Duct system cannot calculate the flow

[Anonymous]

I set up two return air vents on the air handler, but one return air vent at the end. The connecting piece at the return air outlet of the air handler is set to the inlet, The connecting piece at the end of the tuyere is the outlet. The two air vents at the air handler are required to evenly divide the air volume, Checking the system shows that the flow cannot be calculated.

Can anyone help me get the flow?

Thanks in advance

[hmunsell]

In the warning message it looks like Revit is telling you how to fix it. did you try what the message is recommending?

• can you upload a sample RVT file with the content you are showing in your screen capture for us to look at.

[Mahmoud.Ziedan]

@Anonymous 

1-edit the family 

2-Select the connectors

3-Make sure the connector Flow configuration is set to Calculated or system if you want the connector to be a percentage of the flow.

I think this will solve your issue
Also, I recommend uploading your family.

Please, if this solved your issue, marked as an answer to help others.:)  

[Anonymous]

Yes. This is the REVIT file of the 2021 version, There are two return air outlets on the AHU equipment, and two return air ducts are connected, and the two return air ducts are connected to a common external return air outlet.

[Anonymous]

1.  I selected the connector but the problem was not resolved;

2.  set the connector at the AHU as the system, and the corresponding assigned flow would appear when the air duct was selected, but there were still problems during the system inspection and it was not resolved；

3.  Currently trying to establish a combined family, hoping to solve the problem；

[iainsavage]

That is, in my experience, a very strange duct layout and I’m confused as to why you would want to connect it like that - maybe Revit is confused too? The solution though is probably to follow the instructions in the warning message.

[Anonymous]

In fact, this is a segmented air conditioning unit, but there is no segmentation when the family is built. The two return air outlets represent the fresh air to enter on the two groups;
According to the warning message, all pipe fittings are set to global and calculated, but the warning is still not eliminated.

[Anonymous]

I divided the family into different groups and nested together, but the problem is still not solved;

I don’t know if there are other solutions

[iainsavage]

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@Anonymous wrote:

In fact, this is a segmented air conditioning unit, but there is no segmentation when the family is built. The two return air outlets represent the fresh air to enter on the two groups;

---

I have no idea what that means - is there a product data sheet or catalogue for this unit, I would be interested to know what it is. 36 years in the trade and every day still brings something new to learn.

[RobDraw]

Read the warning. The first sentence says that there is equipment that is configured wrong. Is the AHU set as a terminal unit?

Are there any VAVs or similar equipment that are set as a terminal unit?

That duct configuration looks wrong. More likely is that one return is for outside air and the other is for return air from the space. If not, it could be an alternate connetion (either or) or additional connection for multiple returns not splitting the line from a single return. Splitting the return just doesn't make sense.

i cannot test with that family as I've only got 2020 with me. Like @iainsavage above, please share the cut sheet for the equipment or give us the manufacturer and model #. That might help.

[hmunsell]

I didn't see anyone suggest this when i read thru the replies.... 

When I linked the connectors and set the horizontal connector to Primary the error went away.  not sure how this effects any calculations though :-)....

[iainsavage]

I would still like to understand the real-world application of this unit. I don’t understand the airflow process but am always keen to learn new things.

[Anonymous]

The equipment is a rotary dehumidifier. The two return air openings I drew on the equipment represent the two outdoor fresh air inlets in the equipment, and the fresh air is used to take away the moisture on the runners.

[Anonymous]

It still has errors. I ultimately need to calculate the air duct pressure drop. Any error will cause the duct pressure drop to fail to be output. Maybe the Revit thinks my connection is unreasonable.

[iainsavage]

So are those dessicant wheels that are shown? Is the bottom deck the regeneration stream and the upper deck the process side?

Are the labels at the various parts your own labels, or is that the manufacturer’s own diagram?

I’m just trying to understand the air flow process so that the correct connector configurations can be worked out.

[Anonymous]

The label is my own labels, the picture is the airflow process.

[iainsavage]

Okay, that makes a lot more sense.

Couple of questions though:

1. Is there definitely exhaust air between stages on the regen stream (top of your latest diagram)? So is there less air passing through the regen part of the second (left) wheel?
2. Is there not any exhaust air from the room-side stream? How is the mass balance preserved when the return air and outdoor air are added together compared to the supply air volume - is the outdoor air volume offset by passive leakage from the room?