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Duct Fitting & ASHRAE Table

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Message 1 of 37
CM-Black
8967 Views, 36 Replies

Duct Fitting & ASHRAE Table

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

36 REPLIES 36
Message 2 of 37

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

Message 3 of 37

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.

Message 4 of 37
Martin__Schmid
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
Product Line Manager
Mechanical Detailing and Electrical Design
Architecture, Engineering, and Construction
Autodesk, Inc.

Message 5 of 37
CM-Black
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.

Message 6 of 37
peterworley
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

Message 7 of 37

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
Product Line Manager
Mechanical Detailing and Electrical Design
Architecture, Engineering, and Construction
Autodesk, Inc.

Message 8 of 37
Aheiser716
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

Message 9 of 37
adam.jw
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. 😛 

 

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!
Message 10 of 37
Martin__Schmid
in reply to: adam.jw

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
Product Line Manager
Mechanical Detailing and Electrical Design
Architecture, Engineering, and Construction
Autodesk, Inc.

Message 11 of 37
adam.jw
in reply to: CM-Black

Thanks so much Martin!

 

I think I'll consult some of the Mech engineers in my office about how loss is dealt with in tees. 

 

I have a lot to learn about HVAC design (I design primarily electrical systems), but I want to see if I can do darned near everything inside the box (the box that is Revit MEP). Once I get a better understanding I'll see if I can talk more intelligently about making sure loss is taken into account for Tees (To me Tees seem like funky right angle elbows). 

____________________________________________________
Please give kudos to the MEP Wish List ideas you like, as this will help the Revit development team prioritize functionality additions!
Message 12 of 37

I was unable to get the plugin to load on startup.  I am using Revit 2013.  Please see the atttached image and let me know if you have any ideas....

Message 13 of 37

Hi Mike-

 

In some cases this issue is due to Windows security.  See:

http://blogs.msdn.com/b/brada/archive/2009/12/11/visual-studio-project-sample-loading-error-assembly...

 

The short answer may be to:

1.  browse to where the .dll file is

2. right click the .dll file

3. select Properties

4. Select the General tab

5. Near the bottom, you may see: "Security:  This file came from another computer and might be blocked to help protect this computer".  Next to that is an 'Unblock' button.  Click that.

 

Then, try to re-launch Revit.  This solves the problem in some cases.

 

Cheers-

MS



Martin Schmid
Product Line Manager
Mechanical Detailing and Electrical Design
Architecture, Engineering, and Construction
Autodesk, Inc.

Message 14 of 37
msoren
in reply to: CM-Black

I know this is an old post however, In Revit 2014 it appears that the duct fitting tables for flat oval duct have not been incorporated as the other fittings hav been. tables sf4-1 through sf4-8 were not included in previous releases as well though oddly sf5 tables were. Strange that you would include some of the flat oval but not all of it. our firm primarily uses flat oval duct for our high pressure system without entering in the Coefficient for each of these fittings individually how could I get around this.
Message 15 of 37
adam.jw
in reply to: msoren

Read my EDIT below...l

 

Rather than trying to mess with ASHRAE tables and other weird Revit voodoo --- I think you’ll be better off creating a schedule that groups up all your fittings by elbow, transition, etc (turn OFF itemize each instance), and then assigning them all the same loss value (be conservative, obviously).

This will speed up your calcs, give you a very good estimate (albeit on the conservative side), and allow you to get the project done quickly. Don’t get to detailed on each individual elbow or fitting’s loss value. Unless you’re a contractor building shop drawings, you don’t need that level of accuracy (our take-offs in our firm are quite conservative, which allows for more flexible field adjustments without upsizing the fan or equipment... which can be VERY costly).

 

EDIT: I should point out you should only do this after you are SURE your duct systems correctly have a flow direction. If you're just randomly drawing ducts, hoping to get ASHRAE tables asigned, you'll be dissapointed. There has to be a fully complete and connected system BEFORE all the tables get worked out.

 

Here is a link to one of the projects I created in 2013 called "No Warnings! Hurray!" --- please don't judge the quality of design, it is just an example of a project without warnings:

https://dl.dropboxusercontent.com/u/22838635/revit/No%20Warnings%20Hurray%21-rev2_2013-10-2_10.31.21...

 

 

You'll notice I've manually assigned the duct take offs a specific loss. There was no ASHRAE table for it even after the system was completed. But you'll see the elbows DO have ASHRAE tables.

 

ALSO! This is not a flat oval duct design.

____________________________________________________
Please give kudos to the MEP Wish List ideas you like, as this will help the Revit development team prioritize functionality additions!
Message 16 of 37
adam.jw
in reply to: adam.jw

ALSO! For fun I upgraded this 2013 project to 2014. Then I changed a couple lengths of duct to Oval (using the Change Type tool after a run of ducts and elbows is selected) and it worked perfectly. It pulled up ASHRAE tables for the oval duct elbows.
____________________________________________________
Please give kudos to the MEP Wish List ideas you like, as this will help the Revit development team prioritize functionality additions!
Message 17 of 37
msoren
in reply to: adam.jw

Thanks for your help.

