Problem

Why do I see "N/A" for all fire flow results for all nodes in the Fire Flow Node Table?

In more recent versions, this may be accompanied by the User Notification "Pressure constraints violated before fire flow added. ..."

Solution

You may not have the calculation option set to perform the automated fire flow calculations. Go to Home > Options or Analysis > Options to open the calculation options (in V8i, go to Analysis > Calculation Options). Double-click the active calculation option (designated by the red check mark) to open the calculation options in Properties. Find the property "Calculation Type" and set this to "Fire Flow".

If the Calculation Type is set to Fire Flow, ensure that you are not encountering any red user notifications, which indicate a critical problem that prevents the model from being calculated. This link has common troubleshooting steps for these types of notifications: Troubleshooting the Network Unbalanced or Cannot solve network hydraulic equations user notification.

Results of "N/A" entries can also be caused by omission of the node from the fire flow selection set. Starting with WaterGEMS and WaterCAD CONNECT Edition Update 3 (version 10.03.04.05), the Fire Flow Node Report will be filtered to only display results for nodes included in the selection set used for the Fire Flow Nodes pulldown menu in the Fire Flow alternative. If you have an older version, you can filter the Fire Flow Node Report to remove elements with no results.

"Pressure constraints violated before fire flow added. ..."

In you are using WaterGEMS or WaterCAD CONNECT Edition Update 3 version 10.03.03.72 or later, you may also see a user notification that says: "Pressure constraints violated before fire flow added. Double click for details and use “Nodes to exclude” if needed." This notification occurs when the calculated pressures in the system are already below the pressure constraints before any fire flows are added to a node that is part of the fire flow nodes selection set. This will often happen because of nodes in the same zone as the fireflow nodes, that are on the suction side of the pump (which are more likely to have low pressures during a typical steady state or EPS run if the elevations of the pump and the upstream reservoir or tank have similar elevations.). Meaning, even when no fireflow is applied to a fireflow node, the pressure on the suction side of the pump is below the zone or system pressure constraint. If this occurs and you would like to exclude these low pressure nodes from being considered in the pressure constraint check, you can create a selection set of the elements and select it in the "Nodes to Exclude" dropdown located in the FireFlow alternative. Keep in mind that this applies to zone and system pressure constraints. If the low pressure (before fireflow is applied) occurs at the fireflow node itself (meaning, the residual pressure at the fireflow node is too low even with zero additional fireflow added), then you will still see a Notification about that node failing even if you added it to the "nodes to exclude" selection set. In this situation, it is not valid to even have that nodes as part of the fireflow selection set itself and it should be excluded from the set of fireflow nodes.

The selection set can easily be created by following these steps:

1. Double click on the User Notification in question ("Pressure constraints violated before fire flow added...") to open a list of the low pressure nodes
2. Right click on the first entry in the list of nodes and choose "Select all elements with Message..." - this selects them in the drawing.
3. Right click in the drawing pane and choose "Create Selection Set" - give it a name
4. Select this selection set in the "Nodes to Exclude" dropdown in the fireflow alternative.

See Also

Understanding Automated Fire Flow Results

WaterGEMS and WaterCAD Automated Fire Flow FAQ