Calculation of fire flow availability results

The fire flow availability (FFA) simulation calculates two additional results for nodes:

• FFA Flow
• FFA Residual Pressure

Results are calculated based on nodal pressures (from a normal type simulation) and hydrant characteristics specified on the Fire Flow Options dialog.

The orifice equation is used:

(1) Where: A = Cross Sectional Area calculated from Hydrant Diameter specified on Fire Flow Options dialog g = acceleration due to gravity (9.81 m/s2) P = Nodal Pressure calculated as for simulation type Normal Cq = Flow Coefficient (2) Where: f = Local Loss specified on Fire Flow Options dialog

A single value for Required Fire Flow or Residual Nodal Pressure is specified on the Fire Flow Options dialog. Only one of these may be enforced during a simulation.

Enforce Fire Flow

If the Enforce Fire Flow option is chosen, FFA Results are calculated at each node for each timestep as follows:

1. The Required Fire Flowis assumed at the node
2. Equation 1 is used to calculate the pressure required to provide the Required Fire Flow.

If Required Pressure calculated in Step 2 is less than Nodal Pressure (calculated as for Normal run type):

• FFA Flow = Required Fire Flow
• FFA Residual Pressure= Nodal Pressure - Required Pressure

If Required Pressure calculated in Step 2 is greater than Nodal Pressure (calculated as for Normal run type):

• FFA Residual Pressure= 0
• FFA Flow = Flow calculated from Equation 1, where P = Nodal Pressure

Enforce Pressure

If the Enforce Pressure option is chosen, FFA results are calculated at each node for each timestep as follows:

If Nodal Pressure is less than enforced Residual Nodal Pressure:

• FFA Flow = 0
• FFA Residual Pressure= 0

If Nodal Pressure is greater than enforced Residual Nodal Pressure:

1. The Residual Nodal Pressureis subtracted from nodal pressure results (calculated as for a normal type run).
2. The pressure calculated in Step 1 is used in Equation 1 to calculate Available Fire Flow

If Available Fire Flow calculated in Step 2 is less than Required Fire Flow:

• FFA Residual Pressure = Residual Nodal Pressure
• FFA Flow = Available Fire Flow

If Available Fire flow calculated in Step 2 is greater than Required Fire Flow

• FFA Flow = Required Fire Flow
• FFA Residual Pressure= Nodal Pressure - Required Pressure (calculated from Equation 1, where Q = Required Fire Flow)