EPANET++ is a free web application for modeling water distribution networks, an extension of EPANET.

Fire flow analysis

Each junction in turn draws a fire flow on top of its existing demand. The run uses a copy of the network at the time step on screen, so nothing in the project is changed.

When the project has an extended-period simulation, Reporting step tested selects the condition: the time step on screen, a chosen reporting step, the reporting step of lowest pressure among the junctions tested, or every reporting step. The last option runs the sweep at each reporting step with the tank levels, demand patterns, and link statuses of that step, and shows each junction at its own worst step, the step with the lowest available flow, in the Step of lowest flow column.

Fire flow is normally tested at maximum day demand, so set the network to that condition first.

Each junction tested takes about 16 solves of the whole network, so a large system takes minutes: choose the junctions before you run, and stop at any time to keep the partial results.

What is asked of each junction

Each tested junction gets two tests, on a copy of the network at the time step on screen and in the open scenario. The first asks how much flow the junction can deliver while it holds the residual pressure. A flow is drawn at the junction, and repeated solves narrow it down, up to a ceiling equal to 10000 gpm. A junction that still holds the residual pressure at the ceiling is reported as delivering more than the ceiling. The second test, the design check, draws the required flow at the junction and asks whether any other junction in its scope falls below the Lowest system pressure allowed, or any pipe in its scope runs above the Highest velocity allowed. The design check is not made when its scope is None.

A junction with its own Required fire flow property is tested against that value, and every other junction against the value in the box.

Reading the results

The summary counts the junctions that passed all checks, the junctions that failed the fire flow, and the junctions that affected the rest of the system. The table lists, for each junction tested, the Static pressure before any fire flow is drawn, the Required flow, the Pressure at required flow, the Available flow, the Residual held, the Worst effect and Design limit of the design check, the number of Runs, which is the number of solves of the whole network, and the Failure modes. A cell with no number shows a dash, never a zero. A junction that could not be solved shows its reason in place of numbers. The table prints at most 200 junctions and states how many it did not print.

Rings, Stop, and one analysis at a time

After a run, the circle of each tested junction is outlined on the map according to its result, and the outlines differ in dash pattern as well as in color. Choose Selected junctions to test only the junctions selected on the map; anything else that is selected is counted and not tested. Stop ends a run and keeps the junctions already finished. Only one of the fire flow, criticality, and demand scaling analyses runs at a time.

A fire for a stated duration

When the project has an extended-period simulation, choose A fire for a stated duration under Reporting step tested. The Required fire flow is then drawn at the one junction selected on the map, starting at the time in Fire starts at and lasting for the Fire duration, both whole multiples of the pattern time step. The whole simulation is run on a copy of the network and compared with the same simulation without the fire. The summary states whether the junction holds the Residual pressure to hold during the fire, the lowest pressure anywhere, whether any tank empties, and whether the system recovers after the fire. One table gives the lowest level of each tank, and another gives the pressure at the fire junction at every reporting step.

Example on Net1

Open the Net1 example, choose Water, Analyze, Fire flow analysis…, and click Run with the box as it opens. The time step is 0:00, and the run solves the whole network 135 times. Eight of the nine junctions pass all checks. Junction N32 fails the fire flow: its static pressure is 111 psi, only 1.19 psi remains at the required 1000 gpm, and its available flow is 892 gpm. Junction N31 can deliver 1339 gpm, and Junction N12 more than 10000 gpm.