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Thread: Error with Multiple "System" Pipe Connectors on a One Piece of Mechanical Equipment

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    Error with Multiple "System" Pipe Connectors on a One Piece of Mechanical Equipment

    I'm testing a system for populating connected capacity through a VRF piping system. It works great. Any pipe shows how much capacity (Flow) is connected downstream of it. The outdoor unit is actually a multi-frame unit, so it has three connectors in total that all supply refrigerant into a single pipe. I've got system flow connectors that divide the total flow into each discrete unit and then add it all back together in the family to report it in a schedule. The flow populates correctly in the pipes but I'm getting a rather curious error in the system containing the outdoor unit family:

    "It is not possible to calculate the flow since there is inline equipment that is configured as end of line. Please check equipment in this system and make sure that the equipment connectors used have global system classification and a calculated flow configuration. Global equipment connectors used inline should always be linked to each other."

    It's also preventing me from using the System Inspector, which is not the worst thing, but makes me wary of having unexpected errors down the line.

    A few provisos:
    I do not want a single connector. Modelling the header assembly in the family leads to other problems that I can avoid by making it all pipe in the project.
    I could model each individual unit, but the manufacturer supplies the whole assembly under a separate model number, which would them screw up my schedules, making it a no-go.
    I haven't made the connectors Global, and you can't link three connectors together anyway.
    I haven't removed the other connectors (for refrigerant gas and mixture pipes), since I'll need to connect those systems up in projects too.
    For better or for worse, I'm in Revit 2017.

    Has anyone come across this error before and dealt with it? Or can anyone see an error in the way I've set up the system?

    Attached Thumbnails Attached Thumbnails VRF Flow Test Question 1.png  

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    Forum Addict josephpeel's Avatar
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    I dont know this specific error, but I see immediately one thing that will cause the system not to work.
    Revit expects every system to have a branched tree structure, with all the end unit connections converging to eventually one open end (Or end equipment with a single Calculated connector.). That way the program knows which way flows should go and how they need to be added together in the pipes.

    If you split the pipe where it says 45,000 BTU, everything should work, because then you will have two converging branch systems with an open end.
    So, personally I would model the outdoor and indoor unit networks with different System Types (VRF Primary and secondary or something) and then, if necessary, join them with a family that accepts the calculated flow from the outdoor units and the calculated flow from the terminal network.

    Then you can also build a check into the family to see if the indoor unit network exceeds the capacity of the outdoor units. Add one too many fan coils, so the flow is greater than the outdoor unit flow, and the family will show a warning.

    This is also how I model chillers, with the primary network converging from chillers to the header, then separate, secondary, networks going out to the end units. You can also just stop the open pipes at the header and compare the system totals if you dont want to make the connector family.

    Or, if the problem is in the changeover/group header families, consider which way the information needs to flow. You may want to make all the connections going to the indoor network Calculated, to total up the connected flow, and then one outgoing connector for the outdoor units as Preset, which is set to be the sum of all the others. That way the branched hierarchy of the system will still be clearly maintained through the unit.
    Last edited by josephpeel; January 9th, 2019 at 11:27 AM.

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    Either it's too late in the evening for me to be interpreting your post, or I'm going to need a diagram explaining your first suggestion. I have it set up like the second way you describe; the connector properties I showed in the picture were just for those specific ones on the outdoor unit. Fan coils have a preset value that flows to a calculated connector at the branch controllers (header units). The controller sums all the incoming values and sends it up the way to the next branch controller or the outdoor unit. And the problem isn't that the system doesn't work; like I said in the OP, the pipes all report the correct flow, even the ones splitting to the individual outdoor units. The families are all working as I expected.

    The error is really what's throwing me for a loop. Searching it in Google only brought up API documentation, so it's evidently not the most common of problems. Taking a step back, I might try removing the return connectors (there are two on each unit) to see if that is making Revit think it's a piece of inline equipment. Maybe it has nothing to do with the supply side at all!

    Will report back after I get a free minute to test it at work.

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    Forum Addict josephpeel's Avatar
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    Interesting, thats how it should be.. Maybe just another one of those errors you can ignore

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    Evidently it has to do with having multiple connectors of the same system classification on the piece of equipment. Deleting all but one of the supply connections resolved the error. I think the only way to get the system to work without errors in the way I intend it to work is to model each discrete module of the outdoor unit, which will not suit my purpose. Not ideal, but I see no real reason to pursue this issue further. I'll add this warning to my "known errors to ignore" list with a note "as relating to VRF outdoor units" or something to that effect. Flow populates and schedules, I'll just be satisfied that there's no System Inspector option for those upstream systems.

    If anything changes, I'll update this thread as needed. Thanks for your input.

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    Forum Addict tzframpton's Avatar
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    What about using a Connector family?

    And out of curiosity: why try to manage each individual outdoor units like that? I mean, I know that VRF systems will combine outdoor units on a rack but (and correct me if I'm wrong) it's built to act as a single unit in tandem, correct? I know what you've done is more accurate in terms of how the system is built but the way Revit works I'm not sure it's the best approach. Again, just curious is all.

    -TZ

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    I might see what using a Connector Family would do, but I think Revit would still interpret the whole unit as "inline equipment."

    As for the way VRF systems work, the sub-units do work in tandem (i.e. "twinning"), but they each have their own refrigerant and electrical connections. But the manufacturers supply them as a package with a separate model number. I want that to schedule and the positioning of the sub-units to be consistent more than I want the system to generate no errors. So the single, double, and triple-module models are each a separate family, with one, two, and three sets of connectors each. In terms of model management, modeling each sub-unit as a discrete piece of Mechanical Equipment would be more trouble than it's worth. Schedules screwy, positioning off; the only possible benefit is that Revit wouldn't yell, but it would still be more work for less of a payoff. And it would eventually generate questions, where the answer, "It makes the program work better!" would not fly. As much as I want Revit to be happy, in this instance, field accuracy trumps resolving this really obscure error.

    Unless I've totally misinterpreted your post Tannar, in which case, feel free to correct me.

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    Forum Addict tzframpton's Avatar
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    Makes sense, thanks for the response.

    -TZ

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