This TechNote explains how to configure automated Fire Flow and how to interpret and troubleshoot calculated fire flow results, using WaterCAD or WaterGEMS.
Table of Contents
Fire Flow Alternative
Before reading this Technote, it is recommended that the user complete the Fire flow Quick start lesson. This is located in WaterCAD/WaterGEMS Help documentation, under Contents > Quick Start Lessons > Automated Fire Flow Analysis. You can also find them at File > Help > Quick Start Lessions (for V8i, go to Help > Quick Start Lessons). You can also watch a video here. You can also watch this short video highlighting the ease-of-use enhancements in the latest CONNECT Edition versions.
The automated fire flow analysis is a common tool used in WaterCAD and WaterGEMS to ensure enough protection is provided during fire emergencies. The user is able to enter constraints in order to determine how much fire flow is available at hydrants while maintaining adequate system pressure. Several tools available to aid in understanding fire flow results.
Starting with WaterGEMS V8i SELECTseries 6, the SCADAConnect Simulator tool has a new Fire response option. Fire Response enables you to place a fire demand (or other emergency flows) at a node for a period of time to determine its impact on pressure and flows and possibly test alternative ways of responding to the fire. The following link has information on this: Simulating a Fire Response in SCADAConnect Simulator or WaterOPS.
Note: The automated fire flow steps below are only for WaterGEMS and WaterCAD. Though this feature is mentioned in the HAMMER Help documentation (as of February 2020), this feature is not available in HAMMER.
Note: Starting with the CONNECT Edition Update 3 (version 10.03.03.72) of WaterGEMS and WaterCAD, additional features are included to help review the results, particular when the fire flow run fails. Information on these features can be found below. They can also be found at this link.
Note: For a demonstration, see this Webinar recording.
Fire flows are computed at each node by iteratively assigning demands and computing system pressures. In short, it looks at each node one at a time, and determines the amount of flow available without violating the desired constraints. The following link has further information and details on the workflow: How does the Automated Fire Flow work?
Note: If you are looking for the amount of flow available at a specific pressure, see "Finding the flow available at a certain pressure" in the troubleshooting section below.
Configuration for the automated fire flow analysis is done under the Fire Flow alternative. This is found under Home > Alternatives or Analysis > Alternatives (for CONNECT Edition) and Analysis > Alternatives (for V8i). Find Fire Flow in the list of alternatives and expand this. There will be at least one alternative listed here. You can used Scenario and Alternative management to add more, as needed. When computing the active scenario, the Fire Flow alternative assigned to the scenario is used.
At a minimum, you should specify values for the Fire Flow (Needed), Fire Flow (Upper Limit), Apply Fire Flow By, Pressure (Residual Lower Limit), Pressure (Zone Lower Limit), and select a Fire flow Nodes selection set. Below is an explanation of each of the main fields found in this alternative:
For more information on Fire Flow (Needed) and Fire Flow (Upper Limit), see this link: Understand the Fire Flow (Needed) and Fire Flow (Available) fields for an Automated Fire Flow analysis.
Note: If the above options need to be configured differently for each junction/hydrant, you can specify "local" fire flow constraints by clicking the "Specify Local Fire Flow Constraints?" check box next to the junctions/hydrants in the list at the bottom of the fire flow alternative. If this box is not checked, that particular fire flow node will utilize the global constraints entered at the top of the fire flow alternative.
Note: It is important to understand that for the minimum zone pressure constraint, the program checks pressures for all other nodes in the model that are assigned to the same zone as the fire flow node in question. The zone is an attribute of the node. For example, consider a case where there are two nodes in the fire flow selection set: J-1 and J-2. J-1 is assigned to Zone A and J-2 is assigned to Zone B. Fire flow nodes are checked independently during the analysis, so when J-1 is being computed, the program will check pressures at all other nodes that are also assigned to Zone A and compare against the minimum zone pressure constraint. Then, when the analysis moves on to J-2, it will be checking pressure at all nodes assigned to Zone B. So, the program isn't running a fire flow analysis on a particular zone - it considers pressures at nodes assigned to certain zones, based on the fire flow node it is currently analyzing.
