Using PIPE-FLO Professional for NFPA 15 Hydraulic Calculations

This article shows how PIPE-FLO Professional can be used to determine the hydraulic calculations outlined in the National Fire Protection Association 15 Standard for Water Spray Fixed System for Fire Protection 2007 Edition. 

PIPE-FLO Professional directly calculates pipe velocities, total pressures, differential pressures and flow rates throughout a piping network.  These values can be used to determine additional hydraulic calculations specified in NFPA 15, such as velocity pressure, normal pressure, and allowable velocity.

Calculation of the NFPA 15 values can be automated through the use of the X-Link feature, which provides a link between PIPE-FLO and Excel.  The attached spreadsheet is set-up with the necessary X-Link functions and codes to displays the pipe's name, its upstream and downstream nodes, downstream node elevation, the pipe length, pipe internal diameter, pipe friction lost per 100 feet, pipe friction lost per foot, velocity in feet per second, flow rate in gallons per minute, and downstream node's total pressure.   The spreadsheet then calculates the velocity pressure, static pressure, allowable velocity, and 5% of the total pressure.

By looking at the individual pipe data and the downstream node, the velocity pressure can be calculated with the following equation:

P_v = \frac{0.001123Q^2}{D^4}

The static or normal pressure can then be calculated as the difference of the total and velocity pressure:

P_n = P_t-P_v

The allowable velocity is calculated by the following equation:

v \leq 2.7 \sqrt{P_t}


NFPA 15 Hydraulic Cal.xlsx