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Thread: Air Terminal family

  1. #1
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    Air Terminal family

    I made this 2010 family based on the info in the image below and looking for comments. All loads are type parameters and wonder if the connector is configured properly. Also, I could not get the masking region to mask out the ceiling grid properly so I used a void. Is there a way to achieve this without use of void? Lastly, are there any missing parameters? Thanks in advance.
    Air Terminal family-111.jpg
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    Forum Co-Founder Alfredo Medina's Avatar
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    Hello, Randy,

    Comments:
    • It is not necessary to mask the ceiling grid. The air terminal is located in a cell of the ceiling grid anyway.
    • It is not necessary to try cut the ceiling grid. Hosted Air terminal families are usually placed on the face of a ceiling that is in a linked file (the architect's model). So even if you put a void in this family, a void won't cut an element in a linked file.
    • Instead of worrying about masks and voids, which are not necessary, create a solid that represents the air terminal in section views. Usually, an inverted truncated pyramid.
    • In regards to the connector and parameters, try to imitate what's already there in the default MEP families (look for hosted supply diffusers). At this moment you are providing a round connector, probably for flexible pipe. You may need to have a different version of this family with a rectangular connector for a rigid duct, as well.

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    Thanks for the comments Alf, I hope you are doing well. The mask was just to cover the rare cases when it is not in the cell, as in a upfit. I was not aware it would not cut a linked file, thanks for the useful info.
    The main questions I had are pertaining to how this family functions in a system. From the chart there is a static pressure loss per a given air flow, but it seems to me these are dynamic values and I am not sure if loss from chart should be added to the loss at the end of the duct run calculated by Revit. I originally made the driving parameters TYPE parameters, thinking the loss should be added. Now I wonder if I should remove all the types and just zero out those parameters.

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    Forum Co-Founder Alfredo Medina's Avatar
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    I hope somebody else with more information about the technical details can chime in this thread and answer those other questions for you. In the supply diffuser families that come in the default library of Revit there is only one value for pressure drop and one value for flow, and no more. I assume that the final users can do the rest in their projects. I might be wrong, and I'll be glad to be corrected, but I don't think you need to include more than the default values there, and link the connector to the flow and the pressure drop parameters.
    Last edited by Alfredo Medina; August 1st, 2014 at 11:11 AM. Reason: additional info

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    Forum Addict josephpeel's Avatar
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    If you have a datasheet for a particular grille you can build that info into the family so it gives the pressure drop specified by the manufacturer.

    Set the pressure loss of the connector to Specific Loss and then link it to a family parameter. Then you can either use a formula that fits the manufacturers data, or a lookup table, to set the pressure loss for a particular flow. (I personally prefer formulas because of historic problems with lookup tables, but from 2014 onwards they can be loaded into families which makes them a lot more stable).
    An easy way to fit a formula to data is to graph it in excel and choose Add Trendline and Show Formula.

    You can also use manufacturers data in other useful ways, such as showing the throw of a grille with a dashed circle that changes size according to the flow. Or you can have the grille inform you that the noise level exceeds the design limits if the flow is too high, so you should use a different type or two of them instead.

    Whether to use instance or type parameters kind of depends on what level of design you are doing. If you are selecting/specifying particular models of grille then you should probably make them as types or individual families with the specific manufacturers data built in. If you are doing more of a design with performance specifications intead of particular grille models, it might be better to make one design grille with everything calculated as instance parameters. The results reported by the design grille could then be used later to select a specific model.
    Although I assume air flow will vary for every grille so anything controlled by flow should definitely be instance driven.
    Last edited by josephpeel; August 1st, 2014 at 11:35 AM.

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    Thanks for the input josephpeel. This family is manufacturer content (vertical throw supply diffuser) and since I don't get much feedback I came to the forum to find out what designers/end users need the family to do. The image in original post was the datasheet provided and there 3 connection sizes available. I created 27 types in the catalog per the datasheet and then questioned whether this was correct.
    For example, if a designer requires an air flow value in between the available types, I assume they would select the next higher cfm type. But that does not seem to be accurate.
    So then I thought about using a formula to calculate static pressure using this: Friction Loss in Ducts
    But after finding out the math did not match the datasheet I realized the formula was meant for the ductwork and not the terminal itself. I believe the data was measured, not calculated by the mfr.
    My background is not in HVAC, I imagine this contributes heavily. At this point I may be overthinking it and leaning toward providing types per the 3 connection sizes and calling it a day. Thanks again

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    Ree
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    Did I understand correctly that you are using 2010? If so I would consider not spending too much time because the way systems work change significantly. KIS. If calcs don't add to ROI and are not part of a BIM contracted deliverable then just get the spatial components and design intent in. But of course it is nice to push the envelope and learn what can be done by finding out what can't be done.

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    Forum Addict josephpeel's Avatar
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    Yes, upgrade if you can. so many improvements to MEP stuff in the last few versions

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    Well that is the deciding factor right there, thanks guys. I will zero out parameters and make them instance for now. I know I have got to upgrade (I do have current software), but keep pushing back due to library revisions.

  10. #10
    Forum Co-Founder Alfredo Medina's Avatar
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    Being one or two versions back from the current version of Revit when making families is fine. But four versions behind might be too much. As others have pointed out, some things might not work as expected in newer versions.

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