Note: If you have nodes failing because of low pressures on the suction side of a pump, see this link: Fire flow nodes are failing because of low pressures on the suction side of a pump. Starting with WaterGEMS and WaterCAD version 10.03.03.72, a Nodes to Exclude feature is included. This is a set of nodes that would be excluded when checking the pressure constraints. This field would be used in a case where the calculation of the active fire flow scenario already violates at least one the pressure constraints for some nodes before a fire flow is even applied. In addition, a user notification may be generated that says "Pressure constraints violated before fire flow added. Use 'Node to exclude' if needed."
Note: The minimum system pressure constraint is an optional pressure constraint that accounts for all nodes in the system. If any node in the model, even if it is not in the same pressure zone, is below the pressure constraint, the fire flow run may fail. Pumps and valves can be included in this. If you do not want to consider the pressure at pumps and valves in the calculation, go to the calculation options and set the field "Consider pumps and valves in Min. System Pressure" to False.
After you have configured the fire flow alternative, the next step is to assign that alternative to the scenario you would like to compute.
There are several ways you can view the results of your automated fire flow analysis. Below describes the most common.
After computing the fire flow analysis, open the FlexTables manager by going to Home > FlexTables or View > FlexTables (for V8i, go to View > FlexTables). Open the Fire Flow Node Table. Starting with WaterGEMS and WaterCAD version 10.03.04.05, you can also access the Fire Flow Node Table from the Calculation Summary.
Note: If you are looking at the general results in other FlexTables, such as pressure in the junction FlexTable, you will be viewing the baseline steady state results for your model, without any fire flow demands present. You will need to use the Fire Flow Results Browser and include information for auxiliary reporting in the Fire Flow alternative in order to see additional results in the element FlexTables.One of the first columns is "Satisfies Fire Flow Constraints?" This will be checked only if the particular fire flow node can provide at least the needed fire flow, while satisfying the fire flow constraints. Here is a description of some of the other fields available in the fire flow report. Field colored in red are particularly important for typical troubleshooting.
Note: If you are looking at the general results in other FlexTables, such as pressure in the junction FlexTable, you will be viewing the baseline steady state results for your model, without any fire flow demands present. You will need to use the Fire Flow Results Browser and include information for auxiliary reporting in the Fire Flow alternative in order to see additional results in the element FlexTables.
Note: If your table does not display one or more of the below fields, you can add it using the Edit button at the top of the Fire Flow Node Table.
The Flow (Total Available) is not the flow that will be discharged from a hydrant when open to atmosphere. It is the water that will flow to the node when the pressure at the node is 20 psi (or whatever residual pressure is required). Consider the case where two 48 inch pipes meet at a node. The Fire Flow (Total Available) will be very large. However, if there are no hydrants at/near the node, the available fire flow will be zero. The value reported as Fire Flow (Total Available) is what the Insurance Service Office Fire Suppression Rating Schedule calls Main Capacity. The Test Location Capacity for ISO is the lesser of Main Capacity, Hydrant Distribution and Supply Works Capacity. Except for very large mains, the Main Capacity is usually limiting.
The Fire Flow Results Browser enables you to check results of other elements in your model during individual fire flow runs. The Fire Flow Node Report will show available fire flow, as well as residual pressures at the fire flow node, the minimum zone and system pressures, and select other results, like the maximum pipe velocity in the system.
If you would like to see other results, such as pipe velocities, hydraulic grades, pump results, etc., during a specific fire flow test, you can use Fire Flow Results Browser. First, you will need to make sure that you have set up your Fire Flow Alternative for this function before running the fire flow analysis. The following is a table with information on the fields you will need to use.
