About Fire Sprinkler Design Calculator
The fire sprinkler design calculator sizes a sprinkler system hydraulically using the density/area method of NFPA 13, EN 12845, and AS 2118. It is used by fire protection engineers to determine the number of heads, the design flow and pressure, and whether the available water supply is adequate.
Select a standard and hazard class, set the coverage area and ceiling height, configure the sprinkler K-factor and pipe network, and enter the available supply. The tool returns the design density, head count and spacing, the required flow and pressure at the source, and a pass/fail supply adequacy verdict in real time.
How It Works
- Look up the design density, operating area, and maximum head coverage for the chosen standard and hazard class.
- Compute the number of heads as ceil(operating area / coverage per head) and the head spacing as sqrt(operating area / heads).
- Find the minimum flow as density times operating area, then the head pressure from the K-factor relation P = (Q/K)^2.
- Add the Hazen-Williams friction loss and the elevation pressure to obtain the required source pressure, then check it against the available supply flow and pressure.
Worked Example
NFPA 13 Light Hazard gives design density 4.1 mm/min, operating area 139 m2, and coverage 18.6 m2 per head. Heads = ceil(139 / 18.6) = ceil(7.47) = 8. Head spacing = sqrt(139 / 8) = 4.17 m. Minimum flow = 4.1 * 139 = 569.9 L/min. With a 3 m ceiling the elevation pressure is 3 * 0.098 = 0.294 bar.
Formulas
- Number of sprinkler heads
N = ceil(A_op / A_cov)- Minimum design flow
Q_min = rho * A_op- K-factor head pressure
P = (Q / K)^2- Hazen-Williams friction loss
p = 6.05e5 * Q^1.85 / (C^1.85 * d^4.87)- Required source pressure
P_req = P_head + P_friction + P_elevation
Standards & References
- NFPA 13
- EN 12845
- AS 2118
Frequently Asked Questions
Which sprinkler design standards are supported?
The calculator supports NFPA 13, EN 12845, and AS 2118, each with its own hazard classifications (light, ordinary, and extra/high hazard groups) and corresponding design densities and operating areas.
What is the K-factor and how is it used?
The K-factor relates a sprinkler head discharge to its pressure through Q = K * sqrt(P). The tool inverts this as P = (Q/K)^2 to find the minimum head pressure needed to deliver the required flow.
How is pipe friction loss calculated?
Friction loss uses the Hazen-Williams equation with a default coefficient C of 120 for steel pipe. The per-metre loss is multiplied by the equivalent pipe length and added to the elevation pressure to size the supply.
How does the supply adequacy check work?
The supply is adequate only when the available pressure is at least the required source pressure and the available flow is at least the required design flow. Both conditions must pass for an overall pass verdict.