Forums >> Revit Systems >> Technical Support >> <Family Type> parameter can't be controlled by formula. What else can we do?

Gyvven

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So how else can I do this?

We'd like to be able to have our VAV boxes automatically size with changes to the Airflow parameter. Since we can't use a simple IF statement to select the proper, already existing, nested family how else might we do it?

My thoughts on it are that we can use a simple IF statement to drive a series of Dimension parameters and Tag info. It would leave us with a single family but also with only a single type, so no type parameters allowed. Maybe not the most ideal but if we can get all the appropriate data to schedule then it may not be a bad solution. I think the issue becomes taking the time to generate a family that requires so many formulas. Would the resulting family take less memory because it's not loading multiple types or additional families? Or would it chew up resources because it has so many formulas to calculate?

Does anyone have ideas or suggestions?

***I've posted the solution, see post #27.***

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WWHub

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I don't know what family this is but you can generally control nested families.

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Gyvven

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I know I can manually select the family type after applying a family type parameter and using the drop down list of nested family types, but you can't have Revit select one for you based on a given parameter. It will only apply IF formulas to Text, Numbers and Yes/No values.

But I have a thought that may or may not work, and I'll try it in a bit. But what if you did apply an IF formula and got a text string value (that happens to be the same name as the family type) then have the family type value equal that text string? Is that a work around?

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Gyvven

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Tried telling the Family Type parameter that it's the same as a text string, didn't work.

I'll play with making all of the type parameters dependent on the Airflow parameter. I don't think it should be too difficult to flex the family this way, just tedious. Oh, well, that's what the PE wants. I'll post what I eventually come up with.

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NDArchi03

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Not sure if this is what you are looking for, but you can create types for all the different values of the airflow parameter, then each type can reference a different option in your family type parameter.

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Gyvven

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Could you elaborate on how this can be done?

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NDArchi03

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OK, quick example for two different airflow parameter values and two different VAV boxes.

For this example lets assume the following values.

Airflow parameter values: 30 cfm and 40 cfm

VAV boxes: Box 1 and Box 2 (assuming that Box 1 and Box 2 are types within the nested VAV box family)

First, create a parameter named "Airflow" and choose the discipline and grouping as you see fit, but make it a number type parameter that is a type parameter, not an instance parameter.  Second, create a parameter named "VAV Box Size" and choose the discipline and grouping as you see fit, but make it a <Family Type...> parameter that is also a type parameter, not an instance parameter. Then create two types in your family and name them 30 cfm and 40 cfm respectively.  Change to the 30 cfm type and set the "Airflow" parameter to 30 and from the dropdown for the "VAV Box Size" parameter choose Box 1.  Then change to the 40 cfm type and set the "Airflow" parameter to 40 and from the dropdown for the "VAV Box Size" parameter choose Box 2.

Now you can switch between the two family types (30 cfm and 40 cfm) and the <Family Type...> parameter will switch accordingly, swapping the correctly sized VAV box.

Hopefully this makes sense.  This is by no means an exhaustive explanation so if you need more help I would be happy to provide it.  What version of Revit are you using?  If I have time I might whip up a quick example family for you.

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NDArchi03

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Also, if you have a lot of values for the "Airflow" parameter, it might make sense to create a type catalogue for the family.  Then, when you load the family, instead of Revit loading every type into the project, it will ask you to select which types to load.  I can help with that too, if it is something you are interested in doing.

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Gyvven

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Thanks for the explanation, but I'm looking for a way to automatically select the size the VAV based on the calculated airflow of the diffusers. What you've proposed, unless I'm missing something, is just another way of selcting a box size from a drop down. Here's a detailed step-by-step of what I'm trying to accomplish:

1 - perform load calcs on space

2 - add diffusers and VAV to space

3 - input airflow values to diffusers

4 - create logical system

5 - adjust airflow as needed

6 - VAV box updates size determined by adjusted airflow.

I've already made it so my diffuser neck sizes adjust with airflow, and I'm sure I can do it with my VAVs, but I'll only be able to use one family type with a set of dimension parameters controlled by several IF statements. At least that's the only way I see of making it happen.

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NDArchi03

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I guess I didn't understand fully what you are trying to accomplish.  Since, as you already know, you can't control the <Family Type...> parameter with formulas, what I described is the only way I know to link the two parameters you are trying to link.  I am sorry this approach falls short of what you need to accomplish.  I agree it would be awesome if you could control the <Family Type...> with formulas.  If you figure something out, post the solution here, I would be interested in seeing it.

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Gyvven

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Thanks for your efforts, I was hoping there'd be a simpler solution than creating a couple dozen formulas. I'll have something whipped up here in a bit, I hope.

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NDArchi03

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I guess I didn't understand fully what you are trying to accomplish.  Since, as you already know, you can't control the <Family Type...> parameter with formulas, what I described is the only way I know to link the two parameters you are trying to link.  I am sorry this approach falls short of what you need to accomplish.  I agree it would be awesome if you could control the <Family Type...> with formulas.  If you figure something out, post the solution here, I would be interested in seeing it.

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Gyvven

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I went forward with using the formulas to drive the sizing and I included a text string in the Remarks area to drive a Model name because Revit won't allow me to use a formula to drive the actual Model parameter. I'll just have to adjust my schedule accordingly.

Attached is what I cam eup with. The only problem I had was when I had typed it up in Word and tried to copy paste into the field Revit didn't like the feet and inches marks from Word and would return an error "The following is not a valid family parameter: 0' 8"." Huh? It took me while to notice the difference between marks, what I copied in and what Revit assigned in other parameters. Once I found it and copied into my formula it all worked great.

I've also used this formula to create two air terminals for our DuctSox fabric duct systems, one vertical and one horizontal. I'd like to combine these if someone can help me figure out a way to do it. The formula I used on these included 10 embedded IF statements and works fine. (I've heard that programs like Excel will only allow up to 7.) Now I can assign Airflow to a terminal instead of capping the ducts and putting a number in the Additional Airflow parameter. This allows me to create a logical system and have Revit generate a layout, use the duct size utility and report in the system browser and space schedules.

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Apexlion

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This is exactly what I am looking to do.  How did you get the diffuser to work?  I am new to this revit so any help would be great and muchly appreciated

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Apexlion

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Also, I see no formulas or anything in the attached family.  Am I missing something?  I have Revit MEP 2012

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