Everything is connected with appropriate flow direction still no ashrae table. I tried changing the duct/fitting through the change type function still didn't popluate the table.

I like your idea of using a schedule to input the loss coefficient however I do not see in your example where you would have inputted it and I cannot find that parameter availiable in the schedule fields. It appears to be a system property that duct fittings are not assigned to.
Message 18 of 37
HVAC-Novice
in reply to: CM-Black

Old thread, but it looks like what I may need.

 

I created an elbow fittings with a formula that calculates pressuredrop based on SMACNA data. The problem I have is, the fitting default to using the ASHRAE tables. Revit then adds the ASHRAE pressure drop to my calculated pressure drop.  

what I want to do is disable the ASHRAE table. Only workaround seems to be to select all the fittings in the project and set Loss Method to "Not Defined" - then it only uses my calculated drop. but that obviously could be forgotten, or i may add fittings and then forget to re-do that. 

 

I looked into the XML file, but couldn't really find what to manipulate. I read message #7, but still can't tell which one is referring to elbows. Ideally I can disable the ASHRAE tables in the fitting family so i don't have to do that again with a new Revit version. I'm on R2022. 

 

I created a new duct fitting from scratch, and that shows no ASHRAE tables. But I don't want to re-create the geometries of a fitting, and i fear once it becomes an actual fitting, it will go back to using the ASHRAE tables. No sure, though, how a fitting actually decides what table to use. 

Revit version: R2024.2
Message 19 of 37
iainsavage
in reply to: HVAC-Novice

"want to do is disable the ASHRAE table" - I'm pretty sure this is not possible in native Revit. Revit always defaults to using the ASHRAE table method and you have to manually change that for each Instance of a family (hence right click, select all instances in model, apply alternative loss method).

"Not sure, though, how a fitting actually decides what table to use" - I don't think the fitting decides, I assume its part of the analysis part of the programme which interprets the shape factors and passes that information to the ASHRAE.xml file. The built-in calculators are, I presume, in here: C:\Program Files\Autodesk\Revit 2022\AddIns\MEPCalculation.

This thread might be of interest: https://forums.autodesk.com/t5/revit-mep-forum/working-with-ashrae-tables/td-p/7562417

 

If you're smart enough (I'm not) I think you can create your own calculator using C# but I'm not a programmer so don't take that as hard fact.

 

The only other way that I can think that you could fool the system would be to copy the .tbl files and set all the coefficients in them to zero but in that thread above somebody said they tried to edit the tables and it didn't make any difference - maybe try editing one and see if it achieves what you need?.

 

Bottom line is, from many posts I've read here and on other forums (AUGI, revitforum etc), the ASHRAE table method is unreliable at best but some of that is I think because the OOTB fittings maybe don't conform to the ASHRAE table restrictions e.g. similar to what you alluded to in your other recent post, ASHRAE radiused elbows only allow a 1.5D centreline radius (in UK the default is 1D which is the OOTB fitting that I use), so anything other than 1.5D will default to a different (wrong) table.

 

PS: I found this on one of the help pages (you've probably seen it already)

  • "Third party developers can develop additional loss methods for fittings and accessories which may appear in this list.
  • In order for Revit to apply an ASHRAE table, a fitting or accessory must be part of a well connected system with a known flow direction.
  • There may be cases in which no ASHRAE table is applicable for the selected element, for example, when ASHRAE doesn't have a definition for a fitting or if the flow is not known. In that case, Pressure Drop will display as empty.
  • Specific Coefficient and Specific Loss are not available for a fitting or accessory with more than two connectors."

 

Message 20 of 37
HVAC-Novice
in reply to: iainsavage

Thanks for the reply. 

It looks like the XML file only includes the conditions for each fitting. I'm not sure if the fitting calculator assigns them from there. but I tried to delete the entries for CD3-14 and CD3-17 (shown for one of my fittings) in the XML-file and also deleted the tbl-file for those. Then I restarted my computer and hoped they would disappear. no luck, they still are available for that fitting in my project. I assume those fittings got loaded in my project or my Revit installation a long time ago. 

 

I thought of removing the fitting calculator. But I really only want to use my own calcs for fittings with bad values. For transitions etc. ASHRAE seems to do a better job than I could do by separating supply and return fittings etc. So i don't want to disable fitting calc entirely. and i also don't want to break my system inadvertently. 

 

Could someone explain how those xml and tbl files are used by Revit? or how I could remove certain fittings? I think for now I want to limit myself to manipulating elbows and fittings that for some reason don't have a pressuredrop oob. so I could remove all elbow data. 

 

 

Revit version: R2024.2

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