Hydrant Curve simulations: How is existing demand at the hydrant considered?

H2OMAP Water, InfoWater and H2ONET all offer the “Hydrant Curve” simulation type. This type of simulation allows you to choose any junction in any scenario at any single time step and develop a hydrant curve to indicate the fire flow residual pressures at a range of flows.

Fig. 1. Graph result from a hydrant curve simulation

Nodes with no demand at the timestep of interest: When comparing the pressure (at the same junction, time step and scenario) between the EPS simulation result and the hydrant curve simulation result, you will find that the first data point (Available Flow = 0) of the hydrant curve will have the same residual pressure as the junction pressure reported in the EPS simulation results.

Nodes with positive demand at the timestep of interest: In contrast to the above, you will find that at the first data point of the curve (Available Flow = 0), you residual pressure will be higher than the junction pressure reported in the EPS simulation results.

Reason: The software does not add the ‘Normal Hydrant flow’ (highlighted in Figure 2) to the demand that already exists on the junction in the reference (EPS) scenario.

Fig. 2. Hydrant Curve tab in Run Manager - reference scenario and Normal Hydrant Flow highlighted

Fig. 2. Hydrant Curve tab in Run Manager – reference scenario and Normal Hydrant Flow highlighted

Rather, it starts the hydrant curve residual pressure calculations by assuming that there is no existing demand on the junction. This can be illustrated by:

1. Clicking the ‘Report’ button on the Hydrant Curve graph

2. Scrolling down to the point where the Available Flow matches the demand reported at the same junction, same time step in the reference EPS simulation.

Suggestions to avoid unrealistically high maximum residual pressure values:

a) If your junction of interest has positive demands and you don’t mind adding a new ‘dummy’ junction (with no demand) very close to the junction of interest, then run the hydrant curve simulation using this dummy node to get a more realistic curve

b) Alternatively, if you do not want to add a dummy node and your junction of interest has a high demand, consider exporting your hydrant curve data to a spreasheet and deleting all values below the point where the Available Flow from the Hydrant curve is equal to the junction demand at the same time step in the EPS. This will eliminate all residual pressure values where the ‘normal’ junction demands have not been considered and give a more realistic maximum residual pressure result at the lower available flow values.

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    About Toby Bourke

    Toby has 5 years experience supporting, training and demonstrating H2OMAP Water, InfoWater, H2OMAP SWMM and InfoSWMM. More recently, a strong interest in asset performance has lead to post graduate study in asset management with a focus on renewals planning. This has resulted in a great many hours supporting and promoting InfoMaster, InfoNet and CapPlan software.
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