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Energy Plus: Airflow Distribution Network L-U factorization error

asked 2016-10-05 11:03:17 -0500

updated 2016-10-05 12:03:53 -0500

Hello Everyone,

I have been trying to model a simple building with an airflow distribution network in EnergyPlus, however I keep getting the L-U factorization numerical error, it says that one of the nodes is not connected to the outside via an opening or something similar. I have tried to add window openings with different configurations but the error doesn't go away.

My building is originally 13 levels, which I reduced to 3 for testing, with square geometry (66x66x5 m per floor). It has 50% glazing on all 4 sides. The plan is to model an airflow distribution network the models the HVAC air distribution in these zones, then I'm going to add external zones to model a double skin facade (DSF), which means outside each facade in the inner zones, there will be a cavity zone that has ~100% glazing, the main idea is to direct the exhaust air of the AHU of the inner zones into the DSF zones, where the exhaust ideally will be blowing from the bottom, and an open window will be at the top of the DSF cavity. My HVAC system is a Single Duct VAV with reheat terminal, including an AHU with heat recovery, along with supply and extract fans.

At this stage, I'm just trying to model the basic airflow distribution network of the inner building (without the DSF) but its giving me that error, I went over all examples in Energyplus, I believe my airflow network structure (including nodes and objects) is complete but maybe there is something I'm missing.

Does anyone have an idea about this error and why it persists? I've looked online, it seems that people solved it by changing their openings or windows, I tried different scenarios but I need to know the logic behind it!

P.S, I'm using Energyplus V8.2 because my final system will be connected to BCVTB

I tried to attach the schematic of the nodes and components in the AFN, as well as the idf file I'm using, but for some reason I'm not allowed, maybe because I'm a new user!

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Could you post the complete error message you're seeing?

Jason DeGraw gravatar image Jason DeGraw  ( 2016-10-06 11:08:58 -0500 )edit

I get this error:

* Severe * AirflowNetworkSolver: L-U factorization in Subroutine FACSKY. * ~~~ * The denominator used in L-U factorizationis equal to 0.0 at node = AIRLOOPZONESPLITTEROUTLETNODE3. * ~~~ * One possible cause is that this node may not be connected directly, or indirectly via airflow network connections * ~~~ * (e.g., AirflowNetwork:Multizone:SurfaceCrack, AirflowNetwork:Multizone:Component:SimpleOpening, etc.), to an external * ~~~ * node (AirflowNetwork:MultiZone:Surface). gravatar image  ( 2016-10-06 11:34:13 -0500 )edit

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answered 2016-10-06 19:14:56 -0500

Since the error seems to be referring to a distribution component, you should first check to make sure all of the distribution nodes are connected together as intended. If your simplification from 13 to 3 zones left something hanging, then that could be the issue.

Without the model, it is hard to be certain what is going on, but this error usually means that the node that is reported is not properly connected to the rest of the network. It can be hard to track down, since the "disconnect" can be a consequence of other elements in your model. If your zones are not connected together, then I'd try connecting adjoining zones together (use cracks with a high resistance to flow if necessary) and see if that balances things out.

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Thank you jason. Actually I did the minimization before building the distribution network, I uploaded my model to skydrive: I also attached a drawing showing the components of the model, which (I hope) shows there are no discontinuities in the system, i did a similar drawing for a similar working example, the matched. I really don't know where to go from there? gravatar image  ( 2016-10-09 00:00:04 -0500 )edit Were you ever able to solve this error? At the moment I'm facing the same problem...

BBel gravatar image BBel  ( 2017-06-06 06:27:44 -0500 )edit

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Asked: 2016-10-05 11:03:17 -0500

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Last updated: Oct 06 '16