Design a fire water service for the apartment building at the top of the hill. R

Question

Design a fire water service for the apartment building at the top of the hill. Required fire flow for the building's sprinkler system is 500 gpm at 20 psi residual pressure. According to a nearby hydrant How test. Static pressure of the 12-inch ductile iron water main in the street is 80 psi, and the main produces 900 gpm at 20 psi residual pressure. Assume that the only flow in the 12-inch main is the fire flow at the time of the fire. Ductile iron pipe is required by the local jurisdiction for the water service. Acceptable pipe diameters are those normally available: 2-, 2.5-, 3- 4-, 6-, 8-, 10-. and 12-inch diameter. A) Plot the pressure-flow curve for the 12-inch water main at this location, and use the information from the curve for design. B) Determine the most economical service line diameter.

Explanation / Answer

Fire flows are computed at each node by iteratively assigning demands and computing system pressures. When you execute a fire flow analysis, WaterCADGEMS will: 1.Calculate a steady-state simulation for all nodes designated as fire-flow nodes. At each node, it begins by running a Steady-State simulation using only non-fire demands, to ensure that the fire flow constraints (e.g., minimum residual pressure, minimum zone pressure) that have been set can be met without withdrawing any Fire Flow from any of the nodes. 2.Evaluate the Fire Flow Upper Limit and Available Fire Flow at each of the fire-flow nodes. Assuming the fire flow constraints were met in the initial run, the program performs a series of steady-state runs in which flow is applied to each specified fire-flow node and results are evaluated against fire-flow constraints. Note that the fire flow for each individual node is evaluated using a separate analysis (i.e., needed fire flow is not applied simultaneously to all fire-flow nodes). a.The program performs a series of steady-state analyses in which the Fire Flow Upper Limit discharge is applied to each node in turn. If the fire flow constraints are met for the Fire Flow Upper Limit discharge, the node satisfies the fire flow constraints and no further analysis is required for that node. b.The program then performs a series of steady-state analyses in which it iteratively assigns lesser demands to nodes that do not meet Fire Flow Upper Limit constraint to determine the Avalable Fire Flow. The Available Fire Flow is the maximum fire flow that each node can supply without violating fire flow constraints. c.If the Available Fire Flow is greater than or equal to Needed Fire Flow, the node satisfies the fire flow contraints. If Available Fire Flow is less than Needed, it does not. 3.Run a final Steady-State calculation that does not apply Fire Flow demands to any of the junctions. This provides a baseline of calculated results that can then be compared to the Fire Flow conditions, which can be determined by viewing the results presented on the Fire Flow tab of the individual junction editors, or in the Fire Flow Tabular Report.

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