After you have set up your Auxiliary Output Settings and run the Fire Flow analysis, go to Analysis > Fire Flow Results > Fire Flow Results (for V8i, go to Analysis > Fire Flow Results Browser). Starting with WaterGEMS and WaterCAD version 10.03.04.05, you can also access the Fire Flow Results Browser from the Calculation Summary for scenarios using a fire flow run.
Starting with WaterGEMS and WaterCAD CONNECT Edition Update 3 (version 10.03.03.72), if a fire flow run fails you will see some additional information for why it fails, such as "Residual Pressure Failed." For older version, it will simply state that the fire flow node failed with no additional information on why the node failed.
For more information on the Fire Flow Results Browser, see the following link: Using the Fire Flow Results Browser to view hydraulic results during a fire flow in FlexTables and Properties.
Another good way to review an automated fire flow analysis is to use color coding. For example, you can color code junctions and hydrant based on the values for total available fire flow, to see areas where the available fire flow is lacking. Another useful color coding could be one based on the "Satisfies fire flow constraints?" attribute. For example, you could color code junctions where "Satisfies fire flow constraints?" is "False" shows up as red with a larger size. This would be done by using the "Color and Size" option in the Color Coding dialog.
You can also use color coding with the Fire Flow Results Browser. For example, you could color code pipe velocities so that when you click a fire flow node in the Fire Flow Results Browser list, the color coding will update to show the velocity distribution when fire flow is applied to that particular node.
Starting with WaterGEMS and WaterCAD version 10.03.04.05, if the active scenario is a fire flow scenario, you can find an overview of results. In the Fire Flow Summary tab at the bottom of the Calculation Summary, you can find brief statistical overview of the fire flow results, such as the number of nodes that passed or failed. You can also quickly access the Fire Flow Node Table and the Fire Flow Results Browser from here.
In some cases, you may notice that the results in your fire flow report show "N/A" after computing the model.
In the Fire Flow Node Table, you may notice that one or more fire flow nodes does not satisfy the fire flow constraints. This will occur when the total available fire flow is less than the needed fire flow . There are several reasons why this could occur.
To check which specific node had the lowest pressure in the zone, check the "Junction w/ Minimum Pressure (Zone)" field. This may be a node at the suction side of the pump or at some other location that you may not be concerned with. In such a case, it is recommended that you assign a different zone to these nodes. This way, it will not be in the same zone as any fire flow nodes and thus will not be considered (unless you are using the minimum system pressure constraint).
Note: Starting with WaterGEMS and WaterCAD CONNECT Edition Update 3 (version 10.03.03.72), there is a Nodes to Exclude option in the Fire Flow alternative. You can add nodes on the suction side of pumps to a selection set and set the Nodes to Exclude field to this selection set. The fire flow run will ignore these elements during the calculation.
If the available fire flow is less than the upper limit, yet all the constraints described above are not violated, chances are that this was caused by the network becoming unbalanced. You can confirm if this is the case by checking the "Is Fire Flow Run Balanced?" field in the Fire Flow Node Table. If this occurs, try running a manual fire flow analysis on that junction. For the manual run, just make sure the calculation type in your calculation options is set to “Hydraulics Only” and that you have entered the value for the total needed fire flow as an additional fixed demand on that junction. Run the analysis and check your user notifications for an Network Unbalanced error. One solution to this is to increase the max trials value in the calculation options, but you should also consider investigating other causes, such as data entry errors. See: Troubleshooting the Network Unbalanced or Cannot solve network hydraulic equations user notification
Note: It is possible to apply local fire flow constraints when computing automated fire flow runs. In the table at the bottom of your Fire Flow alternative, you can set node-specific constraints, which override the global constraints set at the top. This could potentially cause confusion when viewing fire flow results. For example, the total available fire flow for a certain node may be less than what you believe the needed fire flow value is, but still showing as satisfying the fire flow constraints. If you had a local "Fire Flow (Needed)" set to a lower value, this could be valid. Make sure you include and check the "Fire Flow (Needed)," "Fire Flow (Upper Limit)," "Pressure (Residual Lower Limit)," and "Pressure (Zone Lower Limit)" fields in your Fire Flow Node Report.
