Duct ASHRAE table for pressure loss

[evgeny.kurbatov]

I have read all the posts regarding the wrong ASHRAE table assigned to duct fittings. And still it doesn't work properly. I can work with fitting pressure loss coefficients, but I want to make the ASHRAE table working.

Here is my case:

My expectation is that Revit assigns the table CD3-1 for the round elbow, it it doesn't.

I would like to understand why incorrect table is assigned?

And why the correct CD3-1 table is not even listed?

Is there a way to fix the table assignment?

Thank you,

Evgeny.

[Anonymous]

Hi @evgeny.kurbatov,

That's an issue I'm also interested in to !

Any information is welcomed !

Cheers,

[LjubanL]

Hi ek01,

the elbow is not listed because if you look a ashrae table (in paper) you will see that you havnt the data for the elbow above 250mm.

For CD3.1 there a data to diameter 250mm if I remember correctly - just put a diameter to 250mm and check.

 But if you want to push revit to pick right elbow from the ASHRAE table Iam not shure is it possible without dynamo, because we have to much parameters , if you deeply look in this table you will see that is to much variable like

:flow/area:

:half of the diameter/diameter…..

also in some cases your Q/A will be out of table value and revit don’t know what to do.

and Iam not sure how revit knows which elbow I want put (or some transition it’s the same princip), we must define this (in family, some additional extra information) and without dynamo Iam not sure is it possible.

regards

[Anonymous]

I'm literally having this exact problem, I have the same a basic bend family that will spit out 2 different default ASHRAE table settings based on a 45deg angle or a 90 deg angle....

I'm surprised that something so basic is so broken... this makes this feature completely useless with regard to static calcs, there is no way it can be expected that you have to double check each fitting for the correct setting, it would be faster to do it by hand.

 

How does revit assign the ASHRAE setting? is this editable so the defaults can be correct?

[EKey]

Hi LjubanL,

It's a good point that a round elbow works for up to 250 mm according ASHRAE.

I have changed the duct size to 200 mm, but Revit still doesn't allow to choose the CD3-1 type.

It seems there is a problem in the Revit deepness.

[LjubanL]

Dear friend,

you must create a elbow with r/d=1.5 because you have the data in ashrae just for this elbow..

ashrae table are table, nothing smart, you must prepare everything

look video below...

I know how you feel about this, the same thing happened to me few years ago, and few times per year I tested new version of revit, is it better then previous version.

regards

[EKey]

@LjubanL Another good point about the duct 1.5 radius multiplier. Sorry, I haven't read the ASHRAE table in full. You know, there is never enough time for that.

[evgeny.kurbatov]

I generated a Duct Pressure Loss Report, and it shows another ASHRAE table: not CD3-11 like in Revit, but CD3-21.

It makes the pressure loss calculations even less predictable and manageable.

[LjubanL]

Hi,

Could you attach your file, because I was perform a duct pressure report on previouse file and It looks all right.

Regards

[evgeny.kurbatov]

Here is the updated version of the file.

[LjubanL]

Hi ek01,

I did a little research (please find jpeg in attachment)

1. Perform calculation in revit 2016

wrong selection from ashrae table like your perform

2.Perform calculation in revit 2018

probably an error in the version 2016 😞

But interesting thing is that is the same loss coeficient, its seems that revit use the correct elbow but the name was wrong, and this error was corrected in the following 2018...

Regards