Space Imported Specified Return/Supply Airflow from excel, conversion?

As one of my first dynamo graphs I chose of course for a fairly simple export/import with an excel file

The aim is to fill in the Specified Return Airflow and Specified supply Airflow from an excel file into the space

A first graph exports some space data to an excel. -> no problems here
The second graph updates space parameters -> here is a problem

The problem:
When updating the Space parameters Specified Supply/Return Airflow something weird happens with the values.
I suppose it’s because of some conversion somewhere …

The test I performed to try to figure out the solution …
The same value is being added to new shared parameters I added to spaces as well as to the revit parameters Specified Return Airflow and Specified Return Airflow.
Result of this test is that the “new parameters” are correct but the revit parameters are divergent.

Just can’t seem to figure out why oh why oh why???
I’ve been looking into the project units but would not expect this to be the problem.
It appears to me as if there is a slight error on “a conversion somewhere” although I don’t do anything specific to that value before updating in Revit.

Another test I perfomed is a graph that overwrites the value of Specified Return Airflow with the value from the added shared parameter in the space … same difference :frowning:

Anybody any experience with this situation and even maybe a solution?

Unfortunately as a new user It seems I can’t add any files to this post …

The used files can be found on Google drive

The folder contains the separate files as well as a zip file :slight_smile:

A screenshot from the space shedule after import
An excel file for the export from revit
A Small revit 2017 model containing three spaces
Dynamo Graphs:
GetSpaceInfo: writes the space information to the excel file
SendFlowInfo: Write parameters in revit model
SaveParameterIntoParameter: a test in which a send a value from a shared parameter to the revit parameter specified return/supply airflow

My initial thought is that you are dealing with a conversion issue. Are the values in Excel in CFM? It would be helpful if you could post a file or even an image of what is happening.

Here is something I’ve posted before that may help:

While Dynamo is unitless, conversions are still needed because Dynamo pulls the common units from Revit whenever applicable. For example, with airflow (CFM), a conversion factor of 60 is needed. Here’s why:

1 CFM = 100 ft3/min = 1.666666666 ft3/s (Dynamo output)

well unfortunately it seems that I can’t upload any files to this post as I’m e new user :unamused:
all values are in cubic meters/hour
This is also set this way in the project units
As for the excel I’ve tried with numbers and “text” vales …
So I don’t get why there is somewhere a conversion or why I should do a conversion.somewhere


You can upload your files in google drive / dropbox and share link here.

@Kulkul OK thx will do that :smile:

jboehning Looks like dividing the value by 109.40 before updating the specified Supply/return Airflow gives them the correct value in m3/h but somehow i Keep finding this a weird thing to do …

@SDH, I’m not a Dynamo developer, but I do know that Dynamo does not see all the units associated with Revit. Even though you have specified the units that you want in the Project Units in Revit, Dynamo still converts it into the common units that it can work with. This happens with most MEP parameters that have units such as CFM, Volts, Watts, BTU, etc.

For example, with my CFM example above and your example, time is involved. Dynamo can work with seconds, but not minutes and hours. Therefore, those values are converted. However, in your case, it appears it is also converting it to cubic feet/second… 1 ft3/s = (approx.) 102 m3/h.

It would be nice to see Dynamo be able to work with MEP units, but for now, I typically export the values I want to work with from Revit to Excel. Then I calculate the conversion factor and add that into the spreadsheet. In other words, make a column of values that you can work with, and then make another column with a conversion. That is the data you can use to write back to Revit.

You’ll probably get used to making the conversions in time, but if you don’t want to you can also use either of these 2 custom nodes from the ‘MEPover’ package:

The GetParameterAsValueString node will return the values as strings though, so for calculation you’ll need to convert to a numeric type first.
The GetParameterAsValueString will return the values as you see them in you Revit Interface.

@T_Pover many many thanks this cleans up the graphs :smiley: and works great
working on the next “Dynamo Handbook excercise #2” --> gettting that in the air terminals :wink:

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Thanks @T_Pover!

On another note, if you use parameter values to set other parameters, you don’t have to worry about conversions. For example, the attached graph sets the air terminal Flow based on the space Specified Supply Airflow. The number of air terminals per space is also considered.

AirTerminals_Flow.dyn (11.8 KB)

@jboehning thanks again :slight_smile: More or less what I was trying to achieve so I continued on that to have a graph doing this for Supply and Return Airflow at once in the sub-sequential correct air terminals and got that to work (at least it looks like it …)

So that little circle is nice and round with the previous graphs yeay

Thanks to all for your input after some more elaborate testing I will add the files

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How could you get just the values for supply air to change so if there were returns already in the space as well. I’ve been working on one and it works until I get more than one space in the model.

@anthony.kitsmiller could you please share the final version of this Dynamo routine including Return Air for multiple spaces