formulae, the ASHRAE table entry for SR3-1 no longer is available… i.e., adjust the fitting so it is no longer 90.

 

<Table Function="S" Geometry="R" Category="3" SequenceNumber="1">

  SR3-1

<SubTable Result="Co" Number="1" Dimensions="2">

  SR3-1 Elbow, 90 Degree, Variable Inlet/Outlet Areas, Supply Air Systems (Idelchik 1986, Diagram 6-4)

  <SubTableData2D X="Wo/W1" Y1="H/W1" />

  <Formula>Theta == 90</Formula>

  <Formula>0.6 <= Wo/W1 && Wo/W1 <= 2.0</Formula>

  <Formula>0.25 <= H/W1 && H/W1 <= 100.0</Formula>

  </SubTable>

  </Table>

 

So, this is how a fitting is linked to a table in the .XML... the .tbl is simply linked based on the name of the Table, in this case, it would use the data from the SR3-1.tbl file.

 

HTH,

 



Martin Schmid, P.E.
Product Manager - Revit MEP
Architecture, Engineering, and Construction
Autodesk, Inc.

New Member
Aheiser716
Posts: 1
Registered: ‎01-11-2011
Message 8 of 17 (2,752 Views)

Re: Duct Fitting & ASHRAE Table

01-11-2011 12:26 PM in reply to: CM-Black

Hi -

 

This thread so far has been very useful.  Thank you all.

 

Two additional questions though.

 

1) Is there anyway to make a fitting look up a certain table.  For instance a beveled tap and eccentric transitions both have tables; however, when you place them in Revit, it doesn't look up the ASHRAE table.  Not sure if it is possible to link these types of transitions to ASHRAE or if you need to still entere loss coefficients by hand. 

1a) For fittings that do link to the ASHRAE tables, is it possible to change what it looks up?

 

2) I'm having the following problem.  I draw a straight duct connected to an end terminal.  I draw an elbow after this main and it finds the table value.  I draw a tap or tee connected to this main.  I then extend the main duct and add a few more turns, and it no longer will find the table values.  It also won't find the table values after the tee/tap.  Any idea for a fix for this?  Do you just draw all the taps/tees at the end?

 

Thanks,

Andrew

Distinguished Contributor
thewrz
Posts: 171
Registered: ‎06-08-2009
Message 9 of 17 (1,934 Views)

Re: Duct Fitting & ASHRAE Table

01-18-2012 09:12 PM in reply to: Aheiser716

Old thread. Don't care. Bumping it. Revit 2012 hasn't solved this. Tees still don't look up ASHRAE tables by default. And the other posts haven't really helped that. Plus, Aheiser716 hasn't been answered yet.

 

Come on Revit team. Make it so we can design ductwork systems in Revit 2013. :smileytongue: 

 

Answer Aheiser716's questions!!!

____________________________________________________
Please give kudos to the MEP Wish List ideas you like, as this will help the Revit development team prioritize functionality additions!
Employee
martin.schmid
Posts: 1,297
Registered: ‎11-16-2005
Message 10 of 17 (1,930 Views)

Re: Duct Fitting & ASHRAE Table

01-19-2012 12:09 AM in reply to: thewrz

Hi thewrz-- thanks for bumping this.

 

To address your inquiry:

Tees still don't look up ASHRAE tables by default. And the other posts haven't really helped that.


[MS] This is a limitation of the version of ASHRAE tables that Revit uses.  For example, if you download the ASHRAE Viewer add-in for Revit MEP (http://inside-the-system.typepad.com/my_weblog/2011/09/ashrae-viewer-available-in-labs.html), and view the table for SR5-5, you will see that the inlet and branch outlet ratios are limited from 0.1 to 0.8, so a straight tee with 12x12 connectors on all ports will not be able to find a table.. even if the branch was 10x12, this is still a ratio of 0.83.  If you have the branch outlet as 8x12, then table SR5-5 becomes available.  Perhaps in a future release more thorough data from ASHRAE will be available that covers additional cases.

 

To address Aheiser716's inquiries:

 

1) Is there anyway to make a fitting look up a certain table.  For instance a beveled tap and eccentric transitions both have tables; however, when you place them in Revit, it doesn't look up the ASHRAE table.  Not sure if it is possible to link these types of transitions to ASHRAE or if you need to still entere loss coefficients by hand. 

 

[MS] depends on your method.. most fittings don't get a table simply by placing them.. in many cases, including transitions and some elbows, the flow direction must be determinant for a table lookup to be possible... so, as a general rule, flow direction must be known before the algorithm attempts to figure out the table.  With regard to the tap, this is currently a limitation, and you will need to utilize a method other than the tables to associate a coefficient.

 

1a) For fittings that do link to the ASHRAE tables, is it possible to change what it looks up?

 

[MS] to an extent, yes.  You *could* modify the .tbl files in the C:\Program Files\Autodesk\Revit MEP 2012\Program\Ashrae folder using a basic text editor, however, these are provided by ASHRAE, and modifying them is not somthing that is supported.  

 

2) I'm having the following problem.  I draw a straight duct connected to an end terminal.  I draw an elbow after this main and it finds the table value.  I draw a tap or tee connected to this main.  I then extend the main duct and add a few more turns, and it no longer will find the table values.  It also won't find the table values after the tee/tap.  Any idea for a fix for this?  Do you just draw all the taps/tees at the end?

 

[MS] it sounds to me that at the tee/tap junction, you have one closed end (at the air terminal you started from) and two open ports.  With two open ports, in most cases, flow can't be determined, and thus, tables can't be looked up.  So, the 'fix' would be to make sure you have a system with at most one open port.

 

 



Martin Schmid, P.E.
Product Manager - Revit MEP
Architecture, Engineering, and Construction
Autodesk, Inc.

Announcements
Are you familiar with the Autodesk Expert Elites? The Expert Elite program is made up of customers that help other customers by sharing knowledge and exemplifying an engaging style of collaboration. To learn more, please visit our Expert Elite website.
Need installation help?

Start with some of our most frequented solutions or visit the Installation and Licensing Forum to get help installing your software.