Consider the following Fire Flow Node Table, with no minimum system pressure or maximum velocity constraints used:
J-10 - This node passed the fire flow test, as indicated by the "Satisfies Fire Flow Constraints?" field. The total available fire flow is 2012.68 gpm, which is above the total needed fire flow of 462.68 gpm and above the fire flow upper limit of 2000 gpm. The Fire Flow alternative was set up to add fire flows to base demands, and there is a base demand of 12.68 gpm on this node. The total available amount of 2012.68 gpm accounts for this base demand as well. Since the fire flow is added to the base demand, the total available fire flow can be above the upper limit without violating any fire flow constraints. The fire flow analysis stopped at the upper limit value (plus the base demand) to prevent unrealistically high flows from being computed.
J-169 - This node passed the fire flow test with a reported total available fire flow of 557.82 gpm. This is above the needed fire flow but below the upper limit. The reason why the fire flow test stopped at this flow is because a higher flow rate would violate the zone pressure constraint. As you can see, the "Pressure (Calculated Zone Lower Limit)" field is equal to the user-defined minimum zone pressure constraint of 20 psi. The "Junction w/ Minimum Pressure (Zone)" field shows J-170 as the node with the lowest pressure in the zone. This means that although the residual pressure at J-169 (24.3 psi) is above the constraints J-170 will cause the fire flow run to stop because of the zone pressure constraint.
J-171 - This node passed the fire flow test with a reported total available fire flow of 489.28 gpm. This is above the needed fire flow but below the upper limit. The reason why the fire flow test stopped at this flow is because a higher flow rate would violate the residual pressure constraint. Although the minimum zone pressure of 23.5 psi is above the 20 psi constraint, the residual pressure calculated pressure at J-171 is equal to the residual pressure constraint of 15 psi. At a higher flow rate than 489.28 gpm, the residual pressure would drop below 15psi, which would violate the pressure constraint.
J-159 - This node failed the fire flow test, as indicated by the unchecked "Satisfies fire flow constraints?" field. This is because the total available fire flow is 327.06 gpm, which is less than the total needed flow of 453.17 gpm. The reason why this node can only supply 327.06 gpm is because of the residual pressure constraint. Even though the minimum zone pressure (60.4 psi) is well above the zone pressure constraint, the calculated residual pressure is equal to the residual pressure constraint. This means that the pressure constraint would be violated at a flow any higher than 327.06 gpm.
J-154 - This node failed the fire flow test, because the available fire flow of 289.24 gpm is less than the needed fire flow of 455.39 gpm. The reason it can only supply this much flow is because of the minimum zone pressure constraint. Although the residual pressure (28.5 psi) is above the constraint, the minimum zone pressure is equal to the constraint, with J-158 as the "Junction w/ Minimum Pressure (Zone)". This means that J-158, which is in the same zone as J-154, is preventing any additional flow from being extracted without violating the minimum zone pressure constraint.
J-3 - This node, along with other junctions below it, show "N/A" for all calculated fields. This is because these nodes are not included in the fire flow nodes selection set, set in the Fire Flow alternative.
J-1 - This node failed the fire flow test with a total available flow of zero. This means that even without any demand at all on J-1, the baseline pressures in the model fall below the constraints. This is indicated by the calculated residual pressure of -1.4 psi. This means that with zero demand on this node, the pressure at J-1 is -1.4 psi. Since this is well below the constraint of 20 psi, the fire flow test fails and the available fire flow is reported as zero. This particular junction is located on the suction side of a pump, so it probably should be excluded from the fire flow nodes selection set so that the fire flow run for this node does not fail.
J-2 - This node also failed the fire flow test with a total available flow of zero. In this case, it is because the minimum zone pressure constraint was violated. This means that without any demand at all on this node, the pressure at J-1 is -1.4 psi. J-1 is in the same zone as J-2 and as seen above, it is at the suction side of the pump. Excluding this node from the zone will help so the fire flow run does not fail.
