Family Instance Parameters Problem

[ayracon89]

I'm having an issue creating a VAV and Air Terminal family using instance parameters. Essentially, I want the size of a VAV and the size of an Air terminal to be determined by the Air Flow (CFM) ex. If Flow < 320 then the neck diameter of the air terminal will be 8". I was able to do this successfully but I'm having an issue when I connect to a system. Since the air flow is an instance parameter (can't use type parameter since the air flow is different for each air terminal) then the neck diameter has to be an instance parameter as well. When I type 320 CFM as the air flow value, the air terminal automatically makes the neck diameter 8", perfect so far, but if I accidentally take a 10" round duct and connect it to my air terminal neck, the neck size changes from 8" to 10". I'm having the same issue with the inlet and outlet dimensions of my VAV box. Everything sizes correctly based off the air flow, but if I connect a different sized duct to the equipment then my inlet/outlet/neck diameter change to whatever size duct is connecting into it. Is there a way for my families to still automatically change dimensions based off the air flow while also preventing any change to the neck diameter/outlet/inlet sizes due to a different sized duct connection to the equipment? I was able to successfully prevent the neck diameter/outlet/inlet size from changing due to a different sized duct connecting to the element, but I only achieved this by changing the parameters from "instance" to "type" which forced all of my air terminals to be 320 CFM, so this approach didn't work either. I'd appreciate any advice on this matter.

[nathan.chapman]

What do you have your Round Connector Dimension set to?  Make sure its Use Diameter not Use Radius and adjust what you need to to accommodate this.  That should solve your issue.

[fabiosato]

Hello,

It seems that your connector properties have some problem, if you post your family it will be possible to check and test.

[nathan.chapman]

I've attached a small project with a VAV setup like it you want.

[ayracon89]

I've attached my current VAV family. I've was messing around with it yesterday, so hopefully I didn't accidentally change the family.

[ayracon89]

My round connector dimension is diameter. I've tried locking the inlet dimension to reference planes as well as the diameter instance parameter, but nothing seems to correct my issue so far.

[ayracon89]

bump

[Anonymous]

Connector elements will always inherit the dimension of the attached duct/pipe/conduit, so you'll either need to be diligent about using the correct duct diameter or create types for each CFM value.

[ayracon89]

I've only found the connector element inherits the dimension of the attached duct/pipe/conduit if the size of the connector element is related to an instance parameter. If the size of the connector is a type parameter than the size will remain the same no matter what size the attached element is. My issue is I can't base the connector element off of a type parameter because the size of the connection is related to the CFM value, which is different for almost every VAV box, so the CFM value has to be an instance parameter which forces my duct connector size to be an instance parameter as well. I'm hoping to find a solution where I can have all the dimensions of my VAV box be determined from the CFM value of the box and lock these dimensions unless the CFM value decreases or increases enough to change the size of the box. I currently have the box modeled correctly so it responds to the CFM values I enter, but if I accidentally connect a different sized duct or pipe, then my box will snap to those new dimensions. I want to avoid this problem because I won't be the only one using this family and I can't guarantee others will be able to understand what to look out for. There has to be a way some how.

[Anonymous]

The closest approximation to what you're trying to achieve is probably this: create a set of different types, each with a defined CFM range that defines the duct/connector diameter. Use type parameters for all of these dimensions so that the connector/inlet diameters won't change if you use the wrong duct dimension. Then create an instance parameter defining the CFM for each individual box for your schedules/tags/whatever documentation method you're using. I don't think there's really another way to do everything you want to do.

I'm assuming here that an 8" duct can accommodate 150-500 CFM (or whatever the actual values are). Most of what I know about HVAC systems is that they are a PITA to coordinate electrically.

[ayracon89]

That's the only solution I've been able to come up with so far to prevent the duct connectors from changing size, but I'd prefer to just have one family type. On projects with hundreds of VAVs I'd have to go back through at the end of a project to confirm the VAVs are correct. CFMs change a few times throughout a project so Revit would generate an error if a VAV box can't handle the cfm; this would be the only downside. This may be the only solution for now until Revit can operate the way I need it to when creating families.

[dbutts7]

Take a look at the default electrical panel families (lighting and appliance panel board - 208V MLO for example). They use a formula (rather long) that uses > max #1 pole breakers to specify a range. The range value is linked to a parameter based on sizes, which can be assigned to the type. This gives you the ability to create a size range based on instance values and associate them with a type value.

I'd have to hack yours out a little bit to make the correct association, but this is the only way I know to do this and keep your types down to a minimum.

thanks - db