Inputs
Example Data Table
| Scenario | Unit system | Density | Area | Nozzles | K | Pressure | Hose | Safety | Duration |
|---|---|---|---|---|---|---|---|---|---|
| Process bay, preliminary | US | 0.30 gpm/ft² | 2,500 ft² | 12 | 5.6 | 30 psi | 250 gpm | 10% | 60 min |
| Loading dock, conservative | Metric | 12.2 L/min/m² | 180 m² | 16 | 80 | 2.1 bar | 950 L/min | 15% | 45 min |
Formula Used
Nozzle discharge
Qnozzle = K × √P
Use a K-factor and pressure that are consistent with your unit system. Q is nozzle flow, K is nozzle coefficient, and P is operating pressure.
Active nozzle demand
Qnozzles = Qnozzle × N
N is the number of simultaneously open nozzles.
Protected-area demand
Qarea = Density × Area
Density is the required application rate over the design area.
Base and final design flow
Qbase = max(Qarea, Qnozzles) + Hose
Qfinal = Qbase × (1 + Safety/100)
Safety factor provides margin for hydraulics, tolerances, and uncertainty.
Water volume
V = Qfinal × Duration
Volume supports tank sizing and available supply verification.
How to Use This Calculator
- Select a unit system and keep all inputs consistent.
- Enter the design density and the protected design area.
- Set the number of nozzles expected to operate together.
- Enter nozzle K-factor and the target operating pressure.
- Add hose allowance and a safety factor suitable for policy.
- Set duration to estimate water volume for the supply.
- Press Calculate Flow to view results above the form.
Design Basis and Inputs
Deluge systems protect defined hazards by applying a target discharge density over a selected design area. This calculator starts with application density, protected area, open nozzle count, nozzle K-factor, and operating pressure. When values are consistent, the model produces a defensible flow demand for preliminary pump and supply sizing. Use project criteria for density and area, and treat the nozzle count as the worst credible simultaneous operation.
Nozzle Demand Versus Area Demand
Two independent demands are evaluated. Area demand is Density × Area, representing the required application rate across the hazard footprint. Nozzle demand is N × (K × √P), representing the hydraulic discharge through active nozzles at the chosen pressure. The governing demand is the higher of these two, because the supply must satisfy both coverage intent and actual nozzle hydraulics. Large differences often indicate spacing or pressure assumptions that need review.
Allowances, Margins, and Practical Checks
A hose stream allowance is added as an explicit flow component when required by local practice or design policy. After that, a safety factor increases the base demand to account for uncertainties such as friction losses, manufacturing tolerances, partial obstructions, and future changes in hazard geometry. For checks, compare the final flow to available pump curves, verify that nozzle pressure includes losses to the most remote point, and confirm that valves, strainers, and deluge trim can pass the demand without excessive pressure drop.
Water Supply Volume and Duration Planning
Flow alone is not enough; duration converts demand into stored or available volume. The calculator multiplies final design flow by duration to estimate total water required for the event. Use this volume to size tanks, evaluate fire water mains, and confirm that refill or make-up capacity matches operational expectations. If supply is limited, consider staged discharge, zoning, or revising the design area while maintaining the required application rate and control philosophy.
Documenting Results for Review and Handover
Exported CSV and PDF outputs support design reviews and field communication. Record the unit system, assumptions, and any hose or safety allowances so others can reproduce results. Attach the table to hydraulic calculations and include notes on nozzle type, spacing, and elevation changes. When the system progresses to detailed hydraulics, replace preliminary pressures with calculated node pressures and update the nozzle count based on final deluge zone boundaries for commissioning alignment.
FAQs
Q: How do I choose the design density and area?
A: Use the hazard classification or project standard that defines the required application rate and design area. Enter the controlling area for the deluge zone, not the entire building footprint, and document the basis in notes.
Q: Why does the calculator compare area demand and nozzle demand?
A: Area demand reflects coverage intent, while nozzle demand reflects actual discharge at pressure and K-factor. The supply must satisfy both, so the higher value is used to avoid under-sizing the pump, valve, and water source.
Q: What does the nozzle K-factor represent?
A: It is the nozzle discharge coefficient used with pressure to estimate flow, where flow equals K times the square root of pressure. Use the K-factor from the nozzle data sheet that matches your unit system.
Q: When should I include a hose allowance?
A: Include it when your design policy or local practice requires a simultaneous hose stream with the deluge discharge. Enter the required flow as an additive allowance so the base demand reflects the combined operational expectation.
Q: How should I set the safety factor?
A: Apply a reasonable margin to cover uncertainty, minor restrictions, and future changes. Typical projects use a small percentage, but the right value depends on governance and how conservative the hydraulic model and inputs are.
Q: Does this replace a full hydraulic calculation?
A: No. It provides a structured preliminary demand and water volume estimate. Detailed design still requires network hydraulics, verified pressures at remote nozzles, friction loss calculations, and confirmation of component ratings and availability.