Note: Starting with WaterGEMS and WaterCAD CONNECT Edition Update 3 (version 10.03.03.72), if the pressure constraints are violated before any fire flows can be added to a fire flow node, there will be a user notification that says "Pressure constraints violated before fire flow added. Double click for details and use 'Nodes to exclude” if needed."' In that case, the fire flow results will be reported as N/A and no results will be available.
If you attempt to use the Fire Flow Results Browser, you may run into problems if it is not configured correctly. Symptoms include:
This is caused by improper configuration in the Fire Flow alternative. Open the Fire Flow alternative and check the "Auxiliary Output" section. If you would like to be able to check auxiliary results for any fire flow node, regardless of whether it passed or failed, select "All nodes" for the "Fire Flow Auxiliary Results Type." Doing this will ensure that all nodes show up in the list. At this point, you will be able to see auxiliary results for pipes adjacent to the fire flow node that you select in the Fire Flow Results Browser. If you would like to see results for more elements, you will need to choose a selection set for the "Auxiliary Output Selection Set". If you want to be able to see auxiliary results for all nodes, you can create a selection set of all nodes. To do this, close the Fire Flow alternative, select all elements in the model, right-click anywhere in the drawing pane, and choose "Create Selection Set." In the Fire Flow alternative, choose the selection set for the Auxiliary Output Selection Set. When you compute the fire flow simulation, you will be able to check results for all elements in the model for a given fire flow node.Note: The more fire flow nodes available in the list and the more elements included in the output selection set, the longer the calculation will take to perform and the more disk space the saved results will take up.
Note: The more fire flow nodes available in the list and the more elements included in the output selection set, the longer the calculation will take to perform and the more disk space the saved results will take up.
The Fire Flow Node Report can display pressure results at the needed fire flow. This can be useful to see how low the residual or zone pressure results will be in order to get to the needed fire flow. In the Fire Flow Node Report, find the fields "Pressure (Calculated Residual @ Total Flow Needed)" and "Pressure (Calculated Zone Lower Limit @ Total Flow Needed)." If the fields are not in the Fire Flow Node Report, you can use the Edit button to add the fields to the report.
In some cases, you may want to know the available fire flow at a node at a specific pressure (such as 20 psi), regardless of the other constraints. However, by default the Fire Flow Node Report will display the total available flow without violating the constraints or upper limit fire flow.
If you want to ensure that the available fire flow always shows the flow available at 20 psi, set the residual pressure constraint to 20 psi, the zone pressure constraint to a very low value such as -999, uncheck the system pressure and velocity constraints, and set the upper limit fire flow to a very high flow. This will ensure that the program continues to try more flow until the pressure at the fire flow node drops to 20 psi, and the available fire flow result will always show the flow at 20 psi.
You can also use the hydrant flow curve option from the right click menu (on a hydrant or junction) to see the curve of flow vs. pressure at the node (so you could look at the flow at 20 psi).
Currently, the pressure at customer meters is not currently part of the zone or system pressure constraint check, nor is it included in the auxiliary results (for use with the fireflow results browser). In a typical model with a large number of customer meters, this would cause too much data to be stored and increase the complexity of the fireflow calculations. Instead, you would need to rely on the pressure at nearby junctions which would typically be a similar elevation.
Introduction to Automated Fire Flow in WaterCAD and WaterGEMS (YouTube)
Enhanced Fire Flow Analysis in WaterGEMS & WaterCAD (YouTube)
WaterGEMS V8 Automated Fire Flow FAQ
Understanding the "Fire Flow (Needed)" and "Fire Flow (Upper Limit)" Fields for a Fire Flow Analysis
General WaterGEMS V8 FAQ
WaterGEMS V8 Modeling FAQ
Hydraulics and Hydrology Forum
SCADAConnect Simulator for WaterGEMS SS6
Simulating a Fire Response in SCADAConnect Simulator