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Thread: Blank Results for Fireflow Outputs

  1. #1

    Join Date
    Feb 2014

    Blank Results for Fireflow Outputs

    Hi. I'm getting Blank results for the following fields when i run a fireflow simulation.

    Design Flow (L/s) Design Pressure (m) Design Fire Node Pressure (m)

    Would there be any reason why this would be returning blank values? The other fields below are returning values.
    ID Total Demand (L/s) Available Flow at Hydrant (L/s) Critical Node ID Critical Node Pressure (m) Critical Node Head (m)

  2. #2
    Forum Moderator

    Innovyze Employee

    Innovyze Employee

    Join Date
    May 2015

    Would you be able to verify Software package are you running this on?

    If you are using InfoWater please make sure to download the latest update (currently Version 12.4 update 2) on this webpage:

    Here is the link for InfoWater 12.4 update 2: InfoWater/Suite 12.4 Update 002 for ArcGIS 10.0-10.6 (218.66 MB), 02/02/2018
    (note please redownload the update to make sure you have the latest recompile of this installer which includes files which should help reduce the blanks observed.

    If you have the latest update installed you may also wish to check the following

    1) What are you using for a search range in the Design Fireflow. If you are using "Entire Network" make sure you do not have junctions that have pressures before the fire is applied that are just barely above your minimum design pressure. When users do this it can make it impossible for the software to find a solution to the Design Fireflow as the flow that would solve this may be zero or very very small due to the low pressure just above the minimum pressure limit. This is often one of the primary causes of blank design Fireflow values.

    For example, I have a small model that generallycalculates all Design Fireflow values without issue. However, if I introduce a single new node in the search range that is just above my minimum pressureof 20 psi (14.6 M), I find that roughly half of the junctions now show up withblank Design Fireflow values. This illustrates how critical junctions justabove the minimum pressure can be in interfering with the design fireflow calculationsand all the blanks show the new node as the critical junction for the fireflow.

    To resolve this issue you can either modify your search range from Entire Network to only include junctions that are more reasonable. It is a good idea to only include nodes in the search range that are not below your minimum pressure before the fire is applied and that are not barely above your minimum pressure so as to not artificially limit the Design fireflow.

    In the US we often use 20 psi (14.6 M) for fireminimum Residual and design pressure and if you have junctions that are betweensay 35-20 (24.6 to 14.6 M) psi before the fire occurs would artificially limitthe available fireflow due to these junctions. It is often best toidentify a domain which includes all model nodes which currently have demand orthat could have demand applied to them. In the US this generallyrepresents locations where the junction pressures before the fire is appliedshould be above 40 psi (28.1 M) (or at least 35 psi or 24.6 M). Locationswith pressures below 35-40 psi (24.6-28.1 M) is often generally in the US notconsidered suitable to serve customers at and therefore would not generallyneed the same minimum fireflow pressure requirement.

    Since InfoWater 12.3 update 4 one can also apply differentdesign pressure to different junctions such that you could use theentire network as the search range but assign lower minimum pressure fireflowvalues to locations in the system that do not need to maintain the 20 psi (14.6 M) minimum pressure used in a fire analysis. These may be on transmission lines or occur out of a pressure zone and should only need to maintain a minimum pressure of say 5 psi (3.5 M) during a fire to maintain a reasonable minimum system pressure. Generally this is associated with junctions having pressures below 35-40 psi (24.6-28.1 M) as these are too low to be used to service customers. If you can identify the junctions with low pressure you can assign these a lower Design Pressure value and then can still include the entire network in the search range. Once can easily do this by selecting these junctions and assigning them all a "zero" fireflow requirement and a residual and design pressure requirement of 5 psi (3.5 m) in the fireflow table. This is most easily done by placing these junctions in a domain and assigning them a zero fireflow using the "Group Editing" Icon (a red satchel with a pencil) (or found in the InfoWater menu-> Edit-> Group Editing command). Once added then open the fireflow demand table in the DB editor using the domain as the data scope in (Fireflow Demand table in the "extended modeling data" folder of the DB Editor). One can then easily group edit the residual pressure and Design Pressure columns and set these to use 5 psi (3.5 m) instead of the default 20 psi (14.6 M) used in the Fireflow tab of the run manager.

    If this does not resolve all your other blank Design Fireflow questions (it should resolve most of them) then you may need to run a manual fireflow on those junctions remaining to see why the software is having difficulty calculating an answer. Most of the time there is either something not allowing the model to converge under the extreme conditions associated with the design fireflow that is not seen under non-fireflow conditions. Manual fire-flows can be completed by either placing a demand on the junction itself and running a standard analysis or by using the multi-fire flow tool and selecting only a single junction. Both options allow you to see how the model is responding at fireflow conditions and to quickly verify where the problems might be. One can also run a hydrant curve for the junction in question. If the hydrant curve cannot show a result at 20 psi, then something is causing the model to be unable to converge at higher flows.

    The good news is, you generally only need to verify if the junction can provide the required fireflow and maintain the minimum system pressure rather than actually verifying the highest flow possible it can serve. This is most easily done using the multi-fireflow tool which will use the assigned required fireflow. With the multi-fireflow tool you will be able to open a junction report using the Multi-fireflow output as the source and verify the pressures in your search range are all above the minimum requirements. If they are you can consider the required fireflow to be the Design Fireflow.

    To best check if there is something causing model instabilities we suggest you manually add a point demand on the junction and run a standard analysis. If this run has difficulties converging there is something in the model setup that would interfere with the fireflow tool being able to get an answer as well.

    Also make sure to check "unbalanced" as continue (instead of STOP) in the simulation options general tab or once an unbalanced run is found all the simulations stop. If this occurred in one of the early fireflow runs in could interfere with other runs being able to take place.

    I will send this information out to you in a direct email as well in case you wish to discuss your specific model issues further.

    Patrick